Tactile localization depends on stimulus intensity

Few experimental data are available about the influence of stimulus intensity on localization of cutaneous stimuli. The localization behavior of an individual as function of the veridical stimulus sites can be represented in the form of a perceptual map. It is unknown how the intensity of cutaneous stimuli influences these perceptual maps. We investigated the effect of stimulus intensity on trial-to-trial localization variability and on perceptual maps. We applied non-painful electrocutaneous stimuli of three different intensities through seven surface electrodes on the lower arm of healthy participants. They localized the stimuli on a tablet monitor mounted directly above their arm, on which a photograph of this arm was presented. The length of the arm over which the stimuli were localized was contracted when compared to the real electrode positions. This length increased toward veridical with increasing stimulus intensity. The trial-to-trial variance of the localizations dropped significantly with increasing intensity. Furthermore, localization biases of individual stimulus positions were shown to decrease with increasing stimulus intensity. We conclude that tactile stimuli are localized closer to veridical with increasing intensity in two respects: the localizations become more consistent and more accurate.