Does Previewing One Stimulus Feature Help Conjunction Search?

Attentional disengagement effect based on relevant features

In visual search tasks, distractors similar to the target can attract our attention and affect the speed of attentional disengagement. The attentional disengagement refers to shifting attention away from stimuli that are not relevant to the task. Previous studies mainly focused on the attentional disengagement of one feature dimension. However, the mechanisms of different feature dimensions on attentional disengagement in single and conjunction visual search remain unclear. In the current study, we adopted the oculomotor disengagement paradigm and used saccade latency as an indicator to explore the effects of different feature dimensions of center stimuli on attentional disengagement. In both single and conjunction feature search tasks, participants began each search by fixating on a center stimulus that appeared simultaneously with search display but would not be the target. Participants were instructed to ensure the first saccade to the target location. In Experiments 1A (single feature search) and 1B (conjunction feature search), we found that the attentional disengagement was significantly delayed or accelerated when center stimuli shared color features with the target or salient distractor, but not in shape feature. Moreover, we found that the difference between the two feature dimensions might be caused by their different search difficulty (Experiment 1C). Therefore, in Experiment 2, we matched the difficulty of searching for color and shape tasks before exploring whether there were differences in the effects of different feature dimensions on attentional disengagement. However, the results in Experiment 2 were similar to those in Experiment 1A, indicating that the different effects of feature dimensions on attentional disengagement were caused by feature asymmetry. Therefore, in Experiment 3, we improved the salient discernibility of shape dimension and matched color search to it. The results showed that although the attentional disengagement was delayed in shape dimension, it was still smaller than that in color dimension. Our results supported that goal-oriented attention sets were the main cause of delayed attentional disengagement. By series of experiments, we found that the utilization of different feature dimensions was associated with task difficulty and the features asymmetry in both single and conjunction visual search.

Guided Search 6.0: An updated model of visual search

This paper describes Guided Search 6.0 (GS6), a revised model of visual search. When we encounter a scene, we can see something everywhere. However, we cannot recognize more than a few items at a time. Attention is used to select items so that their features can be "bound" into recognizable objects. Attention is "guided" so that items can be processed in an intelligent order. In GS6, this guidance comes from five sources of preattentive information: (1) top-down and (2) bottom-up feature guidance, (3) prior history (e.g., priming), (4) reward, and (5) scene syntax and semantics. These sources are combined into a spatial "priority map," a dynamic attentional landscape that evolves over the course of search. Selective attention is guided to the most active location in the priority map approximately 20 times per second. Guidance will not be uniform across the visual field. It will favor items near the point of fixation. Three types of functional visual field (FVFs) describe the nature of these foveal biases. There is a resolution FVF, an FVF governing exploratory eye movements, and an FVF governing covert deployments of attention. To be identified as targets or rejected as distractors, items must be compared to target templates held in memory. The binding and recognition of an attended object is modeled as a diffusion process taking > 150 ms/item. Since selection occurs more frequently than that, it follows that multiple items are undergoing recognition at the same time, though asynchronously, making GS6 a hybrid of serial and parallel processes. In GS6, if a target is not found, search terminates when an accumulating quitting signal reaches a threshold. Setting of that threshold is adaptive, allowing feedback about performance to shape subsequent searches. Simulation shows that the combination of asynchronous diffusion and a quitting signal can produce the basic patterns of response time and error data from a range of search experiments.

Preview of partial stimulus information in search prioritizes features and conjunctions, not locations

Visual search often requires combining information on distinct visual features such as color and orientation, but how the visual system does this is not fully understood. To better understand this, we showed observers a brief preview of part of a search stimulus-either its color or orientation-before they performed a conjunction search task. Our experimental questions were (1) whether observers would use such previews to prioritize either potential target locations or features, and (2) which neural mechanisms might underlie the observed effects. In two experiments, participants searched for a prespecified target in a display consisting of bar elements, each combining one of two possible colors and one of two possible orientations. Participants responded by making an eye movement to the selected bar. In our first experiment, we found that a preview consisting of colored bars with identical orientation improved saccadic target selection performance, while a preview of oriented gray bars substantially decreased performance. In a follow-up experiment, we found that previews consisting of discs of the same color as the bars (and thus without orientation information) hardly affected performance. Thus, performance improved only when the preview combined color and (noninformative) orientation information. Previews apparently result in a prioritization of features and conjunctions rather than of spatial locations (in the latter case, all previews should have had similar effects). Our results thus also indicate that search for, and prioritization of, combinations involve conjunctively tuned neural mechanisms. These probably reside at the level of the primary visual cortex.

Perceptual similarity in visual search for multiple targets

Visual search for multiple targets can cause errors called subsequent search misses (SSM) - a decrease in accuracy at detecting a second target after a first target has been found. One of the possible explanations of SSM errors is perceptual set. After the first target has been found, the subjects become biased to find perceptually similar targets, therefore they are more likely to find perceptually similar targets and less likely to find the targets that are perceptually dissimilar. This study investigated the role of perceptual similarity in SSM errors. The search array in each trial consisted of 20 stimuli (ellipses and crosses, black and white, small and big, oriented horizontally and vertically), which could contain one, two or no targets. In case of two targets, the targets could have two, three or four shared features (in the last case the targets were identical). The error rate decreased with increasing the similarity between the targets. These results state the role of perceptual similarity and have implications for the perceptual set theory.

