Applied Vision Association Christmas Meeting, Leuven, Belgium 19-20 December 2013

摘要

Over a hundred years after Wertheimer's seminal work, the question of how a Gestalt arises in the visual system remains unanswered. Here we applied high-density electroencephalography (EEG) together with the technique of frequency tagging (Regan & Heron, 1969) to define an objective trace of a Gestalt in the visual system. Specifically, by using the Kanizsa square figure, we tracked the emergence of an illusory surface. In the "experimental condition", four pacmen were placed to form an illusory square. In the "control condition", the four pacmen were rotated in arbitrary angles so that the illusory surface disappeared. The two diagonal pacman pairs were 100% contrast-modulated at different frequency rates (f1 = 3.57 and f2 = 2.94 Hz) for 13 seconds. Fourier transform of the EEG recordings (12 participants) showed robust low-level responses specifically at these fundamental frequency rates, which did not differ between conditions. Most importantly, strong nonlinear intermodulation (IM) components (eg, 3.5714 - 2.9412 = 0.6302) appeared in response to the illusory figure. These IMs can only be produced by neuronal populations that integrate the two stimulations nonlinearly (eg, Boremanse et al., 2013), and they were only present in the experimental condition where all the parts (pacmen) are integrated coherently to form an illusory surface. Moreover, changing the support ratio influenced the amplitude and the distributions of IMs, but not the fundamental frequencies. These results indicate that IM components in EEG provide a neural signature of Gestalt configurations.