Search

Abstract-Our recently introduced technique for multi-objective search of conceptual solutions, based on interactive evolutionary computation, is extended. The extension deals with concepts, which are represented by hierarchical trees of sub-concepts. [...]

The evaluative character of a word is called its semantic orientation. Positive semantic orientation indicates praise (e.g., "honest", "intrepid") and negative semantic orientation indicates criticism (e.g., "disturbing", "superfluous"). Semantic orientation varies in both direction (positive or negative) and degree (mild to strong). An automated system for measuring semantic orientation would have application in text classification, text filtering, tracking opinions in online discussions, analysis of survey responses, and automated chat systems (chatbots). This article introduces a method for inferring the semantic orientation of a word from its statistical association with a set of positive and negative paradigm words. Two instances of this approach are evaluated, based on two different statistical measures of word association: pointwise mutual information (PMI) and latent semantic analysis (LSA). The method is experimentally tested with 3,596 words (including adjectives, adverbs, nouns, and verbs) that have been manually labeled positive (1,614 words) and negative (1,982 words). The method attains an accuracy of 82.8% on the full test set, but the accuracy rises above 95% when the algorithm is allowed to abstain from classifying mild words. Categories and Subject Descriptors: H.3.1 [Information Storage and Retrieval]: Content Analysis and Indexing--linguistic processing; H.3.3 [Information Storage and Retrieval]: Information Search and Retrieval--information filtering, search process; 1.2.7 [Artificial Intelligence]: Natural Language Processing--text analysis General Terms: Algorithms, Experimentation Additional Key Words and Phrases: semantic orientation, semantic association, web mining, text mining, text classification, unsupervised learning, mutual information latent semantic analysis

The Reference in Context team at OCLC has been trying to get a better understanding of how people look for information in a library setting. We are using a 'user-centered' design method called Contextual Design to focus our information gathering and data analysis. The study provides many ideas about ways to enhance reference access and will improve our ability to design future end user oriented retrieval systems.

This paper studies the flows of funds into and out of equity mutual funds. Consumers base their fund purchase decisions on prior performance information, but do so asymmetrically, investing disproportionately more in funds that performed very well the prior period. Search costs seem to be an important determinant of fund flows. High performance appears to be most salient for funds that exert higher marketing effort, as measured by higher fees. Flows are directly related to the size of the fund's complex as well as the current media attention received by the fund, which lower consumers' search costs. (Reprinted by permission of the publisher.)

Pigeons searched for two targets that varied in similarity to items in the background. The targets, simulating 'prey,' were small alphabetic characters presented on computer monitors among distractor characters. In the first experiment, the probability of reinforcement for pecking at the targets was manipulated. In the second experiment, the response requirement for one of the targets was varied. Changing the probability of reinforcement led to more efficient search and increased choice for the more reinforced item. This effect carried over to subsequent equal reinforcement baseline conditions. Increasing the response requirement for one item increased response tune for that item and reduced choice of the item. This effect did not carry over to a subsequent baseline condition. The results suggested that a high probability of reinforcement resulted in improved detection of the item, perhaps through perceptual learning, and increased the incentive that motivated response to the item, but that high response requirement resulted only in an incentive shift.

In four experiments, we examined how the spatiotemporal proximity to food of the two elements of a serial conditioned stimulus (CS) influenced the pattern of CS-directed versus food-site-directed behavior in rats. Experiment I showed that only temporal proximity affected responding when the serial CS consisted of two successive 4-sec presentations of either a spatially near or a spatially far lever (NN or FF). However, Experiment 2 showed that behavior depended markedly on whether rats received a near followed by a far lever (NF) or a far followed by a near lever (FN). Experiment 3 showed that the effects of Experiment 2 could be changed by increasing the duration of the second CS element, and Experiment 4 showed that these changes were not related to previous training. We concluded that behavior produced by the spatiotemporal qualities of the lever elements can be attributed to a mapping between the temporal qualities of the CS elements and an underlying sequence of search modes related to finding food.

What is the unit of selection for feature integration in visual search: location or perceptual object? Feature integration theory (A. Treisman, 1988) asserts that it is location. Two alternative models are put forward and tested in a series of 4 experiments using a special conjunctive-search task. In this task, each stimulus item consists of 2 overlapping forms (perceptual objects). In general, the search was more efficient when the search features were linked to the same perceptual object than when they were linked to different perceptual objects at the same stimulus location. This same-object advantage, however, was shown to depend on stimulus discriminability and density, grouping strength, and hierarchical object structure. The results support a hierarchical object-based model, with important implications for feature integration, visual search, late versus early selection, and object-based versus space-based views of attention.

