A larger intensity and shorter somatosensory response  was evoked by the biomimetic surface motion. This result and the associated decrease of theta activity (5–7 Hz) over the posterior parietal cortex suggest that increasing the amount of sensory input processing could make the balance task less challenging when standing on a biomimetic surface. This key point was confirmed by a second experiment (n = 21) where a cognitive task was added, hence decreasing the attentional resources devoted to the balance motor task. Greater efficiency of the postural reaction was observed while standing on the biomimetic than on the control surfaces.Despite numerous studies uncovering the neural signature of tactile processing, tactile afferent inputs relating to the contact surface has not been studied so far. Foot tactile receptors being the first stimulated by the relative movement of the foot skin and the underneath moving support play an important role in the sensorimotor transformation giving rise to a postural reaction. A biomimetic surface, i.e., complying with the skin dermatoglyphs and tactile receptors characteristics should facilitate the cortical processes. Participants (n = 15) stood either on a biomimetic surface or on two control surfaces, when a sudden acceleration of the supporting surface was triggered ( These shear forces, and the consequent skin transient deformations, activate the mechanoreceptors embedded in the skin allowing the brain to identify the direction and amplitude of the perturbation, before being detected by other sensory inputs2 . These tactile inputs contribute to shaping the postural responses during balance perturbations according to the identified limits of postural stability4. Being the first receptors to be stimulated by the relative motion of the foot and the supporting surface, plantar tactile receptors provide crucial information for controlling balance. Their importance is notably evidenced by the impaired balance control of animals  and humans after a loss a foot cutaneous feedback7. Further evidence for the relevance of plantar sensory feedback comes from a study showing that blindfolded human participants are able to scale their postural adjustments according to near-threshold tactile stimulation evoked by small lateral acceleration (~ 0.2 m/s2) of the supporting surface before mediation of vestibular or proprioceptive feedback2. Interestingly, Fabre and colleagues8 recently reported in patients with bilateral vestibular loss that during quiet standing the response of the sensorimotor cortex to foot cutaneous stimulations  was much greater than in age-matched healthy participants.During everyday life, unpredictable circumstances can challenge our equilibrium while standing. This occurs for example when standing passengers are subjected to unexpected acceleration . Exquisitely compliant, the skin of the foot sole is deformed well before the passenger’s postural reaction to the driver’s manoeuvres. This skin deformation is due to the mechanical interaction  generated by the surfaces in contact  and the gravity force acting on the body mass . Although the shear forces are small relative to the weight force during natural quiet standing, they are readily detectable by the tactile receptors2 suggests a high responsiveness of the tactile sensory system. This responsiveness could have a twofold origin. First, it could stem from the richness of the receptor types  and from the characteristics of the receptors’ receptive fields. These units have receptive fields round or oval in shape, extended or small, with sharp or blurred boundaries, with the point or points of highest sensitivity eccentrically located within their receptive fields9. Secondly, it could also stem from the great compliance  of the skin in which the receptors are embedded, which depends, in part, on the footprint  and their orientation. For instance it has been showed that the skin vibrations sought to stimulates the Pacinian tactile receptors, were amplified when using a fake finger with the main geometrical characteristics of the human fingertip than with a smooth finger design 10. Besides, this amplification is all the more enhanced when the ridges of the fingerprints are oriented perpendicular to the scanning direction11.The low perceptual threshold of tactile receptors relative to others  for detecting a relative horizontal acceleration of the support surface13, intriguingly, most of the investigations in the field of balance control have ignored the surface/body contact mechanics. This is particularly surprising given that the foot sole shows footprints (dermatoglyphs) that have similar types and density of forms as fingerprints . Skin deformation during tactile exploration depends not only on the morphological, topographical, and mechanical properties of the skin as mentioned above, but also on the properties of the surface in contact with the skin . In this light, a biomimetic surface, whose texture is inspired by the mechanoreceptors and footprint spatial characteristics should optimise skin deformation and are likely to facilitate the neural encoding of this deformation together with the cortical sensory processes of the tactile inputs. Here, to specifically test this hypothesis while maintaining an upright position, we recorded and compared the amplitude of the cortical response  evoked by the motion of the surface on which the participants were standing. Because it represents the amount of sensory input processing at the cortical level18 the amplitude of the P1N1 SEP component was expected to be greater when the participants stood on a biomimetic surface than on other control surfaces  (Experiment 1).While the interaction between a surface and the skin has been extensively studied during finger exploration of a surface19. This localized change of theta power spreads afterwards over other cortical areas . A similar increase of theta band activity was observed during the preparation of a challenging balance recovery task which required participants to keep the feet in place and to refrain from stepping responses20. Increased theta band activity is also observed in the posterior parietal cortex (PPC) during the transition from a stable to an unstable surface22. This is in line with the responses of the superior PPC to tactile stimulation (in Monkey) which occurred ~ 60 ms following SI responses23. Since the PPC is involved in sensory information integration and generates decision-related activity24, this associative cortical area is likely to be involved in the motor recovery response to balance perturbation.Moreover, since an efficient sensory processing allows a better detection of threats to balance, the use of a biomimetic surface should decrease the cognitive demand associated with maintaining equilibrium during the motion of the support surface. To test this hypothesis, we compared the changes of theta band power (4–7 Hz) evoked by the motion of the biomimetic and control surfaces. Indeed, recent studies have shown that an increased theta power over sensorimotor areas is an electrophysiological biomarker of the increased difficulty of the balance task. For instance, a significant increases of theta power in the left sensorimotor cortex before imminent rightward or leftward loss of balance was found25 facilitating the detection of balance instability when standing on a biomimetic moving surface should decrease the attentional demand required for standing steadily. By using a dual task (DT) paradigm (Experiment 2) in which participants are involved in a high demand cognitive task (identifying numbers), we expected less interference between the postural and cognitive tasks when participants stood on a biomimetic surface compared to other surfaces . This should result in a better performance in the cognitive task or a sharper postural reaction to the surface motion .Based on the premise that balance control requires a minimum state of attention and cognitive resources2,28 = 13.84, p = 6.6 × 10–5; η2 = 0.49). Post-hoc analyses revealed that the force amplitude was greater for the biomimetic  than for the smooth and grooved surfaces , which did not differ significantly . The latency to reach the break down point did not depend on the surface . It occurred a few milliseconds (−26 ± 11 ms) before reaching the maximal value of the platform acceleration for all surfaces . The maximal amplitude reached by the platform acceleration did not differ significantly between surfaces .As shown in Fig. 2,24 = 0.64; p = 0.54). The left FL activity decreased simultaneously with the right FL activation in 10 out to 13 participants. The delay of the changes in the FL muscles activities relative to the break down point suggested that the early shear forces were not muscularly induced, but rather passively evoked by the friction between the stretched skin and the platform. Besides, the fact that the muscular synergy (right FL activation/left FL inhibition) was initiated after the “skin-surface contact transitions”  nor its duration . During the postural reaction, the head started moving  with a latency of 172 ± 38 ms relative to the platform motion onset .During muscle activities, the shear forces continued to increase until a second peak was reached before reducing the forces. This second increase considered as a postural reaction1N1) originated from tactile and/or from vestibular peripheral inputs, we compared the latencies of P1 and N1 relative to the vestibular stimulation onset. The vestibular stimulation threshold was defined as the first instance head acceleration exceeded 0.048 m s−2 . This latency was not significantly affected by the surface texture . Paired t-tests showed that P1 and N1 latencies significantly preceded vestibular stimulation onset for all the surfaces . The P1 latency and P1N1 amplitude did not differ between the control surfaces . It is worth noting that P1 occurred on average 11 ± 10 ms after the early peak force was reached for the biomimetic surface. The P1 short lag relative to the peak force suggests that the SEP is not evoked by the behavioral change  when standing on the biomimetic surface. This is confirmed by the t-test of means against a reference value of 40 ms , considered as the minimum lag required for a tactile stimulus to evoke a cortical response30. Rather this suggests that P1 was evoked by tactile afferent inflow occurring before the peak was reached.Importantly, the latency of P1 latency and greater P1N1 amplitude) observed with the biomimetic surface could be linked to a change in leg muscle activity, we compared the general muscle activation  of the right and left FL during the N1 latency interval . The ANOVA did not show a surface texture effect on the iEMG . These results suggest that the changes in the SEP observed over the somatosensory cortex when the participants stood on the biomimetic surface stemmed from an increased afferent volley from the foot sole mechanoreceptors rather than from an altered motor command .To verify if the SEP facilitation  revealed significant greater activation in the left precuneus . Post-hoc analyses revealed that it was significantly smaller for the biomimetic than for the smooth and grooved surfaces , with no significant difference between the two control surfaces (p = 0.67)   in the PPC because this region activity is considered as a neural signature of imminent loss of balance Fig. a. The re67) Fig. c. This e28) Fig. c.Figure 20 = −0.20; p = 