Visual search for singleton targets redundantly defined in two feature dimensions: Coactive processing of color-motion targets?

In 2 visual search experiments, the role of feature contrast/saliency signals in generating detection responses to singleton feature targets in visual search was investigated using the redundant-target paradigm. Experiment 1 showed that coactive integration of dimensional signals is not restricted to targets defined on the color and orientation dimensions; rather, targets involving any of the combinations of color, orientation, and motion, are integrated coactively, as evidenced by violations of Miller's (1982) race model inequality. Experiment 2 replicated the findings of Experiment 1 for color-motion targets, with the target items' luminance adjusted, individually for each observer, to that of the distractors.

From features to dimensions: cognitive and motor development in pop-out search in children and young adults.

In an experiment involving a total of 124 participants, divided into eight age groups (6-, 8-, 10-, 12-, 14-, 16-, 18-, and 20-year-olds) the development of the processing components underlying visual search for pop-out targets was tracked. Participants indicated the presence or absence of color or orientation feature singleton targets. Observers also solved a detection task, in which they responded to the onset of search arrays.

Salience-based integration of redundant signals in visual pop-out search: evidence from behavioral and electrophysiological measures.

Behavioral and electrophysiological evidence is presented suggesting that, in visual search for feature singleton targets, multidimensional signals are integrated at a preselective stage of processing. Observers searched for a target that was consistently defined by the same features, but differed from the variable context either nonredundantly by one or redundantly by two dimensionally different features. The behavioral results showed reaction time redundancy gains and evidence of coactive processing, and the electrophysiological analyses revealed the latency of the N2pc component of the event-related potential (ERP) to be expedited by redundant relative to nonredundant displays, while the response-related lateralized readiness potential (LRP) remained unaffected.

Happy with a difference, unhappy with an identity: observers' mood determines processing depth in visual search.

Visual search for feature targets was employed to investigate whether the mechanisms underlying visual selective attention are modulated by observers' mood. The effects of induced mood on overall mean reaction times and on changes and repetitions of target-defining features and dimensions across consecutive trials were measured. The results showed that reaction times were significantly slower in the negative than in the positive and neutral mood groups.

Coarse guidance by numerosity in visual search.

In five experiments, we examined whether the number of items can guide visual focal attention. Observers searched for the target area with the largest (or smallest) number of dots (squares in Experiment 4 and "checkerboards" in Experiment 5) among distractor areas with a smaller (or larger) number of dots. Results of Experiments 1 and 2 show that search efficiency is determined by target to distractor dot ratios.

Dynamic weighting of feature dimensions in visual search: behavioral and psychophysiological evidence.

Dimension-based accounts of visual search and selection have significantly contributed to the understanding of the cognitive mechanisms of attention. Extensions of the original approach assuming the existence of dimension-based feature contrast saliency signals that govern the allocation of focal attention have recently been employed to explain the spatial and temporal dynamics of the relative strengths of saliency representations. Here we review behavioral and neurophysiological findings providing evidence for the dynamic trial-by-trial weighting of feature dimensions in a variety of visual search tasks.

Redundancy gains in pop-out visual search are determined by top-down task set: behavioral and electrophysiological evidence.

We combined behavioral and electrophysiological measures to find out whether redundancy gain effects in pop-out visual search are exclusively determined by bottom-up salience or are modulated by top-down task search goals. Search arrays contained feature singletons that could be defined in a single dimension (color or shape) or redundantly in both dimensions. In the baseline condition, both color and shape were task-relevant, and behavioral redundancy gain effects were accompanied by an earlier onset of the N2pc component for redundant as compared to single-dimension targets.

Dimension intertrial and cueing effects in localization: support for pre-attentively weighted one-route models of saliency.

There are several alternative accounts of dimensional intertrial and cueing effects in singleton feature search tasks. Some accounts assume that these effects arise at post-selective processing stages; dual-route accounts assume them to be perceptual in nature, but coming into play only in non-spatial tasks (e.g.

Inter-trial and redundant-signals effects in visual search and discrimination tasks: separable pre-attentive and post-selective effects.

Feature singleton search is faster when the target-defining dimension is repeated, rather than changed, across trials (Found & Müller, 1996). A similar dimension repetition benefit has been observed in a non-search (discrimination) task with a single stimulus (Mortier, Theeuwes, & Starreveld, 2005). Two experiments examined whether these effects in the two tasks originate from the same or different processing stages.

Display probability modulates attentional capture by onset distractors.

Attention can be stimulus-driven and bottom-up or goal-driven and top-down. Bottom-up attention and, particularly, attentional capture are often thought to be strongly automatic, i.e.

The influence of alertness on spatial and nonspatial components of visual attention.

Three experiments investigated whether spatial and nonspatial components of visual attention would be influenced by changes in (healthy, young) subjects' level of alertness and whether such effects on separable components would occur independently of each other. The experiments used a no-cue/alerting-cue design with varying cue-target stimulus onset asynchronies in two different whole-report paradigms based on Bundesen's (1990) theory of visual attention, which permits spatial and nonspatial components of selective attention to be assessed independently. The results revealed the level of alertness to affect both the spatial distribution of attentional weighting and processing speed, but not visual short-term memory capacity, with the effect on processing speed preceding that on the spatial distribution of attentional weighting.

