Social, Cognitive and Affective Neuroscience Unit

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Affective Visual Processing without Awareness

The capacity of affective stimuli to influence behavior even if they remain outside conscious awareness is consistent with the widely acknowledged role of emotional responses in survival: the assessment of a stimulus's significance should start at the early stages of information processing and help preparing adaptive responses before slower, analytic processing has been completed (or even begun). Based on the neuroanatomical connectivity of the amygdala, a brain structure greatly involved in emotion, LeDoux (2000) has proposed a neural mechanism underlying such early affective processing.

According to his influential hypothesis, initial affective assessments in the amygdala may be based on input from the early stages of sensory processing in the thalamus alone: affective processing along this thalamo-amygdalar "low road" does not need to involve the cortex; rather, its output may modulate cortical activity. In support of this idea, brain imaging studies with human participants have found amygdala responses to masked stimuli processed without conscious awareness, which covaried with both thalamic and cortical activation changes.

Although persuasive, this evidence is less than conclusive. First, at presentation times common in brain imaging studies (15 ms and longer), masked stimuli not consciously perceived may still be processed extensively in the cortex. Thus, cortical activity, instead of resulting from them, may have substantially contributed to amygdala responses in previous studies, an ambiguity which only a significant decrease in the duration of masked stimuli can resolve. Second, as these studies have paid little attention to behavior regulation, it remains unclear when affective processing via the "low road" may influence actual behavior, or which brain structures mediate this influence.

Scientists involved:

• Herbert Bauer (SCAN-Unit, University Vienna)
• Florian Ph.S Fischmeister (MR Center of Excellence, Medical University Vienna)
• Claus Lamm (SCAN-Unit, University Vienna)
• Ewald Moser (MR Center of Excellence, Medical University Vienna)
• Christoph Preinsack

Please send questions and comments to:

herbert.bauer@univie.ac.at