Electrophysiological indices of target and distractor processing in visual search

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 reflects 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 (

The attentional blink: Invreasing target salience provides no evidence for resource depletion. A commentary on Dux, Asplund and Marois

The authors have argued elsewhere that the attentional blink (AB; i.e., reduced target detection shortly after presentation of an earlier target) arises from blocked or disrupted perceptual input in response to distractors presented between the targets. When targets replace the intervening distractors, so that three targets (T1, T2, and T3) are presented sequentially, performance on T2 and T3 improves. Dux, Asplund, and Marois (2008) argued that T3 performance improves at the expense of T1, and thus provides evidence for resource depletion. They showed that when T1 is made more salient (and presumably draws more resources), an AB for T3 appears to reemerge. These findings can be better explained, however, by (1) the relationship between T1 and T2 (not T1 and T3) and (2) differential salience for T3 in the long-lag condition of Dux et al.'s study. In conclusion, the Dux et al. study does not present a severe challenge to input control theories of the AB. © 2009 The Psychonomic Society, Inc

Dos and don’ts in response priming research

Response priming is a well-understood but sparsely employed paradigm in cognitive science. The method is powerful and well-suited for exploring early visuomotor processing in a wide range of tasks and research fields. Moreover, response priming can be dissociated from visual awareness, possibly because it is based on the first sweep of feedforward processing of primes and targets. This makes it a theoretically interesting device for separating conscious and unconscious vision. We discuss the major opportunities of the paradigm and give specific recommendations (e.g., tracing the time-course of priming in parametric experiments). Also, we point out typical confounds, design flaws, and data processing artifacts

Modeling metacontrast masking with varying target and mask durations

In metacontrast, a target is rendered invisible by a surrounding mask that appears after the target's offset, providing a tool for investigating temporal aspects of visual coding. Previous manipulations of target and mask duration have used constant stimulus intensity, so that longer-lasting stimuli appear brighter. When brightness is controlled by compensating longer duration with lower intensity, increasing target duration has little effect on U-shaped metacontrast, but increasing mask duration monotonically decreases target visibility when the mask follows a 10 msec target immediately. These results were simulated with four models: efficient masking (Francis), decaying-trace (Anbar & Anbar), two-channel (Weisstein, 1968), and lateral inhibition (Bridgeman). Using parameters in each model that had successfully simulated metacontrast in the past, the efficient masking model yielded a monotonically increasing function of visibility in as target duration increased, while the other models gave U-shaped functions. Testing the remaining models in the increasing mask duration experiment, the decaying-trace model gave an increasing function where the psychophysics showed a decreasing function, the two-channel model showed a plateau of high visibility at low mask duration while the psychophysical function began declining immediately, and the lateral inhibition model accurately simulated the results. We also tested a recurrent processing model (DiLollo, Enns & Rensink), which did well here but does not have the parameters to test the target-duration condition. The lateral inhibition model performed best overall, perhaps because it relies on distributed coding rather than discrete detectors to simulate target visibility. In a single layer of simulated neurons, each cell inhibits six near neighbors; secondary interactions spread stimulus-specific activity across the network