Electrophysiological correlates of common-onset visual masking.

In common-onset visual masking (COVM) the target and the mask come into view simultaneously. Masking occurs when the mask remains on the screen for longer after deletion of the target. Enns and Di Lollo [Enns, J. T., & Di Lollo, V. (2000). What's new in visual masking? Trends in Cognitive Sciences, 4(9), 345-352] have argued that this type of masking can be explained by re-entrant visual processing. In the present studies we used high-density event-related brain potentials (HD-ERP) to obtain neural evidence for re-entrant processing in COVM. In two experiments the participants' task was to indicate the presence or absence of a vertical bar situated at the lower part of a ring highlighted by the mask. The only difference between the experiments was the duration of the target: 13 and 40 ms for the first and second experiment respectively. Behavioral results were consistent between experiments: COVM was stronger as a joint function of a large set size and longer trailing mask duration. Electrophysiological data from both studies revealed modulation of a posterior P2 component around 220 ms post-stimulus onset associated with masking. Further, in the critical experimental condition we revealed a significant relation between the amplitude of the P2 and behavioural response accuracy. We hypothesize that this re-activation of early visual areas reflects re-entrant feedback from higher to lower visual areas, providing converging evidence for re-entrance as an explanation for COVM.