Psychologically induced cooling of a specific body part caused by the illusory ownership of an artificial counterpart

Abstract

The sense of body ownership represents a fundamental aspect of our self-awareness, but is disrupted in many neurological, psychiatric, and psychological conditions that are also characterized by disruption of skin temperature regulation, sometimes in a single limb. We hypothesized that skin temperature in a specific limb could be disrupted by psychologically disrupting the sense of ownership of that limb. In six separate experiments, and by using an established protocol to induce the rubber hand illusion, we demonstrate that skin temperature of the real hand decreases when we take ownership of an artificial counterpart. The decrease in skin temperature is limb-specific: it does not occur in the unstimulated hand, nor in the ipsilateral foot. The effect is not evoked by tactile or visual input per se, nor by simultaneous tactile and visual input per se, nor by a shift in attention toward the experimental side or limb. In fact, taking ownership of an artificial hand slows tactile processing of information from the real hand, which is also observed in patients who demonstrate body disownership after stroke. These findings of psychologically induced limb-specific disruption of temperature regulation provide the first evidence that: taking ownership of an artificial body part has consequences for the real body part; that the awareness of our physical self and the physiological regulation of self are closely linked in a top-down manner; and that cognitive processes that disrupt the sense of body ownership may in turn disrupt temperature regulation in numerous states characterized by both.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Skin temperature, tactile processing, and vividness of the illusion. (A) Mean (bold line) and standard deviation (gray line) vividness of the rubber hand illusion (RHI). (B) Mean (bold line) and standard deviation (gray line) hand skin temperature, and mean foot skin temperature (broken line) during control (Ctl) and RHI conditions. (C) Vividness of the RHI and decrease in hand skin temperature for all participants across RHI and asynchronous stroking. Note: When the RHI is more vivid, so too is the decrease in skin temperature on the real hand. (D) Vividness of the RHI and point of subjective simultaneity (PSS). PSS to the right means that the brain is prioritiszing tactile input from the opposite side over identical tactile input from the experimental hand. *, significant difference at P < 0.02.

Fig. 2.

RHI is associated with slowed tactile processing. Mean ± SD point of subjective simultaneity (PSS) for temporal order judgments (TOJs) made during control trials, during asynchronous stroking of the rubber and the experimental hand, and during the rubber hand illusion (RHI). Positive PSS values indicate that the tactile stimulus had to be presented to the experimental hand before the tactile stimulus was presented to the unstimulated hand in order for them to be perceived as occurring at the same time. *, significant difference at P < 0.01.

Fig. 3.

Experimental setup to induce the rubber hand illusion (RHI). (A) The RHI is typically induced by brushing a participant's unseen hand while synchronously brushing a rubber hand in full view of the participant. The orientation of the rubber hand was aligned with that of the real hand. (B) Sites at which skin temperature was measured on the experimental hand (Experiment 1) and on both the experimental (i.e., stimulated) and unstimulated hands (Experiments 2–4).

Fig. 4.

Experiment setup to evaluate tactile processing (Experiment 6). Temporal order judgment (TOJ) task. Pairs of tactile stimuli were delivered at various interstimulus intervals (one to each index finger). The onset of a visual cue at fixation informed the participant that a pair of stimuli was imminent. The participants responded by lifting their toes off of a footpedal under their left or right foot to indicate the perceived side of the first stimulus. Note that a sham vibrator was fixed to the rubber hand. White noise was delivered through the headphones to conceal any noise made by the vibrators.