Effect of motion sweep duration and number of stations upon interpolation in discontinuous motion

Spatial and temporal vernier offset thresholds were determined for a target moving in discrete spatial steps between stations. In the spatial case, the two bars comprising the target had a relative spatial offset at each station but were synchronous. In the temporal case the two bars appeared at aligning stations with a temporal asynchrony. Temporal thresholds were converted into spatial units by calculating the distance the target would have travelled during the temporal delay. When compared in this way, temporal and spatial thresholds were very similar if the duration of the motion sequence was 300 msec or greater, but at briefer durations temporal thresholds became progressively higher. The possibility that eye pursuit might account for these data was ruled out by recording eye movements and rejecting trials on which tracking occurred. Analysis of eye records revealed the surprising fact that some tracking can occur even when the duration of the motion sequence is as little as 150 msec and random in direction.