Dynamic Displacement Vector Interacts with Tactile Localization

Lucile Dupin,Patrick Haggard

doi:10.1016/j.cub.2018.12.032

Abstract

SummaryLocating a tactile stimulus on the body seems effortless and straightforward. However, the perceived location of a tactile stimulation can differ from its physical location [1, 2, 3]. Tactile mislocalizations can depend on the timing of successive stimulations [2, 4, 5], tactile motion mechanisms [6], or processes that “remap” stimuli from skin locations to external space coordinates [7, 8, 9, 10, 11]. We report six experiments demonstrating that the perception of tactile localization on a static body part is strongly affected by the displacement between the locations of two successive task-irrelevant actions. Participants moved their index finger between two keys. Each keypress triggered synchronous tactile stimulation at a randomized location on the immobilized wrist or forehead. Participants reported the location of the second tactile stimulation relative to the first. The direction of either active finger movements or passive finger displacements biased participants’ tactile orientation judgements (experiment 1). The effect generalized to tactile stimuli delivered to other body sites (experiment 2). Two successive keypresses, by different fingers at distinct locations, reproduced the effect (experiment 3). The effect remained even when the hand that moved was placed far from the tactile stimulation site (experiments 4 and 5). Temporal synchrony within 600 ms between the movement and tactile stimulations was necessary for the effect (experiment 6). Our results indicate that a dynamic displacement vector, defined as the location of one sensorimotor event relative to the one before, plays a strong role in structuring tactile spatial perception.

Highlights

We applied two successive tactile stimulations, defining a ‘‘tactile vector,’’ on the immobile left wrist or the forehead while the participant moved their index finger to press two keys in succession
We hypothesized that a non-informative movement of one body part—the index finger—could change the perceived localization of tactile stimulations on an immobile body part
Such a finding would imply a dynamic reorganization of tactile perception by other sensorimotor inputs, possibly reflecting a supramodal attention mechanism in spatial perception

Summary

Introduction

We applied two successive tactile stimulations, defining a ‘‘tactile vector,’’ on the immobile left wrist or the forehead (see Figures 1A and 1B and Video S1) while the participant moved their index finger to press two keys in succession. Pressing on each response key caused a tap from one of three tactile stimulators strapped to the wrist (or forehead). The location of the first key and their associated tap location were randomized, so that the displacement vector between the keypresses and the tactile vector between the two stimulations could be in either direction (Figure 1C). The instructed delay between the two taps was 1 s in order to prevent apparent motion effects [14]. Participants adjusted a pointer to indicate the perceived direction of the second tap location relative to the first (Figures 1A and 1D)

Methods

Results

Discussion

Conclusion