Abstract
Detection of the onset of motion is essential to navigate the world. Driving a car or crossing the street becomes perilous as our reaction times to motion onset decline with age. It has been established that older adults are slower to react to motion onset in random dot patterns (Ball & Sekuler, 1986; Trick & Silverman, 1991), as well as sinusoidal gratings (Porciatti, Fiorentini, Morrone, & Burr, 1999). Porciatti et al. showed that not all of the increase in reaction times in older adults could be attributed to a decrement in motor activity, implying that at least some of the increase can be attributed to slower perceptual and/or cognitive processes. The question remains, however, as to just how much of the increase can be attributed to non-motoric processes. In our study, participants (younger and older adults) pressed a key with either their right or left hands at the onset of up or down movement in a coherent motion display. We replicated the finding that older adults are slower to respond to motion onset. More importantly, using the lateralized readiness potential (LRP), we quantified the extent to which these slower reaction times arose from slower motor response (response-locked LRP) and slower perceptual/cognitive processing (stimulus-locked LRP). In the future, this methodology could be used to establish the relative contributions of motoric and non-motoric factors to age-related decrements in performance.