Exploration of Speech Induced Suppression using Functional Near-Infrared Spectroscopy (fNIRS)

Speech-Induced Suppression (SIS) is a suppression of brain activity by speech. It is believed to be caused by the internal predictions of the consequences of speech movements which lead to attenuation of related neural activity (1, 2). Previous research (3) showed that SIS of the EEG signal can be observed in some speaking tasks but the results were not consistent. This study found that fNIRS can be used to test neural activity related to speech production. Grand averaged signals showed that conditions involving vocalisation actually elicited higher activity than those without vocalisation. When statistical models were fitted to the obtained data, and controlled for participant-related variation, these results did not hold. No statistically significant differences between conditions were found. Even though haemoglobin concentration changes are slower than ERPs, they capture the neural activity underlying speech-production processes. The current results suggest that fNIRS can be used to study speech production.