Singleton Search Research Articles

Similarity and heterogeneity effects in visual search are mediated by "segmentability".

The heterogeneity of our visual environment typically reduces the speed with which a singleton target can be found. Visual search theories explain this phenomenon via nontarget similarities and dissimilarities that affect grouping, perceptual noise, and so forth. In this study, we show that increasing the heterogeneity of a display can facilitate rather than inhibit visual search for size and orientation singletons when heterogeneous features smoothly fill the transition between highly distinguishable nontargets. We suggest that this smooth transition reduces the "segmentability" of dissimilar items to otherwise separate subsets, causing the visual system to treat them as a near-homogenous set standing apart from a singleton. (PsycINFO Database Record

Distractor rejection in visual search breaks down with more than a single distractor feature.

Previous research has established that interference from irrelevant-but-salient color distractors occurs when observers search for variable-shape singletons among uniform shapes (singleton detection), but not when they look for a specific shape among mixed shapes (feature search). In the current study, we replicated this finding, and additionally, we introduced a random variation of color. Instead of always presenting the same target and distractor colors, colors were swapped randomly from trial to trial. With random color variation, interference from color distractors was generally stronger, and in particular, it also occurred in feature search mode, suggesting that observers were unable to focus on the relevant dimension (shape) even under the most favorable conditions. A second experiment showed that interference in feature search mode occurred with variable distractor color when target color was fixed, but not with variable target color when distractor color was fixed. Overall, the results question the view that interference in feature search is absent because observers monitor a single feature map (i.e., shape). Rather, random variation of an irrelevant feature induces participants to also monitor the irrelevant feature, which results in interference. Thus, complete distractor rejection is limited to situations with a single distractor feature.

Primary Visual Cortex as a Saliency Map: A Parameter-Free Prediction and Its Test by Behavioral Data.

It has been hypothesized that neural activities in the primary visual cortex (V1) represent a saliency map of the visual field to exogenously guide attention. This hypothesis has so far provided only qualitative predictions and their confirmations. We report this hypothesis’ first quantitative prediction, derived without free parameters, and its confirmation by human behavioral data. The hypothesis provides a direct link between V1 neural responses to a visual location and the saliency of that location to guide attention exogenously. In a visual input containing many bars, one of them saliently different from all the other bars which are identical to each other, saliency at the singleton’s location can be measured by the shortness of the reaction time in a visual search for singletons. The hypothesis predicts quantitatively the whole distribution of the reaction times to find a singleton unique in color, orientation, and motion direction from the reaction times to find other types of singletons. The prediction matches human reaction time data. A requirement for this successful prediction is a data-motivated assumption that V1 lacks neurons tuned simultaneously to color, orientation, and motion direction of visual inputs. Since evidence suggests that extrastriate cortices do have such neurons, we discuss the possibility that the extrastriate cortices play no role in guiding exogenous attention so that they can be devoted to other functions like visual decoding and endogenous attention.

Singleton search is guided by knowledge of the target, but maybe it shouldn’t be

Among studies of visual search for a singleton, some studies show evidence of top-down attentional guidance driven by goals, while others do not, leading to uncertainty as to how goal-driven guidance should be included in attentional theories. Six experiments tested this guidance when a target shape is found by locating a singleton feature (color or shape) and an orientation within the target is then reported. Experiments 1 and 2 use the dimensional priming paradigm underlying the most effective arguments against goal-driven guidance, and show evidence for guidance in many circumstances. Experiment 3 extends the results to feature priming, and demonstrates a complex interaction between attentional goals and memory for previous targets. In Experiment 4, symbolic (word) cues were just as effective as image cues, further strengthening the case for goal-driven guidance. In Experiments 5 and 6, as in the previous experiments, valid cues again produced faster responses than invalid cues, showing the advantage of goal-driven guidance. Surprisingly, however, responses were even faster when the cues were uninformative. Furthermore, participants who began the experiment with neutral cues seemed to ignore informative cues later in the experiment. The results show that attention can be guided by goals even in easy searches, but that searchers have much flexibility in the use of this guidance, and may choose not to use it. Furthermore, their decisions about using this guidance are not always well informed, because they are not aware of the relative costs and benefits.

Visual search for shape singletons as a function of visual hemifield

Visual search for shape singletons as a function of visual hemifield

Singleton search performance predicts performance on heterogeneous displays: Evidence in support of the Information Theory of Vision

Singleton search performance predicts performance on heterogeneous displays: Evidence in support of the Information Theory of Vision

The long and the short of priming in visual search.

