The development of organized rehearsal

The purpose of this research was to evaluate the development or organization strategies in rehearsal processes. First-grade (age 7 years), third-grade (age 9 years), and fifth-grade (age 11 years) children were exposed to a memory task which involved multiple overt rehearsal and recall phases. The children were either free to rehearse any words from a taxonomically structured list or they were taught to rehearse in categories. The recall phase was either free or categorically cued. The number of repetitions in rehearsal increased only as a function of age. All of the independent variables facilitated the amount of organized rehearsal and the amount of retention. Children at all ages were able to maximize the relative amount of organized rehearsal when rehearsal was cued. The correlational analysis of the dependent variables indicated that for young children the quantity of rehearsal was linked to retention, but for older children the quality of rehearsal was related to retention. The results were interpreted as demonstrating the bases for production inefficiencies.     

The development of visual search in infants and very young children.

In two experiments, 90 1- to 3-year-olds were trained in a new nonverbal task to touch a video screen that displayed a unique target resembling a popular television character. The target appeared among varying numbers of distractors that resembled another familiar television character and was either a uniquely colored shape (the feature search task) or a unique color-shape combination (the conjunction search task). Each correct response triggered a sound and produced four animated objects on the screen. Irrespective of age and experimental design (between-subjects or within-subjects), children's reaction time (RT) patterns resembled those obtained from adults in corresponding search tasks: The RT slope for feature search was flat and independent of distractor number, whereas the RT slope for conjunction search increased linearly with distractor number. These results extend visual search effects found with adults to infants and very young children and suggest that the basic perceptual processes underlying visual search are qualitatively invariant over ontogeny.     

The contents of visual working memory reduce uncertainty during visual search

Information held in visual working memory (VWM) influences the allocation of attention during visual search, with targets matching the contents of VWM receiving processing benefits over those that do not. Such an effect could arise from multiple mechanisms: First, it is possible that the contents of working memory enhance the perceptual representation of the target. Alternatively, it is possible that when a target is presented among distractor items, the contents of working memory operate postperceptually to reduce uncertainty about the location of the target. In both cases, a match between the contents of VWM and the target should lead to facilitated processing. However, each effect makes distinct predictions regarding set-size manipulations; whereas perceptual enhancement accounts predict processing benefits regardless of set size, uncertainty reduction accounts predict benefits only with set sizes larger than 1, when there is uncertainty regarding the target location. In the present study, in which briefly presented, masked targets were presented in isolation, there was a negligible effect of the information held in VWM on target discrimination. However, in displays containing multiple masked items, information held in VWM strongly affected target discrimination. These results argue that working memory representations act at a postperceptual level to reduce uncertainty during visual search.     

The effect of visualization on visual search performance

Striking results recently demonstrated that visualizing search for a target can facilitate visual search for that target on subsequent trials (Reinhart et al. 2015). This visualization benefit was even greater than the benefit of actually repeating search for the target. We registered a close replication and generalization of the original experiment. Our results show clear benefits of repeatedly searching for the same target, but we found no benefit associated with visualization. The difficulty of the search task and the ability to monitor compliance with instructions to visualize are both possible explanations for the failure to replicate, and both should be carefully considered in future research exploring this interesting phenomenon.     

The influence of cast shadows on visual search

We show that cast shadows can have a significant influence on the speed of visual search. In particular, we find that search based on the shape of a region is affected when the region is darker than the background and corresponds to a shadow formed by lighting from above. Results support the proposal that an early-level system rapidly identifies regions as shadows and then discounts them, making their shapes more difficult to access. Several constraints used by this system are mapped out, including constraints on the luminance and texture of the shadow region, and on the nature of the item casting the shadow. Among other things, this system is found to distinguish between line elements (items containing only edges) and surface elements (items containing visible surfaces), with only the latter deemed capable of casting a shadow.     

The control of fixation duration in visual search

A study is reported how fixation durations are affected as observers voluntarily use information in the visual environment to direct saccades in search of a target. In experiments with direction-coded displays, search fixation durations for correct and incorrectly directed saccades were comparable during image-driven/bottom-up search. In contrast, for knowledge-driven search, the relationship depended on peripheral preview. With ample access to peripheral preview, search fixation durations preceding correct saccades were shorter than those preceding incorrectly directed saccades. However, they were longer when preview was constrained by a gaze-contingent moving window. Fixation control was modeled as sigmoid functions.     

