The Time Course of Visual Processing: From Early Perception to Decision-Making

  • Authors:

  • Rufin Vanrullen;Simon J. Thorpe

  • Affiliations:

  • Centre de Recherche Cerveau et Cognition, France;Centre de Recherche Cerveau et Cognition, France

  • Venue:
  • Journal of Cognitive Neuroscience
  • Year:
  • 2001

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Abstract

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.