Chapter 20: Extended Body Hypothesis and Peripersonal Space

Extended Body Hypothesis and Peripersonal Space begins by contrasting futuristic artistic modifications, such as those by Stelarc, with everyday tool use to determine if artifacts merely extend the range of action or fundamentally alter the spatial representation of the body itself. The text examines neuroscientific evidence regarding peripersonal space, citing studies on macaque neural plasticity and human kinematics to demonstrate that using reach-extending tools triggers a dynamic update of the body schema, effectively causing the brain to process the tool as a lengthened limb. A critical distinction is established between transitive sensations, where users directly perceive external properties like texture or resistance at the tip of a tool (similar to a blind person's cane), and intransitive sensations, such as pain, itch, or tickle, which surprisingly remain confined to the biological body. The author argues that while tools achieve sensorimotor and spatial embodiment, they fail to achieve affective embodiment; because users do not experience genuine ownership or nociception within the tool, the cognitive system maintains a stable "body by default" that ensures biological protection and allows for rapid recalibration once the tool is discarded. Finally, the chapter critiques the concept of exosomesthesia (feeling touch in external objects) by analyzing phenomena like the rubber hand illusion and referred sensations in empty space, concluding that these experiences are driven by predictive processing within a body-centered reference frame rather than a complete detachment of sensation from the biological form.