Systems, Man & Cybernetics - January 2016 - 6

Glossokinetic
Potentials for a
Tongue-Machine
Interface
How Can We Trace Tongue Movements with Electrodes?
by Yunjun Nam, Bonkon Koo, Andrzej Cichocki, and Seungjin Choi

G

lossokinetic 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.

Digital Object Identifier 10.1109/MSMC.2015.2490674
Date of publication: 6 June 2016

6

IEEE SyStEmS, man, & CybErnEtICS magazInE Janu ar y 2016

A Complex Organ
The human tongue is a special organ with dynamic mobility.
One may test the following tongue movements to realize its
variety. The tongue can be bent up/down, moved left/right,
stuck out forward/retracted backward, rolled clockwise/
counterclockwise, flattened, or rounded. Some people even
can fold the lateral edges of the tongue upward to form a
tube, commonly referenced as a "tongue-rolling" trait in oldfashioned introductory genetics courses [1].
]. This fascinating
mobility is assisted by eight muscles occupying most of the
space inside the body of the mandible. With their support,
the tongue can move very quickly and accurately with little
fatigue [2].
]. This flexible mobility enables complex vocalization and ingestion tasks essential in our daily lives.
In this article, we attempt to introduce an electric potential response generated from this special organ, which is
referred to as the GKP [3], [4]. The tip of the tongue has a
negative electrical charge with respect to the root, thus,
when the tip touches the tissues inside the mouth, the
charge decreases the potential levels near the point of contact [3]. Generally, this GKP had been regarded as a signal
artifact distorting EEG signals. However, in recent studies, it began to be utilized as a new tool to trace tongue
movements [5], [6]. That is, by analyzing the spatial pattern of decreased potentials, we could inversely identify
the position of the contact that is an important feature to
trace tongue movements. We review the fundamental
2333-942X/16©2016IEEE



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Systems, Man & Cybernetics - January 2016 - Cover3
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