When trying to remember verbal information from memory, people look at spatial locations that have been associated with visual stimuli during encoding, even when the visual stimuli are no longer present. It has been shown that such "eye movements to nothing" can influence retrieval performance for verbal information, but the mechanism underlying this functional relationship is unclear. More precisely, covert in comparison to overt shifts of attention could be sufficient to elicit the observed differences in retrieval performance. To test if covert shifts of attention explain the functional role of the looking-at-nothing phenomenon, we asked participants to remember verbal information that had been associated with a spatial location during an encoding phase. Additionally, during the retrieval phase, all participants solved an unrelated visual tracking task that appeared in either an associated (congruent) or an incongruent spatial location. Half the participants were instructed to look at the tracking task, half to shift their attention covertly (while keeping the eyes fixed). In two experiments, we found that memory retrieval depended on the location to which participants shifted their attention covertly. Thus, covert shifts of attention seem to be sufficient to cause differences in retrieval performance. The results extend the literature on the relationship between visuospatial attention, eye movements, and verbal memory retrieval and provide deep insights into the nature of the looking-at-nothing phenomenon.

Sequential abductive reasoning is the process of finding the best explanation for a set of observations. Explanations can be multicausal and require the retrieval of previously found ones from memory. The theory of abductive reasoning (TAR) allows detailed predictions on what information is stored and retrieved from memory during reasoning. In the research to date, however, these predictions have never been directly tested. In this study, we tested process assumptions such as the construction of a mental representation from TAR using memory indexing, an eye-tracking method that makes it possible to trace the retrieval of explanations currently held in working memory. Gaze analysis revealed that participants encode the presented evidence (i.e., observations) together with possible explanations into memory. When new observations are presented, the previously presented evidence and explanations are retrieved. Observations that are not explained immediately are encoded as abstractly explained. Abstract explanations enter a refinement process in which they become concrete before they enter the situation model. With the memory indexing method, we were able to assess the process of information retrieval in abductive reasoning, which was previously believed to be unobservable. We discuss the results in the light of TAR and other current theories on the diagnostic reasoning process.

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Abductive reasoning describes the process of deriving an explanation from given observations. The theory of abductive reasoning (TAR; Johnson and Krems, Cognitive Science 25:903–939, 2001) assumes that when information is presented sequentially, new information is integrated into a mental representation, a situation model, the central data structure on which all reasoning processes are based. Because working memory capacity is limited, the question arises how reasoning might change with the amount of information that has to be processed in memory. Thus, we conducted an experiment (N = 34) in which we manipulated whether previous observation information and previously found explanations had to be retrieved from memory or were still visually present. Our results provide evidence that people experience differences in task difficulty when more information has to be retrieved from memory. This is also evident in changes in the mental representation as reflected by eye tracking measures. However, no differences are found between groups in the reasoning outcome. These findings suggest that individuals construct their situation model from both information in memory as well as external memory stores. The complexity of the model depends on the task: when memory demands are high, only relevant information is included. With this compensation strategy, people are able to achieve similar reasoning outcomes even when faced with tasks that are more difficult. This implies that people are able to adapt their strategy to the task in order to keep their reasoning successful.

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Abductive reasoning describes the process of deriving an explanation from given observations. The Theory of Abductive Reasoning (TAR; Johnson & Krems, 2001) assumes that when information is presented sequentially, new information is integrated into a mental representation, a situation model, the central data structure on which all reasoning processes are based. Because working memory capacity is limited, the question arises how reasoning might change with the amount of information that has to be processed in memory. Thus, we conducted an experiment (N = 34) in which we manipulated whether previous observation information and previously found explanations had to be retrieved from memory or were still visually present. Our results provide evidence that people experience differences in task difficulty when more information has to be retrieved from memory. This is also evident in changes in the mental representation as reflected by eye tracking measures. However, no differences are found between groups in the reasoning outcome. These findings suggest that individuals construct their situation model from both information in memory as well as external memory stores. The complexity of the model depends on the task: when memory demands are high, only relevant information is included. With this compensation strategy, people are able to achieve similar reasoning outcomes even when faced with tasks that are more difficult. This implies that people are able to adapt their strategy to the task in order to keep their reasoning successful.

Abductive reasoning is the process of finding the best explanation for a set of observations. As the number of possible observations and corresponding explanations may be very high, it is commonly accepted that the capacity of working memory is closely related to successful abductive reasoning. However, the precise relationship between reasoning and working memory capacity remains largely opaque. In a reanalysis of two experiments (N = 59), we first investigated whether reasoning performance differs due to differences in working memory capacity. Second, using eye tracking, we explored the relationship between the facets of working memory and the process of visuospatial reasoning. We used working memory tests of both components (verbal-numerical/spatial) as well as an intelligence measure. Results show a clear relationship between reasoning accuracy and spatial storage components as well as intelligence. Process measures suggest that high working memory ability might lead to the use of strategies to optimize the content and complexity of the mental representation on which abductive reasoning is based. Results are discussed in relation to current theories and the existing literature on the effects of memory on eye movements.

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