Memory affects visual search, as is particularly evident from findings that when target features are repeated from one trial to the next, selection is faster. Two views have emerged on the nature of the memory representations and mechanisms that cause these intertrial priming effects: independent feature weighting versus episodic retrieval of previous trials. Previous research has attempted to disentangle these views focusing on short term effects. Here, we illustrate that the episodic retrieval models make the unique prediction of long-term priming: biasing one target type will result in priming of this target type for a much longer time, well after the bias has disappeared. We demonstrate that such long-term priming is indeed found for the visual feature of color, but only in conjunction search and not in singleton search. Two follow-up experiments showed that it was the kind of search (conjunction versus singleton) and not the difficulty, that determined whether long-term priming occurred. Long term priming persisted unaltered for at least 200 trials, and could not be explained as the result of explicit strategy. We propose that episodic memory may affect search more consistently than previously thought, and that the mechanisms for intertrial priming may be qualitatively different for singleton and conjunction search. Electronic supplementary material The online version of this article (doi:10.3758/s13414-015-0860-2) contains supplementary material, which is available to authorized users.

Attention capture while switching search strategies: Evidence for a breakdown in top-down attentional control

Whereas capture experiments typically repeat a single task many times, real world cognition is characterized by frequent switching. Lien, Ruthruff, and Johnston (2010) reported that the attentional control system can rapidly and fully switch between different search settings (e.g., red to green), with no carryover and no intertrial priming. The present study examined whether this impressive flexibility is possible even when the switch is not between different features along the same dimension, but between mutually incompatible search modes. On each trial, participants were prompted to find and identify the letter that was in a specific colour (feature search mode) or was uniquely coloured (singleton search mode). Within each block, search mode was either pure or mixed; the mixed blocks contained a fixed AABB search sequence (singleton-singleton-feature-feature) in Experiment 1 and a random sequence in Experiment 2. The target display was preceded by a noninformative cue display containing a nontarget colour singleton. In pure feature search blocks, these irrelevant singleton cues were generally unable to capture attention, replicating previous findings of “contingent capture”. In mixed blocks, however, irrelevant colour singletons captured attention on feature search trials. This breakdown indicates a limitation in the sharpness of attentional control following mode switches, which might be common in the real world.

The right temporo-parietal junction contributes to visual feature binding

We investigated the neural basis of conjoined processing of color and spatial frequency with functional magnetic resonance imaging (fMRI). A multivariate classification algorithm was trained to differentiate between either isolated color or spatial frequency differences, or between conjoint differences in both feature dimensions. All displays were presented in a singleton search task, avoiding confounds between conjunctive feature processing and search difficulty that arose in previous studies contrasting single feature and conjunction search tasks. Based on patient studies, we expected the right temporo-parietal junction (TPJ) to be involved in conjunctive feature processing. This hypothesis was confirmed in that only conjoined color and spatial frequency differences, but not isolated feature differences could be classified above chance level in this area. Furthermore, we could show that the accuracy of a classification of differences in both feature dimensions was superadditive compared to the classification accuracies of isolated color or spatial frequency differences within the right TPJ. These data provide evidence for the processing of feature conjunctions, here color and spatial frequency, in the right TPJ.

On the link between mind wandering and task performance over time.

Here we test the hypothesis that fluctuations in subjective reports of mind wandering over time-on-task are associated with fluctuations in performance over time-on-task. In Study 1, we employed a singleton search task and found that performance did not differ prior to on- and off-task reports, nor did individual differences in mind wandering predict differences in performance (so-called standard analytic methods). Importantly however, we find that fluctuations in mind wandering over time are strongly associated with fluctuations in behavior. In Study 2, we provide a replication of the relation between mind wandering and performance over time found in Study 1, using a Flanker interference task. These data indicate (1) a tight coupling between mind wandering and performance over time and (2) that a temporal-analytic approach can reveal effects of mind wandering on performance in tasks where standard analyses fail to do so. The theoretical and methodological implications of these findings are discussed.

Random reward priming is task-contingent: the robustness of the 1-trial reward priming effect.

Consistent financial reward of particular features influences the allocation of visual attention in many ways. More surprising are 1-trial reward priming effects on attention where reward schedules are random and reward on one trial influences attentional allocation on the next. Those findings are thought to reflect that rewarded features become more salient than unrewarded ones on the subsequent trial. Here we attempt to conceptually replicate this effect, testing its generalizability. In three versions of an analogous paradigm to the additional singleton paradigm involving singleton search for a Gabor patch of odd spatial frequency we found no evidence of reward priming, while we only partially replicate the reward priming in the exact original paradigm tested by Hickey and colleagues. The results cast doubt on the proposal that random reward enhances salience, suggested in the original papers, and highlight the need for a more nuanced account. In many other paradigms reward effects have been found to progress gradually, becoming stronger as they build up, and we argue that for robust reward priming, reward schedules need to be more consistent than in the original 1-trial reward priming paradigm.

