While scanning a textured surface with fingers, tactile information is encoded both spatially,
by differential activation of adjacent receptors, and temporally, by changes in receptor activation
during movements of the fingers across the surface. We used a tactile discrimination task to examine
the dependence of human tactile perception on the availability of spatial and temporal cues.
Subjects discriminated between spatial frequencies of metal gratings 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 separation of the subjects into two groups: "spatiotemporal" (ST) and "latent-temporal" (LT).
Under normal conditions, the performance of ST subjects was significantly better than that of the
LT subjects. Prevention of lateral movements impaired performance of both ST and LT subjects.
However, when only temporal cues were available, the performance of ST subjects was significantly
impaired, whereas that of the LT subjects either improved or did not change.
Under the latter condition, LT subjects changed strategy to scanning with alternating hands,
at velocities similar to the velocities normally used by ST subjects. These velocities
generated temporal frequencies between 15 and 30 Hz. The LT subjects were unaware of their
improved performance. Nine of ten LT subjects significantly improved their performance under
normal conditions when trained to scan gratings using alternating hands and velocities similar
to those used by ST subjects. We conclude that (1) temporal cues are essential for
spatial-frequency discrimination, (2) human subjects vary in the tactile strategies they use
for texture exploration, and (3) poor tactile performers can significantly improve by using
strategies that emphasize temporal cues.