Biomedical subjects

Howard E Egeth

Publications and source records attributed to Howard E Egeth.

11 recordsLinked to original sources

PubMed2006

Biased competition and visual search: the role of luminance and size contrast.

The biased-competition theory of attention proposes that objects compete for cortical representation in a mutually inhibitory network; competition is biased in favor of the attended item. Here we test two predictions derived from the biased-competition theory. First we assessed whether increasing an object's relative brightness (luminance contrast) biased competition in favor of (i.e., prioritized) the brighter object. Second we assessed whether increasing an object's size biased competition in favor of the larger object. In fulfillment of these aims we used an attentional capture paradigm to test whether a featural singleton (an item unique with respect to a feature such as size or brightness) can impact attentional priority even when those features are irrelevant to finding the target. The results support the prediction that a singleton with respect to luminance contrast receives attentional prioritization and extend the biased-competition account to include size contrast, because a large singleton also receives attentional prioritization.

Attention↗

PubMed2006

Effects of search mode and intertrial priming on singleton search.

There is no consensus as to what information guides search for a singleton target. Does the most salient display element capture attention, regardless of the observer's attentional set? Do observers adopt a default salience-based search mode? Does knowledge of the target's defining featural property (when available) affect search? Finally, can intertrial contingencies account for the disparate results in the literature? We investigated search for a shape singleton when (1) the target and nontarget shapes switched unpredictably from trial to trial, (2) the target feature remained fixed, and (3) the target was a singleton on only one third of the trials. We examined overall reaction times, search slopes, errors, and the magnitude of the slowing caused by a cross-dimensional singleton distractor. Our results argue against the idea that search is guided solely by stimulus-driven factors or that subjects adopt a singleton detection mode that is blind to feature information. They show also that intertrial contingencies, although potent, cannot account for the variety of results in the literature.

Attention↗

PubMed2006

It's under control: top-down search strategies can override attentional capture.

Bacon and Egeth (1994) proposed that observed instances of attentional capture by feature singletons (e.g., color) were the result of a salience-based strategy adopted by subjects (singleton detection mode) and, thus, were not automatic. They showed that subjects could override capture by adopting strategies based on searching for specific target features (feature search mode). However, Theeuwes (2004) has recently argued that Bacon and Egeth's results arose from experimental confounds. He elaborated a model in which attentional capture must be expected when salient distractors fall within a spatial window of attention. According to Theeuwes's (2004) model, there exist two essential criteria for examining stimulus-driven capture. First, search latencies cannot increase with display size, since the search must be parallel; second, the salience of the irrelevant distractor must not be compromised by characteristics of the search display. Contrary to the predictions of Theeuwes's (2004) model, we provide evidence that involuntary capture can be overridden when both of these criteria are met. Our results are consistent with Bacon and Egeth's proposal.

Attention↗

PubMed2006

Effects of top-down guidance and singleton priming on visual search.

Recent literature suggests that observers can use advance knowledge of the target feature to guide their search but fail to do so whenever the target is reliably a singleton. Instead, they engage in singleton-detection mode--that is, they search for the most salient object. In the present study, we aimed to test the notion of a default salience-based search mode. Using several measures, we compared search for a known target when it is always a singleton (fixed-singleton search) relative to when it is incidentally a singleton (multiple-target search). We examined the relative contributions of strategic factors (knowledge that the target is a singleton) and intertrial repetition effects (singleton priming, or the advantage of responding to a singleton target if the target on the previous trial had also been a singleton). In two experiments, singleton priming eliminated all the differences in performance between fixed-singleton and multiple-target search, suggesting that search for a known singleton may be feature based rather than salience based.

Exploratory Behavior↗

PubMed2006

Target-nontarget similarity modulates stimulus-driven control in visual search.

The literature contains conflicting results concerning whether an irrelevant featural singleton (an item unique with respect to a feature such as color or brightness) can control attention in a stimulus-driven manner. The present study explores whether target-nontarget similarity influences stimulus-driven shifts of attention to a distractor. An experiment evaluated whether manipulating target-nontarget similarity by varying orientation would modulate distraction by an irrelevant feature (a bright singleton). We found that increasing target-nontarget similarity resulted in a decreased impact of a uniquely bright object on visual search. This method of manipulating the target-nontarget similarity independent of the salience of a distracting feature suggests that the extent to which visual attention is stimulus-driven depends on the target-nontarget similarity.

Attention↗

PubMed2005

Coordination of voluntary and stimulus-driven attentional control in human cortex.

