Young children's spontaneous inspection of negative instances in a search task

Forty children 1 1/2 to 3 1/2 years of age searched for stickers that were hidden underneath two discretely different classes of objects embedded in arrays containing several classes. The paper focuses on a previously unobserved strategy that appeared at 3 1/2. Whereas the younger children searched underneath those objects that looked like the objects the children knew had stickers, the 3 1/2-year-olds systematically explored not only the objects that did, but also the objects that did not, have stickers. Eight adults performed similarly to the 3 1/2-year-olds. Analyses of developmental trends in the data and the observation of individual children performing the tasks suggest that the children's increased inspection of the negative objects was not merely the result of a random or more exhaustive search. The children appear to have been attempting to determine which kinds of choices were the wrong ones. The attempt to define and delimit negative cases is a central aspect of reflective thought.     

Task preparation and task repetition: two-component model of task switching.

The switch cost (the disadvantage of performing a new task vs. a repeated task) has been attributed to lack of preparation for the switched task or priming of the repeated task. These sources were examined by manipulating foreknowledge of task transition (repeat or switch), response-to-stimulus interval (RSI), and practice level. Regardless of foreknowledge, the cost decreased with RSI and practice. The reduction was greater with foreknowledge than with no foreknowledge, and the amount of switch cost did not depend on foreknowledge. These results suggest that the switch cost with foreknowledge may consist of both inadequate preparation and repetition benefit but the switch cost with no foreknowledge may reflect repetition benefit only. An ACT-R (adaptive control of thought-rational) model was proposed, accommodating both preparation and priming effect with 2 independent processes: conflict resolution among productions and decay of chunk activation.     

Visual search and foraging compared in a large-scale search task

It has been argued that visual search is a valid model for human foraging. However, the two tasks differ greatly in terms of the coding of space and the effort required to search. Here we describe a direct comparison between visually guided searches (as studied in visual search tasks) and foraging that is not based upon a visually distinct target, within the same context. The experiment was conducted in a novel apparatus, where search locations were indicated by an array of lights embedded in the floor. In visually guided conditions participants searched for a target defined by the presence of a feature (red target amongst green distractors) or the absence of a feature (green target amongst red and green distractors). Despite the expanded search scale and the different response requirements, these conditions followed the pattern found in conventional visual search paradigms: feature-present search latencies were not linearly related to display size, whereas feature-absent searches were longer as the number of distractors increased. In a non-visually guided foraging condition, participants searched for a target that was only visible once the switch was activated. This resulted in far longer latencies that rose markedly with display size. Compared to eye-movements in previous visual search studies, there were few revisit errors to previously inspected locations in this condition. This demonstrates the important distinction between visually guided and non-visually guided foraging processes, and shows that the visual search paradigm is an equivocal model for general search in any context. We suggest a comprehensive model of human spatial search behaviour needs to include search at a small and large scale as well as visually guided and non-visually guided search.     

Implicit sequence learning in a search task

This study investigated the effects of selection demands on implicit sequence learning. Participants in a search condition looked for a target among seven distractors and responded on the target identity. The responses followed a deterministic sequence, and sequence learning was compared to that found in two control conditions in which the targets were presented alone, either at a central location or over a series of unpredictable locations. Sequence learning was obtained in all conditions, and it was equivalent for the two variable location conditions, regardless of the perceptual demands. Larger effects of learning were observed in the central location, both on the indirect measures and on the measures taken from a cued-generation task. The expression of learning decreased selectively in this condition when the sequence validity was reduced over a test block. These results are consistent with the claims that implicit and explicit learning are mixed in this central condition and that implicit learning is not affected by selection difficulty.     

