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Journal of Cognitive Neuroscience

May 15, 2001, Vol. 13, No. 4, Pages 454-461
(doi: 10.1162/08989290152001880)
© 2001 Massachusetts Institute of Technology
The Time Course of Visual Processing: From Early Perception to Decision-Making
Article PDF (6.85 MB)

Experiments investigating the mechanisms involved in visual processing often fail to separate low-level encoding mechanisms from higher-level behaviorally relevant ones. Using an alternating dual-task event-related potential (ERP) experimental paradigm (animals or vehicles categorization) where targets of one task are intermixed among distractors of the other, we show that visual categorization of a natural scene involves different mechanisms with different time courses: a perceptual, task-independent mechanism, followed by a task-related, category-independent process. Although average ERP responses reflect the visual category of the stimulus shortly after visual processing has begun (e.g. 75-80 msec), this difference is not correlated with the subject's behavior until 150 msec poststimulus.