Shine-through occurs 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. However, vernier offset discrimination is strongly impeded if two of the lines in the grating are omitted. In this study, we investigated the neural correlates of the large perceptual differences associated with these nearly identical stimuli. 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 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 statistically significant effects of interest, the response-locked analysis showed an interaction effect on the global field power around 740 ms before the button-press, namely a stronger response for the shine-through condition than for the masking condition. This suggests that the differences in processing might be locked to the response rather than stimulus onset. This work was supported by ProDoc "Processes of Perception" of the Swiss National Science Foundation.