A (fascinating) litmus test for human retino- vs. non-retinotopic processing.

In human vision, the optics of the eye map neighboring points of the environment onto neighboring photoreceptors in the retina. This retinotopic encoding principle is preserved in the early visual areas. Under normal viewing conditions, due to the motion of objects and to eye movements, the retinotopic representation of the environment undergoes fast and drastic shifts.

Perceptual basis of redundancy gains in visual pop-out search.

The redundant-signals effect (RSE) refers to a speed-up of RT when the response is triggered by two, rather than just one, response-relevant target elements. Although there is agreement that in the visual modality RSEs observed with dimensionally redundant signals originating from the same location are generated by coactive processing architectures, there has been a debate as to the exact stage(s)--preattentive versus postselective--of processing at which coactivation arises. To determine the origin(s) of redundancy gains in visual pop-out search, the present study combined mental chronometry with electrophysiological markers that reflect purely preattentive perceptual (posterior-contralateral negativity [PCN]), preattentive and postselective perceptual plus response selection-related (stimulus-locked lateralized readiness potential [LRP]), or purely response production-related processes (response-locked LRP).

The detection of feature singletons defined in two dimensions is based on salience summation, rather than on serial exhaustive or interactive race architectures.

Influential models of visual search assume that dimension-specific feature contrast signals are summed into a master saliency map in a coactive fashion. The main source of evidence for coactivation models, and against parallel race models, is violations of the race model inequality (RMI; Miller, 1982) by redundantly defined singleton feature targets. However, RMI violations do not rule out serial exhaustive (Townsend & Nozawa, 1997) or interactive race (Mordkoff & Yantis, 1991) architectures.

Sources of top-down control in visual search.

Endogenous control of visual search can influence search guidance at the level of a supradimensional topographic saliency map [Wolfe, J. M. Guided Search 2.

Attentional capture by salient color singleton distractors is modulated by top-down dimensional set.

Three experiments examined whether salient color singleton distractors automatically interfere with the detection singleton form targets in visual search (e.g., J.

Dimension- and space-based intertrial effects in visual pop-out search: modulation by task demands for focal-attentional processing.

Two experiments compared reaction times (RTs) in visual search for singleton feature targets defined, variably across trials, in either the color or the orientation dimension. Experiment 1 required observers to simply discern target presence versus absence (simple-detection task); Experiment 2 required them to respond to a detection-irrelevant form attribute of the target (compound-search task). Experiment 1 revealed a marked dimensional intertrial effect of 34 ms for an target defined in a changed versus a repeated dimension, and an intertrial target distance effect, with an 4-ms increase in RTs (per unit of distance) as the separation of the current relative to the preceding target increased.

Object-based selection in the Baylis and Driver (1993) paradigm is subject to space-based attentional modulation.

Three experiments re-examined Baylis and Driver's (1993) strong evidence for object-based selection, that making relative apex location judgments is harder between two objects than within a single object, with object (figure-ground) segmentation determined solely by color-based perceptual set. Using variations of the Baylis and Driver paradigm, the experiments replicated a two-object cost. However, they also showed a large part of the two-object cost to be attributable to space-based factors, though there remained an irreducible cost consistent with 'true' object-based selection.

The redundant-signals paradigm and preattentive visual processing.

Physiological and cognitive models of vision agree that the pre-attentive processing of visual stimuli is organized in a parallel and segregated fashion. However, several incompatible models have been proposed for the subsequent processing stages. They differ in their assumptions about architecture (serial, parallel, or coactive/integrative), stopping-rules (self-terminating, or exhaustive), spatial specificity of saliency signal coding (signal pooling across locations, or spatially distinct processing), and dependency of target detection on the prior allocation of attention (pre-attentive, or post-selective).

Expectancies modulate attentional capture by salient color singletons.

In singleton feature search for a form-defined target, the presentation of a task-irrelevant, but salient singleton color distractor is known to interfere with target detection [Theeuwes, J. (1991). Cross-dimensional perceptual selectivity.

Cross-trial priming of element positions in visual pop-out search is dependent on stimulus arrangement.

Two experiments examined cross-trial positional priming (V. Maljkovic & K. Nakayama, 1994, 1996, 2000) in visual pop-out search.

Brain electrical correlates of dimensional weighting: an ERP study.

In visual search, there is a reaction time (RT) cost for targets on a given trial if the previous target was defined in a different dimension. According to the "dimension-weighting" account (Müller, Heller, & Ziegler, 1995), limited attentional weight needs to be shifted to the new dimension, resulting in slower RTs. The present study aimed at identifying brain electrical correlates associated with the weight shift.

Cross-trial priming in visual search for singleton conjunction targets: role of repeated target and distractor features.

Kristjánsson, Wang, and Nakayama (2002) demonstrated that visual search for conjunctively defined targets can be substantially expedited ("primed") when target and distractor features are repeated on consecutive trials. Two experiments were conducted to examine whether the search response time (RT) facilitation on target-present trials results from repetition of target-defining features, distractor features, or both. The experiments used a multiple conjunctive search paradigm (adapted from Kristjánsson et al.