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When on the move, cognitive resources are reserved partly for passively monitoring and reacting to contexts and events, and partly for actively constructing them. The Resource Competition Framework (RCF), building on the Multiple Resources Theory, explains how psychosocial tasks typical of mobile situations compete for cognitive resources and then suggests that this leads to the depletion of resources for task interaction and eventually results in the breakdown of fluent interaction. RCF predictions were tested in a semi-naturalistic field study measuring attention during the performance of assigned Web search tasks on mobile phone while moving through nine varied but typical urban situations. Notably, we discovered up to eight-fold differentials between micro-level measurements of attentional resource fragmentation, for example from spans of over 16 seconds in a laboratory condition dropping to bursts of just a few seconds in difficult mobile situations. By calibrating perceptual sampling, reducing resource usage for tasks of secondary importance, and resisting the impulse to switch tasks before finalization, participants compensated for the resource depletion. The findings are compared to previous studies in office contexts. The work is valuable in many areas of HCI dealing with mobility. ACM Classification Keywords: H5.m. Information interfaces and presentation (e.g., HCI): Miscellaneous

The control of routine action is a complex process subject both to minor lapses in normals and to more severe breakdown followingcertain forms of neurological damage. A number of recent empirical studies (e.g. Humphreys & Ford, 1998; Schwartz et al., 1991, 1995, 1998) have examined the details of breakdown in certain classes of patient, and attempted to relate the findings to existing psychological theory. This paper complements those studies by presenting a computational model of the selection of routine actions based on competitive activation within a hierarchically organised network of action schemas (cf. Norman & Shallice, 1980, 1986). Simulations are reported which demonstrate that the model is capable of organised sequential action selection in a complex naturalistic domain. It is further demonstrated that, after lesioning, the model exhibits behaviour qualitatively equivalent to that observed by Schwartz et al., in their action disorganisation syndrome patients.

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A new theoretical framework, the EPIC (Executive-Process/Interactive-Control) architecture, provides the basis for accurate detailed computational models of human multipletask performance. Contrary to the traditional response-selection bottleneck hypothesis, EPIC's cognitive processor can select responses and do other procedural operations simultaneously for multiple concurrent tasks. Using this capacity together with flexible executive control of peripheral perceptual-motor components, EPIC computational models account well for various patterns of mean reaction times,. systematic individual differences in multiple-task performance, and influences of special training on people's task-coordination strategies. These diverse phenomena, and EPIC's success at modeling them, raise strong doubts about the existence of a pervasive immutable response-selection bottleneck in the human information-processing system. The present research therefore helps further characterize the nature of discrete versus continuous information processing.

Over more than a half century of experience in research on learning, memory, and decision, I have come to believe that the most substantial and enduring advances have not been in the accumulation of empirical facts or the construction of models, but in the production of fruitful interactions between models and experimental research. Most experimental facts require continual reinterpretation and most models drop by the wayside like autumn leaves, but the results of interactions between models and experiments constitute most of our generalizable knowledge. Success in the interactive research effort depends not only on clearly formulated models and well-conducted experiments, but, just as importantly, on sound interpretations of the results of applying the models to the experiments. This interpretive phase of the effort is in some respects the most difficult, and I take as my main task in this article an account of some of the issues that have to be resolved and some of the traps that have to be avoided in order for the process to run to a successful conclusion. As a preliminary, I turn to a review of the basic concept of applying a model to data as it has evolved since its first rudimentary instantiation in the literature of memory and decision more than a century ago. Applying Models to Experiments Details of techniques for fitting curves, or, more broadly, formal models, whether mathematical or computer imple-This article presents in substance the author’s Governing Board Keynote

Four observers completed perceptual matching, identification, and categorization tasks using separable-dimension stimuli. A unified quantitative approach relating perceptual matching, identification, and categorization was proposed and tested. The approach derives from general recognition theory (Ashby & Townsend, 1986) and provides a powerful method for quantifying the separate influences of perceptual processes and decisional processes within and across tasks. Good accounts of the identification data were obtained from an initial perceptual representation derived from perceptual matching. The same perceptual representation provided a good account of the categorization data, except when selective attention to one stimulus dimension was required. Selective attention altered the perceptual representation by decreasing the perceptual variance along the attended dimension. These findings suggest that a complete understanding of identification and categorization performance requires an understanding of perceptual and decisional processes. Implications for other psychological tasks are discussed. An important goal of psychological inquiry is to understand how behavior is influenced by the environmental stimulation and the task at hand. Information about the environment

this article should be addressed to W. Todd Maddox, Department of Psychology, Mezes Hall 330 Mail Code B3800, University of Texas, Austin, Texas, 78712. E-mail: maddox@psy.utexas.edu

Dual-task differences in younger and older adults were explored by presenting two simple tasks, either a color judgment or a tone judgment followed by a letter identity judgment, with the onset of the second task relative to the first task carefully controlled. The possibility of an age-related reduction in the ability to generate and execute two similar motor programs was explored by requiring either a manual response to both tasks or a manual response to the first and an oral response to the second. This possibility was confirmed by the evidence. The possibility of an age-related reduction in the capacity to process two tasks in the same perceptual input modality was explored by presenting both tasks in the visual modality or the first task in the auditory modality and the second task, in the visual. The evidence did not support this possibility. Age differences in dual-task interference appear quite localized to response-generation processes. Dual-task Interference Page 3 Age Diff...

Human--computer interaction is currently shifting its focus from desktop-based interaction to interaction with "beyond the desktop", which is embedded into everyday activities. In order to support users more elegantly, these mobile, wearable, and ubiquitous computing devices are envisioned to adapt inte lligently to their context. Thus far, however, the mobile use contexts per se have received attention, as most research has been technology-driven. Drawing from cognitive psychology, user modeling in human-computer interaction, and ethnomethodology, a framework is put forward here to analyse mobile use situations from the point of view of resource competition. The framework assumes that mobility is inherently multitasking and easily leads to competition for cognitive and other human resources. This "cognitive resource competition" framework is elaborated and associated with the psychological principles of capacity and multitasking. It looks at the typical social, interactional, cognitive, and physical tasks in mobility, relates them to the typical cognitive resources they compete for, and, based on known capacities of cognitive faculties, pinpoints restrictions and resources for action that can emerge in a given mobile situation. It is argued that the approach is useful for identifying the perceptual, attentional, and cognitive capabilities of a user in a mobile situation. The approach has implications for the design and innovation of intelligent, context-sensitive user interfaces and services. Furthermore, a practical method for making human resources visible in a design session is proposed and evaluated. Keywords Mobility, context-awareness, human-computer interaction, cognitive psychology, ethnomethodology, user modeling, attention, memory, central capacity Deposito...