Abstract& Attentional selection of a target presented among distractors can be indexed with an event-related potential (ERP) component known as the N2pc. Theoretical interpretation of the N2pc has suggested that it ref lects a fundamental mechanism of attention that shelters the cortical representation of targets by suppressing neural activity stemming from distractors. Results from fields other than human electrophysiology, however, suggest that attention does not act solely through distractor suppression; rather, it modulates the processing of both target and distractors. We conducted four ERP experiments designed to investigate whether the N2pc reflects multiple attentional mechanisms. Our goal was to reconcile ostensibly conflicting outcomes obtained in electrophysiological studies of attention with those obtained using other methodologies. Participants viewed visual search arrays containing one target and one distractor. In Experiments 1 through 3, the distractor was isoluminant with the background, and therefore, did not elicit early lateralized ERP activity. This work revealed a novel contralateral ERP component that appears to reflect direct suppression of the cortical representation of the distractor. We accordingly name this component the distractor positivity (P D ). In Experiment 4, an ERP component associated with target processing was additionally isolated. We refer to this component as the target negativity (N T ). We believe that the N2pc ref lects the summation of the P D and N T , and that these discrete components may have been confounded in earlier electrophysiological studies. Overall, this study demonstrates that attention acts on both target and distractor representations, and that this can be indexed in the visual ERP. &

We investigated the ability of salient yet task-irrelevant stimuli to capture attention in two visual search experiments. Participants were presented with circular search arrays that contained a highly salient distractor singleton defined by color and a less salient target singleton defined by form. A component of the event-related potential called the N2pc was used to track the allocation of attention to lateralized positions in the arrays. In Experiment 1, a lateralized distractor elicited an N2pc when a concurrent target was presented on the vertical meridian and thus could not elicit lateralized components such as the N2pc. A similar distractor-elicited N2pc was found in Experiment 2, which was conducted to rule out certain voluntary search strategies. Additionally, in Experiment 2 both the distractor and the target elicited the N2pc component when the two stimuli were presented on opposite sides of the search array. Critically, the distractor-elicited N2pc preceded the target-elicited N2pc on these trials. These results demonstrate that participants shifted attention to the target only after shifting attention to the more salient but task-irrelevant distractor. This pattern of results is in line with theories of attention in which stimulus-driven control plays an integral role.

To find objects of interest in a cluttered and continually changing visual environment, humans must often ignore salient stimuli that are not currently relevant to the task at hand. Recent neuroimaging results indicate that the ability to prevent salience-driven distraction depends on the current level of attentional control activity in frontal cortex, but the specific mechanism by which this control activity prevents salience-driven distraction is still poorly understood. Here, we asked whether salience-driven distraction is prevented by suppressing salient distractors or by preferentially up-weighting the relevant visual dimension. We found that salient distractors were suppressed even when they resided in the same feature dimension as the target (that is, when dimensional weighting was not a viable selection strategy). Our neurophysiological measure of suppression-the P D component of the event-related potential-was associated with variations in the amount of time it took to perform the search task: distractors triggered the P D on fast-response trials, but on slow-response trials they triggered activity associated with working memory representation instead. These results demonstrate that during search salience-driven distraction is mitigated by a suppressive mechanism that reduces the salience of potentially distracting visual objects.

To perceive real-world objects and events, we need to integrate several stimulus features belonging to different sensory modalities. Although the neural mechanisms and behavioural consequences of intersensory integration have been extensively studied, the processes that enable us to pay attention to multimodal objects are still poorly understood. An important question is whether a stimulus in one sensory modality automatically attracts attention to spatially coincident stimuli that appear subsequently in other modalities, thereby enhancing their perceptual salience. The occurrence of an irrelevant sound does facilitate motor responses to a subsequent light appearing nearby. However, because participants in previous studies made speeded responses rather than psychophysical judgements, it remains unclear whether involuntary auditory attention actually affects the perceptibility of visual stimuli as opposed to postperceptual decision and response processes. Here we provide psychophysical evidence that a sudden sound improves the detectability of a subsequent flash appearing at the same location. These data show that the involuntary orienting of attention to sound enhances early perceptual processing of visual stimuli.

No abstract