Differential contributions of selective attention and sensory integration to the decline in driving skills in aging and early Alzheimer's disease

Abstract

Deficits in selective attention have been associated with poorer driving ability in older drivers. Along with declines in selective attention, Alzheimer's disease (AD) patients also show deficits in effectively integrating stimulus features processed within distinct cortical areas due to the disruption of corticortical connections. This study examined the relative contribution of selective attention and sensory integration processes to on-road driving in healthy elderly and patients with very mild dementia. Forty-one healthy elderly and twenty-three early AD patients were administered two visual search tasks identical in selective attention demands but differing in demands placed on cross-cortical interactions: Subjects were required to integrate a target's motion with either a) its luminance contrast (black or white) or b) its isoluminant color (red or green). Because luminance and motion are both processed within the dorsal stream while color is processed within the ventral stream, motion/color integration places greater demands on cross-cortical interactions than motion/luminance integration. Step-wise regression analyses were performed separately for each group on task summary measures (slope, search accuracy, overall response time) as predictors of subjects' performance on a standardized road test. Road test error rates were higher in AD than healthy elderly drivers. While healthy elderly performed comparably on the two search tasks (indicating intact sensory binding), AD patients displayed a selective decrease in search accuracy in the motion/color task (indicating an additional decline in cross-cortical sensory binding). Slopes of both tasks and motion/luminance search accuracy were significant predictors of road test score for healthy elderly, whereas motion/color slope and search accuracy were significant predictors of road test score for AD patients. These results provide confirmation of a sensory binding deficit associated with neocortical disconnectivity in AD, and suggest that the relative contribution of selective attention and sensory integration deficits to driving performance differs across healthy elderly and AD patients: In healthy elderly, selective attention measures most strongly predicted driving performance, whereas cross-cortical binding measures were more sensitive driving predictors in AD patients. Computerized tasks designed to specifically assess these distinct processes may therefore prove particularly effective in differentially predicting driving risk in aging and AD.