In a random number generation task, participants are asked to generate a random sequence of numbers, most typically the digits 1 to 9. Such number sequences are not mathematically random, and both extent and type of bias allow one to characterize the brain's “internal random number generator”. We assume that certain patterns and their variations will frequently occur in humanly generated random number sequences. Thus, we introduce a pattern-based analysis of random number sequences. Twenty healthy subjects randomly generated two sequences of 300 numbers each. Sequences were analysed to identify the patterns of numbers predominantly used by the subjects and to calculate the frequency of a specific pattern and its variations within the number sequence. This pattern analysis is based on the Damerau-Levenshtein distance, which counts the number of edit operations that are needed to convert one string into another. We built a model that predicts not only the next item in a humanly generated random number sequence based on the item′s immediate history, but also the deployment of patterns in another sequence generated by the same subject. When a history of seven items was computed, the mean correct prediction rate rose up to 27% . Furthermore, we assumed that when predicting one subject′s sequence, predictions based on statistical information from the same subject should yield a higher success rate than predictions based on statistical information from a different subject. When provided with two sequences from the same subject and one from a different subject, an algorithm identifies the foreign sequence in up to 88% of the cases. In conclusion, the pattern-based analysis using the Levenshtein-Damarau distance is both able to predict humanly generated random number sequences and to identify person-specific information within a humanly generated random number sequence. In a Random Generation Task (RGT) the subject is asked to generate a random sequence of items. The most popular variant is the Random Number Generation Task (RNGT) in which subjects are requested to repeatedly pick a number from a given range . Earlier research showed that human beings are far from perfect in producing random sequences. They typically avoid number repetitions and systematically deviate from mathematical randomness The RNGT is a demanding task as it requires the subject to utilise a variety of criteria that constitute perceived randomness. There are established methods to analyse humanly generated random number sequences  has been established in a person’s choice of numbers, two predictions can be made: First, a detailed analysis of the individual patterns should make it possible to predict the future course of the generated number sequence of that person. Secondly, if the patterns show inter-individual differences, and to a lesser degree, intra-individual differences, the pattern analysis may allow us to identify a person on the basis of his or her patterns. The aim of the present study is to build a pattern analysis that predicts an individual’s humanly generated random number sequences and even makes it possible to identify a person using complex information provided by his or her individual patterns.Participants were students  recruited from the Christian Albrecht University Kiel, Germany. All subjects were non-smokers and reported that they were in good health, without any systemic diseases, and without any history of neurologic or psychiatric disease. They had not taken any medication or consumed any illicit drugs in a 3-month interval before the study. The study procedure was approved by the local ethics committee of the Christian Albrecht University and subjects gave written informed consent before participating in the study.For the RNGT, subjects were instructed to generate two series of 300 single digits between 1 and 9 in random order. This was paced by a tone (1 Hz). Participants rested for 7 minutes after the first series of the RNGT. The concept of randomness was explained using standard procedures . A test trial was undertaken.l as the generation of a sequence of l drawn from a finite set (target quantity D) with replacement. The generated random sequence we called i), zi(z ∈ D. As a pattern m of length n we denoted any n-tuple i),mi is shown. To mathematically measure “the similarity” of a pattern to a given sequence we introduced the function s, which takes a sequence and a pattern as input and returns a real number. The value s indicates how often the pattern is contained in the sequence. We call it score s of pattern m on random sequence z. To calculate the score of a pattern on every position of the humanly generated random number sequence, the Levenshtein-Damerau distance d of the pattern to the corresponding part of the random sequence was computed.We defined a RNGT of length  example , a pattescore of the pattern on the random sequence. The sum of the inverses of the distances, divided by the sequence length, results in the i)x consisting of 300 numbers to generate a statistical model which was applied to predict the second sequence i) for all patterns m of length n. Thus, when we tried to predict the next element of ky,(y) we chose the element which, combined with the past n-1 elements of k(y), resulted in the pattern most often used in sequence i(x). We defined k-(n-1)q(j) = s,x)y so that we could call the element j ∈ D which maximized q(j), the best estimate for the next item of the sequence. Of course this approach is not limited to one source sequence and q(j) can be computed from any number of given sequences. The following example should illustrate this method: Let the sequences consist of numbers picked from D = {1,…,9}. Let the source sequence be i) = q. We analyse the source sequence for patterns of length n = 3 (that is a computed history h of 2 items). Let the target sequence be i) =  for the patterns  for every i in {1,…,9} and choose the number s with the minimal score as the prediction for the successor of 4y.In this first application of the pattern analysis approach, we tested whether information on predominant patterns of a subject would be sufficient to predict future sequences generated by this subject. In our attempt to predict a random sequence we applied the following procedure: For each subject we used one random sequence . For each subject we use the first sequence a,zb,h) and ζ for sequences originating from different subjects . Additionally, we assumed that, when predicting one subject’s sequence, predictions based on statistical information from the same subject should yield a higher success rate than predictions based on statistical information from a different subject. Thus we took three sequences, one reference sequence, one sequence of the same subject and one of a different subject, and tried to predict the reference sequence. If it was ζsame > ζdifferent, we considered the origin of the sequence to be identified correctly. We checked ζsame > ζdifferent for every sequence triplet in the data set and called the relative frequency of correct identifications η(h) for any given h. As in the prediction experiment, we analysed the history lengths h from 0 to 10.In a second application of the pattern analysis approach, we tested the hypothesis that patterns derived from a humanly generated random number sequence show inter-individual differences. This hypothesis points to the fact that the Markov transition matrices (and/or the order of the Markov chain) of different subjects would not be identical. Both random number sequences of the 20 subjects were analysed. We calculated ζh = 0 and a maximum of 27% of correct predictions at h = 7. The prediction rate with h = 0 is significantly higher than chance performance  and the difference between chance performance and the prediction rate increases with the length of computed sequence history . h>2. In some subjects occasional differences in predictability between the two prediction directions are evident , the prediction rate of a sequence from the same subject is significantly higher than the prediction rate of a sequence of another subject , indicating that the subjects had strong preferences for individual digits. The differences between the prediction rate for the sequence of the same subject and the prediction rate for a different subject increase as the length of sequence history increases . Both the prediction rates for the same subject and the prediction rates for different subjects increase with a greater length of number history . The increase in prediction rate in different subjects might reflect the fact that common rules such as repetition avoidance exist in most healthy subjects h × subject (prediction for the same subject vs. prediction for a different subject) interaction , demonstrating better prediction in sequences of the same subject with increasing length of number history. Individual identification rates are given in D = {1,…,9}) and every route within this Markov rule system has the same probability of being chosen. This model resembles Monte Carlo systems in computer sciences Both of our predictions were confirmed: Firstly, we showed that a detailed analysis of the individual’s patterns predicts the future course of the sequence for that person. The prediction rate reaches a maximum of 45% correct predictions for individual cases, far above the chance performance of 11% correct prediction in a number setting of 1 to 9. In the second hypothesis, we assumed that the patterns in the number sequence would differ less between same subject trials than trials between different subjects. When provided with two sequences of the same subject and one of a different subject, we tried to identify the alien sequence based on the intersequence predictability. The pattern-based approach showed a correct identification rate with a maximum of 88% correct identifications. The high identification rate is based on strong individual preferences and strategies in the generation of numbers. The analysis detects person-specific patterns - a biometric feature - like a mental fingerprint shining through in the humanly generated random number sequences. Both hypotheses are two sides of one coin and can be seen by using an algorithm that characterises specific patterns in a humanly generated random number sequence. This algorithm can not only predict the future course of a person’s number sequence, but also makes it possible to identify a person on the basis of his or her individual patterns. These results emphasize the idea of a complex hidden Markov rule system that underlies humanly generated random number sequences. Randomness can be described using Markov rule systems that connect all items of a given range (e.g. The pattern analysis based on the Damerau-Levenshtein distance simply counts the number of edit operations necessary to convert one pattern into another. Despite this simple principle, prediction rate and identification rate are remarkably high. Further modifications might improve this analysis. However, in the present study, we searched for preferential patterns, but did not explicitly analyse patterns that are neglected or avoided by a participant. The avoidance of specific patterns might also be person-specific. Our definition of the prediction rate only includes exact hits but may well be extended to consider probability estimates to give a more accurate assessment of the prediction quality. Furthermore, the number and the type of edit operation used to calculate the Levenshtein-Damerau distance might also include person-specific information. The weighting of edit operations might also improve prediction and identification rates. Additional information can be extracted from the humanly generated random number sequences that might enable us to find further mathematical correlates for cognitive functions and to develop computational models of the cognitive functions involved in random number generation.There is further need to explore the place of pattern analysis in the field of random number generation research. Firstly, statistics correlating the results of a pattern analysis and the established indices of random number generation are definitely needed. Secondly, although we showed that the individual patterns are at least partially stable for a short time interval of seven minutes, it remains to be seen whether these patterns are stable over a longer time interval. Thirdly, due to the fact that subjects must keep their number choices in their working memory, further analysis of pattern length and working memory capacity might be interesting. And finally, pharmacological interventions, physiological stressors to the brain such as sleep deprivation


