Abstract
Tracking tasks, such as monitoring traffic while driving or supervising children on a playground, would seem to require continuous visual attention. In fact, we can track multiple moving objects even through disruptions to the task, such as looking away. How do we do this? We have previously suggested a mechanism that stores information about tracked objects offline during disruption, so the visual system can perform a secondary task, then later resume tracking without complete loss (Horowitz et al., 2006).
Here we studied the timecourse of target recovery following a brief disruption. Participants tracked a set of moving targets among identical moving distractors. During tracking, all objects disappeared simultaneously, then reappeared after a brief gap. Objects continued to move during the gap. At a delay between 0-1280 ms following reappearance, one object was probed. Participants identified the probed object as a target or distractor. In different experiments, we varied the gap duration from 133-507 ms, the tracking load from 1-4 targets, and the set of probe delays. In all experiments, RT decreased over probe delays of roughly 0-50 ms following reappearance, then remained constant.
We assumed that the visual system takes some amount of time to recover the targets following the gap. Under this assumption, RT should decline linearly as a function of probe delay with a slope of -1. Recovery time may be estimated as the probe delay at which RT reaches baseline and stops declining. Recovery time was estimated to be about 45 ms in all experiments, regardless of gap duration or tracking load. These results suggest that recovery of tracked objects following disruption occurs rapidly and in parallel.
Supported by NIH Grant MH65576 to TSH.