Biomedical subjects

Michael A Riley

Publications and source records attributed to Michael A Riley.

7 recordsLinked to original sources

PubMed2005

Dynamic patterns of postural sway in ballet dancers and track athletes.

We compared the variability and spatiotemporal profile of postural sway of trained ballet dancers to college varsity track athletes under variations in the availability of vision and rigidity of the support surface. We found no differences between the groups according to the variability measures, but variability increased for both groups with eyes closed and on a foam surface. Recurrence quantification analysis revealed that the postural sway of dancers was less regular (lower recurrence), less stable (lower maxline), less complex (lower entropy), and more stationary (lower absolute trend) than that of track athletes. Dancers, possibly as a result of focused balance training, exhibited different dynamic patterns of postural sway.

Adult↗

PubMed2004

Prism aftereffects disrupt interlimb rhythmic coordination.

The authors examined effects of prism-induced proprioceptive aftereffects on coordination of 95 participants and compared interlimb rhythmic coordination performed before versus after exposure to prisms of varying optical displacements. The observed steady states of relative phase for postprism exposure coordination were shifted by a small but significant amount, but not across all prism conditions. Phase-shift direction was not specific to the direction of optical displacement and was not, across all conditions, proportional to the magnitude of optical displacement. Prism exposure was associated with increased relative phase variability for all prism conditions. A no-prism control group showed no changes in interlimb rhythmic coordination. The results suggest that prism-induced proprioceptive aftereffects have general, disruptive effects on interlimb rhythmic coordination.

Adaptation, Physiological↗

PubMed2003

Inverse relation between postural variability and difficulty of a concurrent short-term memory task.

We measured postural stability while participants simply stood or stood while performing a digit rehearsal task of varying levels of difficulty in order to examine the effects on postural control of concurrent short-term memory demands. The rehearsal task manipulation avoided factors that contaminate postural sway measurements, such as vocal articulation or visual fixation during posture data collection. When participants performed the more difficult digit tasks (longer digit strings), postural sway was reduced relative to when performing an easy version of the task (few digits). The results identified a complex relation between postural control and cognitive or attentional demands.

Analysis of Variance↗

PubMed2003

Recurrence analysis of human postural sway during the sensory organization test.

The present study examined how the availability of and alterations in sensory information during the sensory organization test (SOT) influenced the amount, variability, and temporal structure of spontaneous postural sway in young, healthy adults. Findings indicated that postural sway tended to increase in amount and variability as the SOT condition became increasingly difficult (i.e. as the SOT condition moved from eyes open to eyes closed, to sway-referenced visual surround or support surface, and to sway-reference surface and visual surround). In addition, recurrence quantification analysis revealed that the temporal structure of postural sway tended to become increasingly regular as the SOT condition increased in difficulty. The functional utility of the observed changes in the temporal structure of postural sway across sensory conditions was discussed.

Adult↗

PubMed2003

Prism exposure affects the proprioceptive frames of reference for interlimb rhythmic coordination.

Adaptation to prisms can produce a change in felt arm position, termed proprioceptive shift. We studied the effects of prism-induced proprioceptive shift on interlimb rhythmic coordination performed under proprioceptive guidance, in the absence of vision. Relative to interlimb rhythmic coordination performed before prism exposure, the observed steady states of relative phase for postexposure coordination were shifted by a small but reliable amount. The shift was in the direction expected, given the direction of optical displacement. The amount of variability of interlimb rhythmic coordination was unaffected by prism exposure. The results suggest that the same spatial frames of reference altered by prism adaptation are involved in the production of interlimb rhythmic coordination patterns.

Adult↗

PubMed2002

Perceptual behavior: recurrence analysis of a haptic exploratory procedure.

Various object properties are perceptible by wielding. We asked whether the dynamics of wielding differed as a function of the to-be-perceived property. Wielding motions were analyzed to determine if they differed under the intention to perceive or not perceive rod length (experiment 1), to perceive object height versus object width (experiment 2), and to perceive the length forward of where the rod was grasped versus the position of the grasp (experiment 3). Perceiving these different properties is known to depend on different components of the object's inertia tensor. Analyses of the subtle recurrent patterns in the phase space of the hand motions revealed differences in wielding across the different perceptual intentions. Haptic exploratory procedures may exhibit distinct exploratory dynamics.

Adult↗

PubMed2002

Variability and Determinism in Motor Behavior

In investigations into perception-action systems, variability of observable behavior may be considered to (a) interfere with inquiry, (b) be neither detrimental nor particularly useful to inquiry, or (c) play a crucial role in inquiry. The authors underscore recent suggestions that alternative (c) is a preferred strategy for the study of many motor behaviors. In tutorial fashion, the authors review the concepts of variability and determinism with respect to postural and rhythmic movements. Study of the variability of those behaviors has revealed crucial features suggestive of underlying mechanisms and control, such as particular blends of noise and determinism (piecewise determinism). It has also revealed general lessons (for example, more variable does not mean more random and more controllable does not mean more deterministic) that may extend to other classes of perceptual behavior.

Genetics, Behavioral↗