Tactile pattern perception and its perturbations.

One of the problems encountered in conveying information to the skin by means of vibratory patterns is that presenting patterns, such as letters of the alphabet, in close spatial and temporal proximity, may result in considerable masking. Generally, there is more interference when the masking stimulus follows the target (backward masking) than when it precedes it (forward masking). Masking has also been demonstrated with vibrotactile patterns derived from speech signals. Masking may be reduced by increasing the temporal and spatial separation between patterns; however, other problems may arise when such separations are made. Because stimulus onset asynchrony appears to be the critical temporal dimension for masking, it may prove difficult to reduce masking by increasing the temporal separation between patterns without also reducing the rate at which the patterns are presented. Increasing the spatial separation between patterns may lead to problems in combining the patterns from spatially distinct sites on the skin. This latter difficulty may be due to problems in attending to several sites of stimulation simultaneously.