Effect of Spoken Speech in Decoding Imagined Speech from Non-Invasive Human Brain Signals

Decoding imagined speech from human brain signals is a challenging and important issue that may enable human communication via brain signals. While imagined speech can be the paradigm for silent communication via brain signals, it is always hard to collect enough stable data to train the decoding model. Meanwhile, spoken speech data is relatively easy and to obtain, implying the significance of utilizing spoken speech brain signals to decode imagined speech. In this paper, we performed a preliminary analysis to check whether if it would be possible to utilize spoken speech electroencephalography data to decode imagined speech, by simply applying the pre-trained model with spoken speech brain signals to decode imagined speech brain signals. While the classification performance of imagined speech data solely used to train and validation was 30.5 \%, the transferred performance of spoken speech based classifier to imagined speech data was 26.8 \% with no significant difference found compared to the imagined speech based classifier (p = 0.0983, chi-square = 4.64). For more comprehensive analysis, we compared the result with the visual imagery dataset, which would naturally be less related to spoken speech compared to the imagined speech. As a result, visual imagery have shown solely trained performance of 31.8 \% and transferred performance of 26.3 \% which had shown significant statistical difference between each other (p = 0.022, chi-square = 7.64). Our results imply the potential of applying spoken speech to decode imagined speech, as well as their underlying common features.