0.85; 24 ± 11.5%). As shown in Fig. 31. Note that no such activities of the frontal lobe were observed in the 2 participants that were discarded from the analyses, due to their high error rate.To identify the magnitude of the interference in the dual task paradigm we analysed cognitive and balance-related motor task performances. For the cognitive task, participants were instructed to silently count the number of times that 7 was part of a series of ten different three-digit numbers that were spelled out at high speed and an error was counted each time that the participant reported an incorrect number of occurrences of the number 7. A paired t-test did not reveal significant difference in the percentage of errors between the biomimetic and the grooved surfaces , and when standing on the biomimetic as compared to the grooved surface  . The ANOVA also revealed that the duration of the postural reaction was shorter when performing a dual task  and when standing on the biomimetic surface  . Although the ANOVAs performed on the variables relating to the postural reaction did not reveal significant Task × Surface texture interactions, the results of planned contrasts post-hoc tests revealed that the postural reaction was of greater amplitude  and smaller duration  when standing on a biomimetic surface and performing the dual task than the in the other conditions  than the single motor task (F25) Fig. c. No sig1N1), with respect to both control surfaces . The greater amplitude of the SEP, when standing on the biomimetic surface, suggests augmented cutaneous afferent processes18. The increase P1N1 amplitude and the shortening of the evoked response latency  could be due to an accentuation of the deformation of the compliant skin when interacting with the biomimetic surface. One could argue that the increase P1N1 amplitude and the shortening of the evoked response latency  could be due to the increase amplitude of the peak force. However, the latency of P1 relative to this peak (about ~ 10 ms) suggests that the inputs come from the skin/surface contact before the peak of the transient skin deformation was reached. This reduces the possibility for a significant role of the peak force in generating the SEP. Nevertheless, the larger peak amplitude represents the enhanced skin deformations while no concomitant change of its duration was observed. This is in line with a study showing that a greater deformation of the fingers’ skin generates greater friction force, and stress that induce stronger tactile stimulation of the mechanoreceptors32. Similarly, the interaction of the foot and the biomimetic surface increased the intensity of the skin mechanoreceptors stimulation, which in turn boosted the transmission of tactile signals to the primary somatosensory cortex (SI) where neurons respond to various tactile stimulations34.Complying with both dermatoglyphs and mechanoreceptors characteristics, the biomimetic surface in contact with the feet evoked faster and greater cortical response to the platform lateral motion  for the biomimetic surface, with respect to both control surfaces, in line with functional interactions  between the precuneus and the thalamus37. In this light, the shared connectivity between the precuneus and the extrastriate body area (EBA)38, which showed an enhanced activity with the biomimetic surface texture, is consistent with the role of the EBA in enhancing the local spatial processing of body information on the direction of a stimuli out of view39, such as the skin stretch under the feet in the current study.The source analyses showed that changing the standing surface texture significantly altered the current in the left PPC but had no significant effect on the current recorded in SI. This suggests that the sensory facilitation observed with the biomimetic surface may have involved direct thalamocortical projections to the PPC. The basis for this suggestion is twofold. First, neuroanatomical studies in the macaque have shown direct projections of cutaneous information from the thalamus to the PPC41. However, the evoked potentials that arise from the stimulation of the lower limb nerve endings exhibit much shorter latencies  than those observed in the current study . Furthermore, the increased activity of the leg muscles induced by the translation of the biomimetic surface occurred ~ 160 ms after the onset of the translation, i.e., after the P1 occurrence. This reduces the possibility for a significant role of muscle-stretch receptors in generating the SEP when the participants stood on the translating surface, irrespectively of the supporting surface texture. Vestibular input is also an unlikely candidate for evoking the cortical response, as P1 and N1 had shorter latencies than the latency with which the head reached the acceleration threshold for activating vestibular receptors .The shorter latencies of the SEP observed when the participants stood on the moving biomimetic surface could suggest some contribution of muscle-stretch receptors, as it is well-established that muscle spindle endings are extremely sensitive stretch receptors 22. Our participants showed a significant decrease in the power of theta oscillations in the left PPC when they stood on the biomimetic surface compared to the control surfaces . Since theta oscillations are considered as a neural correlate of a need for attentional demand in challenging balance tasks  and ACC of the left hemisphere observed when the tactile salience of the surface decreases, as when standing on a smooth surface (as compared to either the biomimetic or grooved surfaces). Previous studies have suggested that the SMA plays an important role in the control of demanding balance tasks43. This was notably evidenced by the significant structural and functional adaptation of the SMA activity after balance training43. Therefore, the enhanced activity of the SMA, found when individuals stood on the smooth surface  may suggest that the standing task was more demanding with this surface than with textured surfaces (biomimetic or grooved). The increased activity observed in the ACC would also be consistent with this suggestion as the role of this cortical region is well-recognized when individuals are uncertain about fulfilling the required task appropriately44 or in error-recognition45. These interpretations are also supported by the proposed function of the ACC in the regulation of attention and cognitive control46. Enhancing the need for attention when standing on a smooth surface could be a mean for withholding potentially erroneous responses due to impoverished tactile cues related to platform motion until other sensory modalities  can resolve the ambiguity of the support displacement. In addition to the increased theta oscillations power for the control grooved surface, the source analyses revealed an increased activation of the right PPC. This findings are consistent with the crucial role of this cortical area in the processing of somaesthetic gravitational information for postural control, as shown in neglect patients after right hemispheric strokes47.Finally, the results of theta oscillations analyses were consistent with the likely role of the left PPC in attentional processesExperiment 2 confirmed this interpretation. Based on the premise that postural control requires attention25, the postural perturbation observed when performing a simultaneous cognitive task would be due to the sharing of limited attentional resources49. However the intriguing result of Experiment 2 is that the postural reaction observed during the platform motion rather complied with the spatiotemporal characteristics of an efficient postural reaction in the dual task than in the single task . These behavioral features were observed to a greater extent when the participants stood on the biomimetic surface. Therefore, the participants’ engagement in the cognitive task did not have a deleterious consequence on the postural control as often reported in previous studies53. The greatest efficiency of the postural reaction observed in participants standing on the biomimetic surface could stem from a greater capacity to shift the attentional focus from the primary motor task to the secondary cognitive task. Such external focus is known to diminish motor-related conscious attentional processes54 compared to an internal focus of attention55, and improve motor performance. This has been clearly demonstrated in a study in which participants had to make oscillatory movements  when standing of platform mounted on wheels that ran laterally on two bowed rails56. Elastic rubber belts attached to the platform ensured that the platform returned to the center position during the oscillatory movements. The authors showed that the motor performance decreased when the participants’ attention was focused on the force that the feet should exert on the supporting platform  as compared to when their attention was focused on the wheels of the platform . Overall, the results of experiment 2, combined with those of Experiment 1 showing similar postural reactions between the different surfaces, suggest that during small accelerations of the standing platform, the advantage of standing on a biomimetic surface to safeguard stability is solely expressed when one is involved in a dual task (Experiment 2). Although it is often the case that one is engaged in a cognitive task while standing , greater platform accelerations could be needed for the biomimetic surface to express an improvement of the postural reactions compared to other types of surface.Overall, our results point to a reduced difficulty of the balance task when standing on a biomimetic surface. By increasing the attentional load of the balance task, Experiment 1 with this surface. The biomimetic surface may therefore facilitate the use of low-level sensorimotor loops, which are less permeable to cognitive load, and which enable speedy performance54. As mentioned, thalamic projections to the left pre-cuneus37, which has dense interconnections with the motor and premotor cortices57 may have contributed to the facilitation of the neural responses to the tactile stimulation observed with the biomimetic surface . These thalamocortical connections areas could constitute the neural underpinning of the efficient spatiotemporal pattern of the postural reaction when standing on the biomimetic surface.It is possible that the equilibrium demands in response to support motion decreased when standing on a biomimetic surface, as also suggested by the smaller theta power observed in 58 demonstrated that the barefoot condition exhibited a quicker and more efficient balance response than wearing conventional shoes, the shoe sole material might convey as does barefoot, the friction induced vibration generated by the contacted surfaces. For example, Formula-1 footwear was able to dampen the low frequency (30 Hz) vibration transmitted to the foot and to transfer high-frequency stimuli (200 Hz) into the skin59. This particular frequency was reported to be generated by the shear stresses between the foot skin and surface when standing barefoot on the biomimetic surface60.A limitation of the present study is that it does not provide information as to whether the behavioral and neurophysiological changes observed when standing barefoot on the biomimetic surface occur when wearing shoes. Even though Chander and colleaguesFifteen participants (9 women) without any known neurological