Talk: Enacting your body?

An abstract based on the first set of psychological experiments with the Enactive Torch, which were recently conducted at MIC, University of Limerick, has been accepted as a concurrent talk at this year’s Toward a Science of Consciousness conference in Stockholm, Sweden (May 1-8, 2011).

Enacting the body? Use of distal-to-tactile sensory substitution interface does not lead to extension of body image

Tom Froese, Marek McGann, and Anil K. Seth

There is a growing amount of evidence in the cognitive sciences documenting a variety of profound personal and sub-personal transformations entailed by practical tool-use (see Maravita and Iriki 2004). In the neurosciences there is well-known evidence that tools can be incorporated into the body schema during usage. For example, distant object manipulation with rakes leads to an extension of the body schema for the arm (Iriki, et al. 1996). In psychology related effects have been observed in terms of the body image and object perception. For example, when sighted subjects had to complete tasks involving the use of elongated tools, and were subsequently blind-folded and then tapped on their arm, they consistently misjudged the position of the tactile sensations as if their arm had become extended during tool-use (Cardenali, et al. 2009).

What remains unclear is which aspects of tool-use cause these kinds of transformations. Since no such effects are found in control tasks involving the use of laser pointers, tool-based changes of far space to near space, related to reachability, appear to be important (Longo and Lourenco 2006). But is it the fact that elongated tools enable the subject to perceive at a distance, like a blind person using a cane to perceive what is in front of him? Or does it have to do with the fact that such tools enable us to act at a distance, such as when a rake is used to retrieve an object that is outside of reach or when using knife and fork? Comparisons between elongated tools and laser pointers cannot help us to resolve which of these two aspects are necessary and/or sufficient to account for the observed effects (elongated tools enable both factors simultaneously, while laser pointers enable neither of them).

We used a custom-built hand-held sensory substitution device, the Enactive Torch (Froese and Spiers 2007), to investigate this issue. Subjects trained in using this device, which converts distance measurements into tactile vibrations in the hand, readily report a transformation in their perceptual experience that involves the appearance of things ‘out there’ in the world. However, in contrast to the case of using elongated tools, this novel perception at a distance is not accompanied by a change in the possibility for directly acting at a distance. We tested 20 participants with training regimes lasting between 5 minutes to 1 hour, but found no evidence of a transformation in their perceived arm length. This suggests that it is the change in the potential for action, not perception, which is the decisive factor for transformations of the body image.


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