RESEARCH ARTICLE
Bettina Forster Æ Martin Eimer
Vision and gaze direction modulate tactile processing in somatosensory
cortex: evidence from event-related brain potentials
Received: 25 March 2004 / Accepted: 19 December 2004 / Published online: 10 May 2005
Ó Springer-Verlag 2005
Abstract Several behavioural studies have shown that
directing one’s gaze at a body part reduces detection
speed and enhances discrimination of tactile stimuli at
that location. We investigated how vision of a body part
stimulated and manipulations of gaze direction affect
tactile processing. Participants’ gaze was directed to one
of their hands, with vision of this hand either available
or prevented in different experiments. They had to detect
infrequent tactile targets among non-targets. Somato-
sensory event-related brain potentials were recorded in
response to stimulation of the hand towards which gaze
was directed (G+ trials) and in response to stimulation
of the other hand (G– trials). When vision (V+) of the
hand gaze was directed at was available (G+V+), an
early positivity overlapping with the P45 and N80
component was observed for G+V+ trials relative to
G–V– trials. In contrast, when the hands were occluded
from view (V–), an enhanced N140 component followed
by a late negativity was observed for G+V– as com-
pared to G–V– trials. It is suggested that vision of the
body part stimulated can modulate processing in pri-
mary somatosensory cortex (S1), while effects of gaze
direction in the absence of vision of the body part tou-
ched are located in higher order somatosensory areas.
Such effects of vision and gaze on tactile processing may
be mediated by pathways from multimodal brain regions
to somatosensory cortex.
Keywords Gaze direction Æ Vision Æ Mechanical
tactile stimuli Æ Event-related brain potentials Æ
Somatosensory cortex
Introduction
If we expect to be touched at a certain location, we tend
to look at that body part even if we cannot see the
application of the tactile stimulus. One reason for this
might be that we tend to rely more on visual input than
on touch when localizing external events. Another rea-
son might be that vision aids tactile perception. The act
of looking at a body part comprises both adjustments of
gaze direction as well as vision. Here, we defined ‘‘gaze’’
as the orientation of the eyes towards a specific body
part, and ‘‘vision’’ as the actual sensory perception of
this body part. Although gaze and vision usually operate
in unison, this is not always the case. When directing
gaze at a body part it is not guaranteed that we see the
particular body part, as we may be blindfolded or the
body part may be occluded from view (gaze without
vision). Likewise, when a body part is reflected in a
mirror, vision is present although gaze is not in fact
directed to the physical location of this body part (vision
without gaze). Thus, when looking at a body part where
we expect to be touched, both gaze direction and vision
may contribute jointly or independently to our percep-
tion of the subsequent tactile sensation.
Several behavioural studies have investigated the ef-
fect of gaze and of vision on the processing of tactile
stimuli in various discrimination and detection tasks.
These studies have investigated the independent or
combined effects of gaze direction and vision on tactile
processing. To investigate pure effects of vision, Kennett
et al. (2001) examined 2-point threshold discrimination
on the forearm. They found that tactile discrimination
was better under conditions when participants were
viewing their forearm compared to when the arm was
occluded from view, and also relative to a condition
B. Forster Æ M. Eimer
School of Psychology,
Birkbeck College,
University of London,
UK
Present address: B. Forster (&)
Department of Psychology,
City University,
Northampton Square,
London EC1V 0HB, UK
E-mail: b.forster@city.ac.uk
Tel.: +44-20-70404553
Exp Brain Res (2005) 165: 8–18
DOI 10.1007/s00221-005-2274-1