This Grounded Theory study describes the process by which older persons “become” volunteers. Forty interviews of older persons who volunteered for Habitat for Humanity were subjected to secondary content analysis to uncover the process of “becoming” a volunteer. “Helping out” (core category) for older volunteers occurs within the context of “continuity”, “commitment” and “connection” which provide motivation for volunteering. When a need arises, older volunteers “help out” physically and financially as health and resources permit. Benefits described as “blessings” of volunteering become motivators for future volunteering. Findings suggest that older volunteering is a developmental process and learned behavior which should be fostered in older persons by personally inviting them to volunteer. Intergenerational volunteering projects will allow older persons to pass on knowledge and skills and provide positive role modeling for younger volunteers. As the numbers of older adults in developed countries increase, it becomes increasingly necessary to view aging differently than we have in the past. According to U.S. statistics, 12.8% of the population was over the age of 65 in 2009. Further, individuals who reached the age of 65 could expect to live an additional 19.8 years if female, and an additional 17.1 years, if male [One indication of productive aging is volunteering. Older adult volunteering has become a topic for research and discussion in many countries including Spain, Hong Kong, Korea, and Australia –6. RecenThere have been numerous studies exploring volunteering in older adults in the last ten years. These studies have shown many benefits of volunteering to older adults, including: better physical and psychological health, increased well-being, increased life satisfaction, lower mortality risk, lower functional dependence, and lower levels of depression –12. HoweThe purpose of this grounded theory study is to describe the process by which older adults become volunteers. “Become” as used in this study is a term describing how these older adults incorporate volunteering into who they are and not just what they do. It is our hope that understanding of how older adults become volunteers may lead to interventions to engage more numbers of older adults in volunteering.In an attempt to discover why and how older adults volunteer, many studies have explored common motivators regarding older adult volunteering. Altruism has been found to be one of the most significant motivating factors for older adults to volunteer , 13–15. Several studies have identified barriers that hinder older adult volunteering. Among barriers identified in the volunteering research literature are time commitment and financial constraints , 15, 21. Previous studies identifying motivating and hindering factors of volunteering have provided valuable information in understanding older adult volunteers. However, these studies focused on specific factors such as benefits, motivating factors and barriers to volunteering, not on the process of volunteering. This study proposed to address that gap by exploring the process of becoming an older volunteer. Understanding of the process of how an older adult becomes a volunteer will provide a more complete and dynamic viewpoint of older volunteering. In grounded theory research, the theory is derived from the words of the participants. The theory is not derived from another theoretical framework. However, no research is atheoretical. Researchers always possess a perspective or viewpoint of reality. As nurse researchers, we were guided by a nursing theoretical perspective that uniquely framed, but did not dictate the findings, in this study. The theoretical perspective for this study was Margaret Newman's theory of health as expanding consciousness . Within There are choice points or factors in the lives of individuals that represent opportunities for personal growth and facilitate change in person-environment interactions. This growth and change is reflected in patterns of expanding consciousness such as increased relatedness with others or a higher being. Patterns will vary according to the unique configuration of each person-environment situation. However, the theory of health as expanding consciousness posits that there will be similarity of patterns among people who share similar life experiences. This study sought to identify those common patterns. Within this framework, increased interactive patterns of interpersonal relationships such as those formed during volunteer work can be viewed as a manifestation of expanding consciousness. The theory of health as expanding consciousness provided a perspective for interpreting the accounts of the participants and identifying patterns of interaction, thus providing a framework interpreting the development of the emerging theory. Volunteering, in this study, was viewed as a pattern of expanding interactions with others and therefore a manifestation of expanding consciousness.We used a grounded theory secondary data analysis method for this study. After removing any identifiers from original transcripts from an earlier study of a convenience sample of 40 older individuals who volunteered for a Habitat for Humanity “blitz build” , the datTo put the original study in context, a Blitz Build is an intense, physically challenging activity during which a group of volunteers come together through Habitat for Humanity to build a complete home within a week. Habitat for Humanity International is an organization that uses volunteers of all ages to help build affordable houses for those in need. They operate all over the world in 90 countries, all 50 U.S. states, the District of Columbia, Guam, and Puerto Rico . This secondary data analysis study used grounded theory methodology to inductively develop a theory that was grounded in actual experiences and faithful to everyday reality as conveyed by the actual participants' accounts of those events. Grounded theory was chosen because it is especially useful for uncovering process. This method was developed by sociologists for the purpose of “discovery of theory from data systematically obtained from social research” , page 2.Data analysis was carried out in accordance with the techniques recommended by grounded theory researchers, Strauss and Corbin . All quaN = 40) from eleven southeastern states in the U.S. Participants were mostly Caucasian (92.5%). Three participants were Hispanic or other (7.5%). Mean age of participants was 68.64 years . Also, the majority of participants were married (87.5%) and, in most cases, married couples came together to the Habitat Build. Most participants were semiretired (70%), but still working parttime. Eight participants (20%) were still employed fulltime. Many participants had a high-school or higher level of education (82.5%). The sample for the original study  consisteBecoming an Older Volunteer was discovered. The grounded theory is depicted in Through analysis of the transcripts from the 40 participants of the original study, a theory of Helping out was the term they used for their volunteering activities, and this term became the core category of our theory. The older volunteers did not apply the term “volunteer” to themselves, rather they saw themselves as people who “help out.” It was apparent that helping out described common patterns of interaction by the participants with others. They also talked about years of helping out that began back in childhood. This helped us to conceptualize becoming a volunteer as a developmental process that evolves from helping out. Judy, a 65-year-old woman who was very active in her church, described how she helped out: “I help at my church. I help in the dining room when there is a death in a family. I prepare a dish and I've gone and worked in the kitchen and helped serve the meals… I take older friends to their doctor's appointments. That's my routine now. You know, more just helping out, wherever.”Another older woman, 70-year-old Susan, also described her church related activities:“I'm treasurer of my Sunday School and on the finance committee… and my niece has a group of kids she calls “Bible Buddies” and I got started with them. I just thought it was a good idea for me to be there… So, I've been there to just help out with them, anything I can.”When first asked about volunteering activities, the participants often responded that they did not volunteer much, however, they “helped out here and there” continuity, connection, and commitment that formed a contextual background for the core category. All three categories had a