An Investigation of Tactile Hyperacuityl

Whereas the spatial discriminative capacities of vision have been mapped out in some detail, virtually nothing is known about tactile spatial sensitivity aside from two-point resolution, point localization, and size discrimination. The purpose here was to assess several spatial discriminative capacities of the distal pad of the index finger: discrimination of spatial misalignment, spatial interval discrimination, point localization, and spatial resolution. It was found in some cases that judgments of relative spatial position are remark-ably acute-the thresholds for spatial interval discrimination and for detection of misalign-ment in a three-dot target were less than one-fifth the two-point threshold. The threshold for point localization, determined under what were deemed optimal conditions, was approxi-mately 0.17 mm. These results indicate that under some conditions touch is capable of spatial discriminations nearly as acute as those made by vision, as judged by scaling the discrimination thresholds in terms of the respective resolution thresholds. In the usual textbook treatments of cutaneous sensibility, two measures of spatial sensitivity, two-point resolution and point localization, and the difference between them (Boring, 1930, 1942; Weinstein, 1968; Zigler, 1935) are generally given mention but are rarely discussed in terms of underlying process. Similarly, the study of vision has seen a long period where the different measures of spatial sensitivity (minimum visible, minimum separable, vernier acuity) have received little theoretical attention. Recently, however, there has been a renewed effort to reach an understanding of these and related indices of visual capacity (Andrews