The stability of radiance measurements taken by the Sky Quality Meter (SQM) was tested under rapidly changing temperature conditions during exposure to a stable light field in the laboratory. The reported radiance was found to be negatively correlated with temperature, but remained within 7% of the initial reported radiance over a temperature range of −15°C to 35°C, and during temperature changes of −33°C/h and +70°C/h. This is smaller than the manufacturer's quoted unit-to-unit systematic uncertainty of 10%, indicating that the temperature compensation of the SQM is adequate under expected outdoor operating conditions. Until very recently, skyglow had only been measured at a handful of locations around the world e.g., ,2). In t. In t2])Two of the reasons for this increased monitoring are the recognition of the biological importance of darkness, and continued growth in the amount of lighting worldwide . ExposurAn additional reason for the increased monitoring is that quantitative studies of the night sky became easier to perform with the development of low-cost light meters: The “International Year of Astronomy Lightmeter” (IYAL),  producedThe response of the SQM to light was characterized by Cinzano  for a haThe SQM is almost always installed and used out-of-doors, and therefore experiences fairly large temperature fluctuations. Since both ambient temperature and temperature changes can affect the response of light collecting elements and the properties of electronic components, it is prudent to check whether and to what extent SQMs are affected by temperature, and by fluctuations in temperature. In this paper, we investigate the response of two SQMs exposed to a constant light field under conditions of changing temperature in the laboratory.2.2.1.SQM/arcsec2, which are often used by astronomers . The field of view (FOV) is ∼20°  for the SQM-LU (Lens and USB readout) devices considered in this paper. To aid interpretation, all measurements have been converted to values relative to the radiance observed at the start of the measurements, using the formula 100.4Δm, where Δm is the difference between the current and starting measurement in magSQM/arcsec2. The starting radiance in each measurement was approximately 19 magSQM/arcsec2, which is a typical value for the cloud-free night sky above our laboratory in Steglitz, Berlin, Germany [The SQM measures sky radiance in the logarithmic units of mag Germany .The SQM is not weatherproof, and its response can be affected if water enters the device . It must therefore be protected from moisture by installing it in a housing, and in our experience, most users have chosen to use the housing provided by the manufacturer shown in The response of the light sensor of the SQM (TAOS TSL237S) has a well characterized bias with temperature, which is reported by the manufacturer. The SQM's internal software attempts to account for this bias by monitoring the temperature near the light sensor, and correcting the observed signal according to the expected bias. The temperatures that can be expected to be encountered by an SQM in the field will depend on the measurement location and time of year. In the period from 1 April 2010 to 19 August 2013 in Berlin, Steglitz, an SQM-LU mounted on the roof of our institute observed a temperature range from −16.5°C to 30.3°C during darkness. The median rate of temperature change was −0.3°C/h, and the most extreme rates of temperature change observed were −9.0°C/h and +2.6°C/h.2.2.SQM/arcsec2. The stability of the light source was verified by monitoring the SQMs over a period of several days with the power to the chamber off . No variation in measured radiance was observed in either of the two SQMs.The temperature stability of the SQMs was tested by installing them inside of a programmable temperature chamber  designed for materials testing. Two devices were tested simultaneously, one free and one in the standard Unihedron housing as shown in In order to test the response of the device at different stable temperatures, the temperature chamber was programmed to run a series of temperature ramps over two days, with long pauses between the ramps (Test 1). The temperature end points and rates of change of the ramps are shown in The temperature chamber was not designed for optical measurements, and vibrated during operation. Early testing indicated that the pointing direction of the SQMs could shift during operation. The light field on the dark curtains was not perfectly uniform, so a shift in optical alignment would result in a change in observed radiance. For this reason, clamps and a heavy support plate were used to minimize this motion. The humidity of the chamber was not controlled, and dew was occasionally noted on the devices after the rapid temperature shift program completed. This could potentially have some effect on the optics, and therefore affect the observed radiance.3.The results of the temperature stability test (Test 1) for the two SQM-LU devices are shown in The data for the rapid temperature change experiment (Test 2) are shown in rep and SQMcorr are the reported and corrected radiance in magSQM/arcsec2, and T is the temperature reported by the SQM. Applying this correction factor to the data presented in rep to −5% to +1% for SQMcorr.Due to the optical limitations of the experimental setup, it is unclear whether the observed changes in radiance are due to changes in the view direction or incorrect temperature compensation of the device. Under the assumption that most of the observed change is due to a failure in temperature compensation, it is possible to derive a correction factor. The average deviation in one of the SQMs was reasonably well matched to a linear fit, while the second SQM was better described with a second degree polynomial. For the sake of simplicity, an average linear correction for all four datasets was calculated. Reported radiance could be approximately corrected using the formula:With a sample of only two SQMs, it is not possible to conclude whether the correction function defined above applies equally well to all SQM devices. In addition, given that it is known that the alignment of the SQMs changed slightly during running, the correction equation provided above should be used only as an approximate guide in estimating uncertainties for measurements taken at different times with an identical meter. The uncorrected deviation reported here is small in comparison with the manufacturer's much larger quoted unit-to-unit systematic uncertainty in reported radiance of ± 10% . It is conceivable that an improved temperature compensation algorithm based on a larger scale study by the SQM manufacturer could reduce some of the measurement uncertainty.The results of this study should be expected to apply to both the SQM-LE, as well as hand-held SQMs, which have a similar internal design. A number of groups have used an automobile in order to perform hand-held SQM measurements at widely separated distances . For th4.The stability of radiance measurements taken by two SQM-LU low light radiance meters was tested over the temperature range −15°C to 35°C, and the variation in reported radiance was found to be smaller than the 10% unit-to-unit systematic uncertainty quoted by the manufacturer. These same results can reasonably be expected to apply for SQM-LE devices as well as for hand-held SQMs. When operated in urban areas, SQMs routinely observe differences in sky radiance of an order of magnitude due to the presence or absence of clouds . The tem


Peer physical examination (PPE) is a method of training in medical and osteopathic curricula. The aim of this study was to compare the acceptability of PPE in two classes of medical and osteopathic students after their first experience, to obtain comparative information useful for an understanding of the different professional approaches. The leading hypothesis was that osteopathic students enter the curriculum with a more positive attitude to bodily contact.As a secondary aim, this study validated the new version of a questionnaire to assess the acceptability of PPE.Examining Fellow Student [EFS] questionnaire) were used for a cross-sectional survey in a class of 129 3rd year medical students and in two parallel classes of 1st year osteopathic students .A new version of a previously validated questionnaire and an instrument from the literature . The only independent variables that were significantly predictive of the score in a linear regression analysis were gender and the condition of medical or osteopathic student. The EFS mean score also showed a significant difference between the osteopathic and medical students .Factor analysis of the new questionnaire identified three factors  accounting for 62.8% of the variance. Criterion validity was assessed by correlation with the EFS (Pearson’s r coefficient = 0.61). Reliability was expressed in terms of Cronbach’s alpha coefficient, which equals 0.86.These quantitative results are consistent with previous qualitative research on the process of embodiment both in medicine and osteopathy. The new questionnaire proved to be valid and reliable. The objective assessment of the acceptability of PPE is a way to determine differences in students’ attitudes towards contact with the body and can be used for counselling students regarding career choice. This study can also highlight differences between students from different professions and serve as a basis for reflection for improved mutual interprofessional understanding and future interprofessional education. In many countries, osteopathy is a recognised form of healthcare that relies on manual contact for diagnosis and treatment . In ItalThe principles and objectives of osteopathy are not currently taught in Italian medical curricula; although both the medical and osteopathic professions acknowledge the value of interprofessional collaboration ,3, thereIntroduction