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Cold fingers need a Human Touch

December 26, 201316:07

Already my earlier work on proprioceptive drift in the Rubber Hand Illusion left me confused and somewhat skeptical that the subjective experience of owning a rubber hand can be measured by proxy of a more objective measure, like recalibration of perceived hand position. When we measured the results described in my new paper: The Human Touch: Skin Temperature during the Rubber Hand Illusion in Manual and Automated Stroking Procedures, this confusion grew even larger.

To provide some scientific background: If humans see a rubber hand being stroked in the exact time and location that they feel their own, occluded hand being stroked, they get the strong and uncanny subjective feeling that this hand is somehow a part of their body (Rubber Hand Illusion). Among the physiological correlates of the feeling that the rubber hand is part of one’s body is a temperature drop in the stimulated hand (Moseley et al., 2008, PNAS). In the MSc project of Andrew Wold (in collaboration with his former boss Hans-Otto Karnath, Tübingen, 2010), we tried to replicate this result in the robotic stroking setup that I developed for my earlier research. This setup gives rise to a powerful illusory feeling to own the rubber hand.

Main result: hand cooling for the robotic stroking (top) and manual stroking (bottom) setup

Despite our best efforts, we could not replicate the cooling effect; we did not even observe a trend. However, when we copied the original, manual stroking procedure, we observed the same hand cooling reported in the literature (even though it also occurred, to a lesser extent, in the no-vision control condition). This difference between setups does not correspond to a difference in subjective experience, and I have no good explanation for why this is the case – the only thing i can conclude from this research is that also this temperature drop is not directly linked to subjectively experienced body ownership in the RHI and is evidently driven or modulated by other, external factors. The multisensory integration processes involved in body image perception are surely among the least well understood in the field and are truly difficult to study.