The role of priming in conjunctive visual search

To assess the role of priming in conjunctive visual search tasks, we systematically varied the consistency of the target and distractor identity between different conditions. Search was fastest in the standard conjunctive search paradigm where identities remained constant. Search was slowest when potential target identity varied predictably for each successive trial (the 'switch' condition). The role of priming was also demonstrated on a trial-by-trial basis in a 'streak' condition where target and distractor identity was unpredictable yet was consistent within streaks. When the target to be found was the same for a few trials in a row, search performance became similar to that when the potential target was the same on all trials. A similar pattern was found for the target absent trials, suggesting that priming is based on the whole search array rather than just the target in each case. Further analysis indicated that the effects of priming are sufficiently strong to account for the advantage seen for the conjunctive search task. We conclude that the role of priming in visual search is underestimated in current theories of visual search and that differences in search times often attributed to top-down guidance may instead reflect the benefits of priming.     

Linguistically mediated visual search

During an individual's normal interaction with the environment and other humans, visual and linguistic signals often coincide and can be integrated very quickly. This has been clearly demonstrated in recent eyetracking studies showing that visual perception constrains on-line comprehension of spoken language. In a modified visual search task, we found the inverse, that real-time language comprehension can also constrain visual perception. In standard visual search tasks, the number of distractors in the display strongly affects search time for a target defined by a conjunction of features, but not for a target defined by a single feature. However, we found that when a conjunction target was identified by a spoken instruction presented concurrently with the visual display, the incremental processing of spoken language allowed the search process to proceed in a manner considerably less affected by the number of distractors. These results suggest that perceptual systems specialized for language and for vision interact more fluidly than previously thought.     

Collaboration during visual search

Two experiments examine how collaboration influences visual search performance. Working with a partner or on their own, participants reported whether a target was present or absent in briefly presented search displays. We compared the search performance of individuals working together (collaborative pairs) with the pooled responses of the individuals working alone (nominal pairs). Collaborative pairs were less likely than nominal pairs to correctly detect a target and they were less likely to make false alarms. Signal detection analyses revealed that collaborative pairs were more sensitive to the presence of the target and had a more conservative response bias than the nominal pairs. This pattern was observed even when the presence of another individual was matched across pairs. The results are discussed in the context of task-sharing, social loafing and current theories of visual search.     

Reading and visual search

Four experiments were conducted comparing the ways in which reading and search are affected by manipulations of word shape and word boundary. Word shape was manipulated by variations in type (normal, capitals, and alternating upper- and lowercase), while word boundary was manipulated by variations in spacing (normal, filled, and absent). The variations were combined factorially for nine space-type combinations. Experiments I and II were basic studies examining the effects of the manipulations on reading and on search, respectively. Search was found to be 2 to 2.5 times faster than reading. Reading and search both slowed to one-third of the normal speeds when spaces were removed and type altered. A significant interaction of Type by Space was found for reading but not for search. Experiments III and IV examined contextual and typographical effects on high-speed visual search through paragraphs. Form-class expectancy and target word predictability, respectively, were manipulated. In both experiments, subjects found the expected predictable words faster than the unexpected unpredictable words. The data were interpreted as providing support for the peripheral and cognitive search guidance processes hypothesized to be active in reading.     

Selection-for-action in visual search

Grasping an object rather than pointing to it enhances processing of its orientation but not its color. Apparently, visual discrimination is selectively enhanced for a behaviorally relevant feature. In two experiments we investigated the limitations and targets of this bias. Specifically, in Experiment 1 we were interested to find out whether the effect is capacity demanding, therefore we manipulated the set-size of the display. The results indicated a clear cognitive processing capacity requirement, i.e. the magnitude of the effect decreased for a larger set size. Consequently, in Experiment 2, we investigated if the enhancement effect occurs only at the level of behaviorally relevant feature or at a level common to different features. Therefore we manipulated the discriminability of the behaviorally neutral feature (color). Again, results showed that this manipulation influenced the action enhancement of the behaviorally relevant feature. Particularly, the effect of the color manipulation on the action enhancement suggests that the action effect is more likely to bias the competition between different visual features rather than to enhance the processing of the relevant feature. We offer a theoretical account that integrates the action-intention effect within the biased competition model of visual selective attention.     

