Haptic awareness changes when lying down

Kaian Unwalla,David I Shore,Michelle L Cadieux

doi:10.1038/s41598-021-92192-1

Abstract

Accurate localization of touch requires the integration of two reference frames—an internal (e.g., anatomical) and an external (e.g., spatial). Using a tactile temporal order judgement task with the hands crossed over the midline, we investigated the integration of these two reference frames. We manipulated the reliability of the visual and vestibular information, both of which contribute to the external reference frame. Visual information was manipulated between experiments (Experiment 1 was done with full vision and Experiment 2 was done while wearing a blindfold). Vestibular information was manipulated in both experiments by having the two groups of participants complete the task in both an upright posture and one where they were lying down on their side. Using a Bayesian hierarchical model, we estimated the perceptual weight applied to these reference frames. Lying participants on their side reduced the weight applied to the external reference frame and produced a smaller deficit; blindfolding resulted in similar reductions. These findings reinforce the importance of the visual system when weighting tactile reference frames, and highlight the importance of the vestibular system in this integration.

Highlights

Accurate localization of touch requires the integration of two reference frames—an internal and an external
One-sample t-tests comparing the proportion correct difference (PCD) score to 0 confirmed that the crossed-hands deficit was evident with intact vision (Upright: t(19) = 6.16, p < 0.001, d = 1.38; Side: t(19) = 2.37, p = 0.03, d = 0.53) and while blindfolded (Upright: t(19) = 6.12, p < 0.001, d = 1.37; Side: t(19) = 2.23, p = 0.03, d = 0.51); the size of the deficit when lying down and blindfolded was less than 5% the size of the deficit seen when upright with vision
Based on the modelling of these data, we conclude that this reduced deficit emerges primarily from reducing the weight to the external reference frame

Summary

Introduction

Accurate localization of touch requires the integration of two reference frames—an internal (e.g., anatomical) and an external (e.g., spatial). Lying participants on their side reduced the weight applied to the external reference frame and produced a smaller deficit; blindfolding resulted in similar reductions These findings reinforce the importance of the visual system when weighting tactile reference frames, and highlight the importance of the vestibular system in this integration. Multiple cues contribute to the subjective vertical, such as the orientation of mono-oriented objects in the visual environment, the impact of gravity on the vestibular organs, and the pressure felt from surfaces underneath our b ody[10,11] Lying down misaligns these sources of information with respect to the direction of upright and reduces the reliability of the subjective vertical

Methods

Results

Conclusion