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Michael T. Turvey

Recent developments in the study of action and perception have their roots in the contemplations of Giovanni Borelli, a 17th-century Italian mathematician and physicist, and Sir Charles Bell, and 18th-century English physiologist and neuroanatomist. When Borelli looked at muscle and its functional achievements, he saw dynamics with its attendant laws and principles; when Bell looked at muscle, he saw information about muscular states and a smart mechanism for its measurement. Research and theory on the dynamics of coordination and locomotion, and on the perceptual achievements of the haptic subsystem of dynamic touch, are providing affirmation of these visions of Borelli and Bell.

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Christopher C. Pagano and Michael T. Turvey

We report several experiments directed at the ability of humans to perceive the spatial orientation of occluded objects, to position an occluded limb relative to targets or directions in the environment, and to match the spatial orientations of occluded contralateral limbs. Results suggest that each of these abilities is lied to the inertial eigenvectors of each object or limb, which correspond to the object's or limb's principal axes of rotational inertia. Discussion focuses on the dynamic nature of proprioception, the importance of physical invariants for perception, and the relation of invariants to hypothesized frames of reference for proprioception and motor control. It is suggested that the detection of invariants revealed through movement is a major mechanism in kinesthetic perception involving intact limbs, neuropathic or anesthetized limbs, prosthetic devices, and hand-held tools and implements. The inertia tensor is identified as one such invariant.

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Bruce A. Kay, Michael T. Turvey and Onno G. Meijer

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David R. Collins, Hyeongsaeng Park and Michael T. Turvey

Von Holst (1939/1973) parsed intersegmental coordination into relative and absolute to distinguish moderate and extreme forms. Kelso and DeGuzman (1992) discussed an interpretation of relative coordination in terms of the chaotic phenomenon of intermittency. The data of concern (DeGuzman & Kelso, 1991) do not, however, exclude a stochastic interpretation, which is detailed here following earlier suggestions. The key difference is modeling relative coordination by stochastic variability about weak attractors rather than by deterministic variability about remnants of attractors (”ghost attractors”). The intermittency interpretation is not robust in the presence of noise and, therefore, is not well disposed to account for uncertainty in detailing a model of behavioral data or its parameters. In contrast, the stochastic interpretation is based upon an approximation of unknown underlying processes in the form of Gaussian white noise. A stochastic method for estimating model parameters from a stationary probability distribution and a mean first passage time is illustrated using experimental and simulated data.

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Suvobrata Mitra, Polemnia G. Amazeen and Michael T. Turvey

We investigated the 1:1 frequency locking of two hand-held pendulums oscillated parallel to the body's coronal plane. In this configuration, anti-phase defined muscularly is in-phase defined spatially, and vice versa. Coordination equilibria measured by average relative phase were shifted less from muscular anti-phase than from muscular in-phase by detuning (unequal uncoupled pendulum frequencies) and were shifted less in both modes with vision than without. Variability of the equilibria, however, was ordered opposite to their degrees of shift and was unaffected by vision. Demonstrated subcritical pitchfork and tangent bifurcations conformed to the variability classification of anti- and in-phase coordination. Implications for dynamical models, hierarchical control, and definitions of coordination modes were discussed.

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Michael A. Riley, Suvobrata Mitra, Thomas A. Stoffregen and Michael T. Turvey

We examined the potentially exploratory and performatory nature of postural sway. Subjects stood upright or leaned forward, with eyes open or closed. Postural data were analyzed using a statistical mechanics analysis of center of pressure (COP) trajectories, which examines the fractional Brownian nature of postural sway. Positive correlations (persistence) over short time scales are hypothesized to reflect exploratory behavior, and negative correlations (antipersistence) over long time scales are hypothesized to reflect performatory behavior. When leaning, subjects exhibited decreased levels of persistence (decreased correlation) and increased levels of antipersistence (increased correlation) than when upright. With eyes open, subjects showed decreased levels of persistence and decreased levels of antipersistence than with eyes closed. Effects of vision were more pronounced when leaning. Evidence for direction-specific exploration (based upon root mean square variability analysis) was considered. Task-specificity and trade-offs between biomechanical and task constraints in models of postural control were discussed.

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Michael A. Riley, Eric L. Amazeen, Polemnia G. Amazeen, Paul J. Treffner and Michael T. Turvey

Handedness and attentional asymmetries in bimanual rhythmic coordination were examined as a function of movement speed. In an in-phase 1:1 frequency locking task, left-handed and right-handed subjects controlled the oscillations of either the right or the left hand so as to contact spatial targets. The task was performed at three frequencies of coupled movement. Coordination dynamics incorporating the body's functional asymmetry predicted that left-handers and right-handers would deviate from zero relative phase in opposite directions, that the deviation would be greater for preferred-hand targeting, and that this deviation would be greater at higher movement frequencies. The results confirmed the major predictions and suggested that asymmetry due to handedness is magnified by attention.