Noninformative vision improves the spatial resolution of touch in humans

Abstract

Research on sensory perception now often considers more than one sense at a time. This approach reflects real-world situations, such as when a visible object touches us. Indeed, vision and touch show great interdependence: the sight of a body part can reduce tactile target detection times [1], visual and tactile attentional systems are spatially linked [2], and the texture of surfaces that are actively touched with the fingertips is perceived using both vision and touch [3]. However, these previous findings might be mediated by spatial attention [1, 2] or by improved guidance of movement [3] via visually enhanced body position sense [4--6]. Here, we investigate the direct effects of viewing the body on passive touch. We measured tactile two-point discrimination thresholds [7] on the forearm while manipulating the visibility of the arm but holding gaze direction constant. The spatial resolution of touch was better when the arm was visible than when it was not. Tactile performance was further improved when the view of the arm was magnified. In contrast, performance was not improved by viewing a neutral object at the arm's location, ruling out improved spatial orienting as a possible account. Controls confirmed that no information about the tactile stimulation was provided by visibility of the arm. This visual enhancement of touch may point to online reorganization of tactile receptive fields.

Multisensory distortions of the hand have differential effects on tactile perception

“…In line with previous studies (Kennett et al, 2001;de Vignemont et al, 2005) we expected illusory stretching and shrinking to have different effects on tactile perception. Instead, our findings suggested that both stretching and shrinking the finger significantly improved tactile perception compared to a veridical baseline condition.…”

“…Given that previous studies have reported increased tactile acuity following visual enlargement and illusory elongation of a body part (Kennett et al, 2001;de Vignemont et al, 2005) we predicted that correct tactile detections would increase significantly (as a result of increased sensitivity) when the finger appeared to be stretched, compared to the veridical-baseline condition. Shrinking the finger was expected to result in one of two out comes; either no difference in tactile perception between the baseline and shrunken finger conditions (de Vignemont et al, 2005), or a significant reduction compared to baseline (Kennett et al, 2001). The detached condition was included to examine how observing body discontinuity would affect tactile perception.…”

“…Visual modulation of touch is also dependent on particular measures of tactile judgment; viewing the stimulated hand has been found to increase tactile acuity in two-point discrimination tasks in healthy individuals (Kennett, Taylor-Clarke & Haggard, 2001; Taylor-Clarke, Kennett & Haggard, 2004) and in patients suffering from somatosensory deficits (Serino, Farnè, Rinaldesi et al, 2007), whereas non-informative vision of the stimulated body part has been found to impair detection and discrimination of simple near threshold tactile stimuli, but to enhance discrimination between above threshold tactile stimuli (Harris, Arabzadeh, Moore, & Clifford, 2007).…”

“…For instance, whilst visually attending to the hand reduces two-point discrimination thresholds, magnifying the stimulated hand has been found to further improve this effect (Kennett et al, 2001). In line with this finding de Vignemont, Ehrsson and Haggard, (2005) showed that illusory elongation of perceived finger length significantly increased the perceived distance between two simultaneous tactile contacts.…”

Introduction to special issue on body representation: feeling, seeing, moving and observing

“…This can be vision of the body itself (Kennett et al 2001) or visual stimuli presented close to the body. For example, in the crossmodal congruency task developed by Spence et al visual stimuli presented close to the body can inXuence judgements about tactile stimuli presented at the same time (for a review, see Maravita et al 2003).…”