Biomedical subjects

David F Nichols

Publications and source records attributed to David F Nichols.

3 recordsLinked to original sources

PubMed2006

Linking dynamical perceptual decisions at different levels of description in motion pattern formation: computational simulations.

A two-level dynamical model of motion pattern formation is developed in which local motion/ nonmotion perceptual decisions are based on inhibitory competition between area V1 detectors responsive to motion-specifying versus motion-independent stimulus information, and pattern-level perceptual decisions are based on inhibitory competition between area MT motion detectors with orthogonal directional selectivity. The model accounts for the effects of luminance perturbations on the relative size of the pattern-level hysteresis effects reported by Hock and Ploeger (2006) and also accounts for related experimental results reported by Hock, Kelso, and Schöner (1993). Single-trial simulations demonstrated the crucial role of local motion/nonmotion bistability and activation-dependent future-shaping interactions in stabilizing perceived global motion patterns. Such interactions maintain currently perceived motion patterns by inhibiting the soon-to-be-stimulated motion detectors that otherwise would be the basis for the perception of an alternative pattern.

Computer Simulation↗

PubMed2005

Dynamical vs. judgmental comparison: hysteresis effects in motion perception.

Perceptual comparison was investigated by gradually varying the relative length of two apparent motion paths, and independently determining when an initial percept was lost during the course of attribute change and when an alternative percept emerged. Dynamical comparison was indicated by a range of attribute values for which perception was bistable. Within this range, a percept that lost stability was immediately replaced by an alternative percept. Judgmental comparison was indicated by a range of attribute values for which perception was uncertain. When an initial percept was lost, an alternative percept did not immediately emerge because the alternatives being compared could not be distinguished. Differences in the effects of random noise on dynamical vs. judgmental comparison were demonstrated with computational simulations, and implications are discussed for motion energy models and solutions to the motion correspondence problem.

Attention↗

PubMed2004

When motion is not perceived: evidence from adaptation and dynamical stability.

Adaptation was used to probe the perceiver's activation state when either motion or nonmotion percepts are formed for bistable, single-element apparent motion stimuli. Although adaptation was not observed in every instance, when it was observed its effect was to increase the probability of both motion-to-nonmotion and nonmotion-to-motion switches, the time scale of adaptation corresponding to neurophysiological observations for directionally selective cortical cells (Giaschi et al. 1993). This susceptibility to de-stabilizing adaptation effects indicated that the nonmotion percept was not the result of inadequate stimulation producing subthreshold levels of motion detector activation; if that were the case, activation-dependent adaptation would have decreased the nonmotion-to-motion switching rate by reducing activation further below threshold. Above-threshold activation levels are therefore associated with both nonmotion and motion perceptual states, and the failure to perceive motion despite the presence of adequate motion detector stimulation can be attributed to inhibitory competition between detectors activated by motion-specifying stimulus information and detectors activated to similar levels by motion-independent stimulus information, consistent with the dynamical quality of single-element apparent motion.

Adaptation, Ocular↗