In 4 experiments, infants aged 8 to 12 months were tested on A not B search tasks, and nonsearch A not B tasks following the violation-of-expectation paradigm. A 1-location task and 2 control tasks were also conducted. In the nonsearch tasks, a toy was hidden in A, moved to B, and retrieved after a delay from either A (impossible) or B (possible). Results showed significantly longer looking times at impossible events, indicating some memory for where the object was hidden and an expectation of where it should be found. This effect occurred at delays at which infants made the A not B error when searching, and at a longer delay of 15 s. The results showed clearly that infants have some memory for the object's location, even at delays at which they search at the incorrect location. Discussion centers on how these results are accounted for within explanations of the A not B error.'

Three experiments were conducted to explore the determinants of 2-year-olds' perseverative errors in a search task. In Experiment 1, children either retrieved an object during a preswitch phase or merely observed a hiding event. Active search produced perseveration on postswitch trials, but mere observation did not. In Experiment 2, similar results were found, even when active search occurred in the absence of observation. Finally, in Experiment 3, children observed a hiding event at 1 location on some pretest trials and simply retrieved an object at a different location on other trials. On test trials, in which an object was hidden at a 3rd location, children tended to search where they had searched previously. Together, the results indicate that active search is required to elicit perseveration, which points to failures of response control rather than representational inflexibility.

Backward serial conditioned stimuli can control a set of post-food searching behaviors that can influence later pre-food searches. Rats first trained with a backward conditioned stimulus (CS) with proximity to food were then trained with a different CS element. Temporal proximity to food was found to affect the outcome of these experiments.

In two experiments, we explored how the foraging behavior of Norway rats was influenced by different arrangements of artificial paths and vertical landmarks. The rats used the paths successively less for orienting to food in treatments in which paths led to food but were crooked, in which paths led only halfway to food, and in which paths were misaligned with respect to food. The arrangement of paths influenced the rats' rate of energy intake in the beginning of the experiment, whereas the arrangement of beacons did not. With experience, the rats employed different orientation strategies in the presence of different arrangements of paths or beacons, and, by the final 4 days, all groups achieved statistically indistinguishable net rates of return. The rates of energy intake were similar because the rats in different treatments traveled similar distances per session, despite differing arrangements of paths and landmarks.

Pigeons searched for any of several targets in experiments designed to explore attentional priming or search-image formation. Three experiments assessed the runs advantage, seen in improved search efficiency during single-target trial sequences compared with search efficiency during mixed-target sequences. Experiment I varied the number, of items in the search display and the target set. Well-practiced pigeons showed the runs advantage only for a display size of 36 and a target set of 8. Experiments 2 and 3 followed the runs effect over training. For a target set of 4, the runs advantage was present initially but diminished with practice. For a target set of 12, the runs advantage persisted. The data suggest that learning permits a shift from controlled to automatic processing of memory, but constrains the number of items that can be addressed in parallel.

A survey was conducted on studies of autonomous search strategies by robots and animals to identify search methods in two-dimensional Euclidian space. Results show the similarities between animal and robotic search. Literature on animal search and coordination reveals that animal foraging involves the observance of optimization rules and that animals employ local optimization heuristics.

From the behavior systems perspective, a long conditioned stimulus (CS)- unconditioned stimulus (US) interval should differentially condition a general search mode and related behavior, while a short interval should differentially condition a focal search mode and related behavior. Experiments with rats paired a long or a short CS with food and with an extinction test compounded the CS with an unconditioned probe stimulus of a rolling ball bearing. Ball bearing contact was higher in subjects getting the long CS. Nosing for food was higher with the short CS.

In virtual space, humans learn to find an invisible target that remains in a given location relative to distal cues, based on results of three experiments. One experiment showed that people quickly learned to find an invisible target in a computer-generated virtual space. They searched the appropriate place with intensity when the target was removed in probe trial. Two other experiments showed spatial learning and memory implications exist.

Sprague-Dawley rats were exposed to variable patches in 2 controlled laboratory settings where duration and magnitude of yield were systematically varied along with the time intervening between foraging experiences and choice tests. Following relatively short delays, rats chose the patch that was best at the end regardless of its average value. However, as delays lengthened, rats chose the patch with the best average irrespective of its final performance. Despite widely differing procedures, preference shifts were an orderly function of time and patch quality and were predicted with precision by the temporal weighting rule (TWR), a biologically based quantitative model that discounts patch outcomes as a hyperbolic function of time. The laboratory phenomenon of spontaneous recovery is best understood in terms of the dynamic averaging process prescribed by TWR.

