Effects of aging on illusory target motion in a hitting task.

Abstract

Age-related changes in multisensory integration (MSI, brain integration of multiple unisensory signals) were investigated. Accurate MSI is a key component of successful aging and crucial to perform activities of daily living (ADLs). Previous research suggests that with aging, different sources of sensory information are not properly weighted anymore. Twenty healthy younger (YA, age 18-34) and twenty-four healthy older adults (OA, age 60-82) were asked to hit discs moving downwards on a screen with their index finger. Illusory direction of motion was included (moving a checkerboard-like background either to the left or right). The discs disappeared before the screen was reached. Experimental conditions were: sitting (baseline), standing on foam (balance task), and sitting while doing a cognitive dual task (counting task). Participants hit the disc more to the right for left background motion compared to right background motion, conforming the illusory effect. OA show a larger effect of the illusion compared to YA in the baseline and balance conditions (p=.036 and p=.047, respectively). The same tendency was shown in the counting condition. Overall, background motion had a greater influence on the counting condition compared to the other conditions (p=.005 for YA and p=.009 for OA). No significant differences were found for the summed reaction and movement time, and no correlations between hitting performance and results of clinical pretests were found. We conclude that OA are more affected by the background motion than YA, which supports the idea that OA do not weigh information properly. Our finding that a cognitive dual task increases the illusion effect in both groups of participants suggests that cognitive resources are required for proper weighting, which may be a problem for OA. Future research will include OA with ADLs difficulties in order to develop a toolkit for early detection of MSI problems in the elderly population.