Glossokinetic Potentials for a Tongue-Machine Interface: How Can We Trace Tongue Movements with Electrodes?

Glossokinetic potentials (GKPs) refer to electrical responses involving tongue movements that are measured at electrodes placed on the scalp when the tip of the tongue touches tissue inside the mouth. GKP has been considered an electroencephalography (EEG) artifact that is removed to minimize the interference with signals from a cerebral region for successful EEG analysis. In this article, we emphasize a different side of GKP where we analyze its spatial patterns to trace tongue movements developing tongue-machine interfaces. We begin with a brief overview of GKP and its spatial patterns and then describe its potential applications to man-machine interfaces. First, we describe the spatial pattern of GKP for horizontal tongue movements and explain how it can be utilized to identify the position of the tongue. We also introduce a tongue-rudder system where this technique enables smooth control of an electric wheelchair. Then we describe GKP patterns for vertical and frontal tongue movements that are closely related to speech production. Based on this pattern, we discuss its application to silent speech recognition, which allows speech communication without using a sound.