Pigeons' use of landmarks to guide searching behavior was tested in both open-field and touch-screen tasks. Both similarities and differences were observed between landmark control in the open-field and touch-screen settings. No evidence of transfer between the two tasks was found. The pattern of results is consistent with the theory that the pigeons used two-dimensional spatial relationships in the touch-screen task and three-dimensional relationships in the open-field task.

Search is a serial exploration of alternatives. Efficient search involves the ability to minimize costs (i.e., time/energy) and to keep track of alternatives already explored. The search abilities of 4 capuchin monkeys (Cebus apella) were evaluated by means of an apparatus featuring a set of suspended baited containers. The experiment featured conditions with different spatial configurations of the search space. Results show that the monkeys were able to search exhaustively 9 containers spatially distributed either as a 3 x 3 matrix or as 3 'patches' of 3 containers each. Search efficiency was higher in a search space suitable to organization in clusters or spatial chunks. In this condition, evidence for principled organization of search trajectories, as opposed to a random walk through the search space, emerges clearly and parallels search efficiency. This suggests that monkeys impose a structure over the search space and, by doing so, reduce the memory demands of the task.

A comprehensive theoretical framework for understanding consumers' information search behavior is presented. Unlike previous research, our model identifies not only what factors affect consumers' search behavior but also how these factors interact with each other. In particular, the model emphasizes the effect of prior brand perceptions on the search process. We argue that when consumers have brand-specific prior distributions of utility, the existence of relative uncertainty among brands is necessary for search to be useful. Thus, we explain why product class involvement or low search costs may not be sufficient to induce large amounts of search activity and why there may be an inverted-U-shaped relationship between search activity and experience. We test our theory on consumers' search behavior for new automobiles, using data collected contemporaneously with consumers' actual decision process. Our data support our theory. (Reprinted by permission of the publisher.)

During search for multiple targets, reaction time decreases when a given target assumes a relatively high probability of appearance. Three experiments addressed the basis of this frequent-target effect. In a trialwise visual search method, pigeons pecked at the single target symbol embedded in a multisymbol display. In Experiment 1, the course of reaction times to frequent and infrequent targets was followed over extended sessions; reaction time to the frequent target dropped gradually over the first 200-400 trials. In Experiment 2, extinction sessions were introduced; the frequent-target effect persisted in the absence of reinforcement. In Experiment 3, the role of local trial patterns was examined; the frequent-target effect resisted temporary variations in relative target probability. Facilitation of search for high-probability targets appears to be an attentional rather than a conditioning effect; in the present design, information summarized over large sequences of trials appeared to provide pretrial information that primed attention.

Laboratory experiments on black rat snakes showed that the animals exhibited increased rates of tongue flicking after ingestion of prey. The behavior, combined with conventional predator searching behavior (PPCS), represents post-prandial chemosensory searching which increased their chances of locating subsequent prey. PPCS can be compared to the strike-induced chemosensory searching (SICS) of venomous snakes. The occurrence of such behaviors on both venomous and non-venomous snakes suggests that PPCS and SICS are ancestral traits.

In this article, the authors combine models of timing and Bayesian revision of information concerning patch quality to predict foraging behavior. Pigeons earned food by pecking on 2 keys (patches) in an experimental chamber. Food was primed for only 1 of the patches on each trial. There was a constant probability of finding food in a primed patch, but it accumulated only while the animals searched there. The optimal strategy was to choose the better patch first and remain for a fixed duration, thereafter alternating evenly between the patches. Pigeons were nonoptimal in 3 ways: (a) they departed too early, (b) their departure times were variable, and (c) they were biased in their choices after initial departure. The authors review various explanations of these data.

Inhibition-of-return is thought to be a visual search phenomenon characterized by delayed responses to targets presented at recently cued or recently fixated locations. We studied this inhibition effect following the simultaneous presentation of multiple location cues. The results indicated that response inhibition can be associated with as many as four locations at the same time. This suggests that a purely oculomotor account of inhibition-of-return is oversimplified. In short, although oculomotor processes appear to play a role in inhibition-of-return they may not tell the whole story about how it occurs because we can only program and execute eye movements to one location at a time.

