A visual evoked potential correlate of global figure-ground segmentation

Human observers discriminated the global orientation of a texture-defined f igure which segregated from a texture surround. Global figure discriminabil ity was manipulated through within-figure collinearity, figure-surround int eraction, and figure connectedness, while the local orientation contrast at edges between figure and surround was kept constant throughout all the exp eriments. Visual evoked potentials (VEPs) were recorded during onset-offset stimulation in which the figure cyclically appeared and disappeared from a uniform texture background. A difference component was obtained by subtrac tion of offset-from onset-VEP. Two negative peaks of the difference compone nt are found with latencies around 140-160 and 200-260 ms, respectively. En hanced discriminability of the global figure reduced (11-25 ms) the latency of the second peak, hence indicating that the 200-260 ms component was pro duced by global figure-ground segmentation. (C) 1999 Elsevier Science Ltd. All rights reserved.