Functional hierarchy for tactile processing in the visual cortex of sighted adults

Area of Science:

• Neuroscience
• Cognitive Science
• Sensory Perception

Background:

• Traditionally, sensory systems were thought to be separate.
• Emerging evidence shows visual cortex involvement in non-visual tasks like touch and hearing.
• The role of visual cortex in complex tactile processing, such as Braille reading, remains unclear.

Purpose of the Study:

• To investigate the spatiotemporal dynamics of visual cortex involvement in Braille letter recognition.
• To determine if visual cortex activation during tactile tasks follows a hierarchical pattern.
• To explore the metamodal organization of sensory processing in the brain.

Main Methods:

• Sighted participants trained in Braille recognition.
• Transcranial magnetic stimulation (TMS) applied to visual and somatosensory cortices during tactile Braille identification.
• TMS delivered at specific time windows (20-520 ms) post-stimulus onset.

Main Results:

• Disrupting early visual cortex (120-220 ms) and visual word form area (VWFA) (320-420 ms) with TMS impaired Braille recognition accuracy.
• Early somatosensory cortex stimulation caused a general task slowdown, not time-specific accuracy deficits.
• Findings suggest a hierarchical processing of tactile information within the visual cortex.

Conclusions:

• Visual cortex involvement in tactile perception aligns with the canonical visual processing hierarchy.
• Early tactile processing engages early visual areas; advanced processing involves higher visual areas like the VWFA.
• Results support a metamodal account of brain organization, indicating potential sensory-independent spatial processing across the visual cortex.