Individual differences in responses of untrained observers to stroboscopic apparent motion

Time-till-breakdown and VEP measures of short-range apparent motion

Varying short-range apparent motion (AM) stimulus displacements from 2.7 to 21.6 min it was found that VEP amplitudes varied as a function of the limits for short-range AM described using time-till-breakdown as a behavioural measure of AM strength. This VEP amplitude difference was, however, in the reverse direction to that predicted as the "motion" condition elicited lower VEP amplitude responses than the "non-motion" conditions (which did not significantly differ from each other). This direction of VEP amplitude difference was supported by an intensive study of a single subject. The "breakdown effect" enabled VEPs to be gathered during periods in which the subjective experience was of either coherent lateral motion, or breakdown (incoherent motion) without changing any stimulus parameter. The VEP component identified in expt 2, as predicted, was of lower amplitude during motion with respect to periods of breakdown. The results of these experiments are discussed in terms of describing motion and breakdown in short-range AM displays as "coherent" and "incoherent" motion, rather than as "motion" and "non-motion".

Motion components of VEPs to the waggon wheel effect

Visual evoked potentials (VEPs) from eight subjects are presented from scalp sites O1, O2, T5, T6, P3 and P4. A spoked wheel was illuminated by a constantly flashing strobe. By adjusting the real angular speed of the wheel the subjective impression was given of; a stationary wheel, a wheel spinning slowly or spinning rapidly clockwise. Two visually identified components, a negativity and a positivity, were found to be of larger amplitude in response to motion. The results were interpreted as consistent with a model of AM proposing motion information to be processed within the visual system.

Visual evoked potentials to stimuli in apparent motion

Following an extensive single subject pilot study 12 Ss viewed a continuously cycling (3 Hz), two stimulus, apparent motion (AM) display. The "AM breakdown effect" was utilised to gather visual evoked potentials (VEPs) from sites O1, O2, T5, T6, P3, and P4 during periods in which the display elicited either: the percept of motion; or the percept of two discrete alternating stimuli. VEPs displayed components of larger amplitude during motion periods in all right (but no left) hemisphere sites during periods 60-82 msec post left field stimulus onset (positive component) and 100-126 msec post right field stimulus onset (negative component). Results were interpreted as indicating initial extraction of motion information within the occipital lobe, with further motion processing taking place in temporal and parietal lobes.