Visual evoked potentials induced by illusory outlines (Kanizsa's square)

Abstract

This report describes studies of visual evoked potentials (VEP) in ten subjects produced in response to Kanizsa's square and a control stimulus which did not involve a visual illusion but which had a similar spatial organization. The results showed that the amplitude-time characteristics of VEP depended on the illusory outlines. Differences in the parameters of VEP produced using the two stimuli were seen in the occipital, parietal, and temporal areas. VEP amplitude differences between the peaks of the N180 and P230 waves increased and the latent period of the N300 wave decreased on presentation of the illusory outlines as compared with the control stimulus. Interstimulus differences in amplitude were seen in the left and right occipital and left temporal areas, while differences in latency were seen in the left occipital lead. The data supported the suggestion that the visual perception system includes two areas encoding illusory outlines, which are associated with different aspects of visual analysis--encoding of individual signs and their complexes (O1 and O2) and comparing sensory codes with codes stored in memory (T5).

Electrophysiological indexes of illusory contours perception in humans

“…This result indicates an earlier activation of visual cortex if compared to previous electrophysiological studies (i.e. 180-300 ms post-stimulus) [17,31,32] and it is consistent with neuroimaging data as far as neurotopographical localisation and perhaps timing of activation are concerned. Several fMRI, PET, rCBF and neurophysiological studies demonstrated an activation of extra-striate cortex (mainly V2, but also V3a, V4v, V7, V8) associated with illusory contours perception, both in humans and animals.…”

“…The task consisted in a passive viewing paradigm; attention was focused on a central fixation point and not on the (possible) subjective figure, as in the present study. In another VEP study adopting a passive viewing task, Korshunova [17] recorded a peak-to-peak N180-P230 increase in amplitude at mesial occipital areas (O1 and O2 electrode sites) associated with illusory contour perception, along with asymmetric activation of the posterior temporal site (T5), probably near the extrastriate area (area 19).…”

“…Korshunova [17] also recorded VEPs to Kanizsa squares and control configurations in a passive viewing task and discovered a difference in N180/P230 peak-to-peak amplitude and N300 latency at occipital O1 and O2 sites and the left posterior temporal site (T5) associated with subjective contours perception. Although interesting, currently available electrophysiological data did not allow any definitive conclusion about the discussed issue.…”

Visual evoked potential changes related to illusory perception in normal human subjects

“…The functional and neural bases of Kanizsa illusory contours have been investigated in normal human subjects by using evoked potentials [4,7,11], repetitive transcranial magnetic stimulation (rTMS) [2], functional magnetic resonance imaging (fMRI) [6,8 -10], and magnetoencephalography (MEG) [5]. Right occipital stimulation using rTMS significantly increased reaction times for illusory contour perception [2].…”

“…Differences in VEPs related to visual illusory perception have been studied using the Kanizsa square [4,7,11] and the Poggendorff illusory figure [1]. Differences in VEPs produced in normal human subjects using the two stimuli, a Kanizsa square and a control stimulus, were seen in occipital, parietal, and temporal areas [4,7,11].…”