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. These findings suggest that target signal integration in singleton search paradigms occurs pre-attentively, that is, prior to focal-attentional target selection, with observers basing their responses on the detection of featureless saliency signals, even under conditions in which the target features remain constant and are known in advance. These results have implications for theories assuming top-down influences in feature detection.

Visual search for feature singletons: Multiple mechanisms produce sequence effects in visual search

Selection of a feature singleton target in visual search tasks, e.g., a red target among green distractors, is very fast--as if the target "popped out" of the display. Interestingly, reaction times (RTs) sometimes even decrease with an increase in the number of distractors (while keeping the presentation area fixed), i.e., there is a negative RT/display density relationship. Furthermore, repeating--versus changing--target-defining properties across trials also speeds up RTs. The present study investigated how display density influences two similar but dissociable types of such intertrial effects, namely (a) priming of pop-out (PoP), observed when the target-defining dimension is fixed, e.g., color, and only the features of the target and distractors, e.g., red and green, vary across trials and (b) the dimension-repetition effect (DRE), observed when both the features and dimensions of the target vary, e.g., from red circle (color) to blue square (shape target) among blue circles. Experiment 1 examined PoP magnitude with sparse (three-item) versus dense (36-item) displays in conditions in which the distractors' color either (a) varied, i.e., red target, green distractors versus green target, red distractors, or (b) it was fixed (blue). Significant PoP was observed only for sparse distractors conditions. Experiment 2 investigated the DRE magnitude across display densities with distractors always being fixed: Significant DREs of comparable magnitude were observed with both sparse and dense displays. This dissociation between the PoP and DREs suggests, first, the existence of multiple mechanisms of intertrial effects and, second, that PoP is specific to low target-distractor signal-to-noise ratios when the target fails to pop out.

Lighting direction and visual field modulate the brightness of 3D objects

Background: When interpreting the shape of 3D surfaces the visual system assumes that illumination is mostly from above and slightly from the left. Visual search is parallel for below-lit targets amidst top-lit distractors, but not vice versa. However, visual search for oddly-illuminated singletons is serial when the 3D pose of cube targets and distractors is randomized. We asked whether the direction of lighting of randomly posed 3D cubes would influence their brightness (and/or perceived intensity of illumination). Method: An array of nine Lambertian cubes was stereoscopically rendered in low ambient illumination against a dark background. Individual cubes varied in their 3D pose, but all possessed identical triplets of visible faces. The cubes were illuminated from one of four directions: top-left (+60o elevation; -90o azimuth); top-right (+60o; +90o); bottom-left (-60o; -90o); and bottom-right (-60o; +90o). Illumination intensity (arbitrary units) ranged from 1-15 (linear steps). "Standard" cubes were illuminated from top-left at intensity 8; comparison cubes were illuminated from all four possible directions, and appeared in either the left or right visual fields. Using the method of adjustment (N=20, 13 male) we determined comparison cube illumination levels required to establish subjective equality with the standard cubes as a function of comparison cube visual field, illumination elevation, and illumination azimuth. Results: Cubes appeared significantly brighter in the left visual field (p=.008), and when illuminated from below (p<.001). There was a trend for right-lit cubes to appear brighter (p=.069). The enhanced brightness of surfaces lit from below was greatest when also lit from the right (p=.001). Conclusions: Surfaces lit from below appear brighter (more illuminated) than identical surfaces lit from above, due perhaps to long-term adaptation to downward lighting. This effect is modulated by azimuth, being strongest for illumination from the right. Brightness is amplified in the left visual field, presumably via attentional enhancement. Meeting abstract presented at VSS 2013

False Pop Out and "Anti-metamers"

False Pop Out (FPO) occurs when distractor items in a singleton search display pose as targets. The phenomenon is observed in response distributions in which there are a disproportionately large number of responses given to one particular distractor(s) (see Supplement). Such error distributions have been found in various display types: 3 in a row, 4 in a square, and patterns composed of heterogeneous items. These findings are consistent with the Theory of Basic Gestalts (Pomerantz & Portillo, 2011), as these patterns of performance seem to be the result of inter-item grouping in visual search displays. That is, emergent features within search displays guide participants’ perceptions of the displays, resulting in consistent patterns of erroneous responding. Recent research has also searched for pure FPO, in which one distractor falsely receives all responses (see example of one such stimulus in Supplement). In this case, two identical items would look different from one another ("anti-metamers"), and with displays of three or more items (i.e., singleton displays) one of the homogeneous distractors would be incorrectly perceived as the target as much as 100% of the time. Meeting abstract presented at VSS 2013

