Differential modulation on neural activity related to flankers during face processing: a visual crowding study

Abstract

The modulations of visual awareness on the processing of emotional faces have been mainly investigated in masking experiments where stimuli were presented for different durations as an integral process to the masking technique. In this visual crowding study, we manipulated the perceivability of a central crowded face (either a fearful or a neutral face) by varying the similarity between the central face and the surrounding flanker stimuli. We presented participants with pairs of visual clutters and recorded their electroencephalography during an emotion judgement task. In an upright flanker condition where both the target face and flanker faces were upright faces (high similarity), participants were less likely to report seeing the central target face, and their P300 was weakened, compared to a scrambled flanker condition where scrambled face images were used as flankers (low similarity). Additionally, at around 120ms post-stimulus, a posterior negativity was found for the upright flanker condition, compared to the scrambled flanker condition, however only for fearful face targets. We concluded that early neural responses seem to be affected by the perceptual characteristics of both target and flanker stimuli whereas neural activity at a later stage is associated with post-perceptual evaluation of the stimuli in this visual crowding paradigm.