Specification of multiple visual processes in metacontrast masking by means of individual differences

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One approach to examine the processing of visual stimuli for perception and action employs the metacontrast masking paradigm that is characterized by at two-stimulus sequence with a target and a following masking stimulus which does not overlap with the target stimulus. When the stimulus onset asynchrony (SOA) between target and mask is varied, the time course of masking effects results in a masking function which follows a u-shape in some conditions but simply increases with SOA in other conditions. Despite identical conditions, however, we have found stable differences between individuals with visibility functions that varied in the entire range between u-shaped and increasing functions. This finding challenges all accounts of metacontrast masking that assume a single mechanism. The individual differences rather support multi-process accounts of metacontrast masking. Factor analyses of the visibility functions suggest that at least three latent variables can be distinguished. We assume that these latent variables point to three processes which contribute according to an individually different weighting to the performance of individual observers. In the proposed project we want to specify these processes in their function by comparing individual differences in metacontrast masking with individual differences in other functional interpretable experimental conditions. We assume an integration processes which facilitates perception with short SOAs, a motion perception process that contributes to performance with intermediate SOAs, and a segmentation process which supports target perception with long SOAs. In six studies we want to examine how processes related to stimulus contour, motion and depth, as well as temporal integration of two stimuli contribute to individual differences in metacontrast masking. To localize processes in the visual system we compare individual differences in monoptic and dichoptic stimulus conditions and examine electrophysiological responses to the stimulus sequence used in metacontrast. This project can exemplify how individual differences can contribute to general accounts of visual processing. We expect that this approach helps to specify the function of the processes that contribute in a weighted combination to visual perception in metacontrast masking.