Importance of temporal cues for tactile spatial-frequency discrimination

While scanning a textured surface with fingers, tactile information is enco ded both spatially, by differential activation of adjacent receptors, and t emporally, by changes in receptor activation during movements of the finger s across the surface. We used a tactile discrimination task to examine the dependence of human tactile perception on the availability of spatial and t emporal cues. Subjects discriminated between spatial frequencies of metal g ratings presented simultaneously to both hands. Tactile temporal cues were eliminated by preventing lateral hand movements; tactile spatial cues were eliminated by using gloves with an attached rubber pin. Analysis revealed s eparation of the subjects into two groups: "spatiotemporal" (ST) and "laten t-temporal" (LT). Under normal conditions, the performance of ST subjects w as significantly better than that of the LT subjects. Prevention of lateral movements impaired performance of both ST and LT subjects. However, when o nly temporal cues were available, the performance of ST subjects was signif icantly impaired, whereas that of the LT subjects either improved or did no t change. Under the latter condition, LT subjects changed strategy to scann ing with alternating hands, at velocities similar to the velocities normall y used by ST subjects. These velocities generated temporal frequencies betw een 15 and 30 Hz. The LT subjects were unaware of their improved performanc e. Nine of ten LT subjects significantly improved their performance under n ormal conditions when trained to scan gratings using alternating hands and velocities similar to those used by ST subjects. We conclude that (1) tempo ral cues are essential for spatial-frequency discrimination, (2) human subj ects vary in the tactile strategies they use for texture exploration, and ( 3) poor tactile performers can significantly improve by using strategies th at emphasize temporal cues.