Introduction to the Special Issue on Biosignal-Based Spoken Communication

The papers in this special section focus on biosignal-based spoken communication. Speech production is a complex process resulting from human activities initiated in the brain, eventually leading to muscle activities that produce respiratory, laryngeal, and articulatory gestures which finally create acoustic signals. Traditional speech processing systems capture and interpret the acoustic signal of speech. However, speech is not only limited to acoustics - speech-related activities can be measured at each level of speech processing, including the central and peripheral nervous systems, muscular action potentials, and speech kinematics. Their measurement, obtained through recordings from variety of sensor technologies, results in speech-related "biosignals" that have been studied for decades to better understand the underlying mechanisms of human speech processing. However, there is more: speech-related biosignals have the potential to overcome limitations of traditional acoustic-based systems for spoken communication. Biosignals can be captured before the airborne acoustic signal and are thus less prone to environmental noise. Also, they do not rely on the production of audible speech - both features open up newtracks for "Biosignalbased Spoken Communication". Examples of these tracks include Brain-Computer Interfaces allowing for communication by directly decoding cortical brain activity into speech representations, and Silent-Speech Interfaces, which offer a way to communicate privately without disturbing bystanders and to restore spoken communication for people who lost their voice due to severe speech impairments. Furthermore, biosignals could provide valuable articulatory biofeedback to speakers about their own voice production for increasing articulatory awareness in speech therapy or language learning.