Prof. Dr. Patrick Haggard | Somatosensory Qualities: Blix, Müller and beyond

This talk focusses on simple skin sensations such as temperature and touch, but aims to address foundational questions about perception. Why are sensations so qualitatively different from each other, given that they all rely on a common code of action potentials reaching the CNS? ‘Labelled line’ theories explain sensory quality in terms of a ‘label’ carried by the originating receptor and nerve. This powerful idea of neural specificity has become a textbook dogma, but it is not easy to test. I will report two testing attempts. The first study investigates the quality of microsensations generated at sensitive spots in the human skin. The second study uses suprathreshold stimuli and compares thermal detection ("I felt a stimulus") to thermal discrimination ("It was warm/cold"). This allows to investigate whether detection of a thermal stimulus necessarily causes a percept of its sensory quality, as labelled line theories imply. I will suggest that warmth and cold indeed function as labelled lines from the human skin, despite surprising levels of "quality noise" in sensory perception. The implications of specific signalling and quality noise for the hard problem of consciousness are considered.