Electrophysiological modulation in an effort to complete illusory figures: configuration, illusory contour and closure effects

Figure recognition process: From the coarse configuration standing from the background to the closure of a meaningful shape, was investigated by ERP technique. ERP components at different latencies from stimulus onset allowed to tap into the figure recognition process at discrete time-points when different cognitive operations take place. In this study, we present two experiments where the support-ratio (SR) of illusory figures was manipulated to vary continuously the recognition of geometrical figures. In the first experiment three shapes were used to vary the SR and the P1 component (80-130 ms) was modulated by the configuration-effect explained, in part for the first time, with the unbalanced physical stimulation between upper and lower visual field. In the second experiment, we used one shape and varied systematically the SR in a discrimination task. The N1 (130-180 ms) and the N2 (230-270 ms) were modulated by two effects: The Ic-effect, represented by the N1, and the closure-effect, represented by the N2, being larger when the SR was small and the discrimination more difficult with respect to large SRs and easier discrimination. These results showed that figure recognition proceeded from the coarse parsing of the visual scene (configuration-effect), through the completion of a set of illusory borders (Ic-effect) to the final assembling of a meaningful shape (closure-effect).