Roggeveen, Alexa B.

Older adults consistently show slower reaction times (RTs) to the onset of motion. Both cognitive slowing and motor slowing have been suggested as causes of this effect. The lateralized readiness potential (LRP) of the electroencephalogram can be used to separate perceptual and decision processes from motor programming and execution as causes of RT differences. We used the LRP to discern the origin of slowing in RT to motion onset that occurs in elderly individuals. After the onset of motion in a visual display, we asked participants to identify the direction of that motion (up or down) by pressing a button. Older participants showed significantly slower RTs than did younger participants. The LRP showed that the bulk of slowed response arose from slowed motor processes, rather than perceptual processing. We discuss the differences found in amplitude and onset latency of the LRP in the context of theories of motion processing and inhibition in the aging brain.

Inhibition of return (IOR) refers to slower responding to stimuli at previously occupied spatial locations. IOR has been vigorously studied because of its possible deep involvement with attention mechanisms. Although IOR occurs both within and across modalities in several experimental paradigms for simple stimulus detection tasks, it has sometimes been difficult to demonstrate in perceptual discrimination tasks. In the preferred target–target paradigm, in which responses are made to a series of targets that vary in spatial location, failure to find IOR could possibly result from mixing of spatial IOR with the facilitating effects of stimulus and/or response repetition on discrimination response times. In this paper we report the first demonstration of auditory/auditory and cross-modality IOR in a target–target paradigm using a discrimination task. Our results show that IOR occurs in this task only on trials on which stimuli and responses are not repeated. These findings present a challenge to purely visual accounts of IOR and support the view that IOR arises within a more general, supra-modal mechanism of attention.