and motor disorders participated in the experiment . All participants, except two, characterized themselves as right footed. All participants gave their written informed consent to take part in this study, which conformed to the ethical standards set out in the Declaration of Helsinki and all experimental protocols were approved by the STAPS  Research Ethics Committee .61, we verified that none of them had any foot morphological particularities. This was done by measuring the width of the forefoot  and the isthmus width localized in the middle of the foot and connecting the forefoot with the rearfoot. Computing the percentage ratio ((isthmus width)/(forefoot width) × 100) allowed us to identify hollow feet (< 33%), standard feet (33% to 50%) and flat feet (> 50%)61. All participants showed standard feet, therefore none were excluded from the analyses.Participants were requested to stand barefoot with their feet at a natural distance apart on different types of surfaces (see below), fixed in the middle of a movable force platform. They wore a safety harness attached to the ceiling. We ensured that the feet position remained the same throughout the experimental conditions. As the morphology of the foot  can have an impact on body stability27. A movable force platform is placed on two parallel rails and is held stationary by an electromagnet  and was 8.34 ± 0.74 cm s−2. In addition, the latency to reach the peak did not differ between surface  and was 196 ± 15 ms. These results suggest that stimulation intensity was similar across all surfaces.We used a set-up employed in previous studies for stimulating foot tactile afferentsnet Fig. a. A cablAt the start of a trial, the participants looked at a fixation point positioned at eye level, 2 m directly ahead. They were asked to close their eyes upon receiving the verbal information on the nature of the upcoming condition, and to remain still. This information indicated one of these two conditions: platform translation  or platform steady , which were pseudo-randomly distributed. The later set of trials reduces the possibility of adopting a stereotyped postural set linked to the forthcoming body translations . These trials were also used to measure and model the noise contaminating the EEG data (see below). In all trials, the participants had to maintain an upright steady posture during 5 s . The platform translation occurred at any time between 2 and 4 s after providing the information about the platform translation to avoid anticipating the instant of the translation onset. The trials without translation also lasted 5 s. A short break was frequently proposed to the participants during the experiment.Participants stood on three different surfaces which were glued onto the platform: a biomimetic surface, a surface with parallel grooves . These surfaces were created with a 3D printer (Ultimaker 2+) using biopolymer thermoplastic . Three characteristics were selected to build the biomimetic surface: shape, spatial period, and depth of the ridges.62 and the forms of the dermatoglyphs, which exhibit three main circular forms . We verified whether the radius of curvature of the circular shape of the biomimetic surface complied with the participants’ toe prints. To do so, we used the ink dabbing method to collect the toe prints of each participant on a white sheet of paper. Contrary to fingerprints, toe prints have their characteristic features at the lower end of the phalanges14. Then, the rolling of the prints was taken longitudinally from lower end to the upper end of the toe . For each participant, we measured, and then averaged, the radius of curvature of the three most visible ridges from three different toes. A t-test of means against a reference value indicated that the radius of curvature on the toe surfaces (4.3 ± 1.1 mm) did not differ significantly compared to the radius of the loops printed of the biomimetic surface .The biomimetic surface was textured with circular or oval shapes inspired from both the shape of the tactile receptors’ fields that demonstrate a preferential skin strain axis and orientation of this axis, which is not the same for all units13 = −1.66, p = 0.12). Note that the spatial period of the biomimetic surface also corresponded to the distance between the centre of adjacent receptive fields of the mechanoreceptors (from 0.9 to 3.8 mm64).The spatial frequency of the biomimetic surface complied with the spatial frequency of the participants’ toeprint ridges. This was confirmed by the result of the t-test of means against a reference value showing that the mean spatial frequency of the biomimetic surface (0.9 mm) was not significantly different from that of the toeprints ridges (0.87 ± 0.06 mm)  activity was continuously recorded from 64 Ag/AgCl surface electrodes embedded in an elastic cap . Specific to the BioSemi system, “ground” electrodes were replaced by Common Mode Sense active and Driven Right Leg passive electrodes. The signals were pre-amplified at the electrode sites, post amplified with DC amplifiers, and digitized at a sampling rate of 1024 Hz (Actiview acquisition program). The signals of each electrode were referenced to the mean signal of all electrodes. Four Ag/AgCl electrodes placed near the canthus of each eye and under/over the left eye orbital allowed us to control for blinks, and horizontal and vertical eye movements.67. Therefore, this electrode was used to assess the SEPs. We primarily based our analyses on the P1N1 wave evoked by the sensory stimulation induced by the platform translation. The amplitude of P1N1 was measured peak to peak, and its latency was assessed measuring the P1 latency.The continuous EEG signal was segmented into epochs synchronized relative to the onset of the platform translation, which was identified at the onset of the monotonic increase of the shear force. After artefact rejections based on visual inspection, for each participant and surface, a minimum of 96% of the trials were included in the analyses. The signals were filtered off-line with a 50 Hz digital notch filter (24 dB/octave) and with a 0.1–48 Hz band-pass digital filter (48 dB/octave) implemented in BrainVision Analyzer 2 software . For each participant, the SEPs were obtained by averaging all epochs of each surface for each participant. The average amplitude computed 50 ms prior to the platform translation served as baseline. Consistent with studies recording cortical potentials evoked by lower limb stimulation, the SEPs were found to be maximal over the vertex (Cz electrode)68) implemented in the Brainstorm software. A boundary element model (BEM) with three realistic layers  was used to compute the forward model on the anatomical MRI brain template from the Montreal Neurological Institute (MNI Colin27). Using a realistic model has been shown to provide more accurate solution than a simple three concentric spheres model69. We used of a high number of vertices  to enhance the spatial resolution of the brain template. Such EEG source reconstruction has proved to be suited to investigating the activity of outer and inner cortical surfaces with 64 sensors70. Measuring and modelling the noise contaminating the EEG data is beneficial to source estimation. Noise covariance matrices were computed using the eight trials with the platform steady condition, while the participants stood still. The current maps were averaged from the start of the shear forces to N1, for each participant and surface texture.Neural sources of the SEPs were estimated with the dynamical Statistical Parametric Mapping (dSPM71. The power of theta (5–7 Hz) was computed for each trial in the source space in a region of interest  encompassing the left inferior and superior PPC . Then, the signal was expressed as a change of theta power computed over the first 400 ms of the platform translation (which included the P1N1 SEP) with respect to a 350 ms window baseline taken before the translation (−400 to −50 ms). For each participant, the resulting event-related synchronization/desynchronization (ERS/ERD) was then averaged across trials and surface textures. The same procedure was applied with the signals computed in a control ROI (650 vertices) encompassing the inferior and superior PPC of the right hemisphere.The data were transformed into time–frequency domain using Morlet wavelet transforms. We used a 1 Hz central frequency  which offers a good compromise between temporal and spectral resolutionsThe ground reaction forces and moments were recorded with an AMTI force platform  at a sampling rate of 1000 Hz (filtered with a 4th order Butterworth low-pass filter with 10 Hz cut-off frequency). The analysis focused on the shear forces along the mediolateral (M/L) axis. M/L shear forces are horizontal forces that act in parallel to the contact surface, resulting in the relative sliding or friction between contacting surfaces . The onset of the shear forces provided a reliable temporal landmark to determine the onset of the cutaneous stimulation evoked by the platform translation. The onset of this stimulation was defined as the first instant the M/L shear forces started to increase monotonically. Figure (i)The first phase shows a ramp of the platform acceleration (constant jerk) corresponding to a ramp in the traction force; this phase lasted on average 196 ± 15 ms leading to a platform displacement of about 0.54 ± 0.05 mm. Due to the inertia of the body, this displacement is accommodated mainly by the skin deformation. The peak amplitude of this force was measured with respect to its baseline value .(ii)skin-surface contact transitions”), which are directly affected by the topography of both the skin and the surface itself; moreover, local detachments and slipping can occur, leading to transient deformations and waves propagating in the skin, which are likely to activate the mechanoreceptors (“contact stimuli”); a similar phenomenon has been observed in literature, when considering the motion of a surface under a stationary fingertip, showing that the deformation of the skin increases until the frictional force  cannot anymore resist the sliding ; within this phase, the shear forces result from a balance between inertia effects and contact accommodation.In a following transition phase the jerk decreases and eventually becomes negative. This is a crucial phase, where the contact between the skin and the surface is characterized by high superficial shearing, leading to transient variations of the local strain distribution (“(iii)28. The duration of the postural reaction was defined as the time elapsed between these peaks.Afterwards the shear forces continued to increase until a second peak was reached before decreasing. This second increase can be considered as predominantly a postural reactionA general pattern of events emerged:The amplitudes of both peaks of the shear forces were normalized to the body mass index (BMI) of each participant.