Three processes, item identification speed, susceptibility to proactive interference, and memory for order, identified for their potential as sources of memory span differences, were the subjects of the present investigation. A fourth variable, item memory, was included as the experimental complement of order memory (Healy, 1974). Performance on each of these four variables and memory span was obtained for 90 college-aged subjects. Moderate to high reliability was evidenced for each of the tasks. Memory span correlated significantly with each source of differences examined. Additionally, using a multiple regression analysis, each variable was shown to contribute significant, independent variance in the joint prediction of memory span. Subjects' scores on the four predictor variables were used in a cluster analysis which identified four subsets of individuals. An ANOVA determined that the four groups differed in their mean memory span scores. The differences among these groups were examined using a multiple discriminant analysis. The groups were found to differ along three dimensions. Evidence from these analyses indicates that an individual's memory span is the result of complex processes involving, at least, components of item identification speed, susceptibility to proactive interference, order, and item memory. Finally, individuals' performance levels across these tasks were not uniform, indicating possible differential contributions of these processes.

The multiple regression model has been applied to the study of judgment primarily through the paradigms known as policy capturing and multiple cue probability learning (MCPL). The former involves modeling the way the decision maker weights predictive information; the latter focuses on the process by which the decision maker acquires this strategy. In the first part of the paper, the logic underlying the two approaches is examined, and the research generated by each is discussed. Based on this comparative review, it is argued that neither approach has yet lived up to its potential because each has concentrated too narrowly on particular kinds of issues, at least some of which present serious logical difficulties. Policy capturing, for example, has sought to isolate judgment processes through multiple regression despite the fact that it is logically capable of capturing only predictions. For its part, MCPL research has fallen short by limiting itself to variables suggested by Brunswik's lens model. Better use could be made of the model if it were applied in a more functional manner--one in which it is used to index performance rather than to infer cognitive processes. The functional approach serves as a guiding philosophy for a series of experiments that are described in the second part of the paper. The primary question of interest in these experiments was how the format of displaying visual information affects subsequent judgments and decisions. Two types of displays, numerical and graphical, were investigated using the policy capturing paradigm in the first three experiments and MCPL in the fourth one. The most consistent finding was that subjects' cue weighting differed reliably with type of format. Numerical policies tended to be less precise than graphical ones, but accuracy of predictions did not differ with display. The implications of these findings are discussed both from a practical and theoretical perspective.

A review of the literature on alphanumeric displays, especially computer-generated displays, suggests that four basic characteristics of display formats affect how well users can extract information from the displays: (1) Overall density--the number of characters displayed, expressed as a percentage of the total spaces available; (2) Local density--the number of other characters near each character; (3) Grouping--the extent to which characters on the display form well defined perceptual groups; and (4) Layout complexity--the extent to which the arrangement of items on the display follows a predictable visual scheme. Objective ways of measuring these display characteristics have been developed and implemented in a computer program. In Experiment 1, 520 computer-generated displays that varied on these display measures were studied. Search times to locate data items on the diplays were measured as well as subjective ratings of ease of use. Regression equations were developed to predict the search times and subjective ratings using the display measures. The results indicated that both search times (R('2) = .508) and subjective ratings (R('2) = .805) could be predicted quite well. In experiment 2, the regression equations developed in Experiment 1 were used to predict, a priori, search times and subjective ratings for a new set of 150 displays. The regression equations generalized quite well, resulting in high correlations between predicted and actual search times (r = .800) and subjective ratings (r = .799). The regression equations indicate that the most important predictors of search time are two measures associated with the grouping of characters: the number of groups on the display and the average visual angle subtended by those groups. Likewise, the most important predictors of subjective rating are a measure of local density, which is essentially how "tightly packed" the display is, and a measure of layout complexity, which is essentially how well the items on the display are aligned with each other.

Tullis (1983, 1984) identified and quantified six conceptually distinct dimensions of alphanumeric display formats. On the basis of these dimensions, he derived regression equations which predicted performance and user perceptions in a simple search task. The current study sought to extend his findings to other common tasks performed with visually coded information--where the use of several pieces of information from predictable display locations was required. Further, complexity and visual monitoring load were manipulated to study the effects of the Tullis dimensions in a broader task context so that any boundary conditions might be identified. While there did not appear to be any clear effects of format once information was extracted from the display, the time taken to extract the information did vary with the format dimensions. Thus, their importance was not diluted by the predictability of the displays. The relative merits of alternative formats in the Scanning task, however, were not predicted successfully by the Tullis equations. This prediction failure was explained post hoc as being due to an enhancement and reversal of the effect of the Item Uncertainty dimension when display locations are known by users. Further research designed to test this hypothesis directly will be necessary to determine whether an alternative prediction system might be useful for such task situations. In contrast, the Tullis equations did predict the perceived difficulty associated with alternative formats fairly well in all task conditions. Subjects' perceptions seemed to be based largely on the ease with which information was extracted regardless of other task considerations (such as their actual level of performance). Since the regression equations were based on user perceptions of the ease of search, their predictions appear to be robust to major differences in task requirements. Finally, it was suggested that subjects' apparent inability to evaluate their performance accurately under alternative designs should serve as a warning to system designers. That is, where performance is the paramount design criterion, empirical human performance research should be conducted in the absence of a validated prediction system such as the one developed by Tullis for search.

When information is presented on a computer display in support of the human decision maker, but the amount of information is in direct proportion to computer processing powers, the human can quickly be overloaded. Because of its ability to attract and direct attention, color is one of the techniques used to enhance information display. However, the general rule that color is good for a search task, but not for strictly an identification task is limited in its applicability to complex displays: Certain design tradeoffs have to be made. Further, whether color is reported to benefit performance depends on the measure. The experiment reported here was a test of the effectiveness of color in simplifying coding, adding highlighting, and reducing clutter on an actual display, the display used in the US Army's Patriot high altitude air defense weapon system. Trained operators were tested with the existing monochrome display and an experimental color display, which was developed based on guidelines derived from the literature and on knowledge of the human/computer interface, including the operators' conceptual organization, or mental model, of the displayed information. Contrary to expectation, there was no general enhancement due to color with any of the measures taken, including the stated preference of the operators. Looking at the pattern of results over time, however, the trend was in the direction of an enhancement with color, specifically as measured by the timeliness of the engagement decision, by the pattern of activities showing the ability to use step-saving features of the system, and by subjective workload assessment. The lack of more immediate and widespread color benefits can be attributed to having to learn the color-category relationships even though early perceptual processing of color information is effortless, and to the inherent difficulty in designing a structured display to fit an unstructured task.

A review of recent research on risk perception shows that little attention has been given to risk perception for common accidents and injuries such as those that occur in and around the home. The study of common risk perception, however, could be useful in the development of psychological theories of memory and judgment, as well as in the design of better product warnings. In this study, two types of knowledge among "non-expert" individuals was tested, including knowledge about relative levels of risk and knowledge about the ways that injuries occur. Information was gathered about these two types of knowledge using (1) frequency estimation tasks in which subjects estimated annual emergency room injury frequencies for each of ten common consumer products, and (2) scenario recall tasks in which subjects recalled, generated, and organized accident scenarios for the same ten products. While performance on the frequency estimation tasks highlighted a surprising ability to assess accurately and quickly relative levels of risk, the scenario recall and rating tasks showed severe errors in judgment. In the frequency estimation task, estimates that were made within 2 seconds of category presentation were just as accurate as those made after lengthy analysis and review of scenarios. In the scenario recall task, subjects recalled or generated only about 40 percent of the common accident scenarios, and overestimated their own ability to recall scenarios. In short, information about relative levels of risk was readily accessible to individuals, while information about the ways that injuries occur often was not. A second finding concerned individuals' confidence in the relationship between estimated and actual frequencies in conditions where estimates were based on intuition (very fast estimates) or analysis (more deliberate estimates). Though frequency estimation performance did not improve after performing evaluations such as "fault tree analysis", confidence ratings nonetheless increased. This suggests that intuitive judgments can be as accurate as more thoughtful, analytical judgments and that the act of performing an analysis may sometimes lead to overconfidence in judgment. The issue of when analysis improves judgment and when it does not is worthy of further study as a general, theoretical concept.

Recent attention research indicates that attention must focus narrowly on the location of a stimulus before that stimulus can be identified. Focal attention has also been shown to play an important role in the process of localizing and integrating the basic features of stimuli. Although this suggests that little information is available without focal attention, there is picture perception research which suggests that important information is available by means of a global process that is sensitive to the meaningful relationships that exist among objects in scenes. In an attempt to reconcile this discrepancy, attention was focused on a target object while the organization of the surrounding background objects was varied. In Experiment 1, there was general interference from the presence of background objects in the visual field, but no indication that the identities or spatial organization of those objects affected performance. In Experiments 2 and 3, the objects were moved closer together to form more coherent displays. In these two experiments, there was evidence that both the identities and the spatial organization of background objects affected performance. The effects generally persisted even after attention was focused on the target. The processing of unorganized background objects was more affected by attentional manipulations than the processing of organized background objects suggesting that information in organized scenes is, at least in part, available by means of a process that is independent of focal attention.

The research constitutes an investigation of selecting material for remembering, and specifically of the ability to pick out wanted from unwanted items intermixed in the same spoken message. In Experiments 1-4, subjects tried to remember a list of words heard under (a) a no-distraction condition, in which no other words were presented; (b) a precuing condition, in which the to-be-remembered words were intermixed with unwanted words and the to-be-remembered words were specified before list presentation; and (c) a postcuing condition, which differed from the precuing condition in that the to-be-remembered words were not specified until after list presentation. Wanted and unwanted words were distinguished on the basis of semantic category (e.g., colors versus trees). In Experiments 1-3, there were 12 wanted and 12 unwanted words, and the wanted words could be recalled in any order. Recall in the precuing condition was considerably higher than in the postcuing condition and only slightly lower than in the no-distraction condition, indicating a high degree of selective remembering. Interestingly, the degree of selective remembering depended little if any on within-list positions (Experiment 1), rate of word presentation (Experiment 2), or predictability of wanted and unwanted items (Experiment 3). Such results contrast sharply with the suffix effect, in which recall of a list of items is substantially depressed by a single, nominally irrelevant item at the end of a list. Experiment 4 was similar to the first three but incorporated features of the suffix paradigm, namely a short (8-item) list and the requirement that items be recalled in their presentation order. The efficiency of selection, although reduced, was still appreciable. Experiments 5 and 6 sought to reduce the suffix effect by interpolating the suffix item after each to-be-remembered item rather than just the last one, and by presenting the list and suffix items in different voices. The suffix effect was reduced, but only modestly. It is concluded that the last item to be presented is not easily ignored, and that the suffix effect, therefore, represents a special difficulty in selective remembering.

Two prominent theories of perceptual functioning in autism were tested. WCC theory maintains that individuals with autism spectrum disorder (ASD) preferentially attend to local elements. EPF model, on the other hand, maintains that persons with ASD can attend to either the local or the global elements and that they are sensitive to small changes in environmental contingencies. Individuals with ASD and typically developing individuals (TD) performed both the selective attention task, which employed instructions about which level of the hierarchical figure to attend, and the divided attention task, which employed implicit contingencies to bias to which level of the stimulus to attend. A global advantage and global interference were found for both groups. Furthermore, ASD persons demonstrated sensitivity to the contingencies relative to TD persons. This supports the EPF model indicating that individuals with ASD perform as TD individuals for global forms but can more flexibly modify their default level of selection according to changes in environmental contingencies. / Deux théories perceptuels ont été testé. WCC clâme que les personnes qui présentent un trouble envahissant du développement (TED) montrent une inclination aux traitement locaux. EPF dit que les personnes avec TED peuvent traiter les niveau global ou local, et qu'ils sont sensibles aux petites différences dans les éventualités de l'environnement. Les personnes avec TED et le groupe de développement typique (DT) ont exécuté la tâche d'attention sélective, qui a employé des instructions duquel le niveau être présent, et la tâche d'attention divisée, qui a employé des éventualités implicites. Un avantage global et une interférence globale ont été trouvés pour les deux groupes. De plus, seulement les personnes avec TED ont démontré la sensibilité aux éventualités. Ces résultats soutiennent le compte d'EPF, et indiquent que les individus avec TED peuvent performer d'une manière caractéristique la tâche des formes globales, et peuvent modifier leur niveau implicite selon les changements subtils dans l'environnement.

Gastric secretion has been a subject of intensive investigation by a veritable army of investigators for well over a hundred years. The major stimulus for this work originated with the astute observations and pertinent experiments of the American Army Surgeon, William Beaumont, on the French Canadian lumberjack, Alexis St. Martin, in the early nineteenth century.