Implicit sequence learning in a search task

This study investigated the effects of selection demands on implicit sequence learning. Participants in a search condition looked for a target among seven distractors and responded on the target identity. The responses followed a deterministic sequence, and sequence learning was compared to that found in two control conditions in which the targets were presented alone, either at a central location or over a series of unpredictable locations. Sequence learning was obtained in all conditions, and it was equivalent for the two variable location conditions, regardless of the perceptual demands. Larger effects of learning were observed in the central location, both on the indirect measures and on the measures taken from a cued-generation task. The expression of learning decreased selectively in this condition when the sequence validity was reduced over a test block. These results are consistent with the claims that implicit and explicit learning are mixed in this central condition and that implicit learning is not affected by selection difficulty.     

Explanation and verbalization in a computer-assisted search task

Three experiments examine the effects of two different forms of explanation on assisted performance on a complex search task. The task involves determining which of a set of factories is responsible for polluting a river by testing the river for the presence or absence of various pollutants. All subjects receive computer suggestions as to which pollutants they should test for. In addition, some subjects receive an explanation of the principle according to which the advice program works. Two forms of explanation are compared. Experiment 1 shows that subjects who are allowed to ask “why” each computer recommendation is made perform significantly better than those who are provided with a block text of explanation at the start of each trial. Experiment 2 shows that the latter type of explanation is not completely ineffective, however. Subjects who are required to verbalize following the single explanation perform significantly better than do subjects who are required to verbalize but who have not received any form of explanation. Finally, Experiment 3 shows that subjects who receive the multiple “why” explanations or the explanation/verbalization combination maintain a superior performance level on subsequent unaided trials.     

Global statistical learning in a visual search task

Locating a target in a visual search task is facilitated when the target location is repeated on successive trials. Global statistical properties also influence visual search, but have often been confounded with local regularities (i.e., target location repetition). In two experiments, target locations were not repeated for four successive trials, but with a target location bias (i.e., the target appeared on one half of the display twice as often as the other). Participants quickly learned to make more first saccades to the side more likely to contain the target. With item-by-item search first saccades to the target were at chance. With a distributed search strategy first saccades to a target located on the biased side increased above chance. The results confirm that visual search behavior is sensitive to simple global statistics in the absence of trial-to-trial target location repetitions.     

Toddlers' use of cues in a search task

Search for a ball that has undergone hidden motion rapidly improves during the second year of life (Dev. Psychol., 2000; 36 :394–401). In three experiments we investigated whether the poor performance of younger toddlers was due to attentional failure by highlighting the major cue for the hidden object. We observed only slight improvement in search behaviour. We performed two other experiments that tested the depth of understanding of 3‐year‐olds in this task and found that their performance was robust to changes in the apparatus and experimental procedures. Overall, the results point to a rapidly developing ability in the second year of life to either reason about space or select the correct motor response in search tasks. Copyright © 2008 John Wiley & Sons, Ltd.     

Lateralization of a food search task in the domestic chick

Monocularly occluded Warren sex-linked domestic chicks (Gallus domesticus) were presented with a search test which required the differentiation of familiar food grains from unfamiliar pebbles bearing a strong resemblance to food. Male and female chicks using their left eye performed this discrimination significantly more poorly than did chicks using their right eye, both during learning and after asymptotic performance was reached. This left/right difference was superimposed upon a difference between the sexes, with females pecking fewer pebbles than males. Because of the complexity of the search test utilized, it is difficult to determine whether the left/right difference found is attributable to lateralization of visual discrimination ability or to other factors, such as lateralized differences in food search pattern or investigatory responses to novel pebbles. Nevertheless, asymmetric responses of this type provide additional evidence that lateralization of function in the brain, long thought to be a uniquely human phenomenon, is widespread among vertebrates.     

