Working memory is a system that actively holds information to make it available for further processing. Compared
to the working memory associated with vision and audition, the human characteristics of tactile working memory
are largely unknown. In this study, we collected behavioral evidence of delay-dependent tactile grating orientation discrimination
in humans. Nine healthy subjects participated in the experiment. During each trial, two of seven tactile grating
domes of either similar or different orientation were presented to the subject’s right index fingertip. The interstimulus delays
used in the experiment were 1, 5, 10, 15, 20, 25 and 30 seconds. The subjects were asked to discriminate whether the
two orientations were the same. We found that the performance of tactile orientation discrimination improved with larger
differences between the presented stimulus orientations. We also found a same/different effect, in which the accuracy and
reaction time (RT) resulting from the same-orientation discrimination condition differed from that of the differentorientation
discrimination condition. Interestingly, the existence of delay dependence was found under the sameorientation
discrimination condition, in which the performance was reduced as the delay time was increased. However, we
did not find delay dependence in the different-orientation discrimination condition. These findings of non-identical tactile
stimulus discrimination can be understood in the context of tactile memory processing.
Keywords: Decision making, delay, passive touch, somatosensory, tactile orientation discrimination, working memory.
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