Lectures and seminars Neuroscience seminar: "Self-knowledge and somatosensory perception"

Abstract

Somatosensory research often considers how the somatic senses convey information about external objects in contact with the body. I will argue that some basic information about both the body and the self must already be present for somatosensory perception to fulfill this role. Each cutaneous mechanoreceptor signals to the brain whether a contact force is present or not. Contact on many such receptors allows the brain to reconstruct the geometric properties of external objects. However, this reconstruction process only works if the brain ‘knows’ where individual receptors are located within the body. How the brain acquires this latent self-knowledge about the ‘receptor mosaic’ has rarely been studied, though some clues come from studies of hyperacuity and retinotopic transfer of learning in the visual system. I will report studies of tactile distance perception which may shed light on this question. First, Weber’s illusion shows that tactile distances feel larger on densely-innervated than on sparsely-innervated body parts. This might suggest that the brain lacks any internal model of the receptor mosaic and responds only to the strength of signals reaching the cortex from the receptors, and the intracortical interactions between such signals. However, the strength of this illusion is much lower than such receptor-based theories would predict. It is suggested that the brain must contain some secondary transformation process for reconstructing geometric properties of body parts, and of objects touching them, subsequent to the disproportionate signals that initially reach the cortex from the receptors. This form of latent self-knowledge would be a condition of possibility for tactile exteroception. Many lines of this argument are prefigured by Immanuel Kant’s concept of synthetic a priori knowledge.