−2 . We measured the lag between this threshold and shear forces onset to determine if the vestibular stimulation occurred after the stimulation of the foot mechanoreceptors.Head acceleration was measured with a triaxial accelerometer  placed on the participants’ chin. We measured head acceleration to evaluate the latency of the vestibular stimulation induced by the platform translation. The onset of the vestibular stimulation was defined at the first instant head acceleration exceeded 0.048 m s74. The FL EMG signals were pre-amplified at the skin site (1000×), sampled at 1000 Hz, band pass filtered from 20 to 250 Hz, and rectified. Two participants were excluded from the EMG analyses due to noisy EMG signals. To quantify the muscle activity, we computed the integral of the EMG activity (iEMG) over two intervals. The first corresponded to the “resting interval”. It lasted 1 s and ended at the onset of the platform translation. The second interval covered the time elapsed between the platform onset and the N1 component of the SEP. The duration of this second period was specific to each participant. In order to be able to compare muscle activities between the two intervals, we normalized, for each participant, the EMG activity of the resting interval prior translation onset, to the duration of the second interval “N1 latency” (~ 180 ms). We also calculated the latencies of EMG changes relative to the onset of the platform translation. This was done by first computing the mean and standard deviation of the muscle background activity  for each participant and surface. The onsets of the changes in EMG activity were defined as the instant at which the EMG activity increased above or decreased below a threshold level set at twice the standard deviation of the mean background activity.Bipolar surface electromyography  was used to record the activity of the long fibular muscle (FL) of both legs. The FL muscles are responsible (with other muscles) for controlling stance. They contribute to the eversion movement of the foot, and also to the maintenance of the arch of the foot to ensure optimal postural stabilityExperiment 2 was to test whether the attentional demand required for equilibrium maintenance is reduced when standing on the biomimetic surface, compared to a control surface. To further compare the effect between standing on a biomimetic and standing on a non-biomimetic textured surfaces, the grooved surface used in Experiment 1 was selected as the control surface. The choice of the grooved surface was motivated by the fact that its comparison with the biomimetic surface allows for excluding a simple effect of the presence of texture on the surface and can then highlight the role played by a geometrical distribution of the texture mimicking the receptive features of the foot skin.The goal of Twenty-one new participants (7 women) without any known neurological and motor disorders participated in the experiment . All participants gave their written informed consent to take part in this study, which conformed to the ethical standards set out in the Declaration of Helsinki and all experimental protocols were approved by the STAPS  Research Ethics Committee .Experiment 1 with one exception that pertained to the dual task (DT) paradigm. We used a demanding cognitive task to increase the participants’ attentional load while their supporting surface was translated as in Experiment 1. Participants were asked to listen to a series of ten different three-digit numbers spelled out at high speed  which ended at any time before the platform translation. The series of numbers varied across trials but were the same for both surface textures and participants. Participants were instructed to silently count the number of times that 7 was part of the three-digit numbers and to provide their response at an auditory tone occurring 3 s after the platform translation onset . The same procedure was used for the trials in the steady platform condition. We counterbalanced the presentation of the different conditions  across participants but prevented the occurrence of two successive textures involving the dual task for fatigue prevention.The procedure was identical to that in The participants’ performance in the cognitive task was assessed by computing, for each surface texture, the average percentage of errors ((number of errors/10 numbers) × 100). An error was counted each time that the participant reported an incorrect number of occurrences of the number 7.Experiment 1, one-way ANOVAs were used for mean comparisons with the support surface  as the intra-participants factor. We computed statistical maps by contrasting the current maps  computed when standing on a biomimetic surface and control surfaces using t-tests (significance threshold p < 0.05)75. We applied an FDR  correction for multiple comparisons across regions76.The behavioural and EEG data were submitted to separate analysis of variance (ANOVA) with repeated measurements. In Experiment 2, a 2 × 2 ANOVA was used for mean comparisons with the support surface  and task  as intra-participants factors. Significant effects  were further analysed using Newman-Keuls post-hoc tests.In 2) to estimate the effect size of the different effects that had the independent variables on the dependent variables 77.We provided the partial eta squared values (η


Treating and imaging patients in the upright orientation is gaining acceptance in radiation oncology and radiology and has distinct advantages over the recumbent position. An IRB approved study to investigate the positions and orientations of the male pelvic organs between the supine and upright positions was conducted. The study comprised of scanning 15 male volunteers (aged 55–75 years) on a 0.6 T Fonar MRI scanner in the supine and upright positions with a full bladder and in the upright position with an empty bladder.The Pelvic study revealed that in the upright position the1. Position and shape of the prostate are not impacted significantly by bladder fill.2. Distance between the sacrum and the anterior bladder wall is significantly smaller.3. Anterior‐Posterior length and the bladder width is significantly larger.4. Seminal vesicles are pushed down by the bladder.5. Top of the penile bulb is further away from the apex of the prostate.These observed differences could positively impact upright prostate treatments by1. Reducing the risk of small bowel approximating the treatment volume.2. Prostate treatments can be done with a reduced focus on bladder fill.3. Radiation beams for treating intermediate risk prostrate can be made smaller or a larger portion of the seminal vesicles can be treated with the same beam size than typically used for supine treatments.4. Reducing the average dose to the penile bulb. Two recent papers from Sulman et al.,10 Several recent papers address the benefits and possible advantages of upright treatments and the rationale to re‐consider treating patients in the upright orientation again.Nevertheless, the seated position is still used regularly for intracranial treatments at many particle therapy facilities.A recent paper by Boisbouvier et al. showed excellent results for immobilizing the pelvis in the upright orientation using external surface data.Techniques have been developed to reduce the radiation dose to neighboring tissues when treating the prostate in a recumbent position. The use of SpaceOAR GelChanges in rectal content, that is, mainly rectal gas but also stool, can rapidly change the displacement of the prostate in the recumbent position. The appearance (formation) of gas in the rectum has been addressed using a special rectal balloon that has an air release mechanism that allows for rectal air to escape after the balloon has been inserted. The use of a full bladder and a rectal balloon also anchor the prostate in a more stable position during treatment by applying pressure on the prostate in two directions.Considering the forementioned challenges, the question therefore arises whether it is even feasible to treat the prostate in the upright position based on the possible anatomical changes in the male pelvis between the recumbent and upright positions. The goal of the present work is to answer this question by looking at the changes in the prostate position, bladder shape and changes in anatomical distances between the major pelvic structures between the supine and upright orientations. It is postulated that the increased gravitational forces on the pelvic organs in the upright orientation will stabilize and anchor the pelvic organs, more specifically the prostate, and will have a net positive impact towards prostate treatments in the upright position.22.1. Fifteen volunteers with intact prostates were recruited into the study and men that had previous prostate procedures such as radiation therapy to the pelvic region  or ablative procedures were excluded. All participants underwent MRI scans on a FONAR 0.6 T UPRIGHT® MRI at FONAR headquarters in Melville, New York. The UPRIGHT® MRI is equipped with an adjustable patient bed that enables scanning patients at bed angles ranging from 0 degrees  to 84 degrees . Each volunteer spent about 45 min at the facility. The MRI study included T2‐weighted sagittal and axial scans with a semi‐full (at least 70%) bladder in the supine position. Each volunteer was then repositioned in the same scanner, and the scans were repeated in the upright position. The volunteer then went to the bathroom and emptied his bladder. After voiding, the volunteer returned to the scanner for the same T2‐weighted axial and sagittal scans with an empty bladder in the upright position. Sixteen sagittal T2‐weighted images were acquired in 1:35 using a driven‐equilibrium fast spin echo (FSE) sequence  with 2.0 mm × 2.0 mm in‐plane resolution and a 5.0‐mm slice thickness (inter‐slice gap of 1.0 mm). Forty axial T2‐weighted images were acquired in two interleaved 4:56 acquisitions using a FSE sequence without driven equilibrium  with 2.0 mm × 2.0 mm in‐plane resolution and a 3.0‐mm slice thickness (no gap between slices). The displayed field‐of‐view was 260 mm in both cases. The objectives of the scan protocols are listed in Table A study to observe and measure the anatomical changes in the male pelvis between the supine and upright positions using an upright MRI scanner was conducted. The study was designed based on a preliminary study that investigated changes in the prostate position between the supine and upright positions, using an upright MRI scanner, as was reported by Mackie et al.Figure T2‐weighted sequences were chosen for this study because they produce bright signals from urine in the bladder and excellent contrast between surrounding soft tissues and landmark bony structures, as seen in Figure 2.22.2.1www.mim‐software.com). Discrete anatomical landmarks for all the volunteers using the sagittal and axial scans were identified. The 3D coordinates of all the landmarks were exported from MIM using a DICOM format and were used to calculate several metrics to evaluate the anatomical changes between the supine and upright orientations. The anatomical landmarks identified in the central sagittal plane are illustrated in Figure The scans for all the volunteers were analyzed in several ways using the MIM Maestro V6.9.3 platform .The Y and Z coordinates for the supine full bladder and the upright empty bladder were used in Equation  for the 2.2.6N = 15. When the data is best described by a single sample, then a one sample t‐test (OTT) was performed, 2‐sided. The vector position changes that are all positive vector modulus values were checked for significance above random chance with a Chi‐squared test (CHS). The Chi‐squared test provides a right‐sided probability that the observed variations are just by chance alone as one would expect for a normal distribution, or whether something else other than chance is at play if the test fails and the variance exceeds an expectation value that is based on chance from normal variations alone.  