AGE-RELATED DIFFERENCES IN THE IMPACT OF SENSORY DEGRADATION AND VISUAL TASK LOAD ON INFORMATION PROCESSING

Abstract

Background: There is growing evidence that older adults with sensory impairments are at higher risk for developing cognitive impairment/dementia. It is unclear if the link between sensory and cognitive functioning reflects a common underlying cause or whether sensory deficits directly undermine cognitive processing. Here, we addressed this issue by comparing behavioral and event-related potential responses of young and old adults during a working memory paradigm that parametrically varied visual contrast levels and task demands. Methods: Participants included 16 young (mean age1⁄422) and 16 old (mean age1⁄470) cognitively normal adults. No group differences existed for MMSE scores, however old adults had worse corrected visual acuity and contrast sensitivity. Before each experimental block, participants studied 1-4 pairs of faces. One face of each pair was designated as a target. At test, individual faces were shown at one of three contrast levels (100%, 69%, 22%). Participants had to identify each face as a target or non-target (forced choice; 0.50 probability each). The three contrast levels were evenly distributed across trials. Results: Reaction times increased and accuracy decreased in response to diminished contrast or increased task load; the effect of lower contrast on accuracy was larger at higher task load. Old adults generated longer reaction times than young adults, with age differences amplified under higher task load. The amplitude of the P3 event-related potential decreased when processing degraded images. However, this contrast effect only became apparent under increased task load. Unlike their younger counterparts, as task load was augmented, old adults failed to allocate more resources (indexed by P3 amplitude) or vary their processing speed (indexed by P3 latency). Conclusions: The multiplicative relationship between contrast and task load for accuracy and P3 amplitude suggests the impact of degraded visual processing is greater at higher levels of task demand. This interaction disadvantages old adults, who are more likely to experience declines in contrast sensitivity and visual acuity. Old adults have less differentiated responses to changing demands and are at risk for having insufficient resources to process increased task load. These results provide further evidence of the importance of optimizing vision in old adults to mitigate age-associated cognitive decline.