spiritual thread interwoven throughout. When taken together, this contextual background formed the motivational basis for the older volunteer to participate in helping out. Each of these contextual categories will now be discussed. There were three interacting and overlapping contextual categories named continuity in the theory. Many participants related early childhood memories of working together with their parents to help out needy neighbors or do church work. Connection described participants' sense of kinship with others and their love of people. These older adults felt a strong connection to others, generally, to all humankind, and specifically, through their churches and organization involvements. Belonging to a group that was committed to volunteering was a strong motivator for the participants to volunteer. Commitment described the participants' sense of personal responsibility to help others. For many, this sense of commitment had roots in their Christian beliefs. There was a sense of duty to help others expressed by almost all participants. Jeannie, an 80-year-old woman with a life-long connection to the Catholic Church described helping out in her life:A desire to transmit values of caring to others that participants had learned earlier in their lives and their desire to pass on blessings they had received were named (continuity) “I helped my mother… My mother… was the church cleaner in the Catholic church… so I think that's where I got my volunteering from.” helping out:Tom, a 68-year-old who grew up in a rural community, shared how this previous experience influenced his (continuity) “Most of the folks working with our bunch… grew up in the era where you helped your neighbor too.” helping out:Joe, 72 years old, and 40-year member of a fraternal organization that encouraged volunteering by members, described how belonging to the organization influenced his decisions in (connection) “They are like a bunch of brothers, you know… and it's just a good feeling to be part of (civic) group.” He also went on to discuss his own commitment and sense of personal responsibility to help others:(commitment) “I kindda feel a personal responsibility… I just feel led. That's what I need to do… I am my brother's keeper.” This sense of connection to others and a commitment arising from spiritual beliefs was echoed in these two statements by Mike, a 68-year-old retired life insurance salesman: (connection)… “God's got a whole lot for me to do and I feel like this is a part of it.” (commitment) “I love people and I've never had the heart to say no, I guess, so I volunteer when I can.” helping out could begin, an antecedent event had to occur. The antecedent to the entire process was recognizing a need. This recognition of a need could occur in two ways: either an organization or individual asked for help or the older adults saw a need that they felt that they could meet individually or with others. Some participants were reluctant to help unless personally asked to do so, while others actively sought our opportunities to help others. Ron, a 70-year-old retired welder described how he recognized opportunities for helping out:Before the process of  “Well, I, I've learned that I have to fill in where it needs to be filled in… I'm willing to do it.” Ron's wife, 69-year-old Julie, described how she was willing to help out and anticipated being asked to help out every day:“I've found out—what's the use of planning out your day? As soon as the first telephone rings, you know, the whole day is gone because there is somebody that needs me. I just learned not to—you just do every day what needs to be done if there is a need and you see it. I don't think you would think twice about doing for your neighbor, your friend. Whoever in need… I've never been any other way.”Jerry, an 82-year-old man who was less outgoing, did not actively seek opportunities to help out. He described his reluctance in help out unless he was asked to do so: “If somebody says “I need your help”, I'll help em. If they don't, why I don't butt in. That's it!”choosing to help. The process of choosing to help consisted of several steps: First, the older adult determined the worthiness of the request or person needing help. Then, older volunteers evaluated their resources and abilities to give help. Finally, they determined the type of help they could give which could be financial, physical, or supportive help or sharing of knowledge, goods, or skills. Mary, a 65-year-old who assisted several neighbors who were much older than she was by running errands and taking them to appointments described her feelings about choosing to help out:Once a need was recognized, participants begin a deliberative process of “But these are genuine people that need help. They know they can depend on me.”help out:Tom described his past personal experience of being poor and needing help himself at one time and how it influenced his decisions to “I love to help people that, you know, that I feel like they appreciate it and they need it. Because I came from being very poor… so now if I see somebody that I know that they need help, that's got several children and they've become divorced or widowed—I know they need help, you know.”Factors or conditions that could be either hindering or facilitating determined whether or not help was given, and also what kind of help was given. These intervening conditions included, but were not limited to: time to participate in a project or help out, financial resources, need for, and ability to travel, physical abilities or disabilities and general health status, skills and spousal support of the person volunteering. Several of the older adults, especially those 70-years old and older spoke of physical limitations which negatively impacted either the amount or type of volunteering they did. However, many participants considered volunteering to be a priority, and they continued to volunteer, but adapted what they contributed physically by adapting activities to their physical conditions. This area is addressed more completely in another publication . Rebecca(facilitating time) “I mean to us now we feel that we can do it now because we both don't have to say “I have to be home” or “I have my children”. They are all gone and they are all grown up so I feel I'm on my own now.” Sam, a widower and the oldest participant at 88, described how financial stability allowed him to be able to volunteer:(facilitating finances) “As I say, I'm pretty frugal and I invested a little bit… So I have a fairly good little income and I'm glad to share it with something that I think will do some good.” Jim, a 74-year-old who was anticipating a need for a hip replacement, described how this placed physical limitations on him and influenced his ability to help out: “I can't get down, you know, low, because you know, it's hard for me to get back up because of my hip. Ain't actually my hip—it's the muscle in my leg. But uh, yeah, I wish I could do more, but I'm limited in, you know, that way.” helping out was described by participants as being blessed. The words blessed or blessings were used frequently by participants when they described benefits of volunteering. Participants related these as general blessings or as spiritual, social, emotional, or physical benefits gained as a result of the helping out experience. More importantly, these blessings reinforced their volunteering and strengthened the contextual categories of continuity, connection, and commitment, increasing the likelihood that the older volunteer would volunteer again. The result (consequences) of Blessings also increased the likelihood that these older volunteers would actively seek future opportunities to volunteer and choose to help if asked. In fact, the more they helped out, the more they wanted to help out. Julie related blessings she received from volunteering:“… you do something that they ask you to do and… you are accomplishing something and you feel good about yourself.”Sam stated that he looked every day for an opportunity to help others. He related:“It just feels so good to get to share some of the blessings that you had in your life… and I would definitely recommend this to anybody that wanted a blessing out of life. I feel blessed and it is good to share some of your blessings with somebody else.”Ralph, a 69-year-old who was battling his own health problems (lung cancer), but still continued to volunteer whenever he was able, related the following:“I guess, you know, it all just boils down to personal satisfaction. There is not a tremendous amount, I mean, well, there's no monetary really, I don't guess that I know of, but I just enjoy helping people and being with people and working with them.” .Blessings, in the form of physical and mental benefits of volunteering, were discussed by Carl, a very active 82-year-old.