Hence, a small p‐value here confirms the expectation of the normal variation expectation of change. All the other tests had a hypothesized change of zero as the null hypothesis. Therefore, if a significance test passes , then it means a change that is not expected from just measurement variations are observed. If a significance test fails, it should be interpreted as not seeing evidence in these data for a significant change from the change in conditions. Two conditions were studied for significance: (1) bladder fill state: full versus empty, and (2) the patient position, upright versus supine.A few types of statistical tests were performed to assess the significance of observed changes as described by Rosner.3p < 0.001, PTT and p < 0.001, WRGA) and that the distances between the posterior edge of the bladder and the sacrum are significantly smaller in the upright position .The MRI scans for most of the volunteers showed the same interesting trend, that is, that the AP lengths of the bladder are significantly longer in the upright position . This SI shift of the prostate is clearly visible in Figure p>>0.05, OTT and p>>0.05 WRGA). The average change in the Tip of S1 and the bladder neck position in the upright position with a full and empty bladder is only −0.5 ± 2.1 mm.The distances between the Tip of the S1 vertebra and the bladder neck (representing the top of the prostate) for the upright full bladder orientations are significantly larger than in the supine position (p>>0.05), and the vector change also was not significant (p>>0.05). A Chi‐squared test with the expected variation equal to observed variations in each direction shows that changes in bladder conditions, are likely just expected variations . This is the same for the bladder neck position changes. The state of the subject's bladder filling did not have any significant effect on the bladder neck positions, in neither the Y nor the Z directions (p>>0.05). The vector changes in the bladder neck were also not significantly changed with respect to bladder fill (p>>0.05). The same Chi‐squared test as described above showed that the observed changes in bladder conditions with the bladder neck measurement are also likely just due to random variations in both directions, but since it is greater than 0.05, one could say that there are not enough measurements to conclude this with certainty .The changes in the bladder neck and prostate apex positions with a full and empty bladder in the upright position were tested for significance. Each direction, Y and Z for the prostate apex showed no significant changes due to bladder fill in the upright position .The rotations required to align the pelvis for each volunteer for the supine full and upright empty bladder conditions to the upright full bladder orientation revealed that a significant pelvic rotation was required from supine to upright . This correlates with the significant change in position of the prostate between the supine and upright orientations. The change in prostate angle as a result of emptying the bladder in the upright position was, however, not statistically significant which again correlates with the prostate position data .A significant rotation of the prostate occurs in most cases between the supine and upright positions . This average change observed in the apex to penile bulb distance was 2.4 mm ± 3.7 mm (1 SD). The same distance did not change significantly per patient between empty and full bladder conditions in the upright orientation .The distance from the apex to the penile bulb for a full bladder increased significantly when changing from the supine position to the upright orientation  is significantly larger in the upright orientation than in the supine position, indicates that the gravitational forces on the prostate, in the upright position, pushes the prostate inferiorly—see Figure The finding that the shifts in both the bladder neck and apex positions are larger between the supine and upright positions than the shifts introduced because of emptying the bladder in the upright position is easy to understand bearing in mind the gravitational forces exerted on the prostate by the bladder and abdominal contents. The bladder neck points tend to shift more than the apex points which is easy to understand since the bladder is such a large organ and moves significantly in the AP direction. The apex of the prostate is further away from the bladder and is therefore less impacted by the bladder movement. This is confirmed by the rotation of the prostate relative to the prostate angle in the upright full bladder orientation calculated from the bladder neck and apex points. The large rotations in the prostate angle between the supine and upright orientations is mainly due to change in the force vector exerted on the prostate as explained above since the data was re‐aligned to correct for the natural rotation in the pelvis between the supine and upright positions. The change in the prostate angle is primarily due to the shift in the bladder neck point as discussed above.The statistical analyses of the bladder neck and prostate apex positions in the upright orientation with a full and empty bladder, showed that there was no evidence from this study that the prostate position is affected by the bladder fill condition in the upright orientation. This is unlike the supine orientation, where the impact of changes in bladder fill, on the prostate position, is well‐known and documented.The finding that the full bladder is significantly more elongated in the AP direction and that the posterior edge of the bladder is closer to the sacrum in the upright position can be explained by the changes in the gravitational forces on the bladder. The abdominal contents, due to gravitational forces, flop in the anterior and inferior directions (forward and downward) when the patient is in the upright position and primarily posteriorly (backwards) in the supine position. The abdominal contents therefore apply pressure onto the bladder from a more superior and anterior direction pushing the bladder down and backwards while in the supine position the force on the bladder is weaker and in a lateral direction. This is illustrated in Figure The fact that the posterior bladder edge is closer to the sacrum in the upright position is counter intuitive as one would think that gravity would pull the bladder more posteriorly in the supine position. This is further illustrated in Figure A significant pelvic rotation is evident between the supine and the upright orientations as demonstrated by the deviations between points from the supine posture to the upright posture shown in Figure The small statistically significant increase in the distance between prostate apex and the top of the penile bulb when changing from the supine position to upright orientation was a surprise. The fact that this distance was not impacted by bladder fill condition in the upright position is to be expected since the prostate position is not impacted by bladder fill. The small increase in the apex to penile bulb distance in the upright orientation could be ascribed to increased gravitational forces on the muscles inferior to the apex in the upright orientation.The differences in the position of the seminal vesicles shown in Figure The fact that the bladder is more elongated in the AP direction for the upright orientation, suggests that the bladder will be more effective in pushing the small bowel away from the radiation field. Furthermore, since the channel between the sacrum and the bladder is closed or narrower  and apply pressure more superiorly and away from the prostate. The use of a rectal spacer such as the SpaceOAR Gel to create space between the rectum and prostate will most likely be the only option for upright treatments since using a rectal balloon in the upright orientation might be problematic in many regards.5An IRB approved study to investigate the anatomical changes in the male pelvis between the supine and upright positions was conducted. The study revealed that the anatomical changes in the male pelvis could potentially favor the upright position for prostate treatments. The increased downward pressure on the bladder and prostate in the upright position appears to have a stabilization effect on the prostate since the changes in bladder fill did not impact the prostate position and orientation in the same manner as reported in the literature for the supine position. This holds great promise for upright prostate treatments removing the burden of a reproducing the bladder volume at the time of the CT scan.Considering the forces on the bladder and subsequently on the prostate as discussed above, it is expected that concerns about prostate movements during treatment in the upright position might be reduced or even eliminated. Since no significant changes in the prostate position were observed between full and empty bladder conditions, it is expected that the increased gravitational force on the prostate will also reduce the impact of rectal content changes on the prostate position. The fact that the bladder is more extended over the prostate and is also closer to the sacrum in the upright position might reduce the risk of small bowel getting into the treatment beams. The observation that the extended bladder in the upright orientation pushes the seminal vesicles in the inferior direction, will require a smaller radiation field to treat the same amount of the seminal vesicle for intermediate risk prostates treatments in the supine position. Although small, the increased separation between the prostate apex and the penile bulb could result in a small reduction of the average dose to the penile bulb when treated in the upright orientation. It is obvious that the empty bladder condition would not be clinically acceptable for treatment due to the proximity of the small bowel when the bladder is empty as well as the amount of bladder wall that will get irradiated.The primary conclusion therefore is that there was nothing observed in this study of the male pelvic anatomy, that would prevent prostate treatments in the upright orientation. The preliminary data suggests some advantages in treating in upright position but more research including dosimetric comparisons when CT data of the pelvic region becomes available is recommended. Furthermore, based on the data reported by Boisbouvier et al.Niek Schreuder: Conceptualization and study design, obtained IRB approval, collected the data and wrote the paper. Wen‐Chien Hsi: Data analyses using MIM, reviewed and edit the paper. John Greenhalgh: Developed the optimal MRI scan sequences and operated the scanner. Michael Kissick: Statistical analyses of the data. Michelle Lis: Review and edit the paper. Tracy S A Underwood: Review and edit the paper. Harry Freeman: Participated in the study design, data collection and scheduling of volunteers. Michael Bauer: Participated in the study design, data collection and scheduling of volunteers. Stephen Towe: Conceptualization and study design. Rockwell Mackie: Conceptualization and study design as well as critical review and editing of the paper.Niek Schreuder, Michael Kissick, Michelle Lis, Tracy Underwood, Harry Freeman, Michael Bauer, Stephen and Rockwell Mackie‐ No conflict of Interest—but all are full time employees of Leo Cancer Care. Wen‐Chien Hsi—No conflict of interest. John Greenhalgh: No conflict of interest—Employee of Fonar.


