Hand path priming in manual obstacle avoidance: rapid decay of dorsal stream information.

The dorsal, action-related, visual stream has been thought to have little or no memory. This hypothesis has seemed credible because functions related to the dorsal stream have been generally unsusceptible to priming from previous experience. Tests of this claim have yielded inconsistent results, however. We argue that these inconsistencies may be due to methodological differences in the time between primes and test stimuli. In this study we sought to clarify the effect of time between primes and test stimuli by having participants complete a visually guided manual obstacle avoidance task with varying times between trials. Consistent with a previous study using this task, we found that hand path curvature depended on the presence or absence of an obstacle in the previous trial. This hand path priming effect decayed quickly as the time between trials increased, and was almost, though not entirely, eliminated when 1000 ms separated successive trials. The results are consistent with the hypothesis that the dorsal stream can be primed but that this priming attenuates rapidly. We suggest that this outcome may indicate that the period over which the dorsal stream retains information may be related to the sequential statistics of action.