Peripersonal space boundaries around the lower limbs

K D Stone,A Keizer,H C Dijkerman,M Kandula

doi:10.1007/s00221-017-5115-0

Abstract

Neurophysiological investigations in non-human primates have shown that bi- and tri-modal fronto-parietal neurons exist that respond to touch on the body and visual (and/or auditory) stimuli near the body. The receptive fields of these neurons extend into space around the body, producing a zone wherein multisensory information is readily integrated. This space around the body, known as peripersonal space (PPS), has also been investigated behaviourally in humans. Some studies have focused on how far into depth the spatial boundaries of PPS extend. Most of these investigations have focused on the upper body (e.g., hands, face, trunk), while little is known about the size of PPS for the lower body (i.e. legs and feet). Thus, the aim of the current study was to delineate a PPS boundary around the lower limbs in healthy participants using a multisensory interaction task. Participants made speeded responses to the presence of vibrations applied to the toes while a task-irrelevant visual stimulus approached towards (Experiment 1) or receded from (Experiment 2) the feet. Participants responded significantly faster to tactile stimuli when the visual stimulus was within approximately 73 cm from the feet, but only when it approached (and not receded from) the legs. This is the first study, to our knowledge, to outline the size of PPS for the lower limbs. These findings could provide insight into the mechanisms underlying multisensory integration in the lower limbs, and add to the current body of knowledge on PPS representations.

Highlights

In daily life, we encounter many instances where we must interact with objects in the space near our bodies
If the data were better described by a linear function, with the x-axis representing the visual stimulus distance for the feet and the y-axis representing tactile reaction times, this suggests that participants responded faster to the tactile stimulus as the visual stimulus got closer or it suggests that participants consistently responded to the tactile stimulus at the same rate, producing a horizontal line
Participants were asked to respond to a vibro-tactile stimulus on the toes which was administered at different time points during the trajectory of an approaching (Experiment 1) or receding (Experiment 2) visual stimulus

Summary

Introduction

We encounter many instances where we must interact with objects in the space near our bodies. Early neurophysiological studies in non-human primates have shown that there are special fronto-parietal neurons that respond to an object touching a body part and the presence of an object near that same body part (Graziano et al 1994, 1997; Fogassi et al 1996; Graziano and Cooke 2006) These neurons are bi- and tri-modal in nature; their tactile receptive fields overlap with visual and/or auditory receptive fields that extend into space around the body.

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Conclusion