“Well, it will probably make you get more exercise than you would ordinarily. So that helps you, physical exercise and mind and everything else.”As a result of analysis, it became very clear to us that the term “volunteer” described not only what these older volunteers did, but also who they were in a wholistic sense. These older adults incorporated volunteering as an integral part of their personal, emotional, and spiritual identities. The Habitat for Humanity Blitz Build was only one of many volunteering activities that the older participants engaged in. They related stories of volunteering in many different capacities both on a formal basis through organizations and on an informal level through work in their communities and with friends and family. Volunteering activities included work with church and civic organizations, assisting in voter registration and poll work, church mission work in the U.S. and other countries, disaster relief work, food ministry work, helping with disabled children, and many other instances. Further, these participants volunteered often, sometimes on a daily basis.Our research shows that volunteering is a developmental process and a learned behavior. This finding implies that intergenerational volunteering projects should be encouraged, since volunteering is best learned by example. Intergenerational projects will allow older adults to pass on knowledge and skills and provide positive role modeling for younger volunteers. Additionally, younger volunteers can assist older adults with some aspects of volunteering projects that may require more physical strength or agility. Nurses, especially Parish Nurses, are in a unique position to assist in developing faith-based volunteering projects that include both older adults and youth members working together. Volunteering projects that involve several generations support Warburton et al.'s  findingscommitment, connection, or continuity (context), however, is a strong motivator. Older adults, even without previous volunteering experience, can and should, personally be invited to volunteer. Older adults will more likely volunteer if they belong to a group or organization that volunteers. Our findings support previous studies that show that connection with groups is a motivating factor [Previous volunteering experience is not a prerequisite for an older adult to become a volunteer. A sense of g factor , 14, 19.Also, positive volunteering experiences lead to the desire to volunteer more. Once an older adult has volunteered, additional positive volunteering experiences will lead to more volunteering (blessings). Projects where older adults can see the “fruits of their labors” and experience increased social contact will provide more “blessings” and lead to increased volunteering. Nurses should promote volunteering as an activity choice for older adults. The physical and mental benefits of such activities have been well documented in the literature and are supported in this study.helping out became a priority. Health, unless it impacts functioning significantly does not seem to affect older adult volunteering either in this study or in the literature. Older adults will find a way to volunteer within their abilities, and nurses can assist older adults in finding volunteering opportunities that are congruent with the older person's physical abilities. Further, for volunteer activities where there may be a number of older adults participating, nurses can volunteer themselves to be the on-site nurses to provide first aide, check blood pressures, and assist with health related issues. Our findings regarding intervening conditions support findings in other studies , 10, 15 Another barrier, that of limited finances, especially those related to transportation, may hinder lower-income older adults' ability to volunteer. Nurses can assist lower-income older adults with finding free or low-cost transportation through local Offices on Aging or other volunteer transportation services which would increase the ability of older adults to volunteer. Flexibility of scheduling while addressed in the literature  was not recognizing a need represents a choice point for the participants to expand their interactions and connections with others. Helping out becomes a new pattern of relating for these participants in their older years because of more time when they retire and also financial ability, physical health, and spousal support. It becomes apparent that older adults who become volunteers have experienced expanding consciousness though increased sense of connection and interactions with others. These increased connections and the personal growth described by the participants were experienced as blessings in their descriptions of the benefits they derived from volunteering. In addition to increased connection with others, participants described how volunteering strengthened their spiritual connections. All participants felt that they were better people because of their volunteering activities. Thus, we conclude that volunteering leads to expanded consciousness as defined by Newman [When our findings are viewed within the Newman  perspecty Newman . connection to the volunteering of older adults both as a contextual motivating concept and as a consequence of volunteering which includes blessings or benefits of connectedness to others and spiritual connectedness. These patterns of connectedness contributed to satisfaction and quality of life in the older volunteers in this study. This new theory also supports Register Theory by Register and Herman . The Regn = 40), all participants being from the same geographic area, minimal ethnic diversity in the sample, and all participants belonging to the same organization. Additionally, all participants self-identified as Christians. These limitations influence transferability of the findings to similar groups of older volunteers. We hope to address these limitations through future studies with larger samples, in other geographic locations and with more culturally diverse groups. Additionally, other religious groups have humanitarian and volunteer projects and future studies should include older Jewish, Buddhist, and Muslim volunteers.  There were some limitations to our study including small convenience sample size (This paper has implication for nurses, as change agents in their community roles to foster active recruitment and involvement of older volunteers who are a valuable, largely untapped resource. Older adults who are recruited will likely respond, and as they gain positive benefits from volunteering, they will continue to participate in volunteering activities. All communities can be stronger because of older volunteers. These older volunteers can provide valuable needed services that communities cannot afford to have if they have to pay for them. Nurses can act as spokespersons for older adults and assist with education of organizations and individuals regarding the contributions that older adults can make and foster a more positive attitude towards aging. McBride  challengkeep older adults volunteering, thereby leading to increased health for the older volunteers and many benefits for the communities in which they live. This study has provided new important information about the process of how older adults become volunteers. Understanding of this process and how it develops may lead to strategies that better engage older adults in volunteering and, more importantly, strategies that


