The Role of Attention in Processing of Visual Stimuli in Metacontrast Masking

Abstract

By analyzing individual data, Albrecht and colleagues found qualitative inter-individual differences in studies with metacontrast masking, appearing in phenomenological perception as well as in discrimination performance (Albrecht & Mattler, 2012a, 2012b). They used the metacontrast paradigm, where two stimuli are presented sequentially and the visibility of the first stimulus (target) is reduced due to the appearance of the second stimulus (mask). The visibility is a function of the stimulus-onset-asynchrony (SOA). Participants differ in that respect whether the visibility of the target increases with increasing SOA (type A) or whether it is U-shaped (type B). These differences in the objective performance correlate with differences in the phenomenological experience (apparent motion vs. negative afterimage) as well as in the response criteria. A first ERP study also indicated differences in the sensory neural processing. This study aims to clarify whether these neural differences reflect either a different intentional attention on experimental stimuli (top-down) or a different bottom-up processing. For this, participants attended two sessions. In the first session metacontrast stimuli were presented but they had to focus the fixation point and detect an occasionally appearing color change (condition “without attention”). The experimental design in the second session was identical to the first, but participants had to focus their attention on the metacontrast stimuli and to discriminate the shape of the target (condition “with attention”). We expect to find group differences between type A and type B participants in the condition “with attention” and replicate data of the first ERP study. Finding these differences in the condition “without attention” as well would indicate a bottom-up processing; no differences would indicate a different top-down processing.