Effects of Visual Masking and Crowding on Stimulus Visibility and Processing
von Anne Sommerfeld
Datum der mündl. Prüfung:2021-01-11
Erschienen:2023-01-10
Betreuer:Prof. Dr. Uwe Mattler
Gutachter:Dr. Igor Kagan
Gutachter:Prof. Dr. Hannes Rakoczy
Dateien
Name:Dissertation_ASommerfeld_Final_revision_ohneCV.pdf
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Format:PDF
Zusammenfassung
Englisch
The visibility of visual stimuli can be manipulated by various methods such as visual masking or crowding in such a way that the viewer can no longer identify the stimulus. Despite these circumstances, the stimuli can be processed in the brain to a certain degree, which is why these methods are also used to compare the information processing of conscious and unconscious visual stimuli. In this way, conclusions can be drawn about the limits of processing unconscious stimuli or the neuronal correlates of consciousness. This serves as a basis for a better understanding of the function of consciousness or the emergence of consciousness. However, there are indications that the processing depth of unconscious stimuli may depend significantly on the method used to manipulate visibility. The generalizability of individual study results would thus be strongly limited. A more detailed investigation of these relationships could be helpful to understand how stimulus processing is affected by different experimental methods and furthermore at least partially explain the multitude of contradictory study results in this research area. In this context, several masked priming experiments were developed in the present work. In the first study it was shown that the stepwise manipulation of visibility by spatiotemporal crowding had no effect on the processing of this stimulus. This conclusion can be attributed to the fact that priming effects (as a measure of processing) did not depend on the visibility of the prime. In a subsequent study, a direct comparison was made to determine whether the priming effects depended on different masking conditions (backward pattern masking, metacontrast masking, and spatiotemporal crowding). Under the tested conditions, no difference was found between these conditions and priming effects were as pronounced as with visible primes. Taken together, this suggests that these methods are well suited to study the processing of unconscious stimuli, since visibility was reduced regardless of the processing depth. This was shown in the processing of colors, semantic categories and arrow directions. Future studies should verify whether this conclusion can be applied to the processing of more complex visual stimuli. In the present work it will be discussed how different ways of manipulating stimulus visibility differ in this feature in relation to the processing mechanisms that are possibly involved. As long as the mechanisms of individual methods to manipulate stimulus visibility are not sufficiently clarified, conclusions about the processing depth of unconscious stimuli and the neuronal correlates of consciousness should be interpreted in connection with the research methods. Further studies comparing the effects of different methods could improve our knowledge about the mechanisms of visual processing, which seems to be a necessary prerequisite for a better understanding of the mystery of consciousness.
Keywords: Consciousness; Visual Crowding; Visual Priming; Metacontrast Masking