You detect while I search: examining visual search efficiency in a joint search task

Numerous factors impact attentional allocation, with behaviour being strongly influenced by the interaction between individual intent and our visual environment. Traditionally, visual search efficiency has been studied under solo search conditions. Here, we propose a novel joint search paradigm where one individual controls the visual input available to another individual via a gaze contingent window (e.g., Participant 1 controls the window with their eye movements and Participant 2 – in an adjoining room – sees only stimuli that Participant 1 is fixating and responds to the target accordingly). Pairs of participants completed three blocks of a detection task that required them to: (1) search and detect the target individually, (2) search the display while their partner performed the detection task, or (3) detect while their partner searched. Search was most accurate when the person detecting was doing so for the second time while the person controlling the visual input was doing so for the first time, even when compared to participants with advanced solo or joint task experience (Experiments 2 and 3). Through surrendering control of one’s search strategy, we posit that there is a benefit of a reduced working memory load for the detector resulting in more accurate search. This paradigm creates a counterintuitive speed/accuracy trade-off which combines the heightened ability that comes from task experience (discrimination task) with the slower performance times associated with a novel task (the initial search) to create a potentially more efficient method of visual search.     

Stimulus segmentation in the visual search task

Four experiments were conducted in order to study the segmentation process in a visual search task with relevant stimuli (target and distractors) randomly distributed among textural elements. The basic idea was that a parallel segmentation process of the relevant stimuli would contribute to the overall reaction time independently of the contribution of the number of relevant stimuli. In the first experiment, with relevant stimuli and textural elements that differed in the orientation of their component lines, texture presence interacted with number of relevant stimuli and with target presence. These results were not favorable to the parallel segmentation hypothesis. In the second and third experiments, in which the relevant and the textural stimuli differed in orientation and in the luminance contrast of their component lines, the results support a parallel segmentation process for the higher contrast conditions. In these experiments, the effect of texture presence was greater on target-absent than on target-present trials. Experiment 4 shows that the search can be restricted to the high-contrast relevant stimuli when the number of these stimuli is constant and the number of textural stimuli changes from trial to trial. The present results suggest that the relevant stimuli can be segmented in parallel and then submitted to a restricted analysis, even when they are scattered among textural stimuli.     

Control of fixation duration in a simple search task

To obtain insight into the control of fixation duration during visual search, we had 4 subjects perform simple search tasks in which we systematically varied the discriminability of the target. The experiment was carried out under two conditions. Under the first condition (blocked), the discriminability of the target was kept constant during a session. Under the second condition (mixed), the discriminability of the target varied per trial. Under the blocked condition, fixation duration increased with decreasing discriminability. For 2 subjects, we found much shorter fixation durations in difficult trials with the mixed condition than in difficult trials with the blocked condition. Overall, the subjects fixated the target, continued to search, and then went back to the target in 5%–55% of the correct trials. In these trials, the result of the analysis of the foveal target was not used for preparing the next saccade. The results support a preprogramming model of the control of fixation duration. In a simple search task, control of fixation duration appears to be indirect.     

Object boundaries influence toddlers' performance in a search task

Previous research has shown that young children have difficulty searching for a hidden object whose location depends on the position of a partly visible physical barrier. Across four experiments, we tested whether children's search errors are affected by two variables that influence adults' object-directed attention: object boundaries and proximity relations. Toddlers searched for a car that rolled down a ramp behind an occluding panel and stopped on contact with a barrier. The car's location on each trial depended on the placement of the barrier behind one of two doors in the panel. In Experiment 1, when a part of the car (a pompom on an antenna) was visible at the same distance from the object as the barrier wall in past research, search performance was above chance but below ceiling. In Experiments 2 and 3, when the visible part was close to the hidden body of the car and could be seen through one of two windows in the doors of the occluding panel, performance was near ceiling. In Experiment 4, when only the barrier was visible through one of the same windows, performance was at chance. Toddlers' search for a hidden object therefore is affected by the proximity of a visible part of the object, though not by the proximity of a separate visible landmark. These findings suggest a parallel between the object representations of young children and those of adults, whose attention is directed to objects and spreads in a gradient-like fashion within an object.     

An informational analysis of a visual search task

An earlier paper examined a visual-search task that required a S to locate a two-digit symbol from an array of digits. The results were not subjected to a detailed theoretical analysis. The present paper suggests an information-theory analysis of the data and shows that all of the data can be reduced to a consistent format. It is also argued that such an analysis may prove fruitful in the investigation of search strategies.