Little is known about the role of working memory in conditional reasoning. This paper reports three experiments that examine the contributions of the visuo-spatial scratch pad (VSSP), the articulatory loop, and the central executive components of Baddeley and Hitch's (1974) model of working memory to conditional reasoning. The first experiment employs a spatial memory task that is presented concurrently with two putative spatial interference tasks (tapping and tracking), articulatory suppression, and a verbal memory load. Only the tracking and memory load impaired performance, suggesting that these tap the VSSP and central executive, respectively. Having established the potency of these interference tasks two further experiments examined the effects of tapping and tracking (Experiment 2) and articulation and memory load (Experiment 3) on a conditional reasoning task. Neither tracking nor tapping affected the number of inferences accepted or response latency. Articulation also failed to affect conditional reasoning but memory load selectively reduced acceptance of modus tollens inferences. These results are discussed in terms of both rule-based and mental models theories of reasoning. While these data cannot discriminate between the two perspectives they provide support for one of the central assumptions in each: that some errors in reasoning are attributable directly to working memory demands. Taken together these experiments suggest that conditional reasoning requires an abstract working memory medium for representation; it does not require either the VSSP or the articulatory loop. It is concluded that the central executive provides the necessary substrate.

Recent discussions of visuospatial working memory have suggested that this subsystem may incorporate a visual buffer which holds visuospatial information relatively passively. Empirical investigations of visual interference with information held within a visuospatial subsystem have yielded somewhat equivocal results. Nonetheless, evidence from Logie (1986) has indicated that visuospatial processing can be disrupted by passive exposure to irrelevant visual material in a manner analogous to the disruption of serial verbal recall by exposure to irrelevant speech. This paper reports two experiments which explore whether such irrelevant visual input is disruptive to storage of imaginal information in a primarily spatial task--the Brooks spatial matrix task. Experiment 1 shows that exposure to irrelevant visual input during encoding selectively disrupts performance on a spatial, but not a verbal, version of the task. The extent of such disruption is shown to be independent of the visual complexity of the material, its similarity to the to-be-remembered information, or a change in state, with a static white square pattern yielding equivalent disruption to that produced by changing matrix patterns. The second experiment indicates that this pattern of effects is robust, and that such disruption is evident at an equivalent level when the visual material is present only during a 20-second retention interval. These results are interpreted as evidence of obligatory access of external visual material to a passive visual buffer. Implications for the nature of a visuospatial subsystem in working memory are discussed.

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The processing demands of two strategies for symptom interpretation in a fault-finding task were considered. It was predicted that a more demanding, eliminative strategy would result in improved performance when supported by an external memory aid, and impaired performance when unsupported, as compared with a less demanding strategy involving tracing backward from bad system outputs. The nature of such demands, whether primarily verbal or visuospatial, was also examined. Results indicated that the eliminative strategy improved symptom interpretation accuracy slightly when supported by a visual memory aid and depressed performance when combined with a verbal memory aid. When no memory aid was permitted, subjects were apparently unable to use this strategy. No difference between visual and verbal memory aids was indicated with the less demanding strategy. These results are discussed with reference to their implications for the manner in which individuals utilize and represent problem information.

The aim of this study is to examine some of the components involved up to and including choice of the first test in a network fault-finding task. The components investigated were identifying the set of possible faults or consistent fault set (CFS), applying the half-split rule to a specified CFS, and making the first test without the CFS being specified. Factors of network size (54 units and 24 units) and complexity, as defined by four types of CFS configuration, were manipulated. Results indicated that errors occurring in identification of the CFS are mostly omission errors. Performance of this component is degraded by increasing both network size and complexity of the CFS. The same pattern of effects is observed in selecting the first test when the CFS is not specified. Ability to select a half-split test from a given CFS is affected only by complexity of the CFS configuration. Future studies need to differentiate further the psychological demands imposed during the initial stages of faultfinding.