Abstract
We examined characteristics of EEC associated with global structures which are considered to activate the extrastriate cortex (V4). Three test stimuli (concentric, radial and parallel) were composed of random dots in which pairs of dots were placed so that the orientation of each dot pair was tangential to contours of global form for each stimulus. Control stimulus was composed of randomly oriented dot pairs, so that the comparison of the EEG to the control with that to the test stimuli enabled us to analyze the visual processing of global structure. Two stimulus presentation conditions (steady state and transient) were used. In the steady state condition, significant large response was obtained for the concentric pattern while no large response was obtained for the radial or parallel patterns. The response to the concentric pattern decreased to noise level within the initial 2 seconds. In the transient condition, the responses from 200 msec onwards after transition from the control stimulus differed in nature between the concentric and parallel patterns. A fMRl experiment was conducted in order to investigate the cortex activated by concentric shape.