to Clinical Medicine in the 3rd year of a six-year-long program of study. PPE is also a basic method used in osteopathic schools to train students in osteopathic manipulative treatment (OMT) from the beginning of the curriculum.Peer physical examination (PPE) is the learning activity in which students act as models for each other in learning skills in physical examination and simple non-invasive procedures . This tePPE is a widespread educational practice, and most medical students are comfortable with PPE -9; howevbody work’ refers to the work of healthcare providers that involves a distinctive and often intimate relation to the bodies of consumers, clients or patients [body talk’ as the way in which the embodied patient is able to communicate with the practitioner, not only through verbal interaction but also through a ‘dialogue with the tissues’ during diagnostic palpation and through physical appearance during direct observation. Gale highlighted ‘the centrality of embodied interaction at the investigative stage of the osteopathic healing process’.The rationale of our study relies on previous empirical research ,23 aboutpatients . In his patients  describereframed to exclude some of its symbolic properties, especially sexual ones’. Moreover, the body is transformed into an object of scrutiny in the context of the social contract upon which medical practice relies. The dual attention to the body as incarnate and disincarnate is handled by a delicate ‘etiquette of touch’. Gale’s and Young’s qualitative findings suggest a difference in the attitude to bodily contact between medical doctors and osteopaths and led us to hypothesise that students who choose the profession of osteopathy may enter the curriculum with a more positive attitude towards bodily contact.In a set of case studies, Young  examinedThe objective of this study, then, was to measure the acceptability to PPE among two groups of medical and osteopathic students after their first experience with the technique; the data were obtained to develop comparative information to understand the different professional approaches. The study also aimed to revalidate a revised version of a previously designed questionnaire as an objective instrument of assessment of the acceptability of PPE in students. Both the FMD and CERDO faculties were interested in developing an objective instrument to quickly measure the acceptability of PPE and address some of the components of a relational and cognitive nature. A first version of the questionnaire was developed and validated in a previous study . BecauseIntroduction to Clinical Medicine, in which PPE is used to develop their skills in physical examinations. CERDO runs a 6-year long curriculum in osteopathy in conformance with ROI standards. The school offers a full-time curriculum for lay students and a part-time curriculum for medical doctors and physiotherapists. PPE is introduced during the first year as the preferred method for teaching diagnostic palpation and OMT.The FMD runs a discipline-based medical curriculum that spans 6 years. After the first two years of basic preclinical science, students encounter clinical subjects during their third year in the course Examining Fellow Student (EFS) questionnaire [We performed a cross sectional survey of a class of 129 3rd year medical students and two parallel classes of 1st year osteopathic students  enrolled in either the full or part-time curriculum. During the survey, we administered our new questionnaire, and we simultaneously administered the ionnaire  as a poiThe study received ethical approval from both schools. Data were collected in an anonymous format and with the oral consent of the students.Comparisons of the mean scores for stratified subgroups among the two groups were performed using the Kruskal-Wallis test because the distribution of the scores was likely to be non-normal, with an acceptable alpha error of <0.05. Correlation of personal and cultural data with the scores on the questionnaires as a dependent outcome variable was analysed using multivariate linear regression. All statistical calculations were performed using Statistica® software.The demographics and relevant cultural data of the surveyed students are presented in Table The response rate was 100% of the students attending class on the day of the survey, which were 129 out of the 140 enrolled 3rd year medical students (92.14%) and 112 of the 115 enrolled 1st year osteopathic students (97.4%).To measure the acceptability of PPE, we used both the EFS questionnaire and a new questionnaire we developed to gain a deeper understanding of the elements composing the overall construct of acceptability of PPE. The EFS questionnaire explored the overall acceptability of performing and undergoing PPE on various body regions, without any other consideration of possible different dimensions of the construct. Our questionnaire was designed to measure two different although related elements on a five-point Likert scale , as follows:● the acceptability of the practice of PPE, explored in different contexts and potentially problematic situations ● the students’ opinion of the educational value of the PPE (items 12 to 16)The scores on the items were assigned equivalent points on a 0 to 4 scale, except for items 3 through 7 and item 12, which were assigned points in a reverse way. The maximum possible score was 64 points.The questionnaire also contained a few other items that asked students their opinions regarding organisational topics  and about their personal and cultural characteristics.In this sample of students, we assessed construct validity by principal components factor analysis and criterion validity by comparison with the score on the EFS questionnaire. Table The Pearson’s r coefficient between the scores on our questionnaire and the scores on the EFS was 0.61; this finding indicates a good correlation. Reliability was assessed as internal consistency, according to the classical item analysis with Cronbach’s alpha coefficient. This coefficient of reliability showed an acceptable value of 0.86.The mean and standard deviation of the scores from our new questionnaire were, respectively, 48.09 and 9.29 . The Shapiro-Wilk test for normality showed refusal of the hypothesis of normal distribution of values (p < 0.001).The mean score on the new questionnaire was 43.4 ± 8.9 for medical students vs. 53.4 ± 6.3 for osteopathic students (p < 0.01). This difference was significant when considering either the full-time (51.07 ± 5.6) or the part-time (54.28 ± 6.21) students of osteopathy. The difference between the two groups of osteopathic students was significant as well (p < 0.05). Overall, PPE was viewed as acceptable by a large majority of the surveyed students: only 3% of the students scored 0 or 1 on the first questionnaire item  and 12% did the same on the second item . Nevertheless, when the students were asked if PPE was an appropriate practice (items 13 and 14), the numbers of subjects who gave a 0 or 1 score decreased to 1 student (active role) and 4% (passive role).Overall, women showed a lower mean score on our questionnaire than men . This difference was present among the medical students  but was not observed among the osteopathic students . Table 2 = 0.34, see Table The scores showed only a weak correlation with age (Pearson’s r = 0.26) in the group of osteopathic students. No significant difference in scores was observed between the subgroups stratified by declared religious beliefs and for the area of origin in Italy for any of the classes. The only independent variables significantly predictive of the scores on the new questionnaire with linear regression analysis were gender and the role of the medical or osteopathic student. The best predictive model accounted for 34% of the variance . The distribution of scores was strongly skewed, with a peak towards the upper end, as shown by the value of the median, which is close to the maximum score.The EFS mean score showed a significant difference between medical and osteopathic students , but there was not a significant difference between full and part-time osteopathic students (30.27 ± 2.6 vs. 30.96 ± 3.0).Women scored lower than did men among medical students, while a significant gender difference was not observed among either part-time or full-time osteopathic students.Table Our study confirmed the hypothesis that osteopathic students show a higher acceptance of PPE than did medical students after their first experience and that this difference is not explained by any of the demographic or sociocultural variables we considered. This difference was significant in the responses to both our questionnaire and the EFS questionnaire.These results are consistent with the idea that osteopathic students approach their curriculum with a stronger acceptance of bodily contact. A possible explanation for the difference we observed can be based on the different social expectations of the students of these two professional groups when entering their respective training programs. Students do not begin a training program as blank slates but rather holding certain ideas of professional values and roles. Blue et al.  showed tlearning to interact with the bodies of their patients, develop a new orientation to their own bodies’ [In a qualitative analysis of students’ comments concerning PPE, in the light of Engeström model of activity theory , the aut bodies’  and are When considering the distribution of the scores of our questionnaire in greater detail, students ranking in the lowest quintile (under a score of 40) received, as expected, on average, a lower contribution to their total scores from the items associated with the “appropriateness” and “passive role” subscales  than did students in the second quintile (67.6% and 47.0%), while the difference in the “sexual” subscale was more limited (85.4% vs. 94.4%). The distribution of the scores for this last subscale was skewed towards the highest scores, and the lowest scores identified a small subset of students not always ranking in the lowest two quintiles of the overall score. This can be an important indication and a topic of personal counselling with students who may have had a past negative sexual experience, as reported by Power et al [Female medical students showed a higher level of concern regarding PPE than did men; this finding is similar to previously reported results -16. ThisWe did not observe that cultural factors, such as religious belief and geographic area of origin, were significant factors, in contrast to previously reported results . Those wOur questionnaire was developed in accordance with the methodology proposed by Wilson  in four ‘I just think I’m embarrassed about my body image, my body and people seeing it’), a construct that is not directly linked to sexuality but rather to cultural notions of body image.With regard to construct validity, factor analysis showed three factors accounting for 62% of total variance. These three components had high factor loadings and suggested a robust structure of the construct, consistent with our hypothesis when we designed the instrument, even if slightly different. The two components of general attitude and perceived educational value identified in the conceptual design went together in the first