Thermal grill illusion

The thermal grill illusion is a sensory illusion originally demonstrated in 1896 by T. Thunberg. [cite journal|author=Thunberg T|title=Förnimmelserne vid till samma ställe lokaliserad, samtidigt pägäende köld-och värmeretning|journal=Uppsala Läkfören Förh|year=1896|issue=1|pages=489–95.] The illusion is created by an interlaced grill of warm (e.g., 40°C) and cool (20°C) bars. When someone presses a hand against the grill, he or she experiences the illusion of burning heat. But if the person presses against only a cool bar, only coolness is experienced; if the person presses against only a warm bar, only warmth is experienced.

Researches have used the illusion to demonstrate that cold pain sensation is in fact a mixture of both cold and heat pain and that it is only the inhibition of the cold pain "channel" that reveals the heat component.

Notes

References

* Thunberg T., Förnimmelserne vid till samma ställe lokaliserad, samtidigt pägäende köld-och värmeretning. "Uppsala Läkfören Förh". 1896; 1: 489–95.
* Craig AD, Bushnell MC. The thermal grill illusion: unmasking the burn of cold pain. "Science." 1994; 265: 252–5.
* Defrin R, Ohry A, Blumen N, Urca G. Sensory determinants of thermal pain. "Brain." 2002; 125: 501–10. [http://brain.oxfordjournals.org/cgi/content/full/125/3/501]