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Journal ArticleDOI

The organization of human postural movements: A formal basis and experimental synthesis

01 Mar 1985-Behavioral and Brain Sciences (Cambridge University Press)-Vol. 8, Iss: 1, pp 135-172
TL;DR: It is shown that organization of postural movements into combinations of distinct strategies simplifies the interpretation of sensory inputs and provides a framework compatible with both mechanical and physiological information and amenable to experimental testing.
Abstract: A scheme for understanding the organization of human postural movements is developed in the format of a position paper. The structural characteristics of the body and the geometry of muscular actions are incorporated into a three-dimensional graphical representation of human movement mechanics in the sagittal plane. A series of neural organizational hypotheses limit a theoretically infinite number of combinations of muscle contractions and associated movement trajectories for performing postural corrections: (1) Controls are organized to use the minimum number of muscles; (2) frequently performed movements are organized to require a minimum of neural decision-making.These hypotheses lead to the prediction that postural movements are composed of muscle contractile strategies derived from a limited set of distinct contractile patterns. The imposition of two mechanical constraints related to the configuration of support and to requirements for body stability with respect to gravity predict the conditions under which individual movement strategies will be deployed.A complementary organizational scheme for the senses is developed. We show that organization of postural movements into combinations of distinct strategies simplifies the interpretation of sensory inputs. The fine-tuning of movement strategies can be accomplished by breaking down the complex array of feedback information into a series of scalar quantities related to the parameters of the movement strategies. For example, the magnitude, aim, and curvature of the movement trajectory generated by an individual strategy can be adjusted independently.The second half of the report compares theoretical predictions with a series of actual experimental observations on normal subjects and patients with known sensory and motor disorders. Actual postural movements conform to theoretical predictions about the composition of individual movement strategies and the conditions under which each strategy is used. Observations on patients suggest how breakdowns in individual steps within the logical process of organization can lead to specific movement abnormalities.Discussion focuses on the areas needing further experimentation and on the implications of the proposed organizational scheme. We conclude that although our organizational scheme is not new in demonstrating the need for simplifying the neural control of movement, it is perhaps original in imposing discrete logical control upon a continuous mechanical system. The attraction of the scheme is that it provides a framework compatible with both mechanical and physiological information and amenable to experimental testing.
Citations
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Journal ArticleDOI
TL;DR: Exposing subjects to horizontal surface perturbations while standing on support surfaces intermediate in length between the shortest and longest elicited more complex postural movements and associated muscle activation patterns that resembled ankle and hip strategies combined in different temporal relations.
Abstract: We studied the extent to which automatic postural actions in standing human subjects are organized by a limited repertoire of central motor programs. Subjects stood on support surfaces of various lengths, which forced them to adopt different postural movement strategies to compensate for the same external perturbations. We assessed whether a continuum or a limited set of muscle activation patterns was used to produce different movement patterns and the extent to which movement patterns were influenced by prior experience. Exposing subjects standing on a normal support surface to brief forward and backward horizontal surface perturbations elicited relatively stereotyped patterns of leg and trunk muscle activation with 73- to 110-ms latencies. Activity began in the ankle joint muscles and then radiated in sequence to thigh and then trunk muscles on the same dorsal or ventral aspect of the body. This activation pattern exerted compensatory torques about the ankle joints, which restored equilibrium by moving the body center of mass forward or backward. This pattern has been termed the ankle strategy because it restores equilibrium by moving the body primarily around the ankle joints. To successfully maintain balance while standing on a support surface short in relation to foot length, subjects activated leg and trunk muscles at similar latencies but organized the activity differently. The trunk and thigh muscles antagonistic to those used in the ankle strategy were activated in the opposite proximal-to-distal sequence, whereas the ankle muscles were generally unresponsive. This activation pattern produced a compensatory horizontal shear force against the support surface but little, if any, ankle torque. This pattern has been termed the hip strategy, because the resulting motion is focused primarily about the hip joints. Exposing subjects to horizontal surface perturbations while standing on support surfaces intermediate in length between the shortest and longest elicited more complex postural movements and associated muscle activation patterns that resembled ankle and hip strategies combined in different temporal relations. These complex postural movements were executed with combinations of torque and horizontal shear forces and motions of ankle and hip joints. During the first 5-20 practice trials immediately following changes from one support surface length to another, response latencies were unchanged. The activation patterns, however, were complex and resembled the patterns observed during well-practiced stance on surfaces of intermediate lengths.(ABSTRACT TRUNCATED AT 400 WORDS)

2,212 citations

Journal ArticleDOI
TL;DR: This chapter discusses anticipatory postural adjustments associated with equilibrium maintenance in the context of dual-modular approach to posture versus global approach to equilibrium.

1,510 citations

Journal ArticleDOI
TL;DR: An operational meaning to ” controlled” and ”uncontrolled” is given and a method of analysis through which hypotheses about controlled and uncontrolled degrees of freedom can be tested is described, finding that, for the task of sit-to-stand, the position of the center of mass in the sagittal plane was controlled.
Abstract: The degrees of freedom problem is often posed by asking which of the many possible degrees of freedom does the nervous system control? By implication, other degrees of freedom are not controlled. We give an operational meaning to "controlled" and "uncontrolled" and describe a method of analysis through which hypotheses about controlled and uncontrolled degrees of freedom can be tested. In this conception, control refers to stabilization, so that lack of control implies reduced stability. The method was used to analyze an experiment on the sit-to-stand transition. By testing different hypotheses about the controlled variables, we systematically approximated the structure of control in joint space. We found that, for the task of sit-to-stand, the position of the center of mass in the sagittal plane was controlled. The horizontal head position and the position of the hand were controlled less stably, while vertical head position appears to be no more controlled than joint motions.