factor, while two other rather independent components emerged, connected with sexual issues and the passive role of exposing one’s own body to physical examination by a peer. The first factor was somehow expected. The latter can be connected to what other researchers  denoted Some items had similar loadings across two factors , and this finding may reflect the complexity of the underlying construct. In three out of the four items, the two overlapping factors were the “appropriateness and usefulness” and “passive role”, which share a common meaning that the instrument fails to discriminate.Although the EFS questionnaire cannot be considered a gold standard, it is currently the most used tool in the literature to measure the acceptability of PPE; thus, we thought it could serve as a good point of reference for criterion validity. The EFS questionnaire and our questionnaire differ in terms of their basic conceptual structure: the EFS is used to evaluate the performance of PPE focusing on various body areas, whereas ours is used to investigate global perceptions and beliefs. EFS contains a free response section, in which students are to write comments. These comments have been qualitatively analysed  and the This study has some limitations. The first one is that it is based on a convenience sample, introducing a possible bias and limiting the possibility of fully exploring some of the variables, such as the geographic origin. Only 4 students were from northern Italy, and therefore this subgroup could not be considered large enough for valid analysis. The absence of a sampling strategy also prevented correct calculation of the dimensions of the sample. Hence some conclusions, particularly regarding the absence of effect, must be considered cautiously. More robust conclusions could be derived from a larger, more ethnically diverse, nationwide study.A second limitation is the design of the cross-sectional study. The construct of the acceptability of PPE may vary over time during the curriculum, and this should be considered in the interpretation of our data, which must considered valid only as an instantaneous measure of attitudes at the end of the semester after the first experience with PPE. Some other studies investigated the longitudinal variations with time in acceptability of PPE ,19,33, rA second consequence of our cross-sectional design is that we cannot provide data regarding the reproducibility of  and responsiveness to changes in the questionnaire. These topics are open to discussion, especially in view of the routine use of the instrument in formative assessment, and they need to be addressed with a specific longitudinal study.A third possible limitation could be the differences in years of the curriculum. We compared 1st year osteopathic students to 3rd year medical students; this can imply a difference in age and a possible impact of previous experiences. A first observation is that medical students were as old as full-time osteopathic students (22.1 ± 3.4 vs. 22.6 ± 6.7), while the part-time osteopathic students were older (28.7 ± 6.7) because they were already graduated healthcare professionals. The difference in scores between the two subgroups of osteopathic students could then be related to a difference in age and professional experience, as already discussed and in agreement with the above-mentioned results for nursing students . NeverthOverall, PPE was acceptable to medical and osteopathic students, although to different extents. Although 12% of medical students felt embarrassed while undergoing PPE, and only 4% considered it inappropriate. There is still much debate regarding whether PPE should be a mandatory or elective learning activity . Our datThe FMD and CERDO started their cooperation with the comparative evaluation of a teaching/learning activity that we thought would be able to yield information regarding the inner nature of the two professional processes of allopathic medicine and osteopathy. The results of this study were also meant to validate an instrument to be used in routine formative assessment.At the FMD, PPE is performed throughout the 3rd year to train students in physical examination skills, so the scores on the questionnaires at the end of the first semester will be used to identify students with possible issues with PPE after their first experience with the technique. The FMD established a framework for the assessment of professionalism, according to a multimodal longitudinal perspective . Data frAt CERDO, it is important to identify, as early as possible, students with serious concerns regarding contact with the body because OMT is a core competence in osteopathic practice and PPE is taught and used throughout the 6 years of the curriculum.Contact with the body, in particular PPE, proved to be a topic of study valuable to this goal of CERDO, and the results of this study – which have been presented to students and discussed during a joint meeting among teachers – may contribute to the reflection by teachers and students on their own practice and to mutual understanding and acknowledgement between the osteopathic and medical professions. The experience of collaboration between the two schools in this project served as a basis for further joint learning and research activities with the aim of developing guidelines and scientific evidence for further collaborative patient-centred practice.The authors declare that they have no competing interests.FC conceived and coordinated the study, performed the statistical analysis and drafted the manuscript. Questionnaires were administered and the scores were calculated by RM and AP for medical students and by GC and JZ for osteopathic students. All authors participated in the design, data analysis and helped to revise the manuscript. All authors read and approved the final manuscript.The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1472-6920/13/111/prepub


Unlike reactions performed in the laboratory—which use homogeneous solutions having spatially uniform concentration profiles of each reactant—reactions that occur in biological systems often involve reactants that are present in concentration gradients and can display unexpected kinetic properties.Our system is based on Abelson tyrosine kinase (Abl) which has both a catalytic domain and a Src homology 2 (SH2) domain that binds to the phosphopeptide product of the phosphorylation reaction. For example, Abl phosphorylates the substrate peptide AIYENPFARKC to give AIpYENPFARKC , and the kinase can then bind to pY. Previously, we used SAMs of alkanetiolates on gold to demonstrate that Abl can operate autocatalytically on an immobilized substrate Figure .14 The SWe patterned a monolayer into alternate regions that presented the phosphopeptide and the peptide substrate. We reasoned that those peptide substrates located immediately adjacent to regions that present phosphopeptide would be phosphorylated most rapidly, because only at the boundary can tethered enzyme interact with the substrate. Hence, we expected that the reaction would show a spatial propagation in time Figure . To test−1 for a surface presenting the peptide substrate at a density of 1 % relative to total alkanethiolates. The experiment was repeated using a monolayer that presented the peptide at a density of 0.5 % and we measured a propagation velocity for the reaction of 0.51 μm min−1  in the reaction buffer but included increasing concentrations of the non-hydrolyzable ATP analogue adenosine 5′-triphosphate (AMP-PNP) which is a competitive inhibitor for ATP and therefore reduces the turnover number of the kinase. Indeed, we found that the propagation rate decreases with increasing concentrations of AMP-PNP  increased linearly with the boundary density (Figure The finding that the reaction proceeds most rapidly at the boundary between phosphorylated and unphosphorylated peptides suggests that relative rates for a reaction on patterned surfaces would depend on the spatial arrangement of the pattern and not only on the ratio of the two peptides on the surface. If the rate is averaged over a region of the surface that is large compared to the feature sizes of the patterns, we reasoned that it would increase with the “boundary density” of the pattern, defined as the integrated length of the perimeter of phosphopeptide-terminated regions of the monolayer per unit area of the monolayer. To explore this possibility, we utilized four patterns that had the phosphopeptide organized in circular features or zig-zag lines, each at two different sizes Figure . The smay Figure . We alsoy Figure . We founThis study demonstrates a reaction system that shows a spatial propagation of product, despite the uniform concentration of enzyme catalyst throughout the system. This example is significant because it describes an approach to engineering reactions to give spatio-temporal control over the products and progression of reactions in a system. The use of self-assembled monolayers was important to this work for several reasons.26


Could it be possible that, in the not-so-distant future, we will be able to reshape the human body so as to have extra limbs? A third arm helping us out with the weekly shopping in the local grocery store, or an extra artificial limb assisting a paralysed person? Here we report a perceptual illusion in which a rubber right hand, placed beside the real hand in full view of the participant, is perceived as a supernumerary limb belonging to the participant's own body. This effect was supported by questionnaire data in conjunction with physiological evidence obtained from skin conductance responses when physically threatening either the rubber hand or the real one. In four well-controlled experiments, we demonstrate the minimal required conditions for the elicitation of this “supernumerary hand illusion”. In the fifth, and final experiment, we show that the illusion reported here is qualitatively different from the traditional rubber hand illusion as it is characterised by less disownership of the real hand and a stronger feeling of having two right hands. These results suggest that the artificial hand ‘borrows’ some of the multisensory processes that represent the real hand, leading to duplication of touch and ownership of two right arms. This work represents a major advance because it challenges the traditional view of the gross morphology of the human body as a fundamental constraint on what we can come to experience as our physical self, by showing that the body representation can easily be updated to incorporate an additional limb. An organism's body plan refers to the symmetry and the number of segments and limbs of the body. It is a blueprint of the morphology of the organism that is regulated by specific genes (homeogenes) during development Interestingly, in the neurological literature, there are case reports of people with cortical or subcortical lesions who experience having extra limbs, so-called supernumerary phantom limbs. These phantoms are typically experienced as an additional arm or leg From the study of body illusions in healthy individuals we know that the body representation is inherently malleable and dynamic One such illusion, the rubber hand illusion Interestingly and intriguingly, a few recent reports have suggested that it is