Impacts of imagined lexical tone on Mandarin speech imagery BCI performance

Abstract

Speech imagery brain computer interfaces (BCIs) empower people with motor disorders to communicate their thoughts and intentions to their environment in a natural, user-friendly way. Due to its portability, non-invasiveness, safety, and low cost, functional near-infrared spectroscopy (fNIRS) is advanced as a brain imaging method for developing BCIs. To improve operators' speech imagery BCI performance, a new paradigm was studied in this work by modifying imagined lexical tone in Mandarin speech imagery BCIs motivated by the fact that speech processing with perceptual pitch variation exhibited more extensive activations in brain than that without perceptual pitch variation. For the traditional ternary yes and no Mandarin speech imagery paradigm, the subjects were asked to answer questions by covertly repeating the Mandarin syllable ('yes' in English, and with tone 4 in Mandarin) or ‘ (‘no’ in English, and with tone 3 in Mandarin) in mind and an unconstrained rest task was also contained. In the proposed paradigm, the subjects were asked to imagine with tone 1 and with tone 3. Compared with the traditional paradigm, tone difference in Mandarin speech imagery of the proposed paradigm could generate more discriminative brain activities among different tasks, and the mean classification accuracy was significantly improved from 49.06% to 53.85%. These results suggest that modifying imagined lexical tone in Mandarin speech imagery could influence brain activation and is promising for improving the decoding accuracy of Mandarin speech imagery BCIs.