Hard and fast rules about the body: contributions of the action stream to judging body space

Abstract

Analogously to the visual system, somatosensory processing may be segregated into two streams, with the body constituting either part of the action system or a perceptual object. Experimental studies with participants free from neurological disease which test this hypothesis are rare, however. The present study explored the contributions of the two putative streams to a task that requires participants to estimate the spatial properties of their own body. Two manipulations from the visuospatial literature were included. First, participants were required to point either backward towards pre-defined landmarks on their own body (egocentric reference frame) or to a forward projection of their own body (allocentric representation). Second, a manipulation of movement mode was included, requiring participants to perform pointing movements either immediately, or after a fixed delay, following instruction. Results show that accessing an allocentric representation of one's own body results in performance changes. Specifically, the spatial bias shown to exist for body space when pointing backward at one's own body disappears when participants are requested to mentally project their body to a pre-defined location in front space. Conversely, delayed execution of pointing movements does not result in performance changes. Altogether, these findings provide support for a constrained dual stream hypothesis of somatosensory processing and are the first to show similarities in the processing of body space and peripersonal space.

Perceptual and Conceptual Distortions of Implicit Hand Maps

“…Similar distortions have been found for the left and right hands ( Longo and Haggard, 2010 , Experiment 3), when the hand is rotated relative to the rest of the body ( Longo and Haggard, 2010 , Experiment 2), when participants respond with vision or while blindfolded ( Longo, 2014 ), whether landmarks are cued using verbal labels or touch ( Mattioni and Longo, 2014 ), and on the dorsal and palmar hand surfaces ( Longo and Haggard, 2012a ), though their magnitude is reduced on the palm. Other studies have described analogous distortions across wider regions of the body surface (e.g., Cardinali et al, 2009 , 2011 ; Hach and Schütz-Bosbach, 2010 ; Hach et al, 2011 ).…”

Self and Body Part Localization in Virtual Reality: Comparing a Headset and a Large-Screen Immersive Display

“…Also, in the study of body representations, pointing to one's own body parts with one's own hand has been employed as a measure of body part locating ability (Paillard, 1999). In studies of personal or body space (the space that your physical body occupies), Hach and colleagues asked participants to point with their hand-with or without the help of a laser pointer-to several landmarks on their own physical bodies while their body except their face was hidden from view (Hach and Schütz-Bosbach, 2010), and to body parts on their own bodies imagined in front of oneself (Hach et al, 2011). Longo and colleagues (Longo and Haggard, 2010;Tamè et al, 2017) had participants indicate with a baton where they perceived specific spatial landmarks on their occluded hands.…”

The magic hand: Plasticity of mental hand representation

“…These studies highlight the detrimental impact that distorted body representations have on our ability to relate with the environment in everyday tasks. However, some degree of body misrepresentation is also common in the healthy population (e.g., Cardinali et al, 2009; Hach, Ishihara, Keller, & Schütz-Bosbach, 2011; Longo & Haggard, 2010, 2012; Longo, Mattioni, & Ganea, 2015; Saulton, Dodds, Bülthoff, & de la Rosa, 2015), which suggests that internal representations are highly malleable. Indeed, a growing body of evidence demonstrates that sensory information can modulate our body representation.…”