title: Thermal referral: evidence for a thermoceptive uniformity illusion without touch.
abstract: When warm thermal stimulators are placed on the ring and index fingers of one hand, and a neutral-temperature stimulator on the middle finger, all three fingers feel warm. This illusion is known as thermal referral (TR). On one interpretation, the heterogenous thermal signals are overridden by homogenous tactile signals. This cross-modal thermo-tactile interaction could reflect a process of object recognition, based on the prior that many objects are thermally homogenous. Interestingly, the illusion was reported to disappear when the middle digit was lifted off the thermal stimulator, suggesting that tactile stimulation is necessary. However, no study has investigated whether purely thermal stimulation might induce TR, without any tactile object to which temperature can be attributed. We used radiant thermal stimulation to deliver purely thermal stimuli, which either were or were not accompanied by simultaneous touch. We found identical TR effects in both the original thermo-tactile condition, and in a purely thermoceptive condition where no tactile object was present. Control experiments ruled out explanations based on poor spatial discrimination of warm signals. Our purely thermoceptive results suggest that TR could reflect low-level organization of the thermoceptive pathway, rather than a cognitive intermodal modulation based on tactile object perception.
authors: Institute of Cognitive Neuroscience, University College London, UK.|Centre for studies and researches in Cognitive Neuroscience, University of Bologna, Italy.
authors: Antonio
authors: A
authors: Cataldo
authors: Institute of Cognitive Neuroscience, University College London, UK.|Department of Psychology, Royal Holloway University of London, UK.
authors: Elisa Raffaella
authors: ER
authors: Ferrè
authors: Centre for studies and researches in Cognitive Neuroscience, University of Bologna, Italy.
authors: Giuseppe
authors: G
authors: di Pellegrino
authors: Institute of Cognitive Neuroscience, University College London, UK.
authors: Patrick
authors: P
authors: Haggard
mesh_terms: D000328:Adult; D003952:Diagnostic Imaging; D005260:Female; D005385:Fingers / Q000502:physiology*; D006801:Humans; D007088:Illusions / Q000502:physiology*; D007259:Infrared Rays; D008297:Male; D010812:Physical Stimulation; D013697:Thermosensing / Q000502:physiology*; D014110:Touch / Q000502:physiology*; D055698:Touch Perception / Q000502:physiology*