First, three case studies are presented of psychotic patients having in common an inability to hold something down or out. In line with other theories on psychosis, we propose that a key change is at the efference copy system. Going back to Freud’s mental apparatus, we propose that the messages of discharge of the motor neurons, mobilized to direct perception, also called “indications of reality,” are equivalent to the modern efference copies. With this key, the reading of the cases is coherent with the psychodynamic understanding of psychosis, being a downplay of secondary processes, and consequently, a dominance of primary processes. Moreover, putting together the sensorimotor idea of a failure of efference copy-mediated inhibition with the psychoanalytic idea of a failing repression in psychosis, the hypothesis emerges that the attenuation enabled by the efference copy dynamics is, in some instances, the physiological instantiation of repression. Second, we applied this idea to the mental organization in neurosis. Indeed, the efference copy-mediated attenuation is thought to be the mechanism through which sustained activation of an intention, without reaching it – i.e., inhibition of an action – gives rise to mental imagery. Therefore, as inhibition is needed for any targeted action or for normal language understanding, acting in the world, or processing language, structurally induces mental imagery, constituting a subjective unconscious mental reality. Repression is a special instance of inhibition for emotionally threatening stimuli. These stimuli require stronger inhibition, leaving (the attenuation of) the motor intentions totally unanswered, in order to radically prevent execution which would lead to development of excess affect. This inhibition, then, yields a specific type of motor imagery, called “phantoms,” which induce mental preoccupation, as well as symptoms which, especially through their form, refer to the repressed motor fragments. He complains of penetrating sensations, people and things sticking onto his body, onto his skin, of people walking through him, of things penetrating him. In other words, he has great difficulty to create an experience of distance between him and his percepts. To restore a bearable relation to the world, he has to physically move back and forth around his visual targets: he frequently backs up on his steps, to move forward again; he opens doors by opening them partially, then closing them again partially, then reopening them, etc.; he does and undoes repeatedly, either completely or partially, some of his gestures, both in the forward and in the backward direction.Specifically, one chain of events is painful to him: suddenly moving people or things in the world cause a “fizz” or a “pinching feeling” on his retina, which then constitutes the unique and direct cause of an “undesirable image.” These undesirable images are often of an incisive and penetrating content, such as described on the following note which he keeps in his coat“11-09-1995. In Dymfna. That dirty coat of fat, basement slices. A needle in the eye. The disintegration of my photo-apparatus when G. C. went by the closet in the first living. Sucking out my eye. 28-11-‘95 A penis through my knife 28-11-1995. My pectoral muscle torn when P. L went through the corridor. Around that time transferred to St. Cornelius. My viscera extirpated by C. C. at the old laundry house on 21-12-’97. 21-11-98. When the occupational therapist went to the bookbinding place, Lieve C. instead of Koen C. When J. D. went from the place where the opener hangs to his chair. My balls unhooked or melted. When the fire chief went to the farm. My colon ruptured a little. When M. D. went from the toilet to the outside. My balls extirpated.To undo the undesirable image, the moving target is asked to undo the movement: he asks people around him to back up, to undo in backward direction what they did in the first place. When they agree to do so, he watches the scene fixedly, firmly closes his eye, and holds this pose for a second, before looking up again. In case they do not submit to his request, he remains pursued by the painful image. Places where he has been, are thus occupied with an accumulation of as-yet-undone undesirable images, which continue to haunt him.at the surface of the skin, but when the device is actively manipulated by the subject, a spectacular capacity of form recognition is observed as well as the exterior locating of the percepts: the objects observed are perceived in a distal space, over there in front of the subject.” . Strikingly, though the light sources are located at a distance, under specific conditions , they are perceived “at the surface of the skin,” which corresponds literally to what Hervé sometimes describes for targets at a distance. Moreover, his complaint is exactly his inability, at moments, to perceive objects in a distal space “over there in front of” him. In other words, immobilizing the device makes the participant have a perceptual modality which resembles Hervé’s at moments. The coherence between the two situations even increases when Lenay  have come to the fore again, schizophrenics are not estranged by these mechanisms any more.» [Italics added].In the Freudian model of psychosis, processes typical for the unconscious are present in conscious mental life: “As regards the relation of the two psychical systems [the conscious and the unconscious], all observers have been struck by the fact that in schizophrenia a great deal is expressed as being conscious which in the transference neuroses can only be shown to be present in the ” Freud, , p. 197.” Freud, , p. 11 a” Freud, , p. 422 ” Freud, , p. 422 Indeed, Freud’s  architecefferent, i.e., in the direction of motility  explain Hervé’s different symptoms coherently; (2) fit with a psychodynamic account if we accept an equivalence between efference copies and indications of reality; and (3) fit with a neuroscientific account of other described phenomena in psychosis. In this sense, surprisingly, it is an parsimonious proposition.First, concerning Hervé’s symptoms. If the efference copies are not functioning “properly,” the pursuit eye movement would still occur, but would not be recognized as being under command of the self. In other words, it would feel as if the eyes were forced by some external agent to make small movements to follow the target, something one could tentatively describe as a “pinching” on the retina, which is what Hervé reports about his experience. Moreover and importantly, if something is disturbed at the level of the efference copies, Hervé is (at moments) without the means to appropriate his own eye movements which gather the retinal information, i.e., he has no means to feel how moving his eyes is efficient in influencing the incoming retinal stimulation. Now, according to the efference copy modelsSecond, concerning a psychodynamic account of Hervé’s problems. If we would accept the idea of an equivalence between sensorimotor efference copies and Freudian indications of reality, we would be entitled to understand Hervé’s particular perceptual modalities as resulting from a faltering secondary processing of perception, resulting in primary process predominance.  Restated in this approach, Hervé’s perceptual symptoms – though a superficial account of some of them  might lead to classify them as, e.g., obsessional – become coherent with a diagnosis of psychosis, and thereby with his other psychotic symptoms . Moreover, this psychodynamic account helps to make sense of another striking symptom of Hervé, which can not as directly find an explanation in a sensorimotor account, namely his profusion of “undesirable images” upon perceptual intrusion. Indeed, if we consider that it is the primary process, which in Hervé dominates perception, this explains not only his deficit in conferring the incoming visual stimuli the tag of “percept” (the primary process is not concerned with criteria to discriminate the sources of the processed stimuli), but moreover, these incoming stimuli are now preferentially treated in a decontextualized, associative way typical for the primary process. Hence, Hervé produces in an associative way an unrestrained range of memory and fantasy contentsThird, concerning a neuroscientific account of other described phenomena in psychosis. The proposition that the efference copy dynamics are altered in Hervé coincides with Frith’s hypothesis  I have to force my mind not to be lead by it all the same. I am a fighter, but mentally. This system of counter-computing, I try to apply it to everything now, perhaps with time it will become automatic, if I’m lucky.» This state of affairs obliges Denis to invest structurally an amount of time in his daily program dedicated to the activity of counter-thinking. He gets so mentally tired of this, that he is no longer able to keep energy for the simple tasks of life or to live an independent life.Denis says that these questions do not really interest him; he is simply taken by them: “You can ask yourself a million of questions if you want and on how many questions will you have answers? The more you know, the more you realize that you do not know. There is some resemblance between Denis’ symptoms and the clinical picture of dorsal simultagnosia, a condition caused by a bilateral parietal lesion, where the patient is able to direct his attention to only one single visual element after which his attention remains attached to that. Jeannerod