Working memory representations

Several studies have reported evidence for cross-domain feature associations to be maintained as an integrated representation. This integration has mainly been demonstrated through a change detection paradigm by comparing exact feature probes with recombined feature probes. Prabhakaran et al. (2000), Morey (2011) and Elsley and Parmentier (2009) have all shown that letters and locations were recognized better and/or faster when presented at test in their exact combination than as recombined feature probes . This result could indeed only occur if feature associations are maintained integrated. Elsley and Parmentier (2009) had however shown that attention plays an important role in this integrated maintenance. We have explained in the previous section our reticence on the interpretation of their results and no other study investigated the topic. Additional evidence on the underlying representations for the maintenance of cross-domain associations was thus indispensable, especially in case of reduced attentional availability.

A series of three experiments was performed to test the hypothesis that cross-domain associations are maintained integrated and that this integrated maintenance is not particularly dependent on attentional resources. The first experiment was an extension of Experiments 3.

In this experiment we had compared the maintenance of a same number of features, presented integrated or isolated and under different cognitive loads. To anticipate the results, we

observed better memory performance in the integrated presentation mode, and no differential impact of cognitive