Human characteristics on tactile angle discrimination by object movement condition

Two-dimensional shapes can be represented on a planar surface as a series of raised edges in which the spatial relationship among all the edges is crossed or parallel. Therefore, the size of the angle between two edges constitutes an important feature of these tactile stimuli. The purpose of present study was to confirm the human capacity for tactile discrimination among raised angles under object movement condition (i.e., hand is static and stimulus is floating). We used a raised angle consisting of five standard angles (30°, 60°, 90°, 120°, and 150°) and 10 comparison angles for each standard angle. In the present study, subjects were asked to identify the larger angle of each pair by object movement condition. The results indicate that the angle discrimination threshold increased as the standard angles increased as well as when the standard angles were smaller than 90°; however, discrimination thresholds remained stable when the standard angles were greater than 90°. We concluded that angle discrimination ability with regard to raised angles is determined by the percentage of impulse rates to which slowly adapting type I (SAI) and rapidly adapting type (RA) afferents respond.