and Jacob , p. 310 The sensorimotor hypothesis for Denis then is that, as in Hervé’s case, his inability to disengage attention is connected to a difficulty involving the efference copy-mechanism. More specifically, the withdrawal of attention would require the attenuating effect brought about by the efference copies. Indeed, say we also consider the allocation of attention as a movement of the subject, then the efference copies not only would yield a way to appropriate the attentional movement (“I choose to pay attention to this”) but also, thanks to their possibility of targeted inhibitionI get stuck for one to two seconds and each time I have to re-adjust… I have built in an internal system whereby I can think away the obsessive thought in one second… when I think of something that is, then I think “stop that!” and so I do not go on… in normal people this happens seamlessly… (…) That system of subtraction, I try to apply that all over, maybe over the years it will become fluid.”This forward model crucially makes use of efference copies, i.e., copies of the attention movement signal Taylor, , p. 990 reflex attention) will act to Ψ biologically as a signal to send out a quantity of cathexis in the same directions.” In other words, the indices of reality function as a criterion for the flexible investment of mental means. So, again, we find a striking parallel between the Freudian indications of reality and the sensorimotor efference copies. For this reason, the idea is that Denis has an altered dynamic of his indications of reality, and consequently, at the level of the secondary process treatment of attention. The resulting primary process predominance can, moreover, help understand the delusional tendency with which Denis tries to make sense of his experience: « The misery starts with the things made by man, they harass meFreud , p. 326 inhibition system. Both for Hervé and for Denis what is proposed is that their observed relative failure of inhibition would be related with changed dynamics at the level of the indications of reality, and therefore, the secondary process from a psychodynamic point of view and of the efference copies from a sensorimotor perspective. Note that this proposed failing inhibition in psychosis is not in contradiction – and might actually fit quite well – with some of the prevailing neuroscientific theories on schizophrenia which state a diminished inhibitory prefrontal functioning, such as the hypofrontality theory  what is at stake in their symptomatology and their suffering, is situated at the level of the repressiona ciel ouvert”At this point, let’s dare a further proposition. Indeed, the fundamental metapsychological difference between a neurotic and a psychotic structure is supposed to be the presence, resp. the  absence of When I meet Zacarie, he is 52 and he is at the psychiatric center of Beernemtake place. Zac did not understand the wordings of the doctor which also suggested the eventuality of the outing not taking place. He suspected malice, and this malice for him was clear and even proved by the doctor’s choice of word: “taking place” – which is “doorgaan” in Dutch. This word “doorgaan” had put Zac in disarray. “Doorgaan,” after all, he tells me, is divided into “door” and “gaan.” “Door” is the inverse of “rood,” meaning “red” and red is the color of blood. “Rood. In vain,” he says, using the English “in vain” and playing on both readings, “in vain” (“hopeless”) but also “in the veins.” “Door hart,” he continues, which means “through the heart” and he clarifies “steek door mijn hart” (“stab through my heart”). The second part of the word “gaan” means “go.” “Gaan” rhymes with “aan.” “Zet maar aan,” he says, which means: “Blow off.” “Aan” is the inverse of “naa” which leads to “naald,” which means “syringe.” In other words, he finally concludes about the doctor’s word, “doorgaan” refers to [twice its reverse] “a red syringe,” and then: “Let me have an injection and that I’d be put in the cellOne of Zac’s major difficulties is that often in an emotionally challenging context, received language fragments “explode” in chains of associative meanings. For example, during one of his visits, the doctor had expressed hope that Zac’s next outing would indeed Here is an excerpt of a session on a metonymic rather than an alliterative fashion: “I speak like a boy cow, holy cow, a truth as a cowphonological variants , be it by the simple fact that the pauses in speech taken by the speaker do not match the boundaries of words. The linguists Cutler et al. , for exaThis is, of course, what we propose for Zac: when at  moments his inhibition system fails or works less well, he has to do with an explosive linguistic stimulus which requires a gigantic interpretation effort from him. Zac’s problems have been classically described for psychotic patients before. Starting from the earliest nosographic descriptions of psychosis, a loosening of language associations has been reported  to ward off the incoming signalIn other words, through Zac’s case, we propose that “normally” easily anticipated language is structurally attenuated and that this attenuation stops the reverberation of interpretative activation. For the unanticipated fragments, the non-attenuated, positive somatosensory activation would trigger a mental mobilization, i.e., would lead to the disinhibition of interpretative or identificatory activationWorries in my head, digits and letters in my head, reversed digits and letters, I can’t silence it, everything twists and turns, words, digits, this spinning makes me mad.” In a psychodynamic framework, this type of language, which is governed by an associative principle of the “anything goes,” is a language on the primary process mode. By contrast, the secondary process allows a symbolic type of language, which is characterized by the fact that the intention of the linguistic act governs its organization  as well as high language associativity.Taking together our three case studies – having in common an inability to hold something down or out – we propose, as others have done Frith, , that a The aim of this second part is to check if the application of the hypothesis which we concluded from our psychotic case studies – namely that the attenuation enabled by the efference copy dynamics is, in some instances, the physiological instantiation of the mental mechanism of repression – makes sense in neurosis, where repression is precisely thought to be the main defense mechanism. As the efference copy dynamics refer to motor control regulation, we start this exercise by thinking repression in an action selection framework.hallucinates the coveted object, i.e., has an inner imagery experience independent of the mobilization of his perceptual apparatus.The moment where something truly mental comes into being can be situated very minutely in Freud’s oeuvre. We propose that it is precisely when the hungry baby, having been (breast-)fed before, is again taken by hunger and cries, but no mother, no breast, or no food comes along and the baby What actually happens at this point has also been described, independently of Freud, by the neuroscientist Marc Jeannerod. Jeannerod  in the cunable to reach the desired goal, e.g., when there is no breast: « these neurons encode final configurations  as they should arise at the end of the action, and (…) they remain active until the requested configuration has been obtained. If the goal [of an action plan] were not reached, the sustained discharge would be interpreted centrally as a pure representational activity and give rise to mental imagery.» . In other words, to the extent that a movement is not leading to an intended goal, mental imagery arises centrally on the basis of the desired final configuration. For example, this is the principle which explains the phenomenon of phantom limbs. Since no limb is present, there is insisting motor intention while there is a radical absence of motor execution, resulting in a phantom experience. Ramachandran sensory inhibition would constitute the source of the mental imageryProbes from the outer (and inner) world continuously activate  associated action plans. We are not conscious of these activations, but they can be demonstrated experimentally  all action alternatives associated to the stimulus and available to the particular subject. In a second time, one action choice is selected by inhibition of the other alternatives. Consciousness of the stimulus, and of the reaction upon it, would only arise in this second time, and even – as proposed by Haggard and Eimer  – as a rside-cathexis. Supposing that