On the distinction between visual salience and stimulus-driven attentional capture.

It is often assumed that the efficient detection of salient visual objects in search reflects stimulus-driven attentional capture. Evidence for this assumption, however, comes from tasks in which the salient object is task relevant and therefore may elicit a deliberate deployment of attention. In 9 experiments, participants searched for a nonsalient target (vertical among tilted bars). In each display, 1 bar was highly salient in a different dimension (e.g., color or motion). When the target and salient elements coincided only rarely, reducing the incentive to attend deliberately to the salient stimuli, response times depended little on whether the target was salient, although some interesting exceptions were observed. It is concluded that efficient selection of an element in visual search does not constitute evidence that the element captures attention in a purely stimulus-driven fashion.     

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.     

The ignoring paradox: Cueing distractor features leads first to selection, then to inhibition of to-be-ignored items

Observers find a target item more quickly when they have foreknowledge of target-defining attributes, such as identity, color, or location. However, it is less clear whether foreknowledge of nontarget attributes can also speed search. Munneke, Van der Stigchel, and Theeuwes Acta Psychologica 129:101?C107, (2008) found that observers found the target more quickly when they were cued to ignore a region of space where a target would not appear. Using a similar paradigm, we explored the effects of cueing nontarget features on search. We found that when we cued observers to ignore nontarget features, search was slowed. The results from a probe-dot detection task revealed that this slowing occurred because, paradoxically, observers initially selected an item appearing in the to-be-ignored color. Finally, we found that cueing nontarget features sped search when placeholders matching the location of the to-be-ignored color preceded presentation of the search display by at least 800?ms; thus, it appears that some limited inhibition of to-be-ignored items occurs following selection. Taken together, these results suggest that observers are unable to explicitly avoid selection of items matching known nontarget features. Instead, when nontarget features are cued, observers select the to-be-ignored feature or the locations of objects matching that feature early in search, and only inhibit them after this selection process.     

Two new illusions of the tongue

New illusions resulting from failures in proprioception are described. The Forked Tongue illusion results from weaving the tongue among the prongs of a fork, or from using the prongs of a fork to distort skin on other parts of the body-in these cases, the prongs feel misaligned even though the fork has not bent. The Tongue Twister illusion results from turning the tongue upside down and probing it with a finger or foreign object-the object can be felt to be in the wrong spatial location, opposite to where it actually is on the tongue.     

The role of within-dimension singleton priming in visual search

The authors report a newly identified intertrial priming phenomenon, within-dimension singleton priming, by which search for a target that happens to be a singleton on the current trial is faster when the target on the previous trial had also been a singleton on the same dimension rather than a nonsingleton. This effect was replicated in 6 experiments with different procedures, with singletons on various dimensions, when the featural contrast defining the singleton remained the same or changed within a dimension from one trial to the next, and when the target was a singleton on a target-defining dimension or on an irrelevant dimension. These findings cannot be explained by previously demonstrated intertrial repetition effects such as dimension-specific priming or priming of pop-out. Theoretical implications of the within-dimension singleton priming phenomenon are discussed relative to the dimension-weighting hypothesis, the role of stimulus-driven salience in feature-guided search, and the roles of intertrial priming and goal-directed factors in visual search.     

Overriding stimulus-driven attentional capture

Theeuwes (1992) found a distracting effect of irrelevant-dimension singletons in a task involving search for a known target. He argued from this that selectivity is determined solely by stimulus salience; the parallel stage of visual processing cannot provide top-down guidance to the attentive stage sufficient to permit completely selective use of task-relevant information. We argue that in the task used by Theeuwes, subjects may have adopted the strategy of searching for an odd form even though the specific target form was known. In Experiment 1, we replicated Theeuwes’s findings. Search for a circle target among diamond nontargets was disrupted by the presence of a diamond nontarget that was uniquely colored. In two subsequent experiments, we discouraged the singleton detection strategy, forcing subjects to search for the target feature. There was no distracting effect of a color singleton in these experiments, even with displays physically identical to those of Experiment 1, demonstrating that top-down selectivity is indeed possible during visual search. We conclude that goal-directed selection of a specific known featural identity may override stimulus-driven capture by salient featural singletons.     

Local processes in preattentive feature detection.

Sagi and Julesz (1987) claimed that for a target to be detected preattentively, it must be within some small critical distance of a nontarget. The independent effects of separation and display size, which were confounded in the Sagi and Julesz experiments, were examined. Experiments 1 and 2 revealed that in tasks requiring search for a color-defined target, target-nontarget separation had no effect on reaction time (RT). Display size, however, was inversely related to RT. Experiment 3 ruled out the possibility that the decreasing function of RT with display size was due to arousal caused by higher display luminance. When nontarget grouping was inhibited, (Exp. 4) it was found that RT no longer decreased with increasing display size. This suggests that nontarget grouping may have been the cause of the improved performance at larger display sizes. Experiments 5 and 6 extended the results to line segments, the stimuli used by Sagi and Julesz.     

On the locus of visual dominance

A series of six experiments explored the dominance of vision over audition reported by Colavita (1974). We first confirmed the existence of visual dominance in a paradigm somewhat different from Colavita’s: Mean reaction time (RT) to a light was found to be faster than to a simultaneously presented tone, even though the stimuli were equated in subjective intensity and even though RT to the tone presented alone was faster than to the light presented alone. Additional experiments showed that when subjects did not have to respond to light, tone RT was equal or faster (intersensory facilitation) when a light was present than when it was not. These findings suggest that sensory or perceptual processing of the tone is not affected by the light, i.e., that visual dominance is nonsensory in locus and depends on the relevance of the light stimulus. This interpretation was reinforced by other findings which showed that the degree of visual dominance was sensitive to the probability of light, tone, and light-plus-tone trials and to instructions to attend to a specific modality, but was not sensitive to the intensity of the light.