Effect of Visual Information on Active Touch During Mirror Visual Feedback

Abstract

Several studies have demonstrated that observation of a dummy or mirror-reflected hand being stroked or moving at the same time as the hidden hand evokes a feeling that the dummy hand is one’s own, such as the rubber hand illusion (RHI) and mirror visual feedback (MVF). Under these conditions, participants also report sensing the tactile stimulation applied to the fake hands, suggesting that tactile perception is modulated by visual information during the RHI and MVF. Previous studies have utilized passive stimulation conditions; however, active touch is more common in real-world settings. Therefore, we investigated whether active touch is also modulated by visual information during an MVF scenario. Twenty-three participants (13 men and 10 women; mean age ± SD: 21.6 ± 2.0 years) were required to touch a polyurethane pad with both hands synchronously, and estimate the hardness of the pad while observing the mirror reflection. When participants observed the mirror reflection of the other hand pushing a softer or harder pad, perceived hardness estimates were significantly biased toward softer or harder, respectively, even though the physical hardness of the pad remained constant. Furthermore, perceived hardness exhibited a strong correlation with finger displacement of the mirrored, but not hidden, hand. The modulatory effects on perceived hardness diminished when participants touched the pad with both hands asynchronously or with their eyes closed. Moreover, participants experienced ownership of the mirrored hand when they touched the pad with both hands synchronously but not asynchronously. These results indicate that hardness estimates were modulated by observation of the mirrored hand during synchronous touch conditions. The present study demonstrates that, similar to passive touch, active touch is also modulated by visual input.

Cortical Regions Encoding Hardness Perception Modulated by Visual Information Identified by Functional Magnetic Resonance Imaging With Multivoxel Pattern Analysis

“…Participants touched the pad with both hands synchronously and asynchronously in the SYNC and ASYNC conditions, respectively, while observing the mirror reflection of the left hand. The results were consistent with our previous behavioral study (Katsuyama et al, 2018): the perceived hardness significantly increased as the hardness of the pad in the mirror reflection increased in the SYNC condition and remained constant in the ASYNC condition (Supplementary Figure 1). This result indicated that the visual modulation of hardness perception was induced even while the participant was lying in the MR scanner.…”

“…In the study, we excluded the possibility that the modulation was induced by sensory assimilation and bimanual coordination by demonstrating that the modulation diminished when participants touched the pad with both hands at different times or with their eyes closed. Furthermore, no significant difference was observed in the finger displacement of the hidden hand during touch (Katsuyama et al, 2018). In this study, we excluded control conditions to validate the effect of sensory assimilation and bimanual coordination on the behavioral task, to acquire a sufficient number of trials with visual modulation for multivariate analysis, which requires multiple runs (in the present study, participants underwent 192 trials, over eight runs in the supine position).…”

“…These studies employed virtual reality techniques to experimentally manipulate the visual and haptic stimuli. In our previous study (Katsuyama et al, 2018), we attempted to examine the effect of visual information on hardness perception by active touch under a more natural condition. For this purpose, we used a mirror visual feedback (MVF) paradigm, in which the reflection of the hand appears to be the hand hidden behind the mirror.…”

“…Many studies have demonstrated that tactile illusions, including the rubber hand illusion, referred sensation, and MVF, are accompanied by illusory ownership toward the fake hands (Botvinick and Cohen, 1998; Ehrsson et al, 2004; Tsakiris et al, 2006; Bertamini et al, 2011; Bekrater-Bodmann et al, 2014). In particular, when the dummy and hidden hands are moving simultaneously, participants also experience the sensation that the dummy hand is moved by their own will; this is known as the sense of agency (Sanchez-Vives et al, 2010; Kalckert and Ehrsson, 2012; Jenkinson and Preston, 2015; Katsuyama et al, 2018). Therefore, we also investigated whether participants experienced the sense of hand ownership of the image of the hand in the mirror during the hardness estimation task with MVF.…”

Mirror Visual Feedback Combining Vibrotactile Stimulation Promotes Embodiment Perception: An Electroencephalogram (EEG) Pilot Study

“…According to graded motor imagery, MVF is recognized as a visual induced motor imagery, which may contain components of motor and sensory experiences (Moseley, 2006;Voisin et al, 2011). As a type of visual induced imagery, MVF could generate referred sensations, where sensory stimulus evoked from one hand is referred to as the contralateral one behind the mirror (Ramachandran et al, 1995;Takasugi et al, 2011;Katsuyama et al, 2018). Therefore, we speculated that the vibrotactile sensory stimulus itself and the strengthened proprioceptive feedback could be referred to the dominant side via MVF and contribute to enhance embodiment.…”