Adult age differences in a visual search, luminance contrast discrimination task

Abstract

This thesis examined the ability of younger and older adults to use peripherally presented word cues in a luminance contrast discrimination task. Observers were ten older adults (aged 55 to 69) and ten younger adults (aged 23-29). All observers were screened using the Wechsler Test of Adult Reading and the Digit Symbol subscale of the Wechsler Adult Intelligence Scale (WAISIII). Stimuli were presented on a 13 X 16° high-resolution monochrome monitor with an average background luminance of 70 cd/m2. Target (distractor) stimuli were l°-diameter luminance-incremented (decremented) discs. The spatial location o f the targets were cued using luminance decremented ‘YES’ or ‘NO ’ words presented in 9 x 9 array prior to the presentation of a 9 X 9 array containing one target and eight distractors that were positionally congruent to the cued array. The discriminability (d') between target and distractors was varied and the contrast increment threshold needed to just detect the target was calculated. Contrast increment thresholds and mean correct yes response times were analyzed using a mixed two (Age Group) x two (Sex) X three (Cue Validity) x two (Relevant Set Size) mixed ANOVAs. Pre-testing did detect sensorimotor deficits in the older observers, but there were no significant main effects of Age Group or Sex with respect to contrast increment thresholds or response time. Neither group was able to take advantage of the word cues to allocate visual attention. In fact the sensitivity and response times of all observers improved as cues became less informative. This suggests that the ability to discriminate luminance contrasts is relatively preserved in older adults and that the inhibitory effect o f the cues appeared to effect both age groups in a similar manner.