Michael A. Riley

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A technique (recurrence quantification analysis; RQA) for analyzing center of pressure (COP) signals is presented and applied to data obtained by having participants stand with the head forward or sideways and with eyes open or closed. RQA is suitable for short, nonstationary signals and quantifies dynamical (deterministic) structure and nonstationarity.(More)
We examined a precision aiming task in which a handheld laser pointer was controlled by the postural system. The task was performed in two orientations of the body's coronal plane to the target. In the parallel orientation medio-lateral (ML) sway had to be minimized, in the perpendicular orientation antero-posterior (AP) sway had to be minimized. In the(More)
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(More)
Subjects stood upright with the index finger of the right hand either touching a nearby surface gently or not touching it at all and with the eyes either open or closed. Trajectories of the center of pressure (COP) were analyzed as fractional Brownian motion. The extracted parameters were the effective diffusion (D) coefficients and Hurst (H) exponents for(More)
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(More)
The theory of affordances, a conceptual pillar of the ecological approach to perception and action, has the potential to become a guiding principle for research on perception and action in sport. Affordances are opportunities for action. They describe the environment in terms of behaviors that are possible at a given moment under a given set of conditions.(More)
We exposed standing participants to optic flow in a moving room. Motion sickness was induced by motion that simulated the amplitude and frequency of standing sway. We identified instabilities in displacements of the center of pressure among participants who became sick; these instabilities occurred before the onset of subjective motion sickness symptoms.(More)
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(More)
In 2 experiments, the authors independently varied the degree of cognitive and perceptual difficulty of suprapostural tasks. Participants were 23 students in Experiment 1 and 15 in Experiment 2. Increases in perceptual difficulty tended to be correlated with decreases in the variability of postural sway, consistent with the hypothesized functional(More)
The vertebrate hindbrain contains various sensory-motor networks controlling movements of the eyes, jaw, head, and body. Here we show that stripes of neurons with shared neurotransmitter phenotype that extend throughout the hindbrain of young zebrafish reflect a broad underlying structural and functional patterning. The neurotransmitter stripes contain cell(More)