The time course of visual processing: from early perception to decision-making.
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.
VanRullen
R
R
Centre de Recherche Cerveau et Cognition, France. rufin@cerco.ups-tlse.fr
Thorpe
S J
SJ
D000328:Adult; D000818:Animals; D001519:Behavior / Q000502:physiology; D003657:Decision Making / Q000502:physiology*; D005074:Evoked Potentials, Visual / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008606:Mental Processes / Q000502:physiology*; D008875:Middle Aged; D010470:Perceptual Masking / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D014186:Transportation; D014796:Visual Perception / Q000502:physiology*