Classification of Speech Rhythm Using Brain Rhythm: An EEG Study on Natural Bengali Speech Prosody

This study presents an in-depth investigation into the recognition of speech acts as orders or requests in Bengali, emphasizing the role of intonation. Behavioral and EEG experiments were conducted with native Bengali speakers to examine how intonational cues influence speech act recognition in the absence of lexical context. In the behavioral experiments, participants demonstrated a higher accuracy in recognizing orders over requests, with an average response rating of 4.5 for orders and 4.4 for requests (out of 5). The findings suggested a complexity gradient between these speech acts, with orders being more straightforward and less cognitively demanding than requests. The EEG experiment provided further insights, revealing distinct neural oscillation patterns corresponding to the recognition of orders and requests. Significant differences were observed in the theta (4-7 Hz), alpha (8-12 Hz), and gamma (30-50 Hz) frequency bands. Participants showed longer reaction times in recognizing requests (average 2.4 s) compared to orders (average 1.9 s), indicating higher cognitive load for requests. Alpha and theta bands were more activated and synchronized during the processing of request acts, while the gamma frequency showed increased activation for order act processing. Overall, the study underscores the critical role of intonation in speech act recognition and its neural correlates. The distinct neural patterns associated with different speech acts, as observed in the EEG data, highlight the intricate link between linguistic cues and brain activity in speech comprehension. These findings contribute to a deeper understanding of the neural mechanisms underlying speech act recognition and the significant impact of prosodic features on linguistic interpretation.