Perceptual masking on a tactile apparent motion trajectory

In vision, a target stimulus presented on aa apparent motion trajectory becomes undetectable. In the present study, we investigated whether this perceptual masking phenomenon also occurs in tactile perception. Three vibrotactile stimulators were placed along the hand-to-elbow axis on the medial side of the participant's left arm. When the vibrations were presented alternately from the upper and lower ends, an apparent motion was perceived (apparent motion condition). During the apparent motion presentation, a trial with or without a target stimulus was presented at random timing from the central stimulator. A control condition was also introduced in which the apparent motion was not perceived because the vibrations were presented simultaneously from the upper and lower oscillators. We calculated an index of sensitivity to the target stimulus based on the signal detection theory, and found that the sensitivity was lower in the apparent motion condition than in the control condition. On the other hand, there was no difference in the index of judgment criterion (bias). These results indicate that a perceptual masking effect, i.e., inhibition of tactile input detection, occurs on the tactile apparent motion trajectory.