three pathways lead from a, to b, c, and d (their [amount of] facilitation being in that order), and that d lies in the neighborhood of the wishful cathexis +V, then the consequence may be that the QΦ , in spite of the facilitations, will flow not to c and b but to d, and from there to +V; and thus the pathway W–a–d–+V will be revealed as the one that is being sought. Here there is in operation the principle which we have long recognized that cathexis can divert facilitation and can thus operate against it, and that accordingly a side-cathexis modifies the passage of Qη. (…) The aim of practical thought is identity (…) the need for thought thereupon ceases and that, instead, a full innervation is permitted of the motor images touched upon on the path, which represent what is in the circumstances a justified accessory part of the specific actionb, c, and d are action alternatives elicited by the perceptual stimulus and/or by activation a. It will be in function of the wishful result, and by means of its cathexis, that b and c will be “inhibited”  in favor of the selected pathway d. Contrary to Maze’s  induced unconscious mental images by the mere fact of acting in the world, constitute a mental life with a concrete instantiation, the physiology of which has been spelled out by e.g., Jeannerod . These umatch” and were immediately thereupon presented a sentence where an alternative meaning of the same word is needed: “he won the match,” have a measurable delay in disambiguating the second sentence. This is explained by the supposition that upon the first hearing of the word “match,” all the meanings of the word are first transiently activated, whereupon the meaning of “lighter/fire” is contextually selected and all the non-contextual alternative meanings  are inhibited. If one of these inhibited alternatives by coincidence is thereupon required, activating this meaning costs more since there is a recent inhibition that still has to be overcome. Note that there is some similarity between this dynamic and what Freud  which he had withheld himself from sharing with his companion since it referred to inappropriate sexual content. He did so well in withholding this, that he also inhibited the associated semantic and phonological variants, including the Italian translation of “Herr,” Signor and the phonologically associated Signorelli. Also note that this dynamic, in Freud’s thinking, is an instance of repression.Directed action in the world, and the structural inhibition this requires, would thus continuously induce an (unconscious) mental reality, specific to each subject. What evidence is there for this supposed structural inhibition? The principal indications are indirect, and primarily the fact that inhibition betrays itself by its spill-over effects, i.e., by being too performing and inhibiting elements which are thereupon needed. For example, in the case of action selection, Sumner et al. , p. 699 at Freud , pp. 2–7In summary, voluntary behavior implies a potential for coactivation of action plans. The actual action pathway is computed through an inverse model going backward from a desired goal and alternative action plans are inhibited. This inhibition sometimes betrays itself through its spill-over effects, rendering previously inhibited action avenues momentarily unavailable while they are needed. This was already Freud’s view on the matter in 1895 and 1901. We propose to add to this that the inhibited action alternatives supposedly induce mental images, which constitute an unconscious mental reality, different for each subject.Now, not all action or meaning alternatives upon a probe are equivalent in their probability or in their strength of being associatively activated, in within the same subject. Action or speech fragments with a higher emotional valence pop up more easily, while at the same time, often, their execution is not contextually appropriate. In some cases, their execution might even lead to a threateningly dangerous level of emotional mobilization of the inner body. But, as Freud , p. 178 representationof this motor action) would be inherent to repression is a long established fact”; “to prevent efficiently the expression of motor expression, the part that represses has to ‘represent’ this motor discharge” and “repression is a necessary condition for the establishment and the function of motor representations” [Italics added].At the sensorimotor level, the enduring absence of execution implies an important generation of efference copy-induced somatosensory attenuation, with a systematic absence of compensation of this anticipatory inhibition. As a consequence, these action or language fragments are particularly prone to induce mental imagery, without the subject being necessarily conscious of this. This relationship between repression and motor representation has also been underscored by the metapsychological reading of Le Guen  mental imagery with formal characteristics of the repressed fragment, i.e., phantoms, which result at the level of the psyche in mental preoccupation and symptoms  and (2) spill-over effects which result in the return-of-the-repressed . Therefore the proposed model for the physiological instantiation of repression, with as a key supposition that the efference copy-induced attenuation of motor intentions is totally left unanswered, in order to radically prevent execution of an action which would lead to development of excess affect, yields the mental phenomena characteristic for neurosis . In addition, we have shown that not only in its results, but also in its dynamics, the sensorimotor model corresponds well with what Freud had already proposed starting from his  by Boag , 2012, nIn a first stage, going minutely through three clinical case studies of psychotic patients cross-facing the psychodynamic and the sensorimotor data, has resulted in the proposition of an equivalence between the Freudian indices of reality and the sensorimotor efference copies. Though at the level of different psychological functions, our three cases of psychosis share as a common mechanism a failure of inhibition (at some level and at some moments). We propose to understand this failure of inhibition as equivalent to the psychodynamic understanding of the failure of repression in psychosis. Therefore, we end up with the idea that the attenuation enabled by the efference copy dynamics is, in some instances, the physiological instantiation of the mental mechanism of repression.In a second stage, we have applied this conclusion to the way mental processes are thought to arise, both according to sensorimotor and to Freudian views. The efference copy model is very much at the heart of this proposition; it is the one key mechanism that connects action with a sensory experience without perceptual input and which probably explains the closeness between action and representation. Jeannerod’s idea that sustained activation of an action goal, without reaching it, would give rise to mental imagery, is a second key in the proposed model. Indeed, it links inhibition of motor intentions to mental imagery. As a consequence, as inhibition mechanisms are structural for any targeted action or for normal language understanding, targeted action or disambiguated language processing are thought to structurally induce mental imagery, constituting a subjective unconscious mental reality.Repression, then, is considered a special instance of inhibition for emotionally threatening stimuli. Due to the characteristics of this inhibition, which leaves the motor intentions totally unanswered, it is proposed to yield a specific type of motor imagery, namely “phantoms,” which are in the first place characterized by their form. These phantoms are thought to induce mental preoccupation, as well as symptoms (of everyday life) which especially through their form are thought to refer to the repressed motor fragment. This, then, is especially true for the articulatory form of language, yielding symptoms characterized by the signifier in their form.Going back to psychosis at this point, we propose that there is probably routine sensorimotor inhibition in psychosis, such as there is in neurosis, but that the process is structurally less stable in psychosis. Clinics show us that it is less stable in some modalities in particular  depending on the subject, but next to this modality-specific instability, it might also be less stable in general, since we frequently find (isolated) language, attention, motor, perception etc. disinhibition symptoms in psychotic patients who do no necessarily display dominant symptoms in these respective modalities. In other words, even if some modality may be touched more specifically, the process in itself is less stable. Since repression is defined as a special instance of inhibition for emotionally threatening stimuli, i.e., structurally requiring even stronger than normal inhibition, it makes sense that this process then is structurally failing in psychosis.The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


