A Compact Thermal Grill Illusion Presentation System for Psychophysiological and Engineering Studies

The Thermal Grill Illusion (TGI), a perceptual phenomenon arising from the central integration of spatially interlaced warm and cold stimuli, provides a unique window into the psychological and physiological processes underlying pain perception and central sensitization. While previous studies have primarily explored TGI using large-area thermal arrays, the mechanisms by which TGI can be elicited within a narrow contact area and the relationship between illusory sensations and heat transfer dynamics at the skin interface remain largely unexplored. To address this gap, we developed a compact, smartphone-controlled device capable of delivering precisely regulated, localized TGI stimuli via Peltier elements and copper contact plates. The system incorporates high-accuracy thermistor calibration using the Steinhart–Hart equation and PID-based temperature control within ±1 deg, enabling reproducible manipulation of thermal gradients. Experiments with 17 healthy participants assessed two temperature ranges (20–35 deg, 18–42 deg) applied to the palm and upper arm, demonstrating that greater temperature disparities yield stronger perceptions of warmth and burning, and that site-specific differences emerge under smaller disparities. By enabling controlled induction of TGI in confined regions, this device provides a versatile research tool for investigating the interplay between thermal perception, skin heat transfer, and nociceptive processing—offering a foundation for both basic psychophysiological research and future clinical applications.