Gestalt perception modulates early visual processing

We examined whether early visual processing reflects perceptual properties of a stimulus in addition to physical features. We recorded event-related p otentials (ERPs) of 13 subjects in a visual classification task. We used fo ur different stimuli which were all composed of four identical elements. On e of the stimuli constituted an illusory Kanizsa square, another was compos ed of the same number of collinear line segments but the elements did not f orm a Gestalt. In addition, a target and a control stimulus were used which were arranged differently. These stimuli allow us to differentiate the pro cessing of colinear line elements (stimulus features) and illusory figures (perceptual properties). The visual N170 in response to the illusory figure was significantly larger as compared to the other collinear stimulus. This is taken to indicate that the visual N170 reflects cognitive processes of Gestalt perception in addition to attentional processes and physical stimul us properties. NeuroReport 12:901-904 (C) 2001 Lippincott Williams & Wilkin s.