We propose three primitives as a foundation for a comprehensive theoretical framework that can embrace a wide range of upper- and lower-limb behaviors. Building on previous work that suggested discrete and rhythmic movements as elementary dynamic behaviors, we define submovements and oscillations: as discrete movements cannot be combined with sufficient flexibility, we argue that suitably-defined submovements are primitives. As the term “rhythmic” may be ambiguous, we define oscillations as the corresponding class of primitives. We further propose mechanical impedances as a third class of dynamic primitives, necessary for interaction with the physical environment. Combination of these three classes of primitive requires care. One approach is through a generalized equivalent network: a virtual trajectory composed of simultaneous and/or sequential submovements and/or oscillations that interacts with mechanical impedances to produce observable forces and motions. Reliable experimental identification of these dynamic primitives presents challenges: identification of mechanical impedances is exquisitely sensitive to assumptions about their dynamic structure; identification of submovements and oscillations is sensitive to their assumed form and to details of the algorithm used to extract them. Some methods to address these challenges are presented. Some implications of this theoretical framework for locomotor rehabilitation are considered.Humans achieve locomotor dexterity that far exceeds the capability of modern robots, yet this is achieved despite slower actuators, imprecise sensors, and vastly slower communication. We propose that this spectacular performance arises from encoding motor commands in terms of  In a recent publication, we asserted a pressing need for a fundamental mathematical theory to help organize and structure the prodigious volume of knowledge about sensorimotor control . Moreover, many commonplace actions require integrated control and coordination of upper and lower extremities, indeed of the entire body. For example, drilling a horizontal hole in a vertical wall using a hand-held drill is commonly performed in a standing position. Therefore, the force exerted by the hand on the drill and wall necessitates tangential force on the ground at the feet. In fact, almost all of the body's degrees of freedom must be coordinated—essentially everything between the hands and feet. The horizontal force results in an overturning moment that must be offset by displacing the center of gravity from the center of pressure below the feet, and a sufficiently strong hand force is typically accomplished by moving the center of gravity far beyond the base of support—i.e., by leaning hard into the push or pull  and continuous dynamics (the motion of the skeleton in response to muscular action). With one foot on the ground, the human skeleton has on the order of 200 degrees of freedom; with two feet on the ground, a closed-chain kinematic constraint adds to the complexity. Moreover, kinematically-constrained rigid-body mechanics as described by Lagrange's equations is at best an approximation. Soft tissues contribute significantly to musculo-skeletal dynamics and add more degrees of freedom, e.g., via the deformation of muscles or body fat. For example, the impact due to heel strike can cause the mass of the calf muscles to resonate with the elasticity of passive tissues such as the Achilles tendon  three levels of analysis: an al Marr, . Howeverproduct rather than process. That is, in an attempt to establish a foundation, we focus on the phenomenology of motor behavior, not on specific hypothesized mechanisms that may give rise to that observable behavior. For clarity, we define dynamic primitives in the mechanical domain of motions and forces at the interface (points of contact) between the neuro-mechanical system and the physical world.A failure to distinguish between these levels—observational, combinatorial, and physiological—all too frequently confounds sensorimotor neuroscience. The definitions of dynamic primitives we propose below describe attractors. For example, a reasonably general representation of a dynamic system describes the evolution of behavior in a finite-dimensional state space, x ∈ Rn for finite n. An attractor is a subset of state space with at least two properties: first, it is an invariant set: if the system begins in an invariant set, it never leaves it. Secondly, that invariant set is attractive: if the system starts sufficiently close to it, the system will ultimately converge to the attractor. Attractor sets may have many forms. A point attractor is a single point in state space. An attractor set that is a closed path (or orbit) defines a limit cycle. There are alternatives: any feasible path in state-space—any trajectory—may be an attractor; this may describe discrete reaching movements, which exhibit trajectory stability . Due to the robustness of the attractor, a dynamic primitive should manifest as a common pattern of behavior observable in different contexts and despite the presence of noise or perturbations. This feature may lend itself to experimental testing.An important requirement for a theory based on primitives is “composability”—it should be possible to combine the elements to generate a repertoire of behavior. In previous work we proposed precise quantitative definitions of discrete and rhythmic movements . If it describes the configuration of the entire limb, the number of coordinates may be substantially greater, e.g., all of the relevant joint angles. Each coordinate's speed profile has the same shape which is non-zero for a finite duration d = e − b, where b is the time when the submovement begins and e is the time it ends, i.e., it has finite support:j; σ(t) > 0 if b < t < e and σ(t) = 0 if t ≤ b or e ≤ t. The speed profile has only one peak: there is only one point tp ∈  at which tp) = 1.We define a submovement as an attractor that describes a smooth sigmoidal transition of a variable from one value to another with a stereotyped time-profile. For limb position, the variable is a vector in some coordinate frame Note that this definition is deliberately silent about possible generative dynamic processes that might give rise to submovements. However, some constraints on those processes can be identified. It may seem that a dynamic process with a point attractor is appropriate. However, physiological evidence shows that at least in reaching movements, the CNS does not simply specify final position , |△t| < δ and εj and δ are small constants. This definition allows for the ubiquitous fluctuations exhibited in biological behavior, whether due to stochastic processes (noise) or deterministic chaos  is a sinusoid with period Tk and phase ϕk as parameters, and Evoking Fourier's theorem, it is clear that a wide range of almost-periodic behaviors may be composed by superposition of oscillatory primitives,dynamic operator that determines the force (time-history) evoked by an imposed displacement (time-history). The force and displacement must be energetically conjugate; that is, they must refer to the same point(s) so that incremental mechanical work dW may be defined i.e.,x = t is a vector of positions and f = t is a vector of forces, both defined with respect to any suitable coordinate frame. A mechanical impedance operator Z maps displacement onto the conjugate force.To account for contact and physical interaction with the ground, a third class of dynamic primitives is required, mechanical impedances. Loosely speaking, mechanical impedance is a generalization of stiffness to encompass nonlinear dynamic behavior Hogan, . Mathemaz = t is a vector of state variables and Zs and Zo are algebraic functions. For brevity, we often omit the “mechanical” prefix.The form of this mapping may be nonlinear and time-varying. For convenience we often assume a state-determined representation1, θ2… θn]t, a special case of generalized coordinates  τ = t are defined such that incremental mechanical work may be defined.The displacement inputs need not be at the same physical location in space, provided they can be paired with energetically-conjugate