Spatial discrimination of vibrotactile stimuli around the head

Several studies evaluated vibrotactile stimuli on the head to aid orientation and communication. However, the acuity for vibration of the head's skin still needs to be explored. In this paper, we report the assessment of the spatial resolution on the head. We performed a 2AFC psychophysical experiment systematically varying the distance between pairs of stimuli in a standard-comparison approach. We took into consideration not only the perceptual thresholds but also the reaction times and subjective factors, like workload and vibration pleasantness. Results show that the region around the forehead is not only the most sensitive, with thresholds under 5mm, but it is also the region wherein the spatial discrimination was felt to be easier to perform. We also have found that it is possible to describe acuity on the head for vibrating stimulus as a function of skin type (hairy or glabrous) and of the distance of the stimulated loci from the head midline.