Jeremy Wolfe¹, Cailey Tennyson²; ¹Brigham and Womens Hospital / Harvard Med, ²Brigham and Womens Hospital

In standard visual search experiments, observers typically look for the same target over many trials. Using these repeated searches, researchers have studied observers’ search templates, intertrial priming, distractor suppression, etc. These are important research topics. However, in the real world, many searches are one-time events. After all, we do not search for the VSS registration desk 100 times in a row. Do the conclusions drawn from blocks of repeated search apply to one-time searches? We had observers search for 6-dimensional conjunction targets. Targets were whole items with an enclosed part. Whole and part each had a color, shape, and orientation. On each trial, targets shared a particular number of features (0-5) with all distractors. 24 observers were tested for 300 trials, 50% target present. Set sizes: 6, 9, & 12. On each trial in the unique target condition, a novel target was shown before the trial, never to be shown again. The comparison condition was a single target search with the same target repeated for all trials, again sharing 0-5 features with distractors on each trial. Observers had unlimited time to encode each unique target. Results: Present RTs and Miss error rates were similar for unique and repeated targets. Absent RTs and False Alarms were higher in the unique condition, especially when targets and distractors shared 4 or 5 features. Perhaps observers simply guessed that targets must be present when they became very similar to distractors. A second experiment used only distractors that shared five features with each trial’s target. RTs were significantly slower in the unique condition, but RT x set size slopes were not significantly steeper. False alarms were higher for unique targets. Conclusion: Observers pay a cost when targets are new on every trial, but the fundamentals of search behavior remain similar to classic repeated target tasks.

Acknowledgements: NIH-NEI EY017001