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.
Highlights
Previous studies have demonstrated that observation of a dummy hand being stroked or moving at the same time as the hidden hand evokes a feeling that the dummy hand is one’s own
To determine whether active touch is mediated by visual information, we investigated whether the perception of hardness via active touch is affected by vision using an mirror visual feedback (MVF) experiment
We investigated whether the perception of hardness during active touch is affected by visual input using an MVF scenario
Summary
Previous studies have demonstrated that observation of a dummy hand being stroked or moving at the same time as the hidden hand evokes a feeling that the dummy hand is one’s own (rubber hand illusion, RHI; static dummy hand: Botvinick and Cohen, 1998; Ehrsson et al, 2004; moving dummy hand: Dummer et al, 2009; Kalckert and Ehrsson, 2012; Effect of Visual Information on Active TouchJenkinson and Preston, 2015). Similar illusory hand ownership is experienced when hand images are presented on video (Jeannerod, 2003; Tsakiris et al, 2006; Shimada et al, 2009), via mirror reflection (Bertamini et al, 2011; Medina et al, 2015), or using computer graphics (Hoermann et al, 2012; Bekrater-Bodmann et al, 2014; Kokkinara and Slater, 2014) Observing both dummy hands and fake hand images elicits a change in the proprioceptive sensation of hand position (Botvinick and Cohen, 1998; Holmes et al, 2004, 2006; Tsakiris and Haggard, 2005). After induction of the RHI, observation of the dummy hand being irradiated by a red laser (Durgin et al, 2007) or touched by an ice cube (Kanaya et al, 2012) elicits a warm or cool sensation, respectively, even though no thermal or neutral stimulation is delivered to the hidden hand
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