Abstract
We examined search performance throughout the functional visual field. This has been shown to be an important determinant for performance in daily life tasks. We were interested to see how aging affects performance and whether we could find evidence for compensatory strategies in subjects with visual field defects. The task was to localise a target (C) among 24 distractors (O) and identify the direction of its gap. Subjects were allowed to make eye movements. Using a staircase procedure, performed separately at each of the 25 possible target positions, we determined the stimulus presentation time necessary to reach criterion performance. This method has the advantage over more common reaction time experiments that it is not affected by speed - accuracy trade-offs. Seven young (age 22 – 28 years) and seven old (age 58 – 78 years) subjects with normal vision participated. In addition, we tested older subjects with visual field defects (central defects and hemianopia).
Our results show significant (p<0.0001) age-related differences in the presentation time required for criterion performance. In addition, we found a significant (p<0.0001) interaction between age and target eccentricity, with the largest age-related decline in performance occurring for targets on or near the initial fixation point, and smaller changes occurring for targets further away from this point. Age and target eccentricity turned out to be the main predictors for search performance. We conclude that age significantly affects search performance, but the extent depends on the distance from the initial fixation point. Our results therefore suggest that aging does not equally affect all stages in visual processing. Not surprisingly, field defects influence search performance, but we also found evidence for compensatory strategies.
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