Anatol Feldman | Université de Montréal (original) (raw)
Papers by Anatol Feldman
The lambda model of the equilibrium-point hypothesis (Feldman & Levin, 1995) is an approa... more The lambda model of the equilibrium-point hypothesis (Feldman & Levin, 1995) is an approach to motor control which, like physics, is based on a logical system coordinating empirical data. The model has gone through an interesting period. On one hand, several nontrivial predictions of the model have been successfully verified in recent studies. In addition, the explanatory and predictive capacity of the model has been enhanced by its extension to multimuscle and multijoint systems. On the other hand, claims have recently appeared suggesting that the model should be abandoned. The present paper focuses on these claims and concludes that they are unfounded. Much of the experimental data that have been used to reject the model are actually consistent with it.
Science & Motricité, 2002
Experimental Brain Research, Mar 1, 2011
Locomotion is presumably guided by feedforward shifts in the referent body location in the desire... more Locomotion is presumably guided by feedforward shifts in the referent body location in the desired direction in the environment. We propose that the difference between the actual and the referent body locations is transmitted to neurons that virtually diminish this difference by appropriately changing the referent body configuration, i.e. the body posture at which muscles reach their recruitment thresholds. Muscles are activated depending on the gap between the actual and the referent body configurations resulting in a step being made to minimize this gap. This hypothesis implies that the actual and the referent leg configurations can match each other at certain phases of the gait cycle, resulting in minimization of leg muscle activity. We found several leg configurations at which EMG minima occurred, both during forward and backward gait. It was also found that the set of limb configurations associated with EMG minima can be changed by modifying the pattern of forward and backward gait. Our hypothesis predicts that, in response to perturbations of gait, the rate of shifts in the referent body location can temporarily be changed to avoid falling. The rate influences the phase of rhythmic limb movements during gait. Therefore, following the change in the rate of the referent body location, the whole gait pattern, for all four limbs, will irreversibly be shifted in time (long-lasting and global phase resetting) with only transient changes in the gait speed, swing and stance timing and cycle duration. Aside from transient changes in the duration of the swing and/or stance phase in response to perturbation, few previous studies have documented long-lasting and global phase resetting of human gait in response to perturbation. Such resetting was a robust finding in our study. By confirming the notion that feedforward changes in the referent body location and configuration underlie human locomotion, this study solves the classical problem in the relationship between stability of posture and gait and advances the understanding of how human locomotion involves the whole body and is accomplished in a spatial frame of reference associated with the environment.
2006 International Workshop on Virtual Rehabilitation, 2006
Http Dx Doi Org 10 1080 00222895 1986 10735369, Aug 13, 2013
Journal of Motor Behavior, 1986
Behavioral and Brain Sciences, 1982
Proceedings of the Canadian Engineering Education Association, Aug 17, 2011
This paper presents preliminary results of our ongoing work on the biomimetic muscle-like behavio... more This paper presents preliminary results of our ongoing work on the biomimetic muscle-like behaviour of poly(sodium acrylate) (PSA) hydrogels. Using Hill's model as a basic framework, interpenetrating network (IPN) hydrogels consisting of a contractile PSA network and an elastic poly(vinyl alcohol) PVA network were desinged. The hydrogels so formed reversibly contract in the presence of a critical Ca 2+ concentration via a monovalent-divalent ion exchange mechanism. Ca 2+ is shown to provoke a shortening of the gel through cross-bridge formation akin to biological muscles. The contractile behaviour of these hydrogels in Krebs physiological media is presented. Force-length measurements display a non-linear rubber-like profile of the hydrogel in the relaxed state as well as a stiffening in the contracted state, both of which are characteristic of biological muscles. In addition, there is evidence of both isometric and isotonic contraction.
