Non-informative vision improves spatial tactile discrimination on the shoulder but does not influence detection sensitiv
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RESEARCH ARTICLE
Non‑informative vision improves spatial tactile discrimination on the shoulder but does not influence detection sensitivity Fabrizio Leo1 · Sara Nataletti1,2 · Luca Brayda1,3 Received: 21 February 2020 / Accepted: 6 October 2020 © The Author(s) 2020
Abstract Vision of the body has been reported to improve tactile acuity even when vision is not informative about the actual tactile stimulation. However, it is currently unclear whether this effect is limited to body parts such as hand, forearm or foot that can be normally viewed, or it also generalizes to body locations, such as the shoulder, that are rarely before our own eyes. In this study, subjects consecutively performed a detection threshold task and a numerosity judgment task of tactile stimuli on the shoulder. Meanwhile, they watched either a real-time video showing their shoulder or simply a fixation cross as control condition. We show that non-informative vision improves tactile numerosity judgment which might involve tactile acuity, but not tactile sensitivity. Furthermore, the improvement in tactile accuracy modulated by vision seems to be due to an enhanced ability in discriminating the number of adjacent active electrodes. These results are consistent with the view that bimodal visuotactile neurons sharp tactile receptive fields in an early somatosensory map, probably via top-down modulation of lateral inhibition. Keywords Tactile acuity · Numerosity judgment · Tactile sensitivity · Visuo-tactile · Somatosensory cortex · Visual enhancement of touch
Introduction A consistent body of knowledge has shown that vision can influence touch. For instance, the visual enhancement of touch (VET) effect is the facilitation in spatial acuity we observe when we see the body part being touched without seeing the actual tactile stimulation (Kennett et al. 2001; see, for a review, Eads et al. 2015). While most studies used an object placed in the same position as the body part as a control condition, other studies instead simply occluded the body part from view (e.g. Harris et al. 2007; Catley et al. Communicated by Francesca Frassinetti. Fabrizio Leo and Sara Nataletti have contributed equally to this work. * Fabrizio Leo [email protected] 1
Robotics, Brain, and Cognitive Sciences, Istituto Italiano di Tecnologia, Genoa, Italy
2
DIBRIS, University of Genoa, Genoa, Italy
3
Acoesis s.r.l, Genoa, Italy
2014). Interestingly, the VET does not require proprioceptive orienting towards the stimulated body part, as the participants showed visual enhancement of touch also when they observed the stimulated body part through a monitor (Tipper et al. 1998) or even another person’s body part (Haggard 2006; Beck et al. 2015). Most of the studies investigating the VET effect have tested body locations that can be normally seen by the subjects, in particular the hand and the upper limb but also the foot (Serino et al. 2009). These body parts can be easily the object of visual attention. They are daily before our eyes. It is plausible that these l
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