The Cross Modality Asymmetrical Effect of Stimulus-driven Capture in Audiovisual Additional Singleton Search Task

The Cross Modality Asymmetrical Effect of Stimulus-driven Capture in Audiovisual Additional Singleton Search Task

Age-related interference from irrelevant distracters in visual feature search among heterogeneous distracters

We evaluated age-related variations in the influence of heterogeneous distracters during feature target. Participants in three age groups—6-year-old children, 9-year-old children, and young adults—completed three conditions of search. In a singleton search condition, participants searched for a circle among squares of the same color. In two feature mode search conditions, participants searched for a gray circle or a black circle among gray and black squares. Singleton search was performed at the same level of efficiency for all age groups. In contrast, the two feature mode search conditions yielded age-related performance differences in both conditions. Younger children exhibited a steeper slope than young adults when searching for a gray or black circle. Older children exhibited a steeper slope than young adults when searching for a gray circle but not when searching for a black circle. We concluded that these differences revealed age-related improvements in the relative abilities of adults and children to execute attentional control processes during visual search. In particular, it appears that children found it more difficult to maintain the goal of searching for a circle target than adults and were distracted by the presence of the irrelevant feature dimension of color.

Response retrieval in a go/no-go priming-of-popout task

Priming of popout is the finding that singleton search is faster when features of a target and of nontargets are repeated across trials than when the features switch. Theoretical accounts suggest that intertrial repetition influences perceptual and attentional selection processes, episodic retrieval processes, or both. The present study combined a popout search task with a go/no-go task. In Experiment 1, the nontarget distractors in each display carried the go/no-go feature, and in Experiment 2, the texture of all items carried the go/no-go feature. Results showed that the go/no-go task moderated the intertrial repetition effects. In Experiment 1, the target color elicited retrieval of the preceding distractor color and associated no-go response, resulting in larger interference effects. In Experiment 2, the target color elicited retrieval of the preceding target color and no-go response, resulting in reduced facilitation effects. Additional results from both experiments showed that the colors in a search display also influenced target selection on the following trial. Taken together, the results of both experiments suggest that intertrial repetition influences both early selection and postselection retrieval processes.

Attentional capture during visual search is attenuated by target predictability: Evidence from the N2pc, Pd, and topographic segmentation

Attentional capture by salient distractors has been confirmed by the occurrence of an N2pc to the salient distractor. To clarify some failures to replicate this finding, we varied target predictability to induce different search modes. In the unpredictable target condition, the target shape varied randomly from trial to trial, favoring singleton detection mode. In the predictable target condition, the target shape remained the same in a block of trials, favoring feature search mode. With unpredictable targets, we observed an N2pc toward the salient color distractor, confirming attentional capture in singleton search mode. With predictable targets, there was no N2pc to the salient distractor, but a distractor positivity (Pd), suggesting distractor suppression. Also, differences emerged in the topographic segmentation of N2pc and Pd. Further, the amplitude of the N2pc toward the target was larger with predictable than with unpredictable targets.

Target uncertainty does not lead to greater singleton distractor interference when target shapes are not interchangeable with nontarget shapes

Researchers have investigated whether attentional capture during visual search is driven by top-down processes, i.e. experimental goals and directives, or by bottom-up processes, i.e. the properties of the items within a search display. Some research has demonstrated that subjects cannot avoid attending to a task-irrelevant salient item, such as a singleton distractor, even when the identity of the target item is known. Research has also shown that repeating the target feature across successive search displays will prime the visual pop out effect for a unique target (priming of pop out). However, other research has shown that subjects can strategically guide their attention and may locate a target based on its uniqueness (a singleton search mode) or based on knowing and searching for the target feature (a feature search mode). When using the feature search mode subjects are attuned to the specific target feature and are therefore less susceptible to singleton distractor interference than when using the singleton search mode. Recent research has compared singleton distractor interference for targets that are variable and uncertain to targets that are constant and certain across search displays. When the target is constant subjects can use a feature search mode and should theoretically demonstrate less singleton distractor interference than when targets are variable and they must use a singleton search mode. Indeed, variable targets have historically demonstrated greater singleton distractor interference than constant targets, even when the target feature has been repeated. However, the current experiments found that singleton distractor interference was no greater for variable targets than for constant targets when targets and nontargets did not share shapes across search displays.