Evolutions Psychomotrices, 2001
Advances to the equilibrium-point (EP) theory and solutions to several classical problems of acti... more Advances to the equilibrium-point (EP) theory and solutions to several classical problems of action and perception are suggested and discussed. Among them are (1) the posture-movement problem of how movements away from a stable posture can be made without evoking resistance of posture-stabilizing mechanisms resulting from intrinsic muscle and reflex properties; (2) the problem of kinesthesia or why our sense of limb position is fairly accurate despite ambiguous positional information delivered by proprioceptive and cutaneous signals; (3) the redundancy problems in the control of multiple muscles and degrees of freedom. Central to the EP hypothesis is the notion that there are specific neural structures that represent spatial frames of reference (FRs) selected by the brain in a task-specific way from a set of available FRs. The brain is also able to translate or/and rotate the selected FRs by modifying their major attributes-the origin, metrics, and orientation-and thus substantially influence, in a feed-forward manner, action and perception. The brain does not directly solve redundancy problems: it only limits the amount of redundancy by predetermining where, in spatial coordinates, a task-specific action should emerge and allows all motor elements, including the environment, to interact to deliver a unique action, thus solving the redundancy problem (natural selection of action). The EP theory predicts the existence of specific neurons associated with the control of different attributes of FRs and explains the role of mirror neurons in the inferior frontal gyrus and place cells in the hippocampus.
Human Movement Science, 1989
Exp Brain Res, 1981
The experiments were performed on decerebrate curarized cats with a hindlimb either completely de... more The experiments were performed on decerebrate curarized cats with a hindlimb either completely deafferented or partly deefferented. Through tactile stimulation of the pinna, a fictive scratch reflex was evoked and activity in muscle efferents was then observed, similar to that in actual scratching. The duration of the cycle was about 250 ms, with extensor activity during a short period of
Experimental Brain Research, Jul 18, 2006
We addressed the fundamental questions of which variables underlie the control of arm movement an... more We addressed the fundamental questions of which variables underlie the control of arm movement and how they are stored in motor memory, reproduced and modified in the process of adaptation to changing load conditions. Such variables are defined differently in two major theories of motor control (internal models and threshold control). To resolve the controversy, these theories were tested (experiment 1) based on their ability to explain why active movement away from a stable posture is not opposed by stabilizing mechanisms (the posture-movement problem). The internal model theory suggests that the system counteracts the opposing forces by increasing the muscle activity in proportion to the distance from the initial posture (position-dependent EMG control). In contrast, threshold control fully excludes these opposing forces by shifting muscle activation thresholds and thus resetting the stabilizing mechanisms to a new posture. Subjects were sitting, holding the vertical handle of a double-joint manipulandum with their right hand and were facing a computer screen on which the handle and target to be reached were displayed. In response to an auditory signal, subjects quickly moved the handle from an initial position to one of two (frontal and sagittal) targets. No load was applied during the movement but in separate trials, a brief perturbation was applied to the handle by torque motors controlling the manipulandum. Perturbations were applied prior to or 3 s after movement offset, in the latter case in one of eight directions. The EMG activity of the majority of the seven recorded muscles was at zero level before movement onset and returned to zero level after movement offset. Those muscles that remained active before or after the movement could be made silent whereas previously silent muscles could be activated after a small passive displacement (several millimeters) elicited by perturbations in appropriate directions. Results showed that the activation thresholds of motoneurons of arm muscles were reset from the initial to a final position and that EMG activity was not position-dependent. These results were inconsistent with the internal model theory but confirmed the threshold control theory. Then the ability of threshold control theory to explain rapid movement adaptation to a position-dependent load was investigated (experiment 2 and 3). Subjects produced fast movement to the frontal target with and without a position-dependent load applied to the handle. Trials were organized in blocks alternating between the load and no-load condition (20 blocks in total, with randomly chosen number of five to ten trials in each). Subjects were instructed "do not correct" in experiment 2 and "correct" movement errors during the trial in experiment 3. Five threshold arm configurations underlying the movement production and adaptation were identified. When instructed "do not correct", movement precision was fully restored on average after two trials. No significant improvement was observed as the experiment progressed despite the fact that the same load condition was repeated after one block of trials. Thus, in each block, the adaptation was made anew, implying that subjects relied on short-term memory and could not recall the threshold arm configurations they specified to accurately reach the same target in the same load condition in previous blocks. When instructed to "correct" within each trial, precision was restored faster, on average after one trial. Major aspects of the production and adaptation of arm movement (including the kinematics, movement errors, instruction-dependent behavior, and absence of position-related EMG activity) are explained in terms of threshold control.