possible for healthy participants to experience illusory ownership of supernumerary rubber or virtual hands To address these issues, we designed a novel ‘supernumerary’ version of the traditional rubber hand illusion The study consists of data from five separate experiments involving a total of 154 healthy volunteers. For each experiment, we recruited a separate group of naïve participants: In the first experiment, we tested 30 individuals ; the second one involved 44 participants , the third 25 , the fourth 26  and the fifth 29 subjects . All participants gave their written informed consent prior to participating. The studies were approved by the Regional Ethical Review Board of Stockholm.The experiments took place in a soundproof testing room (40 decibel noise reduction). The participants sat on a comfortable chair and rested their arms on a table in front of them. The experimenter sat opposite the participant.In all experiments and conditions the rubber hand was placed medially to the participant's real right hand . The distance between the index finger of the artificial limb and the index finger of the participant's right hand was 12.5 cm throughout . A piece of cloth covered the space between the participant's shoulder and the proximal end of the rubber hand. It, thus, appeared visually as if the rubber hand could be a real hand see . We usedThe participants' left hand was placed on the table behind a screen and was, thus, hidden from view in all experiments. The participant could only see an artificial limb and their real right hand on the table, again, the only exception was in experiment 5, when a screen precluded vision of the real hand (see below).We carefully matched the velocity, frequency and skin surface stimulated by the brushstrokes in all the experiments. The strokes were applied to the index and middle fingers of the participant's right hand and the corresponding places on the artificial limb. When a rubber right hand was used, we touched the index and middle fingers, and when a rubber foot was used, we stroked the corresponding sections on the two limbs . When a rubber left hand or a rotated rubber right hand were used, the touches were again delivered to the corresponding digits on both hands .In the illusion condition we used an irregular, but synchronous brushing rhythm, since this mode of stimulation is known to maximise the traditional rubber hand illusion (unpublished observations). In the asynchronous (control) condition, the pattern of brushing was irregular and alternating between the real hand and the rubber limb, which is an established method to break down and control for the illusion To quantify the perceptual experiences associated with the illusion, we used questionnaires with visual analogue rating scales which were presented at the end of each condition. The questionnaires were adapted from a previous study investigating perceptual experiences during the traditional rubber hand illusion We used the procedure of physically threatening the rubber limb or the real hand with a knife and measure the brief increases evoked in the conductance of the skin to provide objective evidence for the illusion. The SCR reflects “psychologically” increased sweating attributable to the activation of the autonomic nervous system In the present study we threatened the artificial limb (experiments 2 and 4) and the person's real right hand (experiment 2) with a knife after a period of repeated brushing of the two hands. We always included appropriate control conditions (see the next section) and could therefore relate changes in the SCR to changes in ownership, excluding more general factors such as surprise, general arousal, or unspecific emotional responses related to the presentation of the knife.The SCR were recorded with a Biopac System MP150  following standard published guidelines The knife-threat procedure consisted of moving a kitchen knife slightly above (1–2 cm) the thumb and index finger of the participant's hand or the rubber hand , or above digits I and II on the rubber foot . The visible movement of the knife took approximately one second and was performed so that the knife was always moved along the sagittal axis from the participant's point of view. Great care was taken to perform the same movement with the knife from trial to trial, i.e. controlling the velocity and acceleration of the movement. Before commencing the experiments, the participants were instructed to stop looking at the rubber hand and start looking at the knife as soon as it was presented to make sure that they perceived the threat. The threat-evoked SCR was identified as the peak in the conductance that occurred up to 5 seconds after the onset of the threat stimuli (that is from the first moment the participant saw the knife approaching one of the hands), which was flagged in the SCR recording file. The amplitude of the SCR was calculated as the difference between the maximum and minimum value of the identified response. This analysis was conducted with the scientist performing the analysis being blinded to whether the data in question belonged to the illusion or a control condition. The average of all responses for a participant, including those where no increase in amplitude was apparent, was calculated for each condition separately, and constituted the magnitude of the SCR The first two experiments sought to establish the supernumerary limb illusion and to present subjective (experiment 1) and physiological evidence (experiment 2) substantiating the effect. In experiments 3 and 4, we again used subjective and objective measures to examine which type of limb could be owned as a supernumerary limb. Finally, the fifth experiment compared the perceptual experiences during the supernumerary hand illusion and the traditional rubber hand illusion.All experiments consisted of multiple experimental conditions, which were motivated by the specific hypotheses tested (see below); the order of the stimulation conditions was semi-randomised and balanced across participants in all experiments. Additionally, in the SCR experiments, the target of the physical threat  was balanced across sessions and participants (in experiments 2 and 4).In the first experiment we quantified the perceptual experiences associated with the supernumerary hand illusion. In addition, we examined the possible, simultaneous feeling of disownership of the real hand. Specifically, we tested our prediction that the elicitation of the illusion would depend on the synchronicity of the seen and felt touches, and on the anatomical alignment between the owned rubber hand and the real hand. These factors are known to be crucial for the induction of the traditional rubber hand illusion The aim of the second experiment was two-fold. First, to present objective physiological evidence for the illusion, and second, to examine possible disownership of the real right hand. The experiment consisted of two sessions, each divided into four, one-minute-long periods of synchronous or asynchronous brushing of the participants' real right hand and a rubber right hand. In this experiment, the rubber hand was always oriented in an anatomically congruent position parallel to the real hand. At the end of each stimulation period, the participants observed the scientist holding a knife and moving it towards and above the rubber hand or the real hand as if attempting to cut the hand in question (as described in the paragraph on SCR).Next we investigated which types of limb can be experienced as a supernumerary limb. We hypothesised that they would have to resemble the real stimulated hand in both laterality  and anatomy . For the elicitation of the traditional rubber hand illusion, it is known to be crucial that the rubber hand resembles a human or primate hand In this experiment we used physiological data (SCR) to complement and support the findings in experiments 1 and 3 that only a rubber right hand can be experienced as a supernumerary limb located next to the real right hand. In addition, we tested the hypothesis that the rubber right hand has to be placed in an anatomically plausible orientation with respect to the body and the real hand for the illusion to work.This experiment comprised three sessions, each consisting of four conditions of one minute duration, as follows: a rubber right hand aligned parallel to the participant's real right hand, a rubber right hand rotated through 180 degrees, a rubber left hand orientated parallel to the participant's real right hand and a rubber right foot aligned parallel to the participant's real right hand. In all conditions we used a synchronous mode of brushing. The rubber foot was fixed in a position with 20 degrees plantar flexion in the ankle joint to make the brushing procedure easier for the experimenter  or hidden from view (rubber hand illusion). If, as hypothesised, the present illusion is not merely a weak form of the rubber hand illusion, one would expect a difference in the degree of disownership of the real right hand and a stronger feeling of having two right hands during the supernumerary hand illusion.In this experiment we used the same general procedures as in experiments 1–4, with some important modifications. In the classical rubber hand illusion condition, we used a screen to separate the rubber and the real hands to obscure the real hand from the participant's field of vision see . Owing tA Kolmogorov-Smirnov test was used to check the parametric assumptions of the data in all experiments. For all ANOVAs with a repeated measures factor, we performed Mauchly's sphericity test for compound symmetry. When compound symmetry was not satisfied  we used the Huynh-Feldt epsilon-corrected degrees of freedom. In all of the tests, alpha was set to 5%. We inverted the scores of S3 to facilitate the statistical analysis of S3–S4 in the questionnaires, since low ratings on S3 and high ratings on S4 reflect stronger feelings of real hand disownership.The results in the first experiment demonstrate that the illusion of owning a supernumerary hand requires synchronous visuo-tactile stimulation and a rubber hand orientated in parallel with the real hand. As can be seen in In the statistical analysis we performed three separate 2×3 repeated measures ANOVAs with the main factors being Condition  and Statement. In the first ANOVA, the Statement factor corresponded to the pair of illusion-related statements reflecting “rubber hand ownership” ; in the second ANOVA it was the pair reflecting “real hand disownership” , and in the third one it was the statements related to “the feeling of having two right hands” . We calculated the main effects of the factor Condition for each pair of statements, and the simple contrasts between the levels of Condition (using Synchronous as the reference level) to compare the illusion to each of the control conditions individually. The analysis of S1 and S2 demonstrates that the participants felt significantly stronger ownership of the rubber hand in the synchronous condition than in the asynchronous and rotated ones, respectively   = 44.811, p<0.001 and F  = 16.395, p<0.001, simple contrasts). There was no significant difference in the perception of disowning the real hand during the illusion compared to the control conditions (S3–S4)   = 2.337, p = 0.137 