Reference Production as Search: The Impact of Domain Size on the Production of Distinguishing Descriptions

When producing a description of a target referent in a visual context, speakers need to choose a set of properties that distinguish it from its distractors. Computational models of language production/generation usually model this as a search process and predict that the time taken will increase both with the number of distractors in a scene and with the number of properties required to distinguish the target. These predictions are reminiscent of classic findings in visual search; however, unlike models of reference production, visual search models also predict that search can become very efficient under certain conditions, something that reference production models do not consider. This paper investigates the predictions of these models empirically. In two experiments, we show that the time taken to plan a referring expression-as reflected by speech onset latencies-is influenced by distractor set size and by the number of properties required, but this crucially depends on the discriminability of the properties under consideration. We discuss the implications for current models of reference production and recent work on the role of salience in visual search.

Using feature preview to investigate the roles of top-down and bottom-up processing in conjunction search

The venerable conjunction search paradigm is a widely used tool to investigate how we search for items of interest from among visually complex surroundings. Models of visual search have long predicted that standard conjunction search is guided primarily by top-down processing. Prior attempts to test this claim experimentally have done so by altering some aspect of the standard conjunction search, whether by manipulating the distractor ratio or by including a feature singleton. Although suggestive, these manipulations result in a task that differs slightly from standard conjunction search. To leave the standard conjunction search paradigm intact, we used the feature preview task developed by Olds and Fockler [Olds, E. S., & Fockler, K. A. (2004). Does previewing one stimulus feature help conjunction search? Perception, 33, 195-216]. Our results show that in standard conjunction search the effect of bottom-up activation is not necessarily detrimental to search performance as previously suggested by computational models of visual search. Instead, bottom-up activation limits the scope of search, thereby boosting the efficiency of standard conjunction searches. Subjects also showed a bias to group items by color rather than orientation even when color differences were reduced nearly to threshold, indicating that the salience advantage of color is complemented by a general bottom-up preference for color.

Feature head-start: Conjunction search following progressive feature disclosure

When a colour/orientation conjunction search display is immediately preceded by a display that shows either the colour or the orientation of each upcoming search item, search is faster after colour-preview than after orientation-preview. One explanation for this feature asymmetry is that colour has priority access to attentional selection relative to features such as orientation and size. In support of this hypothesis, we show that this asymmetry persists even after colour and orientation feature search performance is equated. However, this notion was ruled out by our subsequent experiments in which the target was defined by conjunction of colour and size; colour-preview was less helpful than size-preview (even though colour-feature search was faster than size-feature search, for these feature values). A final set of experiments tested size-preview vs. orientation-preview for size/orientation conjunction search, using stimuli for which orientation-feature search was easier than size-feature search. Size-preview produced much faster search than orientation-preview, demonstrating again that ease of feature search does not predict effects of a feature-preview. Overall, size produced the most facilitation when presented as a feature-preview (for both colour/size and size/orientation conjunctions), followed by colour (for colour/orientation conjunction but not for colour/size conjunction) and then orientation (which never facilitated search). Whilst each feature-preview may potentially facilitate search, the transition from feature-preview display to search display could disrupt search processes, because of luminance and/or colour changes. We see evidence for some sort of disruption when the feature-preview slows search. An explanation of this set of results must focus on both facilitation and disruption: these effects are not mutually exclusive, and neither suffices alone, since performance after feature-preview can be significantly better or significantly worse than conjunction baseline.

Inefficient conjunction search made efficient by concurrent spoken delivery of target identity

Visual search based on a conjunction of two features typically elicits reaction times that increase linearly as a function of the number of distractors, whereas search based on a single feature is essentially unaffected by set size. These and related findings have often been interpreted as evidence of a serial search stage that follows a parallel search stage. However, a wide range of studies has been showing a form of blending of these two processes. For example, when a spoken instruction identifies the conjunction target concurrently with the visual display, the effect of set size is significantly reduced, suggesting that incremental linguistic processing of the first feature adjective and then the second feature adjective may facilitate something approximating a parallel extraction of objects during search for the target. Here, we extend these results to a variety of experimental designs. First, we replicate the result with a mixed-trials design (ruling out potential strategies associated with the blocked design of the original study). Second, in a mixed-trials experiment, the order of adjective types in the spoken query varies randomly across conditions. In a third experiment, we extend the effect to a triple-conjunction search task. A fourth (control) experiment demonstrates that these effects are not due to an efficient odd-one-out search that ignores the linguistic input. This series of experiments, along with attractor-network simulations of the phenomena, provide further evidence toward understanding linguistically mediated influences in real-time visual search processing.