1,333 citations

Journal ArticleDOI
Gary Goldberg1
TL;DR: It is suggested that the SMA has an important role to play in the intentional process whereby internal context influences the elaboration of action, and an anatomico-physiologic model of the medial premotor system is proposed which embodies the principles of cyclicity and reentrance.
Abstract: Though its existence has been known for well over 30 years, only recently has the supplementary motor area (SMA) and its role in the cortical organization of movement come to be examined in detail by neuroscientists. Evidence from a wide variety of investigational perspectives is reviewed in an attempt to synthesize a conceptual framework for understanding SMA function. It is suggested that the SMA has an important role to play in the intentional process whereby internal context influences the elaboration of action. It may be viewed as phylogenetically older motor cortex, derived from anterior cingulate periarchicortical limbic cortex, which, as a key part of a medial premotor system, is crucial in the “programming” and fluent execution of extended action sequences which are “projectional” in that they rely on model-based prediction. This medial system can be distinguished from a lateral premotor system postulated to have evolved over phylogeny from a different neural source. An anatomico-physiologic model of the medial premotor system is proposed which embodies the principles of cyclicity and reentrance in the process of selecting those neural components to become active in conjunction with the performance of a particular action. The postulated dynamic action of this model in the microgenesis of a discrete action is outlined. It is concluded that although there is a great deal to be learned about the SMA, a convergence of current evidence can be identified. Such evidence suggests that the SMA plays an important role in the development of the intention-to-act and the specification and elaboration of action through its mediation between medial limbic cortex and primary motor cortex.

1,153 citations

Journal Article

1,091 citations

References
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Book
01 Jan 1979
TL;DR: The relationship between Stimulation and Stimulus Information for visual perception is discussed in detail in this article, where the authors also present experimental evidence for direct perception of motion in the world and movement of the self.
Abstract: Contents: Preface. Introduction. Part I: The Environment To Be Perceived.The Animal And The Environment. Medium, Substances, Surfaces. The Meaningful Environment. Part II: The Information For Visual Perception.The Relationship Between Stimulation And Stimulus Information. The Ambient Optic Array. Events And The Information For Perceiving Events. The Optical Information For Self-Perception. The Theory Of Affordances. Part III: Visual Perception.Experimental Evidence For Direct Perception: Persisting Layout. Experiments On The Perception Of Motion In The World And Movement Of The Self. The Discovery Of The Occluding Edge And Its Implications For Perception. Looking With The Head And Eyes. Locomotion And Manipulation. The Theory Of Information Pickup And Its Consequences. Part IV: Depiction.Pictures And Visual Awareness. Motion Pictures And Visual Awareness. Conclusion. Appendixes: The Principal Terms Used in Ecological Optics. The Concept of Invariants in Ecological Optics.

21,493 citations

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8,937 citations

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6,416 citations

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6,307 citations

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"The organization of human postural ..." refers background in this paper

  • ...Given the universality and importance of global schemes for interpreting sensory information and controlling muscular contractions, it is surprising to find only a few attempts to formulate experimentally testable hypotheses incorporating multi-element interactions: Principles governing the interactions among elements of the sensorimotor system were one of Bernstein's (1967) major interests....

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  • ...In a related way, we think, their references to neural signals that require interpretation, their appeals to memory (presumably of previous trajectories, previous initial conditions, previous sensory consequences, and previous postural achievements), and their supposition of anatomically defined senses uniquely tied to distinct frames of reference seem to run counter to the general Bernsteinian (1967) strategy that they are pursuing, that is, compressing in a principled fashion a movement problem of potentially very many degrees of freedom into a movement problem of very few degrees of freedom....

    [...]

  • ...Given the universality and importance of global schemes for interpreting sensory information and controlling muscular contractions, it is surprising to find only a few attempts to formulate experimentally testable hypotheses incorporating multi-element interactions: Principles governing the interactions among elements of the sensorimotor system were one of Bernstein's (1967) major interests. Through human postural experiments Bernstein's students have attempted to demonstrate his ideas (e.g., Arutyunyan, Gurfinkel & Mirski 1969; Gurfinkel, Kots, Pal'tsev & Feldman 1971). Greene (1972; 1975; 1982) proposed schemes that allow complex behaviors of a limb to be pieced together from a repertoire of elementary units using simplifying assumptions based upon past experience. Grossberg (1983) has developed a theory of nerve network dynamics which would allow such chunking of neural control....

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  • ...The number of controllable elements and control parameters makes the search for simplifying assumptions necessary (Bernstein 1967), but not simple. Nashner & McCollum (N & M) have presented an intriguing and useful scheme for the organization of postural movements based on their elegant experimental work. Their model rests heavily on their simplifying assumptions of: (1) miniminal number of muscles used; and (2) minimal amount of calculated accuracy. Since Bernstein (1967), some necessity for a minimal neural calculation constraint is difficult to dispute....

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  • ...The conceptual model presented in the target article by Nashner & McCollum (N & M) is notable as one of the more advanced experimentally supported applications of the Bernsteinian approach to the physiology of motor control (Bernstein 1967; Whiting 1984) to appear in the Western physiological literature....

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