forces. For example, the several joints of the lower extremity  are in different physical locations. The limb configuration may be described using joint angles, θ = [θJoint mechanical impedance maps joint angular displacements onto the evoked joint torques.Like submovements and oscillations, humans can voluntarily control mechanical impedance Hogan, . The mostemporary permanence that we believe is a hallmark of dynamic primitives.Mechanical impedance is a different kind of primitive than a submovement or oscillation; nevertheless it has properties of an attractor as we identified above. Mechanical impedance is extremely robust to contact and interaction. While the force and motion of the foot are obviously sensitive to contact with the ground, mechanical impedance at, say, the ankle is a property that emerges solely from the dynamics of the neuro-mechanical system supporting the foot and is completely independent of contact. It exhibits the robustness that we require for a dynamic primitive. Neuro-muscular mechanical impedance depends on the intrinsic physical properties of the muscular and skeletal systems but it is also influenced by neural feedback loops, especially those involving muscle spindles and Golgi tendon organs at the spinal level or higher. A compelling case has been made that one important function of these feedback loops is to maintain the mechanical impedance of the neuro-muscular actuator  and actual (non-zero force) trajectories: △x = x0 − x, or in joint coordinates, △θ = θ0 − θ  may be inferred from a knowledge of mechanical impedance Z, force f(t), and actual motion x(t) as x0(t) = x(t) + Z−1{f(t)}. This requires the inverse mapping Z−1{·} to exist. Note that the magnitude of impedance may be small provided it is non-zero.To do so we use the construct of a θ Hogan, . If the equivalent networks widely used in engineering to describe physical interaction between dynamic systems, e.g., an audio amplifier and the speakers it drives  specified by the CNS may be composed of submovements and/or oscillations. Based on the difference between virtual and actual trajectories, impedances specified by the CNS determine the forces evoked by contact. With this representation, much prior engineering insight about dynamic interaction in machines may be re-purposed to help understand physical interaction in locomotion.This is not the only way these three classes of dynamic primitives—submovements, oscillations and impedances—might be combined, but an advantage of this construction is that it defines a non-linear extension of the The virtual trajectory is related to the “lambda” or “equilibrium-point” hypothesis but is also distinct from it in important ways. A common theme running through the several variants of the lambda hypothesis is the proposal that the CNS encodes motor commands as time-varying equilibrium postures Feldman, . This isproduct) and may have no relation to how the CNS goes about producing that behavior (the process). Existence of a virtual trajectory does not require or imply that the CNS knows about or uses this construct for control. Indeed, available evidence suggests that this would be at best an incomplete account  may always be defined. This construct is a consequence of observable neuro-muscular mechanics. It is a description of behavior  steps and in some cases—e.g., the slow pacing used in a funeral march—it may be. Furthermore, what is the role of mechanical impedance?Observations of fictive locomotion in non-human vertebrates provide unequivocal evidence that neural circuits capable of generating an oscillatory dynamic primitive—sustained rhythmic activity—exist in the spinal cord isolated from its periphery, though sensory feedback is known to play a key role Brown, . For uniHowever, the relative contribution of rhythmic pattern generation to unimpaired human locomotion remains unclear. Human infants exhibit a primitive rhythmic stepping reflex but it typically disappears at about 6 weeks after birth without training  of interaction is determined by impedance. However, even the static component of multivariable joint impedance (the relation between torque and angular displacement) may be highly structured. Measurements on unimpaired subjects show a pronounced weakness in inversion-eversion, the direction of most ankle injuries Figure . Increasa-priori assumptions about the order of the dynamics, stochastic methods may be used to identify a locally linear approximation to dynamic behavior , can also be measured experimentally. If the point of interaction is the sole of the foot, then during swing phase the force is identically zero, f ≡ 0, and because △x ≡ 0, the observed motion is the virtual trajectory. During stance phase the force is non-zero, x0(t) may be inferred from a measurement of mechanical impedance, Z, force, f(t), and actual motion, x(t) as x0(t) = x(t) + Z−1{f(t)} provided Z−1 exists. If the point of interaction is at a joint—say, the ankle or the knee—then the dynamics between the joint and the point of force application must be identified and subtracted. The main difficulty is that estimates are exquisitely sensitive to the assumed order of the neuro-muscular impedance model used to infer a virtual trajectory—see Gomi and Kawato , then subtract it and repeat the procedure on the residual until the error between the sum of submovements and the original trajectory falls below a specified threshold. Unfortunately, these methods also yield spurious decompositions Figure . Even inHowever, global optimization methods have been developed which avoid spurious decompositions Figure . With thA theoretical framework based on dynamic primitives may have particular relevance for sensorimotor rehabilitation, both in the development of assistive technologies and in the design of therapeutic procedures.The design and implementation of assistive orthoses and amputation prostheses has unequivocally demonstrated the importance of controllable mechanical impedance. It is a key element of recent highly-successful designs of ankle-foot orthoses and transfemoral prostheses  consists of encoding the parameters of dynamic primitives and subsequently using them to reconstruct the primitives, rather than details of behavior. Support is found in the analysis of infant reaching movements, which initially exhibit submovements but become essentially continuous at around 6 months of age Hofsten, . More reinterface between the CNS and the physical world, inappropriate impedance may hinder the recovery of effective motor actions. We therefore expect normalization of impedance concurrently with recovery. Support is found in recent preliminary studies of how ankle impedance influences recovery of locomotion. The ankle impedance of neurologically impaired subjects was significantly different from that of age-matched healthy subjects  is known, the problem is tractable. Without that knowledge, it is “ill-posed” in the sense that a unique solution may not exist. Some progress has been made on this problem by using optimization to provide regularization, but much remains to be done  but there also appears to be an upper limit to the period of primitive oscillatory actions. Beyond that limit, submovements appear to predominate (Doeringer and Hogan, One essential aspect of our conception of motor control based on primitives is that they are attractors. That prompts the question: which attractors underlie human locomotion? They might be point attractors, e.g., to support foot placement; or trajectory attractors, e.g., to control foot trajectory; or limit-cycle attractors, e.g., to account for the orbital stability of the walking rhythm; or even chaotic attractors as reported by Hausdorff et al.  and HausThis technique, of soliciting many modest contributions to the store of human knowledge, has been the secret of Western science since the seventeenth century, for it achieves a corporate, collective power that is far greater than one individual can exert.To conclude, we do not have the temerity to claim that what we have outlined is yet a complete account of upper- and lower-extremity motor behavior. Yet we do contend that such a theory is possible, necessary and timely—perhaps even overdue. Its development will inevitably require considerable hard work from many contributors. To quote Ziman :This teThe main thing is to get started. This paper is an attempt to do so.Neville Hogan holds equity in Interactive Motion Technologies, Inc., a Massachusetts corporation that manufactures robotic technology for rehabilitation. The other author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.