A generic dynamic growth system for money market fund families is developed to measure organization search and test if it minimizes failure risk. This growth system incorporates specific cost and demand characteristics that affect firm expansion. The condition of the growth system in each time period for a specific firm, as estimated by the Kalman filter, indicates the state of the search process of the firm. Findings demonstrate no supporting evidence that the continually revised coefficients have an impact on the risk of failure. Nevertheless, the cumulative amount of search positively influences exit, in consonant with the structural inertia theory of Hannah and Freeman (1984). Other significant predictors of money market fund failure are founding conditions and money market fund performance.

Evidence for both forward and backward excitatory serial conditioning is consistent with a behavior systems account of conditioning. In experiments with rats, the serial elements exhibited asymmetrical control, especially during compound conditioning. In addition, the specific responses seemed to be more strongly conditioned in forward conditioning than in backward conditioning. Some problems with the traditional associative account can be solved by using a behavior systems framework that incorporates both the adaptive-evolutionary and associative approaches.

Cats' and dogs' search behavior was compared in different problems where an object was visibly moved behind a screen that was then visibly moved to a new position. In Experiments 1 (cats) and 2 (dogs), one group was tested with identical screens and the other group was tested with dissimilar screens. Results showed that in both species, search behavior was based on processing of spatial information rather than on recognition of the visual features of the target screen. Cats and dogs were unable to find the object by inferring its invisible movement. They reached a high level of success only if there was direct perceptual evidence that the object could not be at its initial position. When the position change was indicated by an indirect cue, cats searched more at the object's initial than final position, whereas dogs searched equally at both positions. Interspecific similarities and differences are interpreted in terms of the requirements for resetting working memory.

In 3 experiments, pigeons (Columba livia) searched a digitized image of a gravel patch on a computer monitor for cryptic grains. Experiment 1 demonstrated that the bird's ability to detect a type of grain improved over successive encounters, and detection of alternative targets was attenuated when a search image was active. Experiment 2 demonstrated search-image effects independently for the 2 grains. Perception was biased to detect wheat grains after wheat encounters and was biased to detect bean grains after bean encounters. Experiment 3 demonstrated that when a search image was activated, selective attention was heightened to the visual features of the grain used to discriminate it from the multicolor gravel background. These results provide strong support for the view that search images are selective attention to specific visual features of cryptic prey.

It is not always easy to locate routing signs in the visually noisy environment of public buildings. Guidelines to ensure the conspicuity of an object in a complex field are not readily available. In two previous experiments, aiming to provide such guidelines for use in practice, the stimuli were simple simulations of scenes in public buildings, each containing a uniquely colored target (a routing sign) and a varying number of distractors (advertising signs). The results of these two experiments were opposite: in one experiment pop-out of the targets appeared as predicted by current theories of visual search, but in the other experiment performance significantly decreased when the number of distractors increased. Two new experiments are reported here to clarify this discrepancy. From the results it is concluded that pop-out of easy visual targets does not occur on the first few trials of a task. Subjects must have had sufficient practice for pop-out to develop. This finding implies that, contrary to what is common in experiments on visual search, short and heterogeneous series of stimuli should be used to ensure the practical relevance of the results for applications such as sign posting.

We evaluated the performance of 6 adult rhesus monkeys (Macaca mulatta) on object permanence tasks. In Experiment 1, monkeys received search tasks that correspond to Stages 4, 5, and 6 of object permanence. Subjects were successful on tasks of visible displacements (Stages 4 and 5) but failed to find the object in invisible displacements (Stage 6). The monkeys adopted a search strategy of investigating a specific hiding location. In Experiment 2, monkeys were given a second opportunity to find the object if they investigated a location that was part of the displacement on their first search. Subjects relied on the same search strategy identified in Experiment 1. In Experiment 3, the experimenter hid the object in her hand rather than a container. The monkeys failed to recover the object, and individual differences were found in the strategies used. These results suggest that the upper limit of object permanence in rhesus monkeys is stage 5.

Optimization cost accounts for the deviation of actual behavior from optimal predicted behavior. However, optimization cost may be reduced by experience, especially when the optimal result is associated with the consideration of future events. An individual decision making experiment is undertaken involving constant potential choices and two decision formats, one of which promotes the consideration of future events. The results indicate that decision makers choose optimal alternatives more often as they gain experience.

