Vibrotactile frequency recognition: forward and backward masking effects.

Forward and backward vibrotactile recognition masking was investigated in 4 subjects with 240-Hz and 160-Hz targets of 20 ms duration and four 200-Hz masks, using interstimulus intervals (ISIs) ranging from -500 to 500 ms. Two of the masks (short) were 20 ms and two (long) were 200 ms in duration. One of each set of masks was matched in subjective intensity to the targets, but the others were more intense. The range of ISIs over which masking was obtained was comparable to that found by Massaro (1970) with auditory stimuli. Both short masks produced more masking than either long mask except at short ISIs. Larger mask intensities increased masking only at very short ISIs, and longer mask durations increased backward but not forward masking.