and F  = 3.727, p = 0.063, simple contrasts, respectively). We obtained significantly higher ratings for the statements related to the feeling of owning two right hands during the illusion than in the control conditions (S5–S6)   = 18.065, p<0.001 and F  = 11.879, p = 0.002, simple contrasts, respectively). It can also be pointed out that the main factor Condition was significant for the “rubber hand ownership” (S1–S2)   = 22.529, p<0.001) and the “two hand ownership” (S5–S6)   = 11.339, p<0.001), but not for the “disownership” statements (S3–S4)   = 2.071, p = 0.135).Next, we compared the illusion-related statements and the control statements, and found that the difference between the illusion statements and control ones was greatest in the synchronous conditon  and S7  to make a direct test of whether the participants experienced genuine duplication of touch and were not merely switching between feeling touch on and owning one of the right hands at a time. For this planned comparison, we conducted a two-way paired samples t-test of the scores in the synchronous (illusion) condition only. This revealed a significant difference  indicating that the participants did not experience a switch in the ownership of one hand or the other alternately, but a genuine sensation of duplication of touch and ownership of two right hands. This result is reproduced two more times in this study (see experiments 3 and 5).The key observation was a significantly greater SCR when we threatened the rubber hand in the synchronous condition than in the asynchronous one  . This prWe also employed a 2×2 repeated measures ANOVA to the data. The effect for the main factor, Timing , was not significant   = 2.099, p = 0.155) however the main factor, Hand , was   = 10.912, p = 0.002), which implies that the participants were significantly more afraid when their real hand was threatened. Crucially, there was a significant interaction Timing × Hand   = 8.111, p = 0.007), meaning that the effect of the synchronicity of the brushing was greater for the rubber hand than the real hand. These physiological recordings, in conjunction with the subjective reports in experiment 1 and spontaneous comments made after the experiments, suggest that the participants experienced their real hand as their own, while simultaneously experiencing ownership of the rubber limb.The results of the third experiment demonstrated that the supernumerary limb illusion only worked when a rubber right hand was used  as the illusion was significantly reduced when it was replaced by a rubber left hand or right foot . As in tWe also, somewhat surprisingly since we did not see this in Experiment 1–2, observed significantly stronger ratings for the disownership of the real hand (S3–S4) during the illusion condition than for both of the control conditions (S3–S4)   = 21,573, p<0.001 and F  = 24,808 p<0.001, simple contrasts). Lastly, for the statements related to the feeling of having two right hands (S5–S6), the ratings were significantly higher in the illusion condition than for the rubber right foot control condition (S5–S6)   = 26.810, p<0.001, simple contrast). Unexpectedly, this was not significant for the comparison between the illusion condition and the rubber left hand control condition (S5–S6)   = 3.110, p = 0.091, simple contrast). This was due to the high ratings for the “duplication of touch statement” (S6) for the rubber left hand . Post-hoNext, we compared the illusion-related statements and the control statements, and found that the difference between the illusion statements and control ones was greatest in the synchronous conditon , in good agreement with experiment 1, confirming that people experienced duplication of touch.We observed greater threat-evoked SCR in the illusion condition (i.e. when we used a rubber right hand) than in the three control conditions conducted with a rotated rubber right hand, a rubber left hand or a rubber right foot   = 7.452, p<0.001, repeated measures one-way ANOVA) . PlannedIn this experiment, we compared the supernumerary hand illusion directly with the traditional rubber hand illusion to test our hypothesis that the two perceptual illusions are qualitatively different see . In so dAs expected, both illusions produced greater scores for the illusion-related statements than the control questions   = 122.107, p<0.001). In other words, they both represent genuine perceptual phenomena that cannot be explained in terms of suggestibility, imagination, or task compliance. Interestingly, neither the main factor Illusion type   = 0.0105, p = 0.747), nor the interaction Illusion type × Statement type   = 3.438, p = 0.066) were significant, implying that the “total amount of illusory experience” did not significantly differ between the supernumerary hand illusion and the traditional rubber hand illusion.It was also interesting to see if the two illusions would differ in terms of how the duplication of touch on the two hands was perceived. We examined this by comparing the rating scores of S6 and S7 for the two conditions. For the third time, for the supernumerary hand illusion, we were able to reproduce the significant difference between the ratings of the two statements  (see Experiments 1 and 3). Thus, in this illusion, people have a strong sensation that the single tactile stimulation on the real hand is duplicated and felt on the two hands simultaneously. In striking contrast, no such significant difference was observed in the rubber hand illusion condition . This is consistent with the fact that people tend to experience touch as being located mainly on the rubber hand in the classical rubber hand illusion. This observation again reinforces the qualitative differences between the present illusion and the original rubber hand illusion.The results of our experiments demonstrate that people can have the experience that an artificial hand is a supernumerary limb belonging to their own body. This perceptual illusion arises when a rubber hand is placed beside the participant's real hand in full view and both hands are brushed on corresponding sites in a synchronous manner. This study identifies four factors which are necessary to elicit the illusion on the right hand: the rubber limb must be matched to the real limb in terms of (i) laterality; (ii) limb type (i.e. the illusion does not work with a rubber left hand or a rubber foot); (iii) anatomical alignment ; and (iv) the visual stimulation on the rubber hand and the visuo-tactile stimulation on the real hand must be synchronous. Taken together, these results indicate that ownership of the supernumerary hand depends on achieving a match between the visual information about the spatial orientation of the rubber hand and proprioceptive information about the orientation of the real hand, and on a match between the correlated visual and tactile information from the two hands. These factors bear striking similarities with the traditional rubber hand illusion and suggest that the supernumerary hand ‘borrows’ some of the multisensory processes normally used to identify and localise the real limb What neural mechanisms might be responsible for the present supernumerary limb illusion? According to the multisensory hypothesis of body ownership Why is the real right hand not disowned, as one could reasonably expect if the rubber hand utilises some of the same multisensory processes used to localise and identify the real hand? Although we observed significant disownership in the questionnaire in experiment 3, this was effect was not seen in the questionnaire data in experiment 1 or when analysing the threat-evoked SCR in experiment 2. Thus, even though it is possible that more sensitive methods could discover subtle disownership-related effects in the present set-up, overall, the emerging picture is one of strong ownership of the real hand in the presence of ownership of the rubber one, which is what one could reasonably refer to as a supernumerary hand illusion. It is noteworthy that the threats to the real hand always produced greater a SCR than threats to the rubber one (experiment 2) further confirming that the real hand was still perceived as one's own.These considerations raise an interesting question: Why is the ownership of the real hand so resistant to the supernumerary hand illusion? During this illusion, participants receive visual information about their real right hand in the periphery of their field of vision. The questionnaire results from experiment 5 demonstrate that this hand is disowned to a significantly lesser degree during the supernumerary hand illusion presented here than in the traditional rubber hand illusion where the participant is deprived of visual information from the real hand. Thus, despite experiencing ownership of a rubber right hand, the representation of the real hand is seemingly not impaired because of the visual impression of it being brushed.In experiment 3 we compared the supernumerary illusion with a rubber right hand to a control condition with a rubber left hand. As expected, in the rubber left hand condition people did not experience ownership of the hand, but somewhat surprisingly they reported a rather high degree of touch duplication. It is interesting here to compare these results with a recent study by Petkova and Ehrsson (2009). These authors described an illusion where participants were exposed to synchronous tactile stimulation of a rubber right hand and their real left hand , which induced ownership of the rubber right hand and a duplication of touch from the real left hand to the rubber right hand “across the body midline” The study presented here differs in several important ways from previous ones on supernumerary limb illusions in healthy individuals In Schaefer et al. (2009), participants observed a rubber left hand that had been placed next to their visible real left hand. No synchronous stroking of the hands was employed, making it questionable if an ownership-illusion was ever produced. This concern is further strengthened by the low scores given by the subjects when asked to rate two illusion-statements Our results have bearing on the emerging research field of neuroprosthetics. Over the last decade, a tremendous effort has been made to design brain-machine interface systems, in which paralysed humans and monkeys learn to control an advanced robotic arm prosthesis directly with their brain activity, via electrodes implanted into the cortex or placed on the scalp In summary, after a period of synchronous visuo-tactile stimulation of a rubber right hand and a person's real right hand both in full view, the rubber hand is experienced as a supernumerary limb. Importantly, this perceptual phenomenon is produced by specific multisensory principles which have been identified in this study in a series of well controlled behavioural and psychophysiological experiments. Thus, under certain circumstances, healthy humans can experience somatic sensations that seem to violate the human body plan.Text S1The statistical analysis of the illusion-related statements and the control statements in experiment 1.(DOC)Click here for additional data file.Text S2The statistical analysis of the illusion-related statements and the control statements in experiment 3.(DOC)Click here for additional data file.