Periodic sound reduction at some frequencies and high pressure loss could be considered as the disadvantages of simple expansion silencers. Generally, reactive elements are applied in silencers to optimize their acoustic and aerodynamic performance. In this paper, we were going to investigate the combined and independent effects of reactive elements, baffle and extended tubes at the inlet and outlet of simple expansion silencer, on the acoustic performance and pressure loss of simple expansion silencer. Firstly, simple expansion silencer dimensions were determined based on theoretical calculations to attenuate the noise by 10 dB. Secondly, the simulation was performed using COMSOL acoustical module software based on finite element method to predict silencer sound transmission loss and pressure loss, respectively, before and after adding reactive elements. Then, according to ISO7235, ISO3744 and ISO3746 standards noise insertion loss of various silencers under study was measured in a free field and in the following that silencers pressure loss evaluated. Finally, the predicted results with the software were compared with the experimental ones. The addition of the extended tubes increased the transmission loss and insertion loss at low and medium frequencies and mitigated the pressure loss of the silencer compared to the simple expansion silencer. The baffle increased the transmission loss curve in the medium frequencies compared to the simple expansion silencer. The combination of baffle and extended tube elements caused an extraordinary increase in insertion loss and transmission loss at the medium frequencies and a decrease in pressure loss. It could be concluded from the present study that using extended tube might be probably the best choice to reduce pressure loss and increase the acoustic performance of simple expansion silencer at low and medium frequencies and what's more is that the best acoustic performance in medium frequencies can be achieved by using a combination of baffle and extended tube. Noise pollution not only endangers the lives of most people, but is also one of the important factors of environmental pollution. This affects a person not only physically, but also mentally. For these reasons, noise reduction is very important in societies, and preventing noise is a growing concern in industry and the environment .Noise attenuation in sound generating sources can be categorized as active and passive methods. Passive noise control methods are used more than active ones due to lower costs, small geometries and compatibility with the noise generating device in harsh environmental conditions. Among the types of passive noise control methods, we can mention acoustic silencers, noise barriers and, noise absorbing panels . In the Basically, the acoustic performance of silencers is characterized by parameters such as insertion loss (IL), transmission loss (TL), noise reduction rate (NR). Additionally, aerodynamic performance, commonly known as pressure loss, is measured by the total air flow pressure. The most common parameter used to evaluate the acoustic properties of a silencer is the transmission loss (TL) . The traUsing analytical methods to evaluate the performance of silencers with complex internal geometry is very exhausting and time-consuming. Numerical solution methods such as finite element and boundary element methods are suitable for predicting the performance of reactive and absorptive silencers with different geometries ,10. MiddMany researchers have worked to increase the transmission loss as the first goal in the silencer and reduce the pressure loss as the second goal . AssessiOne of the ways to increase the transmission loss of simple expansion silencers  is to inWhere TL represents the value of sound transmission loss, m is the cross-sectional area ratio (D/d), k is the wave number (k = 2π/λ = 2πf/c = ω/c) and L is the length of the expansion chamber in meters. The maximum amount of sound reduction occurs when L equals to 1/4 of the wavelength or an individual number of 1/4 of the wavelength of the sound frequency under investigation. Therefore, by calculating the length of the silencer from Eq. Generally, the optimum acoustical performance range of expansion silencer was deemed to be below the first cut-off frequency. The following equation, Eq. In this equation, C represents the speed of sound (m/s) and D is denoted as the diameter of the silencer expansion chamber in (m).The use of sound-absorbing fibrous materials inside the expansion chamber improves the above mentioned limitations and increases the transmission loss in medium frequencies and frequencies higher than the cut-off frequency. The escape of sound absorbing materials is associated with problems . SelametMoreover, improvement in the transmission loss of simple expansion silencers could be divided to adding extended tubes at the inlet and outlet of the silencer, baffles, asymmetric inlets and outlets, extended tubes constructed from punched metal sheet and connecting expansion chambers in series . VariousAccording to the location and size, the baffles can extremely reflect the sound waves, like the end part of the expansion chamber, toward sound source and subsequently increase the acoustic performance of the silencer. As if adding baffles could be led to an increment in pressure loss, a cavity or hole on the surface of the baffle is usually used to pass the air flow and adjust pressure loss.However, increasing the length of the extended tube, the type and location of the baffle can improve the performance of expansion silencers, previous work has probably failed to address the acoustic and aerodynamic performance of expansion silencers with different extended inlet and outlet lengths. Moreover, there is some controversy surrounding the acoustic performance and loss pressure of silencers having perforated baffle with the same diameter size as the chamber inlet and outlet tubes. As well as that, it has not been widely understood whether a combination of baffle and extended tubes can optimize silencer performance. Despite this interest, as far as we know no one has studied measuring noise insertion loss in experimental set up with silencers and tubes which had approximately real size. The present paper aims to examine the influence of extended inlet and outlet tube with different sizes, utilizing baffle with a central hole in the middle of chamber and combined aforementioned reactive elements on the acoustic and aerodynamic performance of simple expansion silencers using the computer simulating software COMSOL Multiphysics and the simulation results were verified with experimental ones.22.1The length and diameter of a simple expansion were calculated based on Eqs. In order to identify the effect of the baffle on the performance of the simple expansion silencer, a baffle with a central hole of 15 cm in diameter ) was formed in the middle of the expansion chamber, so the simple expansion chamber was divided by two simple expansion chambers with the same length. .Fig. 4Exa = length of inlet tube, Lb = length of outlet tube, L = length of silencer expansion chamber, δ = final correction factor. The final correction factor was calculated from Eq. For the silencer with extended inlet and outlet , the len0 = 0.005177, a1 = 0.0909, a2 = 0.537, a3 = −0.008594, a4 = 0.02616, a5 = −5.425, tw is the thickness of the inlet and outlet tube (0.2 cm), d is the diameter of the inlet and outlet tube and D is the diameter of an expansion silencer.The values of aUsing the central baffle as a resonator to increase the performance of the simple expansion chamber transforms it into two smaller expansion chambers, so the extended tubes at the inlet and outlet of these new smaller chambers will be half and a quarter of the length of the new chambers, respectively. It should be noted that final correction factor for these new smaller chambers were calculated separately based on their new dimensions .Fig. 6Ex2.22.2.1The geometry of the studied silencers was designed in the pressure acoustics module using COMSOL 5a multiphysics software. The silencer components consist of expansion chamber, inlet and outlet tubes, extended inlet and outlet tubes and, baffle.2.2.1.1The acoustic analysis in the frequency domain is governed by Helmholtz equation, equation number 8, which is expressed as follows Eq.  [[28], .(8)∇.TL=10For the meshing of the silencer, a tetrahedral mesh has been selected. The mesh size was assigned to be one fifth of the wavelength with the highest frequency under investigation (λmin/5)  31].Fig.Fig31].F2.2.1.21All solid surfaces that include the outer walls of the expansion chamber, silencer inlet and outlet tubes, baffle and extended tubes were considered as sound hard boundary and soundproof .2A combination of input and output flat waves was considered for the input surface of the silencer Eq. .0 = 1 Pa is the pressure applied at the opening of the inlet tube and i is an imaginary unit. ω is angular frequency, ρ is air density and c is the sound speed.3An outgoing flat wave was assigned for the outlet port surface of the silencer Eq. .2.2.22.2.2.13), respectively.The investigation of the aerodynamic performance (pressure loss) of the silencers was done with a two-dimensional symmetrical model in the form of steady flow. The equations governing this part of the modeling are the Navier-Stokes, Eqs. T reveals Turbulent viscosity (kg/(m.s)) and is expressed according to Eq. 2/s2) and Turbulent dissipation rate (m2/s3), respectively. The coefficients of these equations are C€1 = 1.44, C€2 = 1.92, Cμ = 0.09, σk = 1 and σ€ = 1.3.The model applied to solve the Navier-Stokes equations is the k-ε turbulence model such that the kinetic energy of the turbulence k and the amount of wasted energy ε are obtained from solving the transition, which are expressed as follows Pk=μAn extra fine tetrahedral mesh was used for meshing .Fig. 8Ex2.2.2.2Air as an ideal gas was used in aerodynamic simulation. Air fluid properties are depicted in 2.3.Black iron sheet with a thickness of 0.2 cm and a flange with a thickness of 0.4 cm were used to prepare silencer. Construction and assembly operations were performed by welding and plasma cutting. At first, a simple expansion silencer was fabricated such that the other silencers under study could be assembled by connecting baffles and extended tubes. In other words, a modular acoustic silencer was designed and constructed .Fig. 9Co2.42.4.1Experimental measurement, in accordance with ISO7235, was performed to determine silencers acoustic insertion loss without air flow condition. This particular method has been chosen on account of the fact that insertion loss equals sound transmission loss. An experimental set up and the schematic diagram adopted to evaluate insertion loss was illustrated in The sound power level should be measured at two distinct modes at the duct's end, with silencer and while substitution duct replaced with silencer, based on ISO 7235. The difference in the sound power level in the two modes indicates the insertion loss of the silencer. The pink noise was created by Cool Edit noise generation software and amplified by an amplifier before delivering to the loudspeaker as a noise source. It should be mentioned that in order to direct all noise generated by speaker into the inlet duct, speaker was surrounded by an acoustic enclosure. All internal surfaces of acoustic enclosure were covered by sound-absorbing materials. The speaker enclosure was a cubic chamber with a length, width and height of 1 m. It was connected to the inlet duct through a connector. The length of the duct used in the distance between the speaker chamber to the silencer and the silencer to the measurement location (silencer outlet) is equal to 3.5 m .Output sound power level of silencer and substitution duct was measured and calculated by ISO3744 and ISO3746 standards in a free field . A microphone array like a hemispherical measurement surface was utilized to measure sound pressure level on 10 different points by a sound level meter. A hygrometer, thermometer and, a PROVA anemometer was used to measure relative humidity, temperature and wind speed, respectively. According to ISO 3744 and based on the fact that the difference between the sound pressure level of the background and sound source was more than 15 dB, the background noise coefficient was considered to be zero and was not applied. Another point was that, referring to the aforementioned standard and taking into account that the measurement was performed in the free field with a reflective plate, the environmental correction factor was also ignored. So, the insertion loss was calculated from Eq. (201 .