Abstract
Abstract: :
Purpose: The visual search ability of visually impaired (VI) subjects was studied, and the possibility to improve their visual search ability through computerized training was investigated. Methods: The stimulus was made of two or eight white squares, arranged in a circle 10, 20 or 40o in radius. Each experiment session contained 40 trials. In 32 of the trials, one square was 2x2o, the target, and the other squares were smaller at 1x1o, the distracters. In the other 8 trials, all squares were distracters. The subject used two keys to indicate the presence or absence of a target. The computer recorded the reaction time (RT) for each trial (the time between onset of the stimulus display and when one of the response keys was pressed). Hit rate (% correct), false alarm rate, and average response RT for hits were calculated at the end of each session. Each subject performed the same tasks everyday from day 1 to 5, and had final testing at day 9. There was no training between day 5 and 9. Twenty–four VI adults participated in the study. Results: VI subjects required more time to process 8 targets than 2 (2.03 sec vs. 1.68 sec at 10o radius). They also required more time to find targets at 40o eccentricity than 20 or 10. Pairwise comparison between day 1 and day 5 results showed that the day 5 RT for 2 and 8 stimuli was significantly shorter, by 13 and 18%, respectively. Hit rates for 2 stimuli were over 90% regardless of day or location. Hit rates for 8 stimuli at 20 and 40o eccentricities increased significantly from 89% on day 1 to 95% on day 5. Comparing day 1 to day 9 results showed that day 9 RT’s were significantly shorter than day 1 but hit rates were the same. Between day 5 and day 9, RT and % correct remained stable. The RT difference between 2 and 8 targets persisted even after training as did the eccentricity effect. Conclusions: Visual search of VI subjects may not be completely parallel. Visual search training reduced the time VI adults took to locate targets among distracters and increased accuracy in the short term. The shortening of RT persisted for at least 4 days after training. Whether or not shorter search times transfer to other tasks such as obstacle avoidance while walking is under investigation.
Keywords: low vision • aging: visual performance • visual search