Ward, Lawrence M.

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.

In a standard inhibition-of-return (IOR) paradigm using a manual key-press response, we examined the effect of IOR both on the amplitude of early sensory event-related brain potential (ERP) components and on the motor-related lateralized readiness potential (LRP). IOR was associated with a delay of premotor processes (target-locked LRP latency) and reduced sensory ERP activity. No effect of IOR was found on motor processes (response-locked LRP latency). Thus, IOR must arise at least in part from changes in perceptual processes, and, at least when measured with manual key presses, IOR does not arise from inhibition of motor processes. These results are consistent with the results of attention-orienting studies and provide support for an inhibition-of-attention explanation for IOR.

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.

Inhibition of return (IOR) is a phenomenon that has been thought to be closely associated with attention mechanisms. In particular, it might arise from the operation of an attentional mechanism that facilitates visual search by inhibiting both covert attention and eye movements from returning to recently inspected locations. Although IOR has received a great deal of research interest, and mechanisms involving sensory, perceptual, and motor consequences have been proposed, no consensus has yet been reached regarding the stages of information processing at which IOR operates. In the present study, we utilized event-related potential (ERP) measures of visual and motor processes to investigate the processing changes underlying IOR. In three experiments, involving localization, detection, or Go–NoGo discrimination, participants were required to make manual responses to target stimuli. In each of these experiments, IOR was associated with a slowing of premotor processes as indicated by a modulation of the onset of the target-locked lateralized readiness potential (LRP). However, the duration of motor processes was not affected (response-locked LRP latency). Consistent with a perceptual locus of IOR, the amplitudes of the occipital ERP peaks were reduced for targets at cued locations relative to those at uncued locations. These and earlier results together provide considerable support for a model in which salience mechanisms that guide attention orienting are also affected by IOR, in that processing a stimulus at a location results in a lowering of its salience for future processing, making orienting to that location, and responding to targets presented there, more time consuming.

There is now convincing evidence that an involuntary shift of spatial attention to a stimulus in one modality can affect the processing of stimuli in other modalities, but inconsistent findings across different paradigms have led to controversy. Such inconsistencies have important implications for theories of cross-modal attention. The authors investigated why orienting attention to a visual event sometimes influences responses to subsequent sounds and why it sometimes fails to do so. They examined visual-cue-on-auditory-target effects in two paradigms--implicit spatial discrimination (ISD) and orthogonal cuing (OC)--that have yielded conflicting findings in the past. Consistent with previous research, visual cues facilitated responses to same-side auditory targets in the ISD paradigm but not in the OC paradigm. Furthermore, in the ISD paradigm, visual cues facilitated responses to auditory targets only when the targets were presented directly at the cued location, not when they appeared above or below the cued location. This pattern of results confirms recent claims that visual cues fail to influence responses to auditory targets in the OC paradigm because the targets fall outside the focus of attention.