Qualitative individual differences in metacontrast masking: An instrument to investigate mechanisms of visual consciousness.

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The conditions that lead to a conscious subjective experience of visual stimuli are in the focus of current research on conscious perception. In the last years we have employed metacontrast masking as a paradigm to examine the processes that contribute to the experience of visual stimuli. Most current accounts of metacontrast masking assume one or two mechanisms. We found individual differences in visibility of the masked target stimulus and took advantage of this fact to examine the mechanisms that contribute to perception in metacontrast masking. Our initial studies provided evidence for the contribution of at least three processes underlying the different conscious experiences in this paradigm. However, our more recent studies point to a number of at least seven qualitatively different subjective percepts that participants can reliably distinguish in metacontrast masking. Interestingly, most of these percepts show a clear temporal dynamic that is very similar across subjects. Based on the assumption that the experience of a percept has to be generated by some (neural) processes, these data suggest that more than two or three processes contribute to metacontrast masking. The here presented proposal comprises two further studies that we deem necessary to successfully complete the project done so far. In the first study we want to examine whether two percepts that show the same temporal dynamic but differ in quality do in fact depend on each other, which would point to a common generating process. In the second experiment we want to take advantage of the fact that subjects report two qualitatively different percepts in trials with identical stimulation to identify the electrophysiological signature of these subjective experiences by comparing trials with identical stimulation and different subjective experiences. This experiment could contribute both to the question whether each percept has its own generating process and to issues regarding the time and topographical signature of conscious subjective experiences of visual stimuli.