Body part-centered and full body-centered peripersonal space representations

Abstract

Dedicated neural systems represent the space surrounding the body, termed Peripersonal space (PPS), by integrating visual or auditory stimuli occurring near the body with somatosensory information. As a behavioral proxy to PPS, we measured participants’ reaction time to tactile stimulation while task-irrelevant auditory or visual stimuli were presented at different distances from their body. In 7 experiments we delineated the critical distance at which auditory or visual stimuli boosted tactile processing on the hand, face, and trunk as a proxy of the PPS extension. Three main findings were obtained. First, the size of PPS varied according to the stimulated body part, being progressively bigger for the hand, then face, and largest for the trunk. Second, while approaching stimuli always modulated tactile processing in a space-dependent manner, receding stimuli did so only for the hand. Finally, the extension of PPS around the hand and the face varied according to their relative positioning and stimuli congruency, whereas the trunk PPS was constant. These results suggest that at least three body-part specific PPS representations exist, differing in extension and directional tuning. These distinct PPS representations, however, are not fully independent from each other, but referenced to the common reference frame of the trunk.

Peripersonal space boundaries around the lower limbs

“…Critically, these reaction times within the approximated PPS are significantly faster than reaction times to unimodal tactile stimulation (i.e., when no visual stimulus is presented in conjunction with the tactile stimulus). Notably, when the stimulus instead recedes from the body, this sigmoidal relationship (usually) disappears (Canzoneri et al 2012;Teneggi et al 2013;Noel et al 2015;Serino et al 2015).This aligns with the aforementioned neurophysiological studies that have shown that neurons in the PPS network preferentially respond to stimuli approaching (in contrast to receding from) the body (Colby et al 1993;Graziano and Gross 1995;Fogassi et al 1996;Graziano et al 1997;Duhamel et al 1998).…”

“…Experiment 1 To measure PPS boundaries, we used a visuo-tactile interaction task using dynamic visual stimuli [similar to the audio-visual interaction tasks in Canzoneri et al (2012) and Serino et al (2015) and to investigations in our lab: Kandula et al (2017) andde Haan et al (2016)]. The task and stimuli were designed and controlled by a custom MATLAB script.…”

“…One's boundary between peri-and extra-personal space can be approximated by asking participants to respond to tactile input while in the presence of irrelevant looming auditory or visual information (Canzoneri et al 2012(Canzoneri et al , 2013bNoel et al 2015;Serino et al 2015;de Haan et al 2016;Kandula et al 2017), as the PPS network is particularly sensitive to dynamic (especially approaching) sensory information. In such a paradigm, a tactile stimulus (vibration) is applied to the participants' limb at different time points along the trajectory of a looming auditory or visual stimulus, and participants are asked to respond (as quickly as possible) to the tactile stimulus only.…”

“…The boundary between PPS and EPS for these body parts has been approximated to be around 30-50 cm for the hands and 60 cm for the head using the paradigm described above [see Serino et al (2015) for a comprehensive examination of body part-centered PPSs]. With respect to the trunk (i.e., upper back/chest), its PPS representation tends to extend much further into space when compared to the hands or head, ranging from 65 to 100 cm.…”

“…It is not surprising, however, that the trunk PPS is modulated also by movement of the legs, as both body parts are involved in full-body actions. Serino et al (2015) speculate that body parts responsible for "whole-body actions" might have tactile-receptive fields with size-appropriate overlapping visual (or auditory)-receptive fields that extend even further into space than body parts whose action space is more confined (e.g., hands are confined to arm space). In other words, it seems that the size of the PPS around a body part is (at least partly) related to the action produced by the specific body part, rendering PPS not only a defensive space but also an action space [see de Vignemont and Iannetti (2015) for a stimulating discussion on the matter].…”