触覚の生じる場所 : 時間順序判断からの示唆(感覚-知覚-行動の神経基盤を探る,第22回大会 シンポジウム1)

抄録

It is generally accepted that the brain can resolve the order of two stimuli that are separated in time by 30ms. This applies to temporal order judgment of two tactile stimuli, delivered one to each hand, as long as the arms are uncrossed. However, crossing the arms caused many subjects to misreport the temporal order. In a quarter of subjects, the judgment was clearly inverted when the two stimuli were separated by 100-300ms. The reversal was not due to simple confusion of hands, because correct judgment was recovered at longer intervals (e.g., 1.5s). These results suggest that subjects cannot be basing their judgments solely on the locations of stimuli on the body surface, but rather on their locations in space. When the stimuli were delivered to the tips of sticks held in each hand, the judgment was altered by crossing the sticks without changing the spatial locations of the hands. Thus, the judgment does not simply depend on the spatial locations of the hands per se, where the mechanoreceptors are located. From the results, we suggest that tactile stimuli are ordered in time only after they are referred to relevant locations in space, where the hands and fingers themselves, or the tips of tools are located.