Neural Correlates of Biological Motion Perception in Sign Language Users
Although widely studied in typically developing populations, the neural basis of biological motion perception has not yet been studied amongst a group that uses action as their primary mode of communication: sign language users. We hypothesized that the continuous perception of biological motions used in sign language may mean that native signers show an increased ability to extract relevant action information. With this EEG study we test whether Deaf signers' (N = 19) sensorimotor systems are differentially sensitive to biological motion presented in two conditions (scrambled vs. unscrambled) compared to hearing non-signers. We predicted greater central alpha event-related desynchronization (ERD) for the unscrambled condition, due to greater demands on sensorimotor cortices when understanding movement. Everyday actions (e.g., jumping jacks, jump rope) were presented using point light displays (PLD). Time-frequency activity in the alpha and beta ranges was computed for each condition at frontal electrodes and central sites overlying the sensorimotor cortex. Paired comparisons showed significantly greater ERD at central electrode sites in response to scrambled PLDs as compared to unscrambled PLDs (p<.05, bootstrapped). This finding suggests that deaf signers may recruit sensorimotor systems more strongly in response to unintelligible actions than coherent action, contrary to our prediction. Frontal electrodes showed the same pattern of ERD (p<.05, bootstrapped), suggesting that executive functions are involved in parsing scrambled PLDs. The results from Deaf native signers were statistically compared to the EEG responses of hearing non-signers. This work provides the first investigation of sensorimotor EEG in Deaf signers during PLD observation.