This article presents a theory of selective attention that is intended to account for the identification of a visual shape in a cluttered display. The selected area of attention is assumed to be controlled by a filter that operates on the location information in a display. The location information selected by the filter in turn determines the feature information that is to be identified. Changes in location of the selected area are assumed to be governed by a gradient of processing resources. Data from three new experiments are fit more parsimoniously by a gradient model than by a moving-spotlight model. The theory is applied to experiments in the recent literature concerned with precuing locations in the visual field, and to the issue of attentional and automatic processing in the identification of words. Finally, data from neuroanatomical experiments are reviewed to suggest ways that the theory might be realized in the primate brain. The identification of shapes and objects in the environment plays an important adaptive role in our daily, moment-to-moment activities. A typical visual scene contains many objects, but there is a limit on the number of objects that we can process at one time. This limitation implies that, at some stage or stages in the information flow through the system, the information arising from some objects must be momentarily excluded from processing. This exclusion from processing may occur by operations that either enhance the information from a target object, or by operations that suppress the information from the distractor objects, or by operations that do both. Described in this manner, exclusion from processing closely resembles what traditionally has been termed selective attention. The notion of selective attention gained a foothold in the mainstream of psychology in the late 1950s, particularly through the influence of Broadbent's (1958) filter theory and Guthrie's (1959) revision of his learning theory ("what is being noticed becomes the signal for what is being done"). Soon aRerward, a controversy arose concerning whether the selection process occurs early (Broadbent, 1958) or late (Deutsch & Deutsch, 1963; Norman, 1968) in the flow of information. The two contrasting views of the locus of selection can be seen in theoretical issues raised two decades later (for reviews, cf. Broadbent, 1982; Johnston & Dark, 1986; Kahneman & Treisman, 1984; Shiffrin, 1988). A strong form of the late-selection theories assumes that all objects in a visual display (falling on an effective area of the receptor surface) are identified and that the selection process chooses the identified object that will be processed fur-We thank E. G. Jones for his helpful comments concerning neuroanatomy, and we thank Ryozo Yoshino for his suggestions in mathematical matters. We also thank Marc Carter, Jan I.awry, and Dale McNulty for reading the manuscript and making valuable comments and criticisms.

Despite laboratory evidence that group brainstormers produce fewer ideas than individual brainstormers, brainstorming groups remain popular in business and industry. Here the authors present a model of the cognitive factors involved in group idea generation. Simulations suggest that group interaction should be beneficial when one group member primes another into thinking of ideas they would not have considered alone, at least not in the context of the task at hand. Many concepts relevant to group cognition can be defined within the model framework (stochastic transition matrices) including fluency, flexibility, category accessibility, convergent/divergent thinking, attention to partners, and the relationship between the knowledge structures of the brainstorming participants. Attention plays a crucial role in the model, linking together individuals in a brainstorming group. Simulations also suggest that convergent group behavior may be the result ofcognitivefactors in addition to the socialfactors outlined by a number of researchers.

In many meetings and work sessions, group members exchange ideas in order to come up with novel, creative solutions for problems and to generate ideas for future innovations. This type of group idea generation or brainstorming process has been studied in detail, and we have discovered much about the cognitive and social processes that underlie group idea generation. It appears that the brainstorming performance of groups is often hindered by various social and cognitive influences, but under the appropriate conditions, group idea exchange can be quite effective. In this article, we summarize the present state of knowledge, point out some significant gaps in our knowledge, and suggest a cognitive-socialmotivational perspective to integrate the major findings and to guide future research in the area of group creativity and group idea generation. 250 Cognitive-Social-Motivational View of Brainstorming

One technique that may facilitate group brainstorming is decomposition of the task so that categories of the problem are considered one at a time rather than simultaneously (A. R. Dennis, J. S. Valacich, T. Connolly, & B. E. Wynne, 1996). Two studies examined this possibility for both solitary and interactive brainstorming in which major categories of a brainstorming problem were presented simultaneously or sequentially. In the 1st study, participants in the sequential presentation condition generated more ideas than did those in the simultaneous condition in both the individual and the group conditions. In the 2nd study, individuals exposed to either a high number or low number of idea categories demonstrated enhanced performance. Simulations of the data demonstrated that the results were consistent with an associative memory model of the idea generation process.