Biological Cybernetics, 1982
The present model of joint angle perception is based on the following hypotheses: the perception ... more The present model of joint angle perception is based on the following hypotheses: the perception and control of joint angle are closely interrelated processes; central motor commands are adequately expressed by shifts of an equilibrium point resulting from the interaction of antagonistic muscles and a load; two fundamental commands--reciprocal (r) and coactivative (c) provide for changes in activity of the antagonistic muscle pair. The dependence of joint angle on static muscle torque and r and c commands is derived (Eq. 5). The following principles of joint position sense are formulated: 1) the r component of the efferent copy plays the role of a reference point which shifts during voluntary regulation of muscle state, but remains unchanged during any passive alterations of joint position; 2) muscle afferent signals deliver not absolute but relative information (i.e. measured relatively to the central reference point). These signals turn out to be related to active muscle torque; 3) the nervous system evaluates muscle afferent signals on the basis of a scale determined by the level of coactivation of the antagonistic muscles. Kinaesthetic illusions appear to be due to disruptions in perception of afferent and/or efferent components of position sense. The present model is consistent with all the variety of kinaesthetic illusions observed experimentally. A qualitative neurophysiological schema for joint angle perception is proposed involving efferent copy and information concerning muscle torque delivered by the tendon organ, muscle spindle, and, perhaps, articular receptors. It is known that the cerebellum incorporates both afferent and efferent information concerning movements. One may presume that it plays an essential role in position sense.
Annales de chirurgie, 1999
The lateral bending test is used for the preoperative evaluation of scoliotic patients in order t... more The lateral bending test is used for the preoperative evaluation of scoliotic patients in order to determine the type of spinal curvatures as well as to assess spine flexibility and possible corrections. However, very few biomechanical studies have been dedicated to the analysis of lateral bending. In this article, a biomechanical model of the human trunk has been used in order to evaluate the possibility of simulating lateral bending tests. This model includes elements representing the osseo-ligamentous structures of the spine, rib cage and pelvis, as well as 160 muscle fascicles represented by bilinear cable elements. For 4 scoliotic patients (right thoracic and left lumbar curvatures), 3D upright standing and bending reconstructions were generated from calibrated x-rays and used to calculate the displacements of the vertebrae T1 and L5. These displacements were applied to the model in standing position in order to simulate lateral bending. The resulting geometry of the deformed m...
The lambda model of the equilibrium-point hypothesis (Feldman & Levin, 1995) is an approa... more The lambda model of the equilibrium-point hypothesis (Feldman & Levin, 1995) is an approach to motor control which, like physics, is based on a logical system coordinating empirical data. The model has gone through an interesting period. On one hand, several nontrivial predictions of the model have been successfully verified in recent studies. In addition, the explanatory and predictive capacity of the model has been enhanced by its extension to multimuscle and multijoint systems. On the other hand, claims have recently appeared suggesting that the model should be abandoned. The present paper focuses on these claims and concludes that they are unfounded. Much of the experimental data that have been used to reject the model are actually consistent with it.
Science & Motricité, 2002
Experimental Brain Research, Mar 1, 2011
Locomotion is presumably guided by feedforward shifts in the referent body location in the desire... more Locomotion is presumably guided by feedforward shifts in the referent body location in the desired direction in the environment. We propose that the difference between the actual and the referent body locations is transmitted to neurons that virtually diminish this difference by appropriately changing the referent body configuration, i.e. the body posture at which muscles reach their recruitment thresholds. Muscles are activated depending on the gap between the actual and the referent body configurations resulting in a step being made to minimize this gap. This hypothesis implies that the actual and the referent leg configurations can match each other at certain phases of the gait cycle, resulting in minimization of leg muscle activity. We found several leg configurations at which EMG minima occurred, both during forward and backward gait. It was also found that the set of limb configurations associated with EMG minima can be changed by modifying the pattern of forward and backward gait. Our hypothesis predicts that, in response to perturbations of gait, the rate of shifts in the referent body location can temporarily be changed to avoid falling. The rate influences the phase of rhythmic limb movements during gait. Therefore, following the change in the rate of the referent body location, the whole gait pattern, for all four limbs, will irreversibly be shifted in time (long-lasting and global phase resetting) with only transient changes in the gait speed, swing and stance timing and cycle duration. Aside from transient changes in the duration of the swing and/or stance phase in response to perturbation, few previous studies have documented long-lasting and global phase resetting of human gait in response to perturbation. Such resetting was a robust finding in our study. By confirming the notion that feedforward changes in the referent body location and configuration underlie human locomotion, this study solves the classical problem in the relationship between stability of posture and gait and advances the understanding of how human locomotion involves the whole body and is accomplished in a spatial frame of reference associated with the environment.
