Temporal order and tactile patterns.

Temporal order judgments (TOJs) were obtained for tactile stimuli presented to subjects' fingerpads. In one set of measurements, pairs of spatial patterns were presented successively to a single fingerpad (same-site condition), to two fingers on the same hand (ipsilateral condition), or to two fingers on opposite hands (bilateral condition). The subjects were instructed to report which one of the two patterns was presented first. TOJs were more accurate in the same-site condition than in either the ipsilateral or the bilateral conditions. In the ipsilateral and bilateral conditions, performance improved when judging which one of two locations received a stimulus first, although performance levels were still lower than in the same-site condition. Increasing the size of the pattern set from which the two patterns to be judged were drawn had only a slight effect on same-site performance and no effect on ipsilateral/bilateral performance; however, changing the nature of the patterns had a considerable effect on same-site performance and a smaller effect on ipsilateral/bilateral performance. Introducing an intensity imbalance between members of the pair of stimuli also had a large effect on same-site TOJs: a less intense stimulus tended to be judged as being presented first. In the bilateral condition, however, there was a small effect in the reverse direction: more intense stimuli tended to be judged as being presented first. The intensity imbalance had no effect in the ipsilateral condition. The results suggest that different mechanisms are responsible for TOJs for patterns presented to the same-site and to separate sites and, furthermore, that separate sites may constitute separate channels for spatial information.