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 underly- ing pain perception and central sensitization. While previous studies have primarily explored TGI using large-area ther- mal 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. Ex- periments with 17 healthy participants assessed two tempera- ture 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.