Visual attention may be voluntarily directed to particular locations or features (voluntary control), or it may be captured by salient stimuli, such as the abrupt appearance of a new perceptual object (stimulus-driven control). Most often, however, the deployment of attention is the result of a dynamic interplay between voluntary attentional control settings (e.g., based on prior knowledge about a target's location or color) and the degree to which stimuli in the visual scene match these voluntary control settings. Consequently, nontarget items in the scene that share a defining feature with the target of visual search can capture attention, a phenomenon termed contingent attentional capture. We used functional magnetic resonance imaging to show that attentional capture by target-colored distractors is accompanied by increased cortical activity in corresponding regions of retinotopically organized visual cortex. Concurrent activation in the temporoparietal junction and ventral frontal cortex suggests that these regions coordinate voluntary and stimulus-driven attentional control settings to determine which stimuli effectively compete for attention.

Adult↗

PubMed2004

Visual attention: bottom-up versus top-down.

Visual attention is attracted by salient stimuli that 'pop out' from their surroundings. Attention can also be voluntarily directed to objects of current importance to the observer. What happens in the brain when these two processes interact?

Attention↗

PubMed2004

Effects of task relevance and stimulus-driven salience in feature-search mode.

Attentional allocation in feature-search mode (W. F. Bacon & H. E. Egeth, 1994) is thought to be solely determined by top-down factors, with no role for stimulus-driven salience. The authors reassessed this conclusion using variants of the spatial cuing and rapid serial visual presentation paradigms developed by C. L. Folk and colleagues (C. L. Folk, R. W. Remington, & J. C. Johnston, 1992; C. L. Folk, A. B. Leber, & H. E. Egeth, 2002). They found that (a) a nonsingleton distractor that possesses the target feature produces attentional capture, (b) such capture is modulated by bottom-up salience, and (c) resistance to capture by irrelevant singletons is mediated by inhibitory processes. These results extend the role of top-down factors in search for a nonsingleton target while arguing against the notion that effects of bottom-up salience and top-down factors on attentional priority are strictly encapsulated within distinct search modes.

Attention↗

PubMed2003

Attentional capture in singleton-detection and feature-search modes.

Six experiments were conducted to determine the circumstances under which an irrelevant singleton captures attention. Subjects searched for a target while ignoring a salient distractor that appeared at different stimulus onset asynchronies (SOAs) prior to each search display. Spatial congruency and interference effects were measured. The strategies available to find the target were controlled (only singleton-detection mode, only feature-search mode, or both search strategies available). An irrelevant abrupt onset captured attention in search for a color target, across SOAs, whatever strategies were available. In contrast, in search for a shape target, an irrelevant color singleton captured attention in the singleton-detection condition but delayed response at its location in the feature-search condition, across SOAs. When both strategies were available, capture was short lived (50- to 100-msec SOAs). The theoretical implications of these findings in relation to current views on attentional capture are discussed. ((c) 2003 APA, all rights reserved)

Adult↗

PubMed2003

Does a salient distractor capture attention early in processing?

Kim and Cave (1999) used spatial probes in order to measure the effects of bottom-up and top-down factors on the allocation of spatial attention over time. Subjects searched for a target with a unique shape, with a uniquely colored distractor present on each trial. The singleton distractor captured attention early in processing, whereas attention homed in on the target's location later on. Kim and Cave (1999) concluded that top-down factors cannot prevent the presence of a salient distractor from delaying target selection. The present study tested the idea that such results were obtained only because subjects adopted the strategy of searching for the most salient item. Kim and Cave's (1999) finding was replicated in Experiment 1. In Experiment 2, instead of a feature search, subjects performed a conjunction search-that is, a task that could not be performed using a salience-based strategy. Probe response times were longest at the salient distractor's location at both the short and the long stimulus onset asynchronies. These results suggest that, early in processing, top-down factors can exert their influence and prevent the capture of attention by a salient distractor.

Attention↗

PubMed2002

Made you blink! Contingent attentional capture produces a spatial blink.

Previous studies have shown that the capture of attention by an irrelevant stimulus can be eliminated by fore knowledge of the spatial location of the relevant target stimulus. To explore whether spatial certainty is sufficient to eliminate capture, four experiments are reported in which the spatial location of the target is certain but the temporal position is uncertain. Subjects viewed a central rapid serial visual presentation stream in which a target letter was defined by a particular color (e.g., red). On critical trials, irrelevant color singletons appeared in the periphery. In Experiments 1 and 2, peripheral singletons produced a decrement in central target identification that was contingent on the match between the singleton color and the target color. Experiments 3 and 4 provided evidence that this decrement reflected a shift of spatial attention to the location of the distractor. The results suggest that spatial certainty is not sufficient to eliminate attentional capture and that attentional capture can result in a spatial "blink" that is conditional on top-down attentional control settings.

Attention↗