Intertrial priming stemming from ambiguity: A new account of priming in visual search.

Sequential effects are ubiquitous in experimental psychology. Within visual search, performance is often speeded when participants search for the same target twice in a row, as opposed to two different targets. Here, we investigate such intertrial priming. Two experiments show that factors influencing search processes affect the presence and size of intertrial priming: It is larger when there are fewer elements in the visual display, and larger when there is a salient distractor present than when the target is the only salient element in the display. A control experiment showed that these increased priming effects were not due to longer baseline RTs. These findings, it is argued, are inconsistent with theories that explain intertrial priming as resulting from either only faster visual selection, or from episodic retrieval of responses. Instead, we propose that ambiguity in the stimulus or task underlies the occurrence of intertrial priming. © 2006 Psychology Press Ltd

An analysis of the time course of attention in preview search.

We used a probe dot procedure to examine the time course of attention in preview search (Watson and Humphreys, 1997). Participants searched for an outline red vertical bar among other new red horizontal bars and old green vertical bars, superimposed on a blue background grid. Following the reaction time response for search, the participants had to decide whether a probe dot had briefly been presented. Previews appeared for 1,000 msec and were immediately followed by search displays. In Experiment 1, we demonstrated a standard preview benefit relative to a conjunction search baseline. In Experiment 2, search was combined with the probe task. Probes were more difficult to detect when they were presented 1,200 msec, relative to 800 msec, after the preview, but at both intervals detection of probes at the locations of old distractors was harder than detection on new distractors or at neutral locations. Experiment 3A demonstrated that there was no difference in the detection of probes at old, neutral, and new locations when probe detection was the primary task and there was also no difference when all of the shapes appeared simultaneously in conjunction search (Experiment 3B). In a final experiment (Experiment 4), we demonstrated that detection on old items was facilitated (relative to neutral locations and probes at the locations of new distractors) when the probes appeared 200 msec after previews, whereas there was worse detection on old items when the probes followed 800 msec after previews. We discuss the results in terms of visual marking and attention capture processes in visual search

The preview search task: Evidence for visual marking.

A series of experiments are reviewed providing evidence for the idea that when new visual objects are prioritized, old objects are inhibited by a top-down controlled suppression mechanism - A process referred to as visual marking. Evidence for the top-down aspect of visual marking is presented, by showing that new object prioritization, as measured in the preview paradigm, depends on task settings and available attentional resources. Evidence for the inhibitory aspect is presented, by showing that selection of new items is impaired when these items share features with the old items. Such negative carryover effects occur within as well as between trials. Alternative accounts and the evidence for them is discussed. It is concluded that the various accounts are not mutually exclusive and that the data is best explained by a combination of mechanisms. © 2006 Psychology Press Ltd

Contributions from cognitive neuroscience to understanding functional mechanisms of visual search.

We argue that cognitive neuroscience can contribute not only information about the neural localization of processes underlying visual search, but also information about the functional nature of these processes. First we present an overview of recent work on whether search for form - colour conjunctions is constrained by processes involved in binding across the two dimensions. Patients with parietal lesions show a selective problem with form - colour conjunctive search relative to a more difficult search task not requiring cross-dimensional binding. This is consistent with an additional process - cross-dimensional binding - being involved in the conjunctive search task. We then review evidence from preview search using electrophysiological, brain imaging, and neuropsychological techniques suggesting preview benefits in search are not simply due to onset capture. Taken together the results highlight the value of using converging evidence from behavioural studies of normal observers and studies using neuroscientific methods. © 2006 Psychology Press Ltd

Distractor Inhibition Predicts Individual Differences in the Attentional Blink

Background: The attentional blink (AB) refers to humans' impaired ability to detect the second of two targets (T2) in a rapid serial visual presentation (RSVP) stream of distractors if it appears within 200-600 ms of the first target (T1). Here we examined whether humans' ability to inhibit distractors in the RSVP stream is a key determinant of individual differences in T1 performance and AB magnitude

Quick Minds Slowed Down: Effects of Rotation and Stimulus Category on the Attentional Blink

BACKGROUND: Most people show a remarkable deficit to report the second of two targets when presented in close temporal succession, reflecting an attentional restriction known as the 'attentional blink' (AB). However, there are large individual differences in the magnitude of the effect, with some people showing no such attentional restrictions. METHODOLOGY/PRINCIPAL FINDINGS: Here we present behavioral and electrophysiological evidence suggesting that these 'non-blinkers' can use alphanumeric category information to select targets at an early processing stage. When such information was unavailable and target selection could only be based on information that is processed relatively late (rotation), even non-blinkers show a substantial AB. Electrophysiologically, in non-blinkers this resulted in enhanced distractor-related prefrontal brain activity, as well as delayed target-related occipito-parietal activity (P3). CONCLUSION/SIGNIFICANCE: These findings shed new light on possible strategic mechanisms that may underlie individual differences in AB magnitude and provide intriguing clues as to how temporal restrictions as reflected in the AB can be overcome