Tactile spatial sensitivity and anisotropy.

A gap detection task was examined for its usefulness as a measure of tactile spatial sensitivity and as a measure of anisotropy. In Experiment 1, sensitivity was measured with a gap detection task both with and without a latex glove at three locations on the hand: the fingerpad, fingerbase, and palm. Results showed that sensitivity varied as a function of location and was correlated with changes in the density of innervation of the primary afferent fibers. In accord with other measures of spatial sensitivity, the glove had a moderate effect on sensitivity in the gap detection task. The results both with and without the glove were more similar to those obtained using another measure of spatial sensitivity, the grating orientation task, than to those obtained using the smooth-grooved task, which is considered an intensive measure. In Experiments 2-4, anisotropy was examined using the gap detection and grating orientation tasks, as well as the smooth-grooved task. Locations on the index finger, palm, and arm were tested. Results indicated that anisotropy was revealed only by tasks that relied on spatial cues. The differences between spatial sensitivity measured in the proximal-distal orientation as compared with the lateral-medial orientation varied by location and were as much as 2.35/1. The results are discussed in terms of what they may reveal about the underlying mechanisms responsible for tactile anisotropy.