In four experiments, pigeons were trained to find hidden food at a constant location with respect to one or two arrays of landmarks. On crucial tests, the birds were presented with conflicting cues associated with two different directions, which were 90[degrees] apart from the center of the search space at the same radial distance. The direction-averaging model predicts that the radial distance of search should not change on these tests, compared with radial distance of search on control tests without conflicting cues. The vector-averaging (vector sum) model predicts that when pigeons average the two conflicting cues, the radial distance of search should be shorter. Results support the direction-averaging model and suggest that distance and direction are independently computed in landmark-based search. Multiple sources are averaged by pigeons in determining direction.

Sequential priming refers to speeded visual search when target identity or location is repeated within a trial sequence. In two experiments with pigeons, we addressed the relative contributions of stimulus-driven factors and learned expectancies to this effect. Pigeons pecked at targets during trialwise presentations of visual-search displays. Random-sequence conditions minimized the role of expectancy by introducing same-target or same-location trial sequences unpredictably. Blocked-sequence conditions added predictability by regular repetition of target and/or location over trials. Intertrial interval varied from 0.5 to 3 sec. The findings revealed significant reductions in reaction time during predictable target or location sequences compared with unpredictable repetitions within random contexts. Stimulus-driven factors do not seem to have an important role in many instances of sequential priming. Expectancy-based priming of target and location followed similar patterns.

The effects of age and experience on visual-cognitive performance were examined by administering a domain-relevant visual search task and a standard letter search task to skilled and control subjects at 2 age levels (young and middle-aged adults). In the skilled task, subjects searched for a designated item within 3-item displays using images of bacteria morphology as targets and distractors. Each target was preceded by a word prime representative of bacteria morphology that was valid, invalid, or neutral with respect to the diagnostic characteristics of the target. Skilled subjects showed an age deficit in letter search performance, but the performance of the young and middle-aged skilled subjects was not different on the domain-relevant task. Valid primes produced benefits for the young and middle-aged skilled participants, whereas control subjects were unaffected by the prime manipulation. Results were consistent with the prediction that experience serves to attenuate age-related declines in visual-cognitive performance in the skilled domain.

Two studies examined spatial organization reflected in searches for objects and descriptions of locations. Six-year-olds and adults retrieved objects hidden on the floors of a house or directed another person about how to retrieve them. Of particular interest was whether children's searches and directions reflected clustering of locations by floors. Six-year-olds' searches were more organized than their directions, but a follow-up study demonstrated that they could produce organized directions if prompted. Analyses of the content and structure of spatial information in directions indicated that children and adults communicated the information in an order of decreasing size of spatial unit. Results are discussed in terms of factors underlying spatially organized searching and direction-giving.

Relationships between abilities and performance in visual search were investigated for young and old adults. Ss received extensive practice on category search task. A consistent version allowed development of an automatic attention response; a varied version allowed general performance improvements. Transfer conditions assessed learning. General ability, induction, semantic knowledge, working memory, perceptual speed, semantic memory access, and psychomotor speed were assessed. LISREL models revealed that general ability and semantic memory access predicted initial performance for both ages. Improvements on both the consistent and varied tasks were predicted by perceptual speed. Ability-performance relationships indexed performance changes but were not predictive of learning (i.e., automatic process vs. general efficiency). Qualitative differences in the ability-transfer models suggest age differences in learning.

Models of visual search that assume spatially serial processing of conjunction stimuli break down when displays contain 2 identical conjunction targets: (a) They fail to account for the slopes of the target-absent reaction time (RT)/display size functions, both when the target-present response requires the detection of only 1 of the 2 targets and when it requires the detection of both targets and (b) under redundant target conditions, the probability of 'fast' present RTs is greater than that expected from the independent (serial) processing of the target stimuli. This article shows that G. W. Humphreys and H. J. Muller's (1993) parallel search via recursive rejection (SERR) model can account for human search performance under dual-target conditions. In SERR, simple form conjunctions are coded and grouped (on the basis of their similarity) in a spatially parallel manner, and targets are detected through the activation of a temporary 'template' or through the recursive rejection of grouped distractors.

Gagnon and Dore (1992) showed that domestic dogs are able to solve a Piagetian object permanence task called the invisible displacement problem. A toy is hidden in a container which is moved behind a screen where the toy is removed and left. Dogs make more errors in these problems than they do in visible displacement tests, in which the object is hidden directly behind the target screen. In Experiment 1, we examined components of the standard procedure of invisible displacements that may make encoding or retention of the hiding location more difficult than it is in visible displacements. In Experiment 2, we compared dogs' performances in visible and invisible displacement problems when delays of 0, 10, and 20 sec were introduced between the object's final disappearance and the subject's release. The results revealed that dogs' poorer performance in invisible displacement tests is related to the complex sequence of events that have to be encoded or remembered as well as to a difficulty in representing the position change that is signaled, but not directly perceived.