(21)IL=L2 is the sound power level without silencer (with substitution duct), and Lw1 is the sound power level with silencer.Lw2.4.21 mean total pressure in upstream and pt2 mean total pressure is in downstream.An experimental set up and the schematic diagram adopted to evaluate the pressure loss of silencers were created, as illustrated in 33.1The results of theoretical calculations for silencers are reported in 3.2According to the calculations, sound transmission loss curve for the aforementioned dimension of simple expansion silencer was presented in Experimental measurement of noise insertion loss for simple expansion silencer are highlighted. Generally speaking, It can be seen that insertion loss is 9 dB in the frequencies of 32 and 63 Hz, 2–3 dB in the frequencies of 125 and 250 Hz, 6–7 dB in the frequencies of 500 and 1000 Hz and, almost negligible after the first cut-off frequency. Overall, The acoustic performance of the simple expansion silencer was poor such that the total insertion loss was about 4 dB.The propagation of sound waves inside the simple expansion silencer up to the first cut-off frequency is in the form of flat and one-dimensional waves. As it can be seen in Considering the effect of reactive elements at frequencies lower than the first cut-off frequency and as well as that the accuracy and precision of the modeling results up to the first cut-off frequency, to investigate carefully the effect of these elements and compare the performance of silencers, transmission loss curve and the sound transmission loss bar charts of the under studying silencers are illustrated in frequencies lower than 2000 Hz in In comparison to simple expansion silencer, the baffled silencer transmission loss curve, as shown in It is interesting to note that changing the length of the expansion chamber by adding a baffle in its middle caused the poor performance of the silencer at the frequency of 500 Hz and its adjacent frequencies. For instance, the transmission loss curve increased in the other investigated frequency (660 Hz) in this silencer. The function of the baffle as a noise barrier inside the expansion chamber increased the transmission loss curve in the medium frequencies. In contrast, baffle reduced the transmission loss curve at low frequencies (below 250 Hz) compared to a simple expansion silencer. In other words, adding a baffle to a simple expansion silencer increased the amount of transmission loss 11–12 dB in octave frequencies (250–1000) and caused a decrease in the transmission loss at 63 and 125 Hz frequencies compared to the simple expansion silencer .Experimental results demonstrated that the baffled silencer is the one with the lowest acoustic performance. The total sound pressure level before installing the silencer (with a substitution duct) and after installing the baffled silencer was measured to be 90.1 and 88 dB, respectively . In otheTherefore, according to the obtained results, it can be concluded that adding a baffle inside the chamber and its location should be based on the target frequency and the length of the chamber. In this study, the baffle had not been designed for a specific target frequency, and the aim was only to investigate its effect on the performance of the simple silencer. So, adding a baffle in the middle part of the chamber accidently improved the performance of the simple expansion silencer in some frequencies and weakened it in others. Adding a baffle with a central hole in the middle part of the silencer operates like a sound barrier in the propagation path of sound waves inside the chamber and returns back of sound waves toward the sound source, similar to what happens at the end of a simple expansion chamber. This phenomenon leads to an increment in sound interference and eventually sound waves dissipate in some frequencies.The distribution of sound pressure level for baffled silencer at frequency 500 Hs was depicted in The acoustic performance assessment of the baffled silencer at other frequencies such as 660 Hz b showed It is fundamental to note that the addition of extended tubes to the simple expansion silencer resulted in the best acoustic performance at frequencies 32–1000 Hz and especially at frequencies 125–500 Hz. In The extended tubes silencer compared to the simple expansion silencer demonstrated a tremendous increase in noise insertion loss in low and medium frequencies, If the length of chamber is considered to be fix and the entry and exit locations of the sound waves are changed, a wide frequency range of sound waves would be trapped between the tubes and the wall of the chamber. As illustrated in A good correlation and consistency were observed between the results of modeling and field measurements of simple expansion and extended tubes silencers. Gupta conducted a research on the simple expansion silencer, the expansion silencer with extended tube at the inlet, the expansion silencer with extended tube at the outlet, and the expansion silencer with extended tubes at both the inlet and outlet using the COMSOL software and experimentally. The expansion silencer with extended tubes at the inlet and outlet simultaneously had the highest noise reduction among the investigated silencers . In GuptAdding two reactive elements at the same time, a baffle and extended tubes, to a simple expansion silencer results in the elimination of all periodic resonances and an increase in the transmission loss curve at medium-range frequencies up to the first cut-off frequency . ExaminiSilencer with extended tubes and baffle experienced more noise insertion loss of 17, 19 and 5.7 dB at frequencies of 500 Hz, 250 Hz, and 1000 Hz, respectively, compared to the simple expansion silencer, as illustrated in The presence of the baffle in this silencer also had a negative impact on lower frequencies, resulting in a decrease in transmission loss at frequencies of 32 Hz, 63 Hz, and 125 Hz. Similar results have been obtained for insertion loss at these frequencies. Although, the overall performance (insertion loss) of this silencer improved by 1.5 dB compared to expansion silencer, the negative effect of the baffle on lower frequencies reduced the overall performance of this silencer by 2.5 dB compared to the silencer with extended tubes without a baffle. So, this silencer can be the best choice for a sound source with dominant frequencies in medium-range. In a study conducted by Middleburg to examine the acoustic performance of various types of simple expansion silencers, baffled silencers, and those with extended inlet and outlet tubes using CFD methods, it was found that baffles and extended tubes had similar effects on the performance of the silencer under investigation . The comThe excellent performance of this silencer at 500 Hz is reported in Comparison of the results of modeled sound transmission loss and measured insertion loss of silencers in octave band frequencies is reported in Comparing the insertion loss and sound transmission loss of a simple expansion silencer and a baffle-equipped silencer in octave band frequencies shows that adding a baffle to the simple expansion silencer reduces the sound transmission loss at frequencies of 32, 63, and 125 Hz. At a frequency of 125 Hz, there is a significant difference in the results of insertion loss and sound transmission loss between the simple expansion silencer and the baffle-equipped silencer.The measurement of the acoustic performance of silencers in this article is conducted in the frequency range of 32–8000 Hz, and the performance of the silencer even partially affects the overall results at frequencies higher than the first cut-off frequency. However, the model results are only applicable and comparable up to the first cut-off frequency due to the use of one-dimensional flat waves in the modeling, in reality as the frequency increases it probably increases scattering non-flat sound waves, which can significantly affect the insertion loss (IL). Nevertheless, there is a correlation and regular pattern in the increase and decrease of the silencer performance in IL and transmission loss (TL) graphs in the corresponding frequencies, as shown in 3.3The results of pressure loss modeling for the studied silencers are reported in Furthermore, the experimental measurement results of the pressure loss for the silencers are reported in Adding extended tubes to a simple expansion silencer has been resulted in a decrease in the speed and overall pressure loss of the airflow inside the silencers. The investigation of pressure loss in the simple expansion silencer showed that an increase in airflow speed at the end section and the constricted section of the expansion chamber led to an increase in pressure loss. Adding baffles, considering the increased number of these constrictions, and with the central hole diameter of the baffle equal to the inlet and outlet diameter of the silencer, caused a partial increase in airflow speed and further pressure loss. Experimental results also indicated that the pressure loss in the baffle silencer was slightly higher than that in the simple expansion silencer for all examined flow speeds. This issue could be mitigated by increasing the diameter of the central hole of the baffle. The pressure loss results in The modeled and experimental results of pressure loss in the silencers have been reported in By comparing the pressure loss of the silencers in In this study, there were limitations in providing requested conditions based on ISO 3744 and ISO 3746 standards for measuring insertion loss such as an environment without reflective surfaces, the influence of wind gusts, and transient sound sources like motorcycle and car noises. These limitations increased the number and duration of measurements. It is suggested to use empirical methods employing microphones inside the ducts to reduce measurement errors when measuring transmission loss. Furthermore, it is recommended to investigate the effects of increasing the baffled hole diameter compared to the inlet diameter and increasing the number of baffles in future studies.4The results of this paper show that the addition of an extended tube to the simple expansion silencer, by increasing the transmission and insertion loss at low and medium frequencies, increases the acoustic performance of the silencer in the frequency ranges up to the first cut-off frequency and also reduces the pressure loss compared to the simple expansion silencer. The addition of a baffle with a central cavity alone increases the transmission and insertion loss at individual frequencies compared to a simple expansion silencer, but reduces the acoustic performance of the entire silencer by reducing the transmission and insertion loss at low frequencies and also increases the pressure loss. The addition of baffle and extended tubes increase the transmission and insertion loss in the medium frequencies and decreases the pressure loss of the silencer compared to the simple expansion silencer and the other silencers studied. The presence of a baffle in this silencer and its negative effect by reducing the transmission and insertion loss at low frequencies reduces the acoustic performance of the silencer compared to the silencer with an extended tube. The results of modeling using COMSOL software as a finite element method have also shown that this method can save time and costs and avoid the errors and problems of the experimental test method.10.13039/501100006396Qazvin University of Medical Sciences.This study has been performed within the framework of a faculty research project under the code of ethics Committee of IR. QUMS.REC.1398.241 . It has been supported by the Research Vice-Chancellor of No additional information is available for this paper.Motaleb rahimi: Conceived and designed the experiments; Performed the experiments; Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data; Ali safary: Contributed reagents, materials, analysis tools or data. Saeid Ahmadi: Conceived and designed the experiments; Analyzed and interpreted the data; Wrote the paper.The data that has been used is confidential.The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.