Colour-cueing in visual search

Several studies have shown that people can selectively attend to stimulus colour, e.g., in visual search, and that preknowledge of a target colour can improve response speed/accuracy. The purpose was to use a form-identification task to determine whether valid colour precues can produce benefits and invalid cues costs. The subject had to identify the orientation of a "T"-shaped element in a ring of randomly-oriented "L"s when either two or four of the elements were differently coloured. Contrary to Moore and Egeth's (1998) recent findings, colour-based attention did affect performance under data-limited conditions: Colour cues produced benefits when processing load was high; when the load was reduced, they incurred only costs. Surprisingly, a valid colour cue succeeded in improving performance in the high-load condition even when its validity was reduced to the chance level. Overall, the results suggest that knowledge of a target colour does not facilitate the processing of the target, but makes it possible to prioritize it.     

Introspection during visual search

Recent advances in the field of metacognition have shown that human participants are introspectively aware of many different cognitive states, such as confidence in a decision. Here we set out to expand the range of experimental introspection by asking whether participants could access, through pure mental monitoring, the nature of the cognitive processes that underlie two visual search tasks: an effortless “pop-out” search, and a difficult, effortful, conjunction search. To this aim, in addition to traditional first order performance measures, we instructed participants to give, on a trial-by-trial basis, an estimate of the number of items scanned before a decision was reached. By controlling response times and eye movements, we assessed the contribution of self-observation of behavior in these subjective estimates. Results showed that introspection is a flexible mechanism and that pure mental monitoring of cognitive processes is possible in elementary tasks.     

Attention demands of visual search

The relation between attention demand and the number of items in the array (array size) was investigated by engaging subjects in a primary search task and measuring spare capacity at different points in time, with a secondary tone task that occurred randomly on half of the trials. The major variables in both tasks were array size 14, 8, or 12 letters and stimulus onset asynchrony (SOA: ?400, ?200, 0, 200, 400, and 600 msec. Subjects were able to perform the tasks quite independently, and me, st of the interference that resulted from nonindependence appeared in tone-task performance. Theamount of interference (i.e., maximum tone reaction time) was independent of array size, but theduration of interference (li.e., the number of SOAs at which tone reaction time was elevated) increased with array size. The findings were interpreted as supporting unlimited-capacity models of visual search performance.     

Hiding and finding: The relationship between visual concealment and visual search

As an initial step toward developing a theory of visual concealment, we assessed whether people would use factors known to influence visual search difficulty when the degree of concealment of objects among distractors was varied. In Experiment 1, participants arranged search objects (shapes, emotional faces, and graphemes) to create displays in which the targets were in plain sight but were either easy or hard to find. Analyses of easy and hard displays created during Experiment 1 revealed that the participants reliably used factors known to influence search difficulty (e.g., eccentricity, target—distractor similarity, presence/absence of a feature) to vary the difficulty of search across displays. In Experiment 2, a new participant group searched for the targets in the displays created by the participants in Experiment 1. Results indicated that search was more difficult in the hard than in the easy condition. In Experiments 3 and 4, participants used presence versus absence of a feature to vary search difficulty with several novel stimulus sets. Taken together, the results reveal a close link between the factors that govern concealment and the factors known to influence search difficulty, suggesting that a visual search theory can be extended to form the basis of a theory of visual concealment.     

The nature of the visual environment induces implicit biases during language-mediated visual search

Four eyetracking experiments examined whether semantic and visual-shape representations are routinely retrieved from printed word displays and used during language-mediated visual search. Participants listened to sentences containing target words that were similar semantically or in shape to concepts invoked by concurrently displayed printed words. In Experiment 1, the displays contained semantic and shape competitors of the targets along with two unrelated words. There were significant shifts in eye gaze as targets were heard toward semantic but not toward shape competitors. In Experiments 2–4, semantic competitors were replaced with unrelated words, semantically richer sentences were presented to encourage visual imagery, or participants rated the shape similarity of the stimuli before doing the eyetracking task. In all cases, there were no immediate shifts in eye gaze to shape competitors, even though, in response to the Experiment 1 spoken materials, participants looked to these competitors when they were presented as pictures (Huettig & McQueen, 2007). There was a late shape-competitor bias (more than 2,500 ms after target onset) in all experiments. These data show that shape information is not used in online search of printed word displays (whereas it is used with picture displays). The nature of the visual environment appears to induce implicit biases toward particular modes of processing during language-mediated visual search.