We consider several ways in which the interpretation of reaction time (RT) data might confound differences in visual search rates with non-search-related factors. To determine whether estimates of search rates for groups differing in age suffered this problem, we compared estimates provided by the RT method with those obtained using a forced-choice method with limited-duration stimuli. The forced-choice method provided faster estimates of search rates. The effects of age, the variable in which we were interested, were comparable, but the difference between results obtained using the two methods suggests the need for caution in using the RT method. We discuss how the forced-choice method can be used, under appropriate circumstances, to provide an independent test of whether subjects are carrying out serial searches and, if they are, to provide search rate estimates even from data obtained using only a single array size.

Asymmetry is demonstrated between conjunctive targets in visual search with no detectable asymmetries between the individual features that compose these targets. Experiment 1 demonstrates this phenomenon for targets composed of color and shape. Experiment 2 and 4 demonstrate this asymmetry for targets composed of size and orientation and for targets composed of contrast level and orientation, respectively. Experiment 3 demonstrates that search rate of individual features cannot predict search rate for conjunctive targets. These results demonstrate the need for 2 levels of representations: one of features and one of conjunction of features. A model related to the modified feature integration theory is proposed to account for these results. The proposed model and other models of visual search are discussed.

Pigeons searched for a small target form (T) among 31 identical distractors (Ds). T and D came from the same small set, which differed by simple features. Each form appeared equally often as T or D. Search reaction time (RT) was measured. In Experiment 1, RT was lower to frequent than to infrequent pairs, whether or not frequency was consistently associated with a featural difference. In Experiment 2, detection of T in the location predicted by D was relatively fast. In Experiment 3, search transferred to new T-D pairs. In Experiment 4, probable T-D pairs and improbable T-D pairs were drawn from different sets. Again, T-D probability affected search RT. It was concluded that probability of T-D combinations, not just of targets, affects search speed; distractors may mediate this effect through within-trial priming of attention. The results are consonant with previous studies of repetition priming, cued search, transfer, and the search image.

Part 1 concerns representation: We demonstrate pop-out for a target that can be distinguished from the distractors only by the relative position of its components and thereby show that simple shape information is represented preattentively. We discuss our findings in terms of the early- versus late-selection debate and in terms of theories of search and texture segregation. Part 2 concerns selection: We demonstrate strong learning in a varied-mapping paradigm and show that preattentive shape information can be used for selection. Finally, we suggest an account of the learning, namely the group scale hypothesis, and present a final experiment to test it. Our results confirm and extend the emphasis placed by Duncan and Humphreys' (1989) attentional engagement theory on grouping processes in visual search.

Three pigeons searched for a unique target form among 31 identical distractors, and search reaction time (RT) was measured. Within experiments, target and distractor on each trial were drawn from the same small set of forms that differed from each other by simple features. Correlations across sessions among RTs to the various form pairs were analyzed. Experiment 1 indicated drifts of attention between the top of the forms, where a gap might appear, and the bottom, where a line might appear, and also suggested drifts of attention to the line as a target feature. Experiment 2 indicated similar drifts between the top and bottom of the forms and between small differences and large differences in target features. Attention to intraform location appeared relatively independent of attention to target features. The method provides a new way to identify functionally separable aspects of stimulus processing and to describe their temporal properties.

The validity ofthe theory of search behavior based on the Subjective Expected Utility Theory (SEUT) was examined in an experiment. Two hundred subjects were selected from the University of York. The subjects were instructed to purchase or search up to when the value of given optimal reservation value is reached. The results ofthe experiment showed that conduct of the subjects did not conform to the conjectures of the SEUT. It was concluded that results of the experiments verified the comparative, though not the absolute correctness of the search behavior theory.

The SEarch via Recursive Rejection (SERR) model of visual search is a connectionistmodel that assumes that visual processing of simple form conjunctions proceeds in a spatially parallel manner. It also proposes that search operates through arecursive rejection of these conjunctions. Experiments revealed that the numberof distractors comprising a single group failed to alter the model's performance. When the number of distracting groups was increased, however, the probability of missing targets became greater. The results were found to be identical with functions generated when human subjects searched displays with variable ditractor group numbers.