The effects of a plastic-film covering on vibrotactile pattern perception with the Optacon

Three experiments were conducted to determine whether the perception of vibrotactile patterns presented to the fingertip on the Optacon (a reading machine for blind persons) would be affected by covering the array with a plastic membrane. Occasionally in psychophysical and physiological studies that involve the Optacon, the array is covered with a plastic film to minimize electrical transients during electrophysiological recording and to maintain cleanliness. In the three studies described here, observers performed a spatial acuity task, identified patterns of a previously learned set, and judged the loudness of vibrotactile noise patterns by means of absolute magnitude estimation, on both the covered and the uncovered-array. Performance in the spatial acuity and pattern identification tasks was not affected by the presence of the protective film. The rate of growth of perceived intensity was also the same with and without the plastic film, although there was a slight increase in vibrotactile detection threshold with the film.