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Motor Synergies and the Equilibrium-Point Hypothesis

Mark L. Latash

The article offers a way to unite three recent developments in the field of motor control and coordination: (1) The notion of synergies is introduced based on the principle of motor abundance; (2) The uncontrolled manifold hypothesis is described as offering a computational framework to identify and quantify synergies; and (3) The equilibrium-point hypothesis is described for a single muscle, single joint, and multijoint systems. Merging these concepts into a single coherent scheme requires focusing on control variables rather than performance variables. The principle of minimal final action is formulated as the guiding principle within the referent configuration hypothesis. Motor actions are associated with setting two types of variables by a controller, those that ultimately define average performance patterns and those that define associated synergies. Predictions of the suggested scheme are reviewed, such as the phenomenon of anticipatory synergy adjustments, quick actions without changes in synergies, atypical synergies, and changes in synergies with practice. A few models are briefly reviewed.

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Two Archetypes of Motor Control Research

Mark L. Latash

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Movement System Variability

Mark L. Latash

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Brain Mechanisms for the Integration of Posture and Movement: (Progress in Brain Research, vol. 143)

Mark L. Latash

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A New Book by Nikolai Bernstein: Contemporary Studies in the Physiology of the Neural Process

Edited by Mark L. Latash

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Bernstein’s Philosophy of Time: An Unknown Manuscript by Nikolai Bernstein (1949)

Mark L. Latash and Vera L. Talis

The authors have presented an unpublished manuscript by Nikolai Aleksandrovich Bernstein written in the form of a diary in 1949. Bernstein focused on the concept of time as a coordinate in four-dimensional space and discussed a variety of issues, including the definition of time, its measurement, time travel, asymmetry of the past and future, and even linguistics. In particular, he offered a definition of life tightly linked to the concept of time. Overall, this manuscript offers a glimpse into Bernstein’s thinking, his sense of humor, and his sarcasm, intimately coupled with the very serious attitude to scientific discourse.

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A Logarithmic Speed-Difficulty Trade-off in Speech Production

Mark L. Latash and Irina L. Mikaelian

We explored the relations between task difficulty and speech time in picture description tasks. Six native speakers of Mandarin Chinese (CH group) and six native speakers or Indo-European languages (IE group) produced quick and accurate verbal descriptions of pictures in a self-paced manner. The pictures always involved two objects, a plate and one of the three objects (a stick, a fork, or a knife) located and oriented differently with respect to the plate in different trials. An index of difficulty was assigned to each picture. CH group showed lower reaction time and much lower speech time. Speech time scaled linearly with the log-transformed index of difficulty in all subjects. The results suggest generality of Fitts’ law for movement and speech tasks, and possibly for other cognitive tasks as well. The differences between the CH and IE groups may be due to specific task features, differences in the grammatical rules of CH and IE languages, and possible use of tone for information transmission.

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Human Movement: In Search of Borderlands Between Philosophy and Physics

Scott Kretchmar and Mark L. Latash

In this essay, we adopt a theory of behavior developed by the French philosopher Maurice Merleau-Ponty in an attempt to find common ground between philosophy and physics. We look for ways to reconcile matter with meaning, physical motion with the principles of ethics, body with mind. We proceed in three steps, first by providing a review of Merleau-Ponty’s theory; second by showing how ethical behavior is constrained and shaped by factors found in physics, chemistry, and biology; and, finally, by describing how physical motion is affected by factors that transcend the laws of classical physics. For the latter purpose, we accept a theory of parametric control of movements with spatial referent coordinates. Our purpose is not to solve specific problems of motor control or moral decision making but, rather, to test a general theoretical scheme that carries a number of practical implications for both research and education, including the need for collaboration between and among diverse research subdisciplines in kinesiology.

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Slobodan Jaric (1951–2018)

Daniel M. Corcos and Mark L. Latash

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The Nature of Finger Enslaving: New Results and Their Implications

Valters Abolins and Mark L. Latash

We present a review on the phenomenon of unintentional finger action seen when other fingers of the hand act intentionally. This phenomenon (enslaving) has been viewed as a consequence of both peripheral (e.g., connective tissue links and multifinger muscles) and neural (e.g., projections of corticospinal pathways) factors. Recent studies have shown relatively large and fast drifts in enslaving toward higher magnitudes, which are not perceived by subjects. These and other results emphasize the defining role of neural factors in enslaving. We analyze enslaving within the framework of the theory of motor control with spatial referent coordinates. This analysis suggests that unintentional finger force changes result from drifts of referent coordinates, possibly reflecting the spread of cortical excitation.