Systems, Man & Cybernetics - January 2016 - 7

feature of GKP by describing its meaning, origin, and spatial patterns. We also explain how it can be used to
identify the position of the tongue and where this technique can be beneficially utilized.
GKP
Generally, GKP means the potential response generated
from tongue movements, but specifically, it refers the
response evoked when the tip of the tongue touches the
tissues inside the mouth. When the tip of the tongue touches the tissues inside the mouth, as shown in Figure 1(a), a
negative electrical charge on the tip [3], [4] generates a

negative electric field spreading out from the point of
the contact. That is, the evoked potential shows the
maximum decrease on the point, and its effect
decreases with distance from the point.
This GKP has been studied primarily within EEG
analysis [3], [7]. If a subject moves his or her tongue
during an EEG recording, the generated electric
field can spread to the facial skin and even to the
scalp. Since it originates from a noncerebral
region, it can interfere with the observation of
brain activities. Thus, GKP was regarded as a
signal artifact that should be prevented during
the recording or actively removed during the preprocessing stage. In [3],
[ [8], and [9], the GKP was
mentioned as a "glossokinetic artifact" rather
than a "glossokinetic potential."
Fortunately, a few years ago, we made an
interesting discovery revealing new applications of this artifact [5].
[ During our extensive
experiments to record EEG signals for motor
imagery tongue movements (the motor imagery means the mental process imagining a
movement of a specific body part, which is
extensively researched in the field of
brain-computer interfaces), we observed
that signals changed according to tongue
movements. That is, if the tongue moves
to the left side while staying in contact
with the buccal wall, the potential levels
in the left hemisphere decrease, and
those in the right region increase and
vice versa. This phenomenon can be
easily explained by the electric field
generated by the charge on the
tongue. If the negatively charged
tongue moves to the left side, the
potentials on the electrodes in the
left hemisphere will gradually
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decrease, and the potentials on the
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right hemisphere will increase proportionally. Based on this phenomenon, we developed a
liner model to translate the measured GKP levels into the
horizontal position of the tongue and implemented a novel
tongue-machine interface (TMI). We applied the interface
to the task of wheelchair control and verified its practical
usefulness. After this research, we do not call the GKP a
glossokinetic artifact anymore. If the signal contains
meaningful information, how can we call it an artifact? In
the next sections, we will explain the detailed patterns of
GKP obtained from our experiments.
GKP for Horizontal Tongue Movements
GKP Patterns for Horizontal Tongue Movements
In this section, we introduce our experimental results
conducted in [5] to investigate GKP responses for
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