Visual cortex activity predicts subjective experience after reading books with colored letters.

Area of Science:

• Neuroscience
• Cognitive Psychology
• Sensory Perception

Background:

• Synesthesia involves perceptual experiences linked to stimuli.
• The nature of acquired cross-modal associations remains unclear.
• Investigating if learned associations can evoke visual cortex activity.

Purpose of the Study:

• To determine if training can induce synesthesia-like visual cortex activation.
• To explore the relationship between acquired letter-color associations and brain activity.
• To differentiate between subjective experience and association strength in visual processing.

Main Methods:

• Non-synesthetes underwent several weeks of training with colored letters.
• Functional magnetic resonance imaging (fMRI) scanned participants viewing trained vs. untrained letters.
• Correlations analyzed between visual cortex activation and subjective reports (color experience, imagery vividness, association strength via Stroop effect).

Main Results:

• Training-induced activation in visual area V4 correlated with subjective color experience.
• Stronger 'associator' types showed altered V4 activation for trained achromatic letters.
• Acquired association strength (Stroop effect) did not correlate with visual cortex activity.
• Visual mental imagery vividness related to veridical color activation, not learned associations.

Conclusions:

• Subjective experiences from a synesthesia-training paradigm are reflected in visual brain activation.
• Learned letter-color associations can influence early visual processing, particularly in area V4.
• Distinguishes between the perceptual quality of experience and the cognitive strength of an association.