This study was undertaken to learn whether the principle of functional specialization that is evident at the level of the prestriate visual cortex extends to areas that are involved in grouping visual stimuli according to attribute, and specifically according to colour and motion. Subjects viewed, in an fMRI scanner, visual stimuli composed of moving dots, which could be either coloured or achromatic; in some stimuli the moving coloured dots were randomly distributed or moved in random directions; in others, some of the moving dots were grouped together according to colour or to direction of motion, with the number of groupings varying from 1 to 3. Increased activation was observed in area V4 in response to colour grouping and in V5 in response to motion grouping while both groupings led to activity in separate though contiguous compartments within the intraparietal cortex. The activity in all the above areas was parametrically related to the number of groupings, as was the prominent activity in Crus I of the cerebellum where the activity resulting from the two types of grouping overlapped. This suggests (a) that, the specialized visual areas of the prestriate cortex have functions beyond the processing of visual signals according to attribute, namely that of grouping signals according to colour (V4) or motion (V5); (b) that the functional separation evident in visual cortical areas devoted to motion and colour, respectively, is maintained at the level of parietal cortex, at least as far as grouping according to attribute is concerned; and (c) that, by contrast, this grouping-related functional segregation is not maintained at the level of the cerebellum. ► Subjects viewed stimuli containing groups defined by motion or colour. ► There was grouping related activity in cerebellum, in prestriate and parietal cortex. ► Activity in parietal cortex, but not cerebellum, was segregated according to modality. In this study, we were especially interested to learn whether there is any specialization for grouping visual signals according to attribute. By grouping, we mean the process of assembling visual stimuli according to common elements. It is a general process that could be applied indifferently to any set of stimuli in any modality , and is In spite of the ubiquity and generality of the process, there was nevertheless the possibility that grouping of stimuli according to visual attribute may be a specialized process, neurologically separate from grouping according to other sensory inputs and possibly even dependent on the specific nature of the visual stimuli to be grouped. One cortical region that has been implicated in visual grouping in monkey is the parietal cortex , and mor17 healthy volunteers, all with normal or corrected-to-normal vision and none with any neurological or psychological disorders were scanned. All subjects gave informed consent prior to participation and the Ethics Committee of University College London approved the study.The first scanning session was used as a pilot experiment and data from it was not included in the analysis since it resulted in some changes to the stimuli presented in subsequent scanning sessions. An additional subject was rejected after pre-scan testing because he could only identify less than 60% of the test stimuli correctly. Of the 17 subjects who were scanned the mean age was 27 , 8 were male and none was left-handed. Subjects were tested with the Farnsworth–Munsell 100-hue colour discrimination test; their mean score was 33 .The stimuli consisted of 2 main categories: a) greyscale moving dots of varying levels of lightness in which there were between 0 (i.e. no grouping) and 3 groupings defined by common motion shared by all the dots in the groupings and b) coloured moving dots consisting of a field of randomly moving coloured dots of varying colours in which there were between 0 and 3 groups defined by a common colour shared by all the dots in all the groups. Additionally there were stimuli consisting of static colour and greyscale dots.www.processing.org) and consisted of 680 dots, each with a diameter of 10 pixels. The dots were initially positioned in a grid across a 1024 × 768 pixel area and their locations adjusted by a random amount of between − 10 and 10 pixels on both the x and y-axes. This resulted in a field of dots with no clear structure but with more even coverage than would be produced by full randomisation of dot positions. In the coloured condition, each dot was assigned a random colour from the full 8-bit red, green, and blue (RGB) range while in the greyscale condition each dot was assigned a grey level equal to the lightness portion of the CIE 1976  colour space value of a randomly selected colour from the coloured condition stimuli. After the dot fields were created, between 0 and 3 circular regions with a diameter of 100 pixels were defined to serve as the groupings. The positions of these regions were random but with the constraint that no two regions should be coincident and no region should extend beyond the edge of the visible area. In the colour grouping condition the regions remained static though the dots within them moved while in the motion grouping condition they were only used during initialisation to define the groups (see below). Each dot's direction was adjusted by a random amount of between − 0.2 and 0.2 rad once per frame. The direction of motion was weighted by adding a vector along the x-axis of 1.5 pixels per frame to each dot's velocity vector so that the dots tended to move from left to right. After randomisation of the direction and applying the left-right weighting the velocity was normalised such that every dot was moved by 1.7 pixels per frame. In all conditions the stimulus was displayed for 5 s followed by a 3 s blank.Stimuli were generated using Processing . This 100 frame period was not conducted in real time or displayed to the subject. In cases where the dots moved out of the visible area they were wrapped around to the opposite edge. An exception to this was the moving greyscale condition in which the dots within groups were prevented from moving off the edge of the screen by reversing the group's direction when an edge was encountered.In the colour grouping condition dots which moved into one of the grouping regions changed colour to a single randomly selected colour (selected from the full RGB space) which characterised all dots within that grouping. When dots left the grouping regions they reverted to their previously assigned colour. When more than one grouping was present the same colour was used for all the groups. The resulting effect was of 1 to 3 coloured patches made up of dots in a field of randomly coloured dots.The positions and colours of the dots were exported to a file that could be read by a MATLAB script for playback to the subject.Three additional categories of stimuli were used: static coloured dots, static greyscale dots and blank. The static stimuli were created by randomly selecting a frame from either the greyscale or coloured stimuli in which there were no groups defined; there were therefore no groups in the static conditions.http://www.vislab.ucl.ac.uk/grouping_movies/grouping.html.A video demonstrating the colour and motion stimuli is available from http://www.vislab.ucl.ac.uk/cogent_2000) running in MATLAB . In the scanner the stimuli were back-projected onto a screen using an LCD projector (at a resolution of 1400 × 1050 pixels) that subjects viewed through an angled mirror. The display arrangement gave a visual field of 24 × 19°, resulting in a single dot having a diameter of approximately 0.2° and moving at a speed of 1.7°sec− 1.Stimuli were presented using Cogent 2000  appeared in the centre of the screen when a stimulus was present (including in the blank condition). The stimuli were presented against a black background. The screen was black between stimuli. During each stimulus presentation subjects used the button box to indicate whether they saw zero, one, two or three groups, by pressing one of four buttons.http://http://www.sr-research.com/) equipped with an MR compatible camera. The eye position was measured at 500 Hz and recorded using the Spike2 software (http://www.ced.co.uk). Tracking data was collected for all 32 scanning sessions (16 subjects and 2 scanning session per subject).Eye movement data was collected using an EyeLink 1000 system from SR Research  to get the positions of the V4 complex  fitted with a 32-channel head-coil. Prior to scanning, a localizer sequence was performed to locate the subject within the scanner and the magnetic field was mapped to correct for the effect of the subject on the static field in the scanner. An echo-planar imaging (EPI) sequence was used for the functional imaging  using 48. Voxel resolution was 3 mm × 3 mm with a 2 mm slice thickness and 1 mm inter-slice gap. Heart rate, breathing and eye movement were recorded during the functional scan. Two sessions of functional data were collected with a short break between the sessions. A different set of stimuli was used in each session and a new order was generated but they were otherwise identical. A T1-weighted anatomical image was acquired for each subject after the functional scanning was completed . After the structural image was acquired, two runs of retinotopic mapping data were