Distractor similarity and category variability effects in search.

Categorical search involves looking for objects based on category information from long-term memory. Previous research has shown that search efficiency in categorical search is influenced by target/distractor similarity and category variability (i.e., heterogeneity). However, the interaction between these factors and their impact on different subprocesses of search remains unclear. This study examined the effects of target/distractor similarity and category variability on processes of categorical search. Using multidimensional scaling, we manipulated target/distractor similarity and measured category variability for target categories that participants searched for. Eye-tracking data were collected to examine attentional guidance and target verification. The results demonstrated that the effect of category variability on response times (RTs) was dependent on the level of target/distractor similarity. Specifically, when distractors were highly similar to target categories, there was a negative relation between RTs and variability, with low variability categories producing longer RTs than higher variability categories. Surprisingly, this trend was only present in the eye-tracking measures of target verification but not attentional guidance. Our results suggest that searchers more effectively guide attention to low-variability categories compared to high-variability categories, regardless of the degree of similarity between targets and distractors. However, low category variability interferes with target match decisions when distractors are highly similar to the category, thus the advantage that low category variability provides to searchers is not equal across processes of search.

Eye movements reflect expertise development in hybrid search.

Domain-specific expertise changes the way people perceive, process, and remember information from that domain. This is often observed in visual domains involving skilled searches, such as athletics referees, or professional visual searchers (e.g., security and medical screeners). Although existing research has compared expert to novice performance in visual search, little work has directly documented how accumulating experiences change behavior. A longitudinal approach to studying visual search performance may permit a finer-grained understanding of experience-dependent changes in visual scanning, and the extent to which various cognitive processes are affected by experience. In this study, participants acquired experience by taking part in many experimental sessions over the course of an academic semester. Searchers looked for 20 categories of targets simultaneously (which appeared with unequal frequency), in displays with 0-3 targets present, while having their eye movements recorded. With experience, accuracy increased and response times decreased. Fixation probabilities and durations decreased with increasing experience, but saccade amplitudes and visual span increased. These findings suggest that the behavioral benefits endowed by expertise emerge from oculomotor behaviors that reflect enhanced reliance on memory to guide attention and the ability to process more of the visual field within individual fixations.

Typicality guides attention during categorical search, but not universally so.

The degree to which an item is rated as being a typical member of its category influences an observer's ability to find that item during word-cued search. However, there are conflicting accounts as to whether or not typicality affects attentional guidance to categorical items, or whether it affects some other aspect of the search process. In this study, we employed word-cued search and eye tracking to disentangle typicality effects on attentional guidance and target verification across differing category cue specificities (i.e., superordinate or basic-level cues), while also varying the degree of similarity between targets and non-targets. We found that typicality influenced attentional guidance when searchers were cued at the superordinate level (e.g., clothing). When cues were provided at the basic level (e.g., pants), typicality did not influence attentional guidance, and only affected target verification when there was featural similarity between targets and non-targets. When a searcher uses a target template comprising features cued at the basic level, therefore, target/non-target similarity produces interference that affects attentional guidance, but we did not find evidence that it also affects target verification.

Scene priming provides clues about target appearance that improve attentional guidance during categorical search.

During categorical search (e.g., "look for a dog"), observers have broad information about their intended target, but no specific details about the target's precise appearance. Research suggests that mental representations used to guide attention during categorical search (or search templates) comprise typical or category consistent features. Unlike laboratory settings, real world search is not conducted in isolation; yet to be understood is how context shapes categorical search templates. Here, participants searched for category items after viewing a contextual scene prime. Response times were consistently faster to context-congruent targets, even though searchers had no incentive to intentionally use the scene to shape their template. Eye movements revealed enhanced attentional guidance during congruent searches, suggesting that context allows searchers to develop more useful templates. Thus, contextual primes may trigger scene-specific schemas that activate object features in memory that can then be used to guide attention. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Categorical templates are more useful when features are consistent: Evidence from eye movements during search for societally important vehicles.

Unlike in laboratory visual search tasks-wherein participants are typically presented with a pictorial representation of the item they are asked to seek out-in real-world searches, the observer rarely has veridical knowledge of the visual features that define their target. During categorical search, observers look for any instance of a categorically defined target (e.g., helping a family member look for their mobile phone). In these circumstances, people may not have information about noncritical features (e.g., the phone's color), and must instead create a broad mental representation using the features that define (or are typical of) the category of objects they are seeking out (e.g., modern phones are typically rectangular and thin). In the current investigation (Experiment 1), using a categorical visual search task, we add to the body of evidence suggesting that categorical templates are effective enough to conduct efficient visual searches. When color information was available (Experiment 1a), attentional guidance, attention restriction, and object identification were enhanced when participants looked for categories with consistent features (e.g., ambulances) relative to categories with more variable features (e.g., sedans). When color information was removed (Experiment 1b), attention benefits disappeared, but object recognition was still better for feature-consistent target categories. In Experiment 2, we empirically validated the relative homogeneity of our societally important vehicle stimuli. Taken together, our results are in line with a category-consistent view of categorical target templates (Yu, Maxfield, & Zelinsky in, Psychological Science, 2016. doi: 10.1177/0956797616640237 ), and suggest that when features of a category are consistent and predictable, searchers can create mental representations that allow for the efficient guidance and restriction of attention as well as swift object identification.

Using multidimensional scaling to quantify similarity in visual search and beyond.

Visual search is one of the most widely studied topics in vision science, both as an independent topic of interest, and as a tool for studying attention and visual cognition. A wide literature exists that seeks to understand how people find things under varying conditions of difficulty and complexity, and in situations ranging from the mundane (e.g., looking for one's keys) to those with significant societal importance (e.g., baggage or medical screening). A primary determinant of the ease and probability of success during search are the similarity relationships that exist in the search environment, such as the similarity between the background and the target, or the likeness of the non-targets to one another. A sense of similarity is often intuitive, but it is seldom quantified directly. This presents a problem in that similarity relationships are imprecisely specified, limiting the capacity of the researcher to examine adequately their influence. In this article, we present a novel approach to overcoming this problem that combines multi-dimensional scaling (MDS) analyses with behavioral and eye-tracking measurements. We propose a method whereby MDS can be repurposed to successfully quantify the similarity of experimental stimuli, thereby opening up theoretical questions in visual search and attention that cannot currently be addressed. These quantifications, in conjunction with behavioral and oculomotor measures, allow for critical observations about how similarity affects performance, information selection, and information processing. We provide a demonstration and tutorial of the approach, identify documented examples of its use, discuss how complementary computer vision methods could also be adopted, and close with a discussion of potential avenues for future application of this technique.