It is well established that there are two limiting types of visual search, a pre-attentive parallel and an attention-related serial process. Such different types of processing may depend upon different regions of the visual cortex and such a measurable dissociation of function could provide a useful marker for particular types of cortical pathology, such as that associated with Parkinson's disease, aging, and Alzheimer's disease. For example, recent studies in this laboratory have shown that people with Parkinson's disease have abnormal parallel but normal serial search functions. Plude and Doussard-Roosevelt (1989 Psychology and Aging4 98 – 105) found no difference in parallel processing between older and young adults, but found that older adults performed worse on a conjunction task. The aim of the present experiment was to extend this research and look at the effect of aging on other types of visual search task and to compare these findings to patients with Parkinson's disease and Alzheimer's disease to determine if different patterns of visual function occur. Twenty-five young adults (mean age 32.6 years) and twenty-five older adults (mean age 63.4 years) performed both a conjunction task and a task involving the detection of a target only slightly larger than the distractors (the ‘size’ task). Our hypothesis was that for both types of visual search there would be an increase in search slope in the older adult group compared to the younger adults. Results of a 2-factor (1 between and 1 within) ANOVA performed on the slope values indicate statistically significant main effects of both age ( F=7.661, p<0.008) and search task ( F=25.426, p<0.0001), where in both the conjunction and size task the slope value was significantly greater for the older than for the younger adults. The slope for the size task was significantly greater than that for the conjunction task for both age groups. The results therefore support our hypothesis and further work is in progress to determine the effects of Alzheimer's disease on different types of visual search processing.
Modeling search guidance: Three parameters for characterizing performance in different types of visual search.
