The Journal of Neuroscience, September 15, 2001, 21(18):7416-7427
Importance of Temporal Cues for Tactile Spatial- Frequency
Discrimination
Efrat
Gamzu and
Ehud
Ahissar
Department of Neurobiology, The Weizmann Institute of Science,
Rehovot 76100, Israel
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.
Key words:
humans; learning; neural code; psychophysics; spatial
coding; tactile discrimination; temporal coding
Copyright © 2001 Society for Neuroscience 0270-6474/01/21187416-12$05.00/0
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