Enhanced heat discrimination in congenital blindness

There is substantial evidence that congenitally blind individuals perform better than normally sighted controls in a variety of auditory, tactile and olfactory discrimination tasks. However, little is known about the capacity of blind individuals to make fine discriminatory judgments in the thermal domain. We therefore compared the capacity to detect small temperature increases in innocuous heat in a group of 12 congenitally blind and 12 age and sex-matched normally sighted participants. In addition, we also tested for group differences in the effects of spatial summation on temperature discrimination. Thermal stimuli were delivered with either a 2.56 or 9 cm2 Peltier-based thermode. We applied for 5-8 s lasting non-painful thermal stimuli to the forearm and asked participants to detect small increments in temperature (ΔT = 0.4, 0.8, 1.2 or 1.6 °C) that occurred at random time intervals. Blank trials (ΔT = 0 °C) were also included to test for false positive responses. We used signal detection theory model to analyze the data. Our data revealed that blind participants have a higher accuracy than the sighted (d′: Blind = 2.4 ± 1.0, Sighted = 1.8 ± 0.7, p = 0.025), regardless of the size of the stimulated skin surface or magnitude of the temperature shift. Increasing the size of the stimulated skin area increased the response criterion in the blind (p = 0.022) but not in the sighted. Together, these findings show that congenitally blind individuals have enhanced temperature discrimination accuracy and are more susceptible to spatial summation of heat.