Can temperature cause surprising sensations?

An exhibit table and headboard with the text 'Can Temperature Cause Surprising Sensations?'. There are a row of discs on the table top.

The thermal grill tactile illusion uses mild temperatures to create an illusion of discomfort.

How it works

Touch metal coils that have been warmed and cooled to around 20°C and 40°C respectively, to generate a thermal tactile illusion. (Some people feel nothing, while others may feel a mild stinging sensation.)

Things to try or ask around the exhibit

  • Do the coils feel safe when you touch them separately?
  • Does it feel uncomfortable or slightly painful when you touch the mixed blue-red coils?
  • Which receptors in your skin are being stimulated when you touch the coils?


This thermal grill illusion (discovered in 1896) is still a mystery to scientists, but it seems to involve pain receptors in your skin being activated when you feel a mixture of temperatures that are actually quite safe (about 20°C and 40°C).

When you touch the mixture of warm-cool coils, three types of receptors seem to be activated:

  • warm thermoreceptors are activated by the warm coils,
  • cool thermoreceptors are activated by the cool coils and
  • nociceptors, which create the stinging sensation of pain.

If you pull your hand away as a reflex after touching the mixed coils, it’s probably because your spinal cord processed and responded to the simultaneous warm-cool signals and interpreted it to be painful, before your brain was conscious of what was happening.

Finding the science in your world

If your nervous system didn’t regulate how hot or cold things can be, you could easily burn your flesh with hot or cold burns (like frostbite).

Your skin is embedded with thermoreceptors that respond to either warm or cool temperatures as well as pain or nocioceptors that respond once the temperature goes past certain thresholds (thought to be above 45°C and below 10°C). If you touch a really hot surface (say about 70°C), your pain receptors, rather than your warm thermoreceptors, are activated.