The neural correlates of the shine-through effect as revealed by high-density EEG

When a briefly presented vernier stimulus is followed by a grating consisting of 25 lines, the vernier appears brighter, longer, wider, and superimposed on the grating (shine-through). However, the vernier is largely invisible if two of the lines in the grating are omitted (gap grating). Here, we investigated the time course of the processing leading to these perceptual differences using EEG. The two types of gratings as well as the vernier offset direction were randomly interleaved, and participants indicated the perceived offset by button-presses. As a control, only the two gratings were displayed and observers instead reported which grating had been presented. We recorded high-density EEG and conducted both stimulus- and response-locked analyses. While the former revealed no effects of interest, the response-locked analysis showed an interaction effect on the global field power roughly 80 ms after stimulus onset in the shine-through condition. This effect indicates a stronger neural response for the shine-through condition than for the gap grating condition. This result suggests that the visibility of the vernier in the shine-through condition gives rise to extra neural processing that is time-locked to the response rather than the stimulus onset, and that this occurs rather early on. This project was supported by ProDoc "Processes of Perception" of the Swiss National Science Foundation.