Moradi, Farshad (2007) Conscious awareness determined by selective gating of information in early visual areas. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-05072007-115624
A number of psychophysical methods that suppress retinal input from reaching awareness have been used to isolate and study the neural correlates of visual consciousness. I describe a novel disappearance phenomenon in which a low-contrast peripheral pattern is vividly erased from awareness: after adapting to the pattern for a few seconds, flashing a high-contrast patch over it can elicit the perceptual disappearance of the stimulus. This finding was explained in terms of nonlinear interaction between adaptation to sustained spatial pattern and rapid gain adjustment to transient change. It was next shown that transient changes contingent upon prior adaptation elicit perceptual alternations in structure from motion, binocular rivalry, Necker cube, and ambiguous apparent motion—linking disappearance phenomena and bistable perception. We next used binocular rivalry and inattentional blindness to examine if invisible inputs influence the neuronal mechanisms that adapt to different aspects of the stimuli. The face identity-specific aftereffect was found to be cancelled by binocular suppression or by inattentional blindness of the inducing face. Conversely, the same suppression did not interfere with the orientation-specific aftereffect. Thus, the competition between incompatible or interfering visual inputs to reach awareness is resolved before those aspects of information that are exploited in face identification are processed. Subsequent experiments showed that face identity aftereffect is invariant to eye movements, but fMRI adaptation in face-selective region of the fusiform cortex did not show such invariance. Therefore identity aftereffect originates either at the same level or subsequent to the level of face processing in the fusiform area. Next, we show that recognition of facial emotional expressions occurs after the level of attentional selection: visual search results were incompatible with preattentive processing of emotional categories. We thus suggest that the invisible or unattended faces are suppressed in early visual areas. This conjecture was experimentally confirmed by showing that when a stimulus is not attended, it evoked a weaker and weaker response in fMRI in subsequent stages of visual processing hierarchy. Thus, attention determines how far the visual input is processed and whether or not a high-level representation of the input would be constructed.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Subject Keywords:||attention; face perception; fMRI; psychophysics; vision|
|Degree Grantor:||California Institute of Technology|
|Major Option:||Computation and Neural Systems|
|Thesis Availability:||Restricted to Caltech community only|
|Defense Date:||7 November 2006|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||04 Jun 2007|
|Last Modified:||26 Dec 2012 02:40|
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