2006 International Workshop on Virtual Rehabilitation, 2006
Http Dx Doi Org 10 1080 00222895 1986 10735369, Aug 13, 2013
Journal of Motor Behavior, 1986
Behavioral and Brain Sciences, 1982
Proceedings of the Canadian Engineering Education Association, Aug 17, 2011
This paper presents preliminary results of our ongoing work on the biomimetic muscle-like behavio... more This paper presents preliminary results of our ongoing work on the biomimetic muscle-like behaviour of poly(sodium acrylate) (PSA) hydrogels. Using Hill's model as a basic framework, interpenetrating network (IPN) hydrogels consisting of a contractile PSA network and an elastic poly(vinyl alcohol) PVA network were desinged. The hydrogels so formed reversibly contract in the presence of a critical Ca 2+ concentration via a monovalent-divalent ion exchange mechanism. Ca 2+ is shown to provoke a shortening of the gel through cross-bridge formation akin to biological muscles. The contractile behaviour of these hydrogels in Krebs physiological media is presented. Force-length measurements display a non-linear rubber-like profile of the hydrogel in the relaxed state as well as a stiffening in the contracted state, both of which are characteristic of biological muscles. In addition, there is evidence of both isometric and isotonic contraction.
Evolutions Psychomotrices, 2001
Advances to the equilibrium-point (EP) theory and solutions to several classical problems of acti... more Advances to the equilibrium-point (EP) theory and solutions to several classical problems of action and perception are suggested and discussed. Among them are (1) the posture-movement problem of how movements away from a stable posture can be made without evoking resistance of posture-stabilizing mechanisms resulting from intrinsic muscle and reflex properties; (2) the problem of kinesthesia or why our sense of limb position is fairly accurate despite ambiguous positional information delivered by proprioceptive and cutaneous signals; (3) the redundancy problems in the control of multiple muscles and degrees of freedom. Central to the EP hypothesis is the notion that there are specific neural structures that represent spatial frames of reference (FRs) selected by the brain in a task-specific way from a set of available FRs. The brain is also able to translate or/and rotate the selected FRs by modifying their major attributes-the origin, metrics, and orientation-and thus substantially influence, in a feed-forward manner, action and perception. The brain does not directly solve redundancy problems: it only limits the amount of redundancy by predetermining where, in spatial coordinates, a task-specific action should emerge and allows all motor elements, including the environment, to interact to deliver a unique action, thus solving the redundancy problem (natural selection of action). The EP theory predicts the existence of specific neurons associated with the control of different attributes of FRs and explains the role of mirror neurons in the inferior frontal gyrus and place cells in the hippocampus.
Human Movement Science, 1989
Exp Brain Res, 1981
The experiments were performed on decerebrate curarized cats with a hindlimb either completely de... more The experiments were performed on decerebrate curarized cats with a hindlimb either completely deafferented or partly deefferented. Through tactile stimulation of the pinna, a fictive scratch reflex was evoked and activity in muscle efferents was then observed, similar to that in actual scratching. The duration of the cycle was about 250 ms, with extensor activity during a short period of
Experimental Brain Research, Jul 18, 2006
We addressed the fundamental questions of which variables underlie the control of arm movement an... more We addressed the fundamental questions of which variables underlie the control of arm movement and how they are stored in motor memory, reproduced and modified in the process of adaptation to changing load conditions. Such variables are defined differently in two major theories of motor control (internal models and threshold control). To resolve the controversy, these theories were tested (experiment 1) based on their ability to explain why active movement away from a stable posture is not opposed by stabilizing mechanisms (the posture-movement problem). The internal model theory suggests that the system counteracts the opposing forces by increasing the muscle activity in proportion to the distance from the initial posture (position-dependent EMG control). In contrast, threshold control fully excludes these opposing forces by shifting muscle activation thresholds and thus resetting the stabilizing mechanisms to a new posture. Subjects were sitting, holding the vertical handle of a double-joint manipulandum with their right hand and were facing a computer screen on which the handle and target to be reached were displayed. In response to an auditory signal, subjects quickly moved the handle from an initial position to one of two (frontal and sagittal) targets. No load was applied during the movement but in separate trials, a brief perturbation was applied to the handle by torque motors controlling the manipulandum. Perturbations were applied prior to or 3 s after movement