Proceedings of The Physiological Society

Physiology 2016 (Dublin, Ireland) (2016) Proc Physiol Soc 37, PCA285

Poster Communications

Tactile history influences perceived location of touch stimuli

J. Brooks1,2, T. Seizova-Cajic3, J. L. Taylor2,1

1. School of Medical Sciences, University of New South Wales, Sydney, New South Wales, Australia. 2. Neuroscience Research Australia, Sydney, New South Wales, Australia. 3. Faculty of Health Sciences, University of Sydney, Sydney, New South Wales, Australia.

Why at times we can feel touch on our skin but not know its location is perplexing. Weak electro-cutaneous stimuli applied to the forearm are erroneously mislocalised towards the forearm's middle [1]. We found that this phenomenon also holds true for mechanical touch stimuli. Therefore, it is does not simply arise from the stimulus modality. This is likely common to other senses when stimuli are presented under conditions of uncertainty. The responsible mechanism is important, as perceiving the ‘what' and ‘when' of things in our environment does not afford an action without knowing the ‘where'. For example, part of the reason more accidents occur in foggy conditions is underestimation of driving speed [2]. One salient reason for an error of ‘where' under uncertainty is the perceptual integration of the recent history of stimuli. We tested if the perceived ‘where' was biased toward the centre of the forearm or toward the centre of the recent stimuli distribution. We touched volunteer participants (n=16) on the forearm with a filament that was barely perceptible. We also used a filament that was manyfold stronger. At each of four locations, stimuli were applied 20 times, in random order. On separate days the locations were centred about either the proximal or distal end of the forearm. Using their other arm participants pointed to where they felt the touch. Surprisingly, responses to strong stimuli were shifted 1.2 ±0.4cm (mean±S.E.M) toward the mid-forearm. With perceived locations expressed relative to actual locations of the stimuli, this shift was seen as a significant main effect of distribution (proximal vs distal forearm) in a three way repeated measures ANOVA (distribution X location X time; F(1,15) = 9.71, p = 0.007). The reason for this is not clear. As subjects returned their pointing hand to a single reference point between trials it might have been a strategy to reduce energy costs of movement. Perceived locations of weak stimuli were computed relative to strong stimuli. They were biased toward the centre of the distribution of stimuli presented in a given experimental session. Regression analysis showed a significant overall compression of 7.8 ±1.7% (p<0.001). This bias suggests that sensory input in the previous minutes or seconds is integrated with the current input to give the ‘where' perception of touch. This likely functions as a mechanism to minimise localisation errors when the location of touch is uncertain.

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