Neural responses to meaningless pseudosigns: evidence for sign-based phonetic processing in superior temporal cortex

Area of Science:

• Neuroscience
• Linguistics
• Cognitive Science

Background:

• The brain's response to linguistic structure is well-studied in spoken languages.
• Understanding how the brain processes visual linguistic input, like sign language, is crucial for a comprehensive view of language processing.
• Neural mechanisms underlying the automatic processing of structured, yet meaningless, visual linguistic elements remain largely unexplored.

Purpose of the Study:

• To investigate neural regions that automatically respond to linguistically structured, but meaningless, manual gestures.
• To compare brain activation patterns in deaf native signers and hearing non-signers when viewing pseudosigns and known American Sign Language (ASL) signs.

Main Methods:

• fMRI study involving 14 deaf native ASL users and 14 hearing non-signers.
• Participants passively viewed pseudosigns (possible but non-existent ASL signs), non-iconic ASL signs, and a fixation baseline.
• Analysis focused on activation differences between conditions using region of interest (VOI) analyses.

Main Results:

• Deaf signers exhibited greater activation in the left posterior superior temporal sulcus (STS) when viewing pseudosigns compared to baseline, unlike hearing non-signers.
• For deaf signers, pseudosigns elicited increased activation in the left posterior superior temporal gyrus (STG) and left inferior frontal cortex compared to known ASL signs.
• No significant differences were observed for hearing non-signers in the pseudosign vs. known sign contrast.

Conclusions:

• The left STS appears to be tuned to the phonological constraints of sign language, showing heightened responses to structured visual movements.
• The left STG may play a role in recognizing linguistic phonetic units, with unfamiliar structural combinations leading to increased activation.
• These findings suggest that the brain automatically processes the linguistic structure of sign language, even in meaningless gestures.