Influence of contact conditions on thermal responses of the hand

A series of experiments was conducted to evaluate how contact pressure and surface roughness influence the heat flux conducted out of the skin or object during contact. Changes in skin temperature assist in identifying objects held in the hand. In the first experiment an infrared thermal imaging system was used to measure skin temperature and contact area as participants generated forces ranging from 0.1 to 6 N with their index finger. The results showed that skin temperature decreased by an average of 5.5degC across the range of forces studied and that the changes were greatest between 0.25-0.35 N and from 4-6 N. The second and third experiments examined the effect of the surface roughness of an object on skin temperature and on the perceived coldness of the object. A set of six copper blocks was machined to create a range of surface profiles. There was a slight decrease in skin temperature as the surface roughness of the object increased, contrary to theoretical predictions. Although small, these changes were perceptible as participants consistently chose the rougher of two stimuli when asked to select the cooler stimulus. These results indicate that contact pressure and surface roughness influence the change in skin temperature during contact and that they can have a perceptible influence on the perceived properties of objects held in the hand. Thermal models need to account for these effects if realistic feedback is to be presented in a thermal display.