acquired using the same EPI sequence as was used to acquire the main functional data. Retinotopic mapping data was only collected for 8 of the subjects . Stimulus events were modelled as boxcar functions. The stimuli were separated into 6 main contrast vectors — moving colour with grouping, moving colour without grouping, moving greyscale with grouping, moving greyscale without grouping, static colour and static greyscale. The subjects' keypresses and head movement parameters  were included in the General Linear Model (GLM) as regressors of no interest. As the event duration was short, time derivatives were added to the GLM for each contrast vector. A high pass filter with a cutoff of 120 s was applied to the data to control for slow signal drift.The MRI data was prepared for analysis in SPM8  was added as a linear parametric modulator. Regressors of no interest, high pass filtering and time derivatives were added to this GLM as described above.Maximum likelihood estimates of the parameters were then taken to the second (between subject) level for random effects inference using the summary statistics approach. This involved taking contrasts or mixtures of parameter estimates summarizing condition-specific effects in each subject and creating SPMs of unpaired t-statistics.All co-ordinates are given in Montreal Neurological Institute (MNI) space.The contrasts for colour grouping > no colour grouping and motion grouping > no motion grouping, as well as the linear parametric activity related to number of groupings for both colour and motion, were assessed for conjunctions  at the sThe reaction times for accurate responses did not differ significantly by number of groupings , from which we conclude that the stimuli with different groupings did not differ in task difficulty.The mean accuracy in terms of responses did not significantly differ for stimuli with 1 grouping (80%) and those with 3 groupings (85%) but was significantly higher for stimuli with two groupings (89%) than those with one (p = 0.011) or three groupings (p = 0.048). This ordering of accuracy in terms of number of groupings bore no relationship with the strength of activations relating number of groupings to the BOLD signal. This reinforces the conclusion that the results cannot be accounted for in terms of task difficulty.For the 14 sessions where good eye-tracking data  was collected, the mean correlation coefficient between the standard deviation of the eye position and a binary signal indicating the presence of grouping was − 0.08 (std. dev. 0.16), indicating that the subjects did not significantly increase or decrease their eye motion in response to the presence of groupings or their numerosity.We were able to identify V1 and V2 in 6 of the 8 subjects used for retinotopic mapping, V3 in 4 subjects and V4 in two. Of the two subjects in whom it was possible to map V4, neither showed any activity in their SPM contrasts when a masking for V4 was applied. This is almost certainly due to the fact that in these two subjects the hottest activity within the V4 complex fell in V4α, which is poorly organized retinotopically  , with a Bonferroni correction for multiple comparisons. We were mainly interested in the following contrasts:Colour > greyscale static and (b) motion > greyscale static, which acted as localizers for visual areas V4 and V5. The former led to activation within dorsal and ventral V2 and in V4 while the latter led to activation within V2, V3, and V5 and in medial parietal cortex .Although we were able to define V4 retinotopically in two subjects, retinotopic identification was more difficult for V5 see  section.The contrast colour grouping > no grouping led to activity in (a) V4 bilaterally  see Tab section;The contrast motion grouping > no motion grouping led to activation within (a) V5, bilaterally .The contrast no colour grouping > grouping led to bilateral deactivation in V1 . The conIt was not possible to map any of the parietal cortex areas using the retinotopic mapping data, possibly because of ‘drop-outs’ in the maps and substantial variability between individuals  see als section.Only 1 out of 16 subjects showed any significant activation in the masked contrast  , suggestWe also wanted to learn (e) whether there was any relationship in the active areas between the BOLD signal and the number of groupings detected. We did not detect any activity that was parametrically related to grouping in areas V2 and V3.The grouping of elements in a visual scene having a common property, to distinguish or segment them from other elements of the same scene not having that common property, is a critical process for visual recognition. Given the functional specialization of the visual brain  and espeDetermining the number of groupings naturally demands attention, making it interesting to consider the role that attention per se may have played in the pattern of activity that we observed. Attentional load enhances strength of activity in both V4  and V5  but thisThe brain's attentional system has been divided into two components, both of which involve parietal cortex but which differ with respect to the part of frontal cortex that each involves : the dorIn summary, it would seem that our results are not explicable by a general attentional mechanism, though a part of ventral attentional system was active presumably because of the behaviourally relevant paradigm in our study. Hence, even accepting that a part of the attentional system is (necessarily) engaged in a task that demands attending to groupings, the fact still remains that, within parietal cortex, the attentional component engages different parts of it.The grouping of signals according to direction of motion or to colour naturally involves some degree of coherence. The relationship between strength of activity in V5 and coherence is problematic; some have reported that the strength of activity in it is related to the degree of coherence  and otheAn increase in the number of groupings entails an extension in the area of the visual field stimulated by groupings. We note, however, that our groupings (whether of colour or of motion) were embedded within a larger stimulus that included the same coloured dots which, though in motion, were not grouped together. Hence the total extent of the visual field stimulated was the same regardless of whether there was a grouping or not. We nevertheless acknowledge that, within the equal extent of visual field stimulated, three groups will involve a larger extent of the visual field stimulated by coherence than one group or no groups. Acknowledging this makes little difference to the principal conclusion of this study, namely that grouping or coherence according to colour or motion engages different compartments within the intraparietal sulcus and the same subdivision of the cerebellum.The parietal cortex has several subdivisions . We trieNumerous studies have now shown that colour stimuli activate V4 and motion stimuli activate V5 , and henParietal cortex has been traditionally associated with the ‘where’ system although many recent studies have shown that it has functions that do not sit neatly within this classification . Among tThe extensive activation in the IPS that we observed in this study runs antero-posteriorly and hence is orthogonal to the axes of the IPS areas 1–4. The close correspondence between the (MNI) co-ordinates given in the study of Numerosity judgement as a principle involved in grouping has been demonstrated in studies of visual, haptic and auditory perception . GroupinWhether the same region of the parietal cortex is engaged with symbolic and non-symbolic numbers has been controversial (see Most papers dealing with numerosity have concentrated on the parietal cortex. In one , activitWhereas most previous studies on attention due to motion have not reported activation in this cerebellar zone, a recent study using attention to motion has linked the cerebellar area active in this study to attentional effects in predictive coding , though We obtained strong activity in medial insula in the contrast motion grouping > no grouping but not in the corresponding contrast for colour. The medial insula has been found to be active in a variety of conditions, not necessarily related to visual perception, and its appearance in this contrast and absence in the corresponding colour contrast is puzzling and one for which we have no explanation. This is also true of the activation in the right precentral gyrus shown in the parametric contrast for number of colour groups but not that for motion and for activity in the right inferior frontal gyrus produced by the contrast colour grouping > no grouping.Our main aim in undertaking this experiment was to learn whether the principle of functional specialization extends beyond visual processing, to functions such as grouping which are general in nature. The results show that the principle extends to grouping of colour and motion within parietal cortex, and that this segregation is reflected as well in registering the number of groupings related to the two visual attributes within the IPS. We have shown in the past that the functional specialization in visual cortex for processing different visual attributes is projected in time, entailing a temporal difference in the perception of colour and motion . Here, w