The time course in perceptual organization: An EEG study

Abstract

Purpose. In order to find empirical evidence for top-down cortical feedback in relation to the neural mechanisms of perceptual organization, we studied the stereokinetic effect. When rotated in the same plane, two eccentric rings initially appear to move relative to each other in that plane. Soon a 3D, mutating truncated cone is perceived, in which the two rings appear to be in different planes, but at the same time move rigidly relative to each other. This effect vividly demonstrates that perceptual organization is at work in “slow motion.” We studied brain activity elicited by this stimulus with EEG because of its high temporal resolution. Methods. A stereokinetic stimulus was presented during EEG recording. Subjects pressed a button as soon as they perceived a vivid 3D structure. The button press was aligned with EEG recordings. With counterbalancing, eight stimuli were presented to each of the 12 subjects. Results. The average activity in secondary visual areas sharply rises 600ms before the button press. This activity reversed in polarity after button press and was sustained for as long as 2600ms. Our preliminary analysis indicated that mechanisms underlying perceptual organization are relatively slow acting learning processes, instead of quick activity based processes.

Footnotes

 Supported by NSF IBN-9817979.