Hemispheric asymmetries in categorical facial expression perception

Area of Science:

• Neuroscience
• Cognitive Psychology
• Psycholinguistics

Background:

• Humans categorize continuous sensory phenomena, like facial expressions, into discrete emotional categories.
• Categorical perception enhances discrimination between categories but impairs within-category discrimination.
• The lateralization of facial expression categorical perception remains debated, with potential links to right-hemisphere face processing or left-hemisphere language biases.

Purpose of the Study:

• To investigate the cerebral lateralization of categorical perception for facial expressions.
• To determine if prior exposure to facial expression categories influences this lateralization.

Main Methods:

• A visual half-field paradigm was employed to assess categorical perception.
• Participants discriminated between morphed facial expressions transitioning between happy-sad and anger-fear.
• Two experiments were conducted, varying participant exposure to facial expression categories.

Main Results:

• Categorical perception was observed in both visual half-fields for participants with prior exposure.
• For naive participants, categorical perception was primarily found in the right visual hemifield (left cerebral hemisphere).
• This indicates that facial expressions are not inherently processed categorically in the right hemisphere.

Conclusions:

• The lateralization of facial expression categorical perception is contingent on prior exposure.
• Naive perception suggests a left-hemisphere role, potentially linked to language-based categorization.
• Experience with emotional categories may facilitate bilateral processing, suggesting learning modulates hemispheric specialization.