Left tactile extinction following visual stimulation of a rubber hand

TLDR

Neuropsychological studies show that the human brain constructs visual maps of space around body parts, and in right‑brain‑damaged patients with tactile extinction, a hand‑centred visual peripersonal space is demonstrated by cross‑modal extinction occurring mainly near the hand. The study reports the first evidence that a hand‑centred visual peripersonal space can be coded relative to a seen rubber hand, as if it were a real hand. The authors attribute the effect to vision dominating proprioception, allowing a plausible‑looking fake hand to deceive the peripersonal space system. In left tactile extinction patients, a visual stimulus near a seen right rubber hand induced strong cross‑modal extinction similar to that near the real hand, but this effect disappeared when the rubber hand was in an implausible posture.

Abstract

In close analogy with neurophysiological findings in monkeys, neuropsychological studies have shown that the human brain constructs visual maps of space surrounding different body parts. In right-brain-damaged patients with tactile extinction, the existence of a visual peripersonal space centred on the hand has been demonstrated by showing that cross-modal visual–tactile extinction is segregated mainly in the space near the hand. That is, tactile stimuli on the contralesional hand are extinguished more consistently by visual stimuli presented near the ipsilesional hand than those presented far from it. Here, we report the first evidence in humans that this hand-centred visual peripersonal space can be coded in relation to a seen rubber replica of the hand, as if it were a real hand. In patients with left tactile extinction, a visual stimulus presented near a seen right rubber hand induced strong cross-modal visual–tactile extinction, similar to that obtained by presenting the same visual stimulus near the patient's right hand. Critically, this specific cross-modal effect was evident when subjects saw the rubber hand as having a plausible posture relative to their own body (i.e. when it was aligned with the subject's right shoulder). In contrast, cross-modal extinction was strongly reduced when the seen rubber hand was arranged in an implausible posture (i.e. misaligned with respect to the subject's right shoulder). We suggest that this phenomenon is due to the dominance of vision over proprioception: the system coding peripersonal space can be `deceived' by the vision of a fake hand, provided that its appearance looks plausible with respect to the subject's body.