offset, in the latter case in one of eight directions. The EMG activity of the majority of the seven recorded muscles was at zero level before movement onset and returned to zero level after movement offset. Those muscles that remained active before or after the movement could be made silent whereas previously silent muscles could be activated after a small passive displacement (several millimeters) elicited by perturbations in appropriate directions. Results showed that the activation thresholds of motoneurons of arm muscles were reset from the initial to a final position and that EMG activity was not position-dependent. These results were inconsistent with the internal model theory but confirmed the threshold control theory. Then the ability of threshold control theory to explain rapid movement adaptation to a position-dependent load was investigated (experiment 2 and 3). Subjects produced fast movement to the frontal target with and without a position-dependent load applied to the handle. Trials were organized in blocks alternating between the load and no-load condition (20 blocks in total, with randomly chosen number of five to ten trials in each). Subjects were instructed "do not correct" in experiment 2 and "correct" movement errors during the trial in experiment 3. Five threshold arm configurations underlying the movement production and adaptation were identified. When instructed "do not correct", movement precision was fully restored on average after two trials. No significant improvement was observed as the experiment progressed despite the fact that the same load condition was repeated after one block of trials. Thus, in each block, the adaptation was made anew, implying that subjects relied on short-term memory and could not recall the threshold arm configurations they specified to accurately reach the same target in the same load condition in previous blocks. When instructed to "correct" within each trial, precision was restored faster, on average after one trial. Major aspects of the production and adaptation of arm movement (including the kinematics, movement errors, instruction-dependent behavior, and absence of position-related EMG activity) are explained in terms of threshold control.
Biological Cybernetics, 1982
The present model of joint angle perception is based on the following hypotheses: the perception ... more The present model of joint angle perception is based on the following hypotheses: the perception and control of joint angle are closely interrelated processes; central motor commands are adequately expressed by shifts of an equilibrium point resulting from the interaction of antagonistic muscles and a load; two fundamental commands--reciprocal (r) and coactivative (c) provide for changes in activity of the antagonistic muscle pair. The dependence of joint angle on static muscle torque and r and c commands is derived (Eq. 5). The following principles of joint position sense are formulated: 1) the r component of the efferent copy plays the role of a reference point which shifts during voluntary regulation of muscle state, but remains unchanged during any passive alterations of joint position; 2) muscle afferent signals deliver not absolute but relative information (i.e. measured relatively to the central reference point). These signals turn out to be related to active muscle torque; 3) the nervous system evaluates muscle afferent signals on the basis of a scale determined by the level of coactivation of the antagonistic muscles. Kinaesthetic illusions appear to be due to disruptions in perception of afferent and/or efferent components of position sense. The present model is consistent with all the variety of kinaesthetic illusions observed experimentally. A qualitative neurophysiological schema for joint angle perception is proposed involving efferent copy and information concerning muscle torque delivered by the tendon organ, muscle spindle, and, perhaps, articular receptors. It is known that the cerebellum incorporates both afferent and efferent information concerning movements. One may presume that it plays an essential role in position sense.
Annales de chirurgie, 1999
The lateral bending test is used for the preoperative evaluation of scoliotic patients in order t... more The lateral bending test is used for the preoperative evaluation of scoliotic patients in order to determine the type of spinal curvatures as well as to assess spine flexibility and possible corrections. However, very few biomechanical studies have been dedicated to the analysis of lateral bending. In this article, a biomechanical model of the human trunk has been used in order to evaluate the possibility of simulating lateral bending tests. This model includes elements representing the osseo-ligamentous structures of the spine, rib cage and pelvis, as well as 160 muscle fascicles represented by bilinear cable elements. For 4 scoliotic patients (right thoracic and left lumbar curvatures), 3D upright standing and bending reconstructions were generated from calibrated x-rays and used to calculate the displacements of the vertebrae T1 and L5. These displacements were applied to the model in standing position in order to simulate lateral bending. The resulting geometry of the deformed m...