| Identification of the visual conditions under which cognitive performance deteriorates is critical for evaluating laboratory-based and real-world functioning in healthy adults and individuals with Alzheimer's disease (AD). The neuropathological processes of AD negatively impact vision and visual cognition at the receptor and cortical levels. A proportion of the cognitive impairment associated with normal aging and AD can be accounted for by deficits in spatial contrast sensitivity. Increasing the contrast of stimuli relative to their background has been shown to significantly improve performance in older adults and those with AD on certain laboratory-based cognitive tasks. Few studies, however, have examined the ecological validity of these findings. The present study comprised an analysis of basic vision, probes of subjective vision-based daily function, and two experiments designed to examine the effect of contrast enhancement on cognitive performance in healthy adults (78 younger, 16 older) and 16 individuals diagnosed with probable AD. Though there were differences among the groups for visual acuity and contrast sensitivity, these were not strongly related to daily functioning. The aim of Experiment 1 was to optimize object detection by manipulating stimulus contrast on a naturalistic ("pill finding") task. Enhanced contrast and luminance levels significantly improved object detection by older adults enough to match the level attained by young adults, as hypothesized, but contrary to predictions this effect was not seen in AD, suggesting that the strength of contrast enhancement was insufficient to benefit this group. Experiment 2 examined vision-based instrumental activities of daily living (IADLs) by comparing AD performance while using ordinary objects to their performance using visually-enhanced objects devised for the general low-vision community. As hypothesized, AD performance became significantly faster and more accurate when using some of these aids. Taken together, the results indicate that contrast enhancement may significantly improve performance on naturalistic laboratory tasks in older adults and on some vision-based IADLs in individuals with AD. Identification of vision-based interventions may enhance cognition, daily function, and hence quality of life in older adults and those with AD. |
