Adaptation and reaction-time techniques were used to examine the role of different spatial-frequency channels in the perception of local and global structure. Subjects were shown figures consisting of a large C composed of smaller Cs and asked to identify the orientation of either the global C or its local elements. Prior to performing the task subjects were adapted to different spatial frequencies and the effect on subsequent performance was assessed. Two main results were found. First, the adapting frequency that most affected the global task was often lower than that most affecting the local task, suggesting that high and low frequencies independently code the structure of an image. Second, reaction time to global figures was often faster than to local figures at all levels of detectability, again suggesting a role of low-frequency channels in global processing.

Several theories assume that practice (a) results in restructuring of component processes and (b) reduces demand on working memory. Eight subjects practiced judgments about digital logic gates for over 8,000 trials. At two practice levels, subjects made judgments while retaining short-term memory loads irrelevant to the judgments, relevant but not accessed, or accessed to make the judgments. Four phenomena together provide constraints for theory: First, performance declined in moving from blocked practice to randomized practice. Second, gate and judgment type strongly affected latency. Third, these effects declined but did not disappear with practice. Fourth, the cost of accessing information in working memory remained substantial. These results are interpreted as reflecting a serial process with constant structure, while component processes become faster. The results challenge theories assuming that all learning results from restructuring or that restructuring is an automatic consequence of practice, and they support a distributed view of working memory. Several current theories of skill acquisition (e.g., Anderson, 1982, 1983, 1987; Rosenbloom & Newell, 1987) share the assumptions that (a) practice results in the reorganization or r£rtrwc/un/7# of component processes, and (b) practice reduces the load on a working memory that serves as a single workspace for carrying out cognitive processes. In the study reported here, we observed the acquisition of procedural skill for judgments about causal rules over the course of approximately 20 hr (over 8,000 trials) of practice. The results challenge the above assumptions and suggest an alternative view in which the organization of component processes and use of working memory remain constant while the speed of component processes increases (and attentional load decreases) with extended practice (see Schneider, 1985). Restructuring and the Acquisition of Cognitive Skill The production system framework currently provides a popular theoretical approach to understanding learning (e.g., Klahr, Langley, & Neches, 1987). Although the idea of restructuring as a learning mechanism is not necessarily tied to the production system framework, production system theories provide the clearest descriptions of restructuring mechanisms. In Anderson's ACT* theory (1982, 1983, 1987), for example, a composition mechanism combines serially executed productions into single productions. Similarly, the chunking model described by Rosenbloom and Newell (1987) attributes per

Individuals must often coordinate information in working memory with information from perception. The demands of coordination have been analyzed in terms of the cost to switch attention. Coordination is considered in terms of the organization of control processes. Ss in 4 experiments performed list-processing tasks that sometimes required alternation between sets of items that were held in working memory or were currently displayed. Experiment 1 demonstrated that performance was slower and more error-prone when alternating between sets than when reporting a single set. On alternation tasks, latency varied with serial position, indicating that Ss paused between pairs of responses. In Experiment 2, this serial position function was observed for tasks requiring alternation between sets of information in the same modality (memory or perception). Experiments 3 and 4 demonstrate that this effect depends on the requirement to generate a new sequence of responses. A model of control processes for coordination is developed and tested.

Researchers and practitioners trying to determine acceptable levels of video quality for actual consumption by consumers may find that the results and methods described here allow for a more accurate assessment of levels of video quality that are acceptable in a fielded service.

Theories of cognitive skill suggest two hypotheses about component task practice. First, component practice increases the speed of executing component skills during problem solving. Second, component practice produces component skills that behave as encapsulated subroutines. Eight college students practiced making judgments about digital logic gates for 1360 trials. At two points during practice, they solved circuit problems that did or did not require logic gate knowledge. Time per move declined with problem-solving practice, but the effects of component training were ambiguous. However, teaching circuit functions did increase problem-solving speed. In a second experiment conducted at the end of practice, the same subjects solved problems designed to test whether the logic gate judgments acted as encapsulated subroutines. Component judgments were slower in the problem-solving context than in isolation, disconfirming this hypothesis. Taken together, the results indicate the need for a more detailed theoretical rationale for component drill.