Visual feedback normally helps guide movements to their goal. When moving one’s hand, such guidance has to deal with a sensorimotor delay of about 100 ms. When moving a cursor, it also has to deal with a delay of tens of milliseconds that arises between the hand moving the mouse and the cursor moving on the screen. Moreover, the cursor is presented at a certain rate, so only positions corresponding with the position of the mouse at certain moments are presented. How does the additional delay and the rate at which cursor positions are updated influence how well the cursor can be guided to the goal? We asked participants to move a cursor to consecutive targets as quickly as they could. They did so for various additional delays and presentation rates. It took longer for the mouse to reach the target when the additional delay was longer. It also took longer when a lower presentation rate was achieved by not presenting the cursor all the time. The fraction of the time during which the cursor was present was more important than the rate at which the cursor’s position was updated. We conclude that the way human arm movements are guided benefits from continuous access to recent visual feedback. Seeing our moving limb influences how we move  until the next frame appears. If the movement is continuously guided by where the cursor is shown, presenting the cursor for a long time at the same position (by reducing the frame rate) might be equivalent to increasing the additional delay, because the time at which the mouse reached the corresponding position gradually increases throughout the presentation at that position. It might be better to present the cursor briefly with extended time intervals during which no cursor is visible, especially if intermediate positions can be inferred from the motion  ASUS TUF VG279QM monitor with a resolution of 1920 by 1080 pixels. This monitor has a fast in-plane switching (IPS) panel on which images remain visible throughout each frame with little overlap between frames. We used frame rates of 60, 120 or 240 Hz in Experiment 1, and a frame rate of 240 Hz in Experiment 2. We used a ROCCAT KONE Pro Gaming mouse to measure participants’ hand movements at 1000 Hz. We determined the delay between motion of the mouse and the cursor with the help of the fast video option of a Sony RX 10Before testing participants, we determined the motion-to-photon latency by placing both the mouse and the cursor within view of the camera and hitting the mouse with a rigid object. We then visually inspected the images of the video recorded by the camera frame by frame, and counted the number of frames  between the moments the mouse and the cursor moved , we determined the additional delay in the manner described above. When we increased the additional delay by drawing the cursor ourselves, the range of measured delays for the 25 repetitions was larger than when the operating system drew the cursor, because the timing of sampling the mouse coordinates and drawing the cursor is no longer optimised. In that case, we found ranges between 13 and 17 ms at 240 Hz and 15 ms at 120 Hz. We will initially ignore this increase in the range of measured delays, and will discuss how it might have influenced our findings in the discussion section.In Experiment 2, we always used the shortest possible additional delay (8 ms at 240 Hz), but we did not always present the cursor on each frame. We either presented it on each frame, or skipped 1, 2, 3, 4, 5, 7, 9 or 11 frames after each presentation, so that the cursor was visible on all frames or only every second, third, fourth, fifth, sixth, eighth, tenth or twelfth frame (nine conditions). Note that we only skipped cursor presentations; the target remained visible. As reducing the time that the cursor was visible reduced its effective contrast, we also included three conditions in which we presented the cursor at 240 Hz with contrasts that matched the time-averaged contrast when skipping selected numbers of frames. Experiment 2 therefore had 12 conditions. To match skipping 3, 7 or 11 frames, we presented the cursor at a contrast of a quarter, an eighth or a twelfth of the original contrast. To do so, we calibrated the luminance of the screen with a Minolta CS 100A Chroma Metre.effective delay will be longer. We define the effective delay as the time between the mouse reaching a presented position and the moment half way between when the cursor was first presented at the corresponding position on the screen and when it was first presented at a different position  and 20 other participants in the second . Since the study was not designed to examine whether we could statistically reject a specific hypothesis, no power analysis was performed. We selected people who normally used their right hand to move the mouse, because the mouse that we used was designed for use with the right hand. All participants volunteered to take part in the experiment after being informed about what they would be required to do and signing a consent form . The participants did not know precisely what we were studying, but in some cases, they could guess what we were manipulating: the longest additional delay was noticeable, the cursor flickered visibly at low presentation rates, and the contrast looked lower when either the presentation rate or the contrast itself was reduced. Participants were informed that they would perform several blocks of movements that would last either 2 min (Experiment 1) or 1 min (Experiment 2). Their task was to move the cursor to as many targets as possible within that time. The participant could adjust the position of the screen, mouse and chair, as well as the height of the screen and chair, to perform the task comfortably. At the distances that they chose, 1 cm on the screen corresponds to approximately 1° of visual angle.The participants’ task was to move a 0.7 cm diameter black disc (the cursor) to a 1.3 cm diameter blue disc (the target) on a white background. The flow of events was determined by the mouse’s movements . If they indicated that they had practised enough, the practice block was terminated before the end of the two minutes. They then performed separate blocks of movements with a black cursor shown on every frame or every 2nd, 3rd, 4th, 5th, 6th, 8th, 10th or 12th frame. In three additional blocks, the cursor had one of three grey levels  and was shown on every frame. The 12 blocks of movements were presented in random order. Participants could rest as long as they liked between the 1-min blocks of movements.Our main measure was the movement time: the time between movement onset and the end of the movement. Movement onset was defined as the moment the mouse coordinates left the region corresponding with the previous target. The end of the movement was defined as the moment the mouse coordinates entered the region corresponding with the current target to remain within that region for 50 ms Fig. . To furtovershoot time: the time between when the mouse coordinates first entered the region corresponding with the current target and the end of the movement. This overshoot time was zero if the mouse entered the target and stayed there, but it was larger than zero if the mouse did not remain within the target for at least 50 ms when it first reached the target. In this case, we obviously used the mean value because the median value is zero. We also determined the fraction of trials in which participants overshot the target.For each block, we characterised the movement time and the reaction time by their median values. We used median values to avoid excessive influences of occasional outliers, such as movements that overshot the target and therefore, lasted exceptionally long because they had to return to bring the cursor within the target. To quantify the time lost in this manner we determined an To further evaluate changes in participants’ movements, we determined velocity profiles. To obtain a velocity profile that we could average across movements, we split the mouse’s path from movement onset until the first moment it entered the target into 50 equal distances, and determined the velocity when the mouse was at each of the 51 positions defined by those distances. The velocity at each of those positions was the combined lateral and sagittal velocity of the mouse, each of which was determined by simultaneous differentiation and smoothing with a Savitzky–Golay filter. We applied this filter to each sampled position of the mouse by fitting a second order polynomial to all points within 20 ms of the moment the mouse reached the position in question. We took the fit value for the first order parameter as the mouse’s velocity at that moment.condition . We were interested in systematic differences across conditions, irrespective of any overall differences in performance across participants. We, therefore, normalised the movement times, reaction times and overshoot times before determining the confidence interval. We divided all of each participant’s values for the measure in question by that participant’s mean value across all conditions. For each condition, we then determined the mean and 95% confidence interval of these scaled values across participants. Finally, we multiplied all the mean values and confidence intervals by the overall mean for that measure. We will refer to the confidence interval that we obtained in this manner as the normalised 95% confidence interval.The five measures  were determined separately for each block of each participant. They were then averaged across participants for blocks of the same As expected, the movement time increased with the effective delay Fig. A. In accFor the 240 Hz conditions, the reaction time also increased with an increasing effective delay . Decreasing the rate at which cursor positions were presented increased the movement time by more than one would expect on the basis of the effective delay  and the time it took to move to the target. This relationship is shown by the curve in Fig. It took longer to move to targets when feedback about the movement was delayed Fig. A, confirThe simplest explanation is that it is not really the presentation rate that matters, but the fraction of the time during which a cursor is visible. That would explain why reducing the screen’s frame rate does not always influence performance, but not presenting the cursor on all frames does. The only finding that is inconsistent with this explanation is the longer movement time than would match the effective delay at a frame rate of 60 Hz  the increase in the movement time was equivalent to having an effective delay of about 80 ms . In retrospect, it would have been better to always have the target appear at a fixed time after the end of the previous trial, which would mean delaying the appearance of new targets for the higher frame rates in Experiment 1. It remains to be seen whether this is enough to equate reaction times, or whether the target has to appear slightly earlier for longer delays to compensate for an influence of waiting for the cursor to reach the target (see Fig. As mentioned in the overshoot time did clearly increase with the delay (at least in Experiment 1; Fig. We had expected delays to make participants overshoot the target, because a long delay makes the cursor appear to have moved less far than it actually had, to which we expected participants to respond by moving the mouse farther. The fraction of trials in which the cursor overshot the target might be slightly larger for longer delays, but participants did not overshoot the target much more often when there was a long delay (insets in Figs. If the cursor being visible more of the time is more important than the number of cursor positions that are shown, we expect performance to be better on modern gaming screens on which the cursor is constantly visible than on old CRT screens on which the cursor is flashed briefly on every frame. MacKenzie and Ware  used a Ctargets are visible more of the time, even when the time-averaged contrast is equated (Goettker et al. Ivkovic et al.  found coOur most important observation is that movements are guided more efficiently when the cursor is visible all the time than when it is only visible part of the time, even when the rate at which new positions are presented is high. The cursor being visible more of the time even seems to be more important than the number of cursor positions that are shown. This is consistent with the idea that people continuously use visual information to guide their movements (Brenner & Smeets