In Experiment 1, subjects responded with a buttonpress to a target letter 0 embedded in a pair of vertical lines. A flanker control method was used to constrain the location and size of the initial attentional focus. The target could appear in one of five locations within a particular horizontal range. There were five ranges, varying from 1.7 0 to 8.6 0 in visual angle. Reaction time measures to the target exhibited V-shaped curves, with the lowest reaction time corresponding to the location of the initial focus of attention. The slopes of the curves decreased monotonically with target ranges. Reaction time measures at the extreme locations ofthe five ranges showed no significant increase with eccentricity, indicating that the influence of retinal sensitivity is negligible in this identification task as compared with the influence of other, presumably attentional, processes. Experiment 2 indicated that within a given range the slopes of the reaction time curves are independent ofthe number oflocations probed. Additional evidence for the attentional range effect was given in Experiments 3 and 4, in which the tasks were detection of an asterisk both with and without flanking vertical lines and identification of the letter 0 with and without flanking lines. These results do not conform to predictions of a shifting focus theory of attention with the velocity of the focus assumed to be constant, or to the predictions of a gradient theory with total processing capacity assumed to be fixed.One way of indicating the involvement of attention in visual processing is to require a subject first to detect an object at one location in the visual field (e.g., a plus sign at the center) and then to detect a second object located at varying distances from the first object (e.g., Eriksen & Hoffman, 1973;Hoffman, 1975;LaBerge, 1983;Posner, Nissen, & Ogden, 1978). The subject's reaction times typically increase with distance between the first and second objects, and this increase has been regarded as a marker of attentional processing, barring possible confounding influences of retinal sensitivity.For example, in one study (LaBerge, 1983), subjects were instructed first to identify the center letter of a horizontal five-letter string and then, when a second string of characters replaced the first string, to identify a specific target located in one of the five positions in the second string. The reaction times for this double-identification task showed a characteristic V shape as a function of target location in the second string, with subjects responding most quickly to the center target.The attentional mechanism that gives rise to such a reaction-time curve may be characterized as a shifting focus or as a gradient of processing capacity. Following the assumptions of current versions of a shifting-focus theory (e.g., Bergen

Much literature on group brainstorming has found it to be less effective than individual brainstorming. However, a cognitive perspective suggests that group brainstorming could be an effective technique for generating creative ideas. Computer simulations of an associative memory model of idea generation in groups suggest that groups have the potential to generate ideas that individuals brainstorming alone are less likely to generate. Exchanging ideas by means of writing or computers, alternating solitary and group brainstorming, and using heterogeneous groups appear to be useful approaches for enhancing group brainstorming.

Three experiments explored the gradual narrowing of visual attention to a letter target when other letters were positioned close by. The method by which attention was narrowed involved presenting a digit target immediately prior to the latter target and in the same location for progressively shorter durations and requiring the subject to identify both the digit target and the letter target before responding. The response time data from the first 2 experiments indicated that shorter durations of the digit reduced the amount of information processed from noise letters positioned on either side of the letter target. In the third experiment, in which separation of letters was increased slightly, the response times indicated that the information from flanking noise letters may have been virtually eliminated.

Experiment 1 examined the effects of additional brainstorming rules for groups and looked at whether the presence of a facilitator who actively enforced the rules of brainstorming was beneficial. Experiments 2 and 3 examined whether the additional rules and brief breaks were beneficial to individual brainwriters and electronic brainstormers working alone. Clear benefits of the additional rules were found under a variety of conditions. The presence of a facilitator to enforce the rules enhanced the efficiency of idea generation (number of words used to express ideas) but not the number of ideas generated. There appears to be a small benefit to taking breaks in brainwriting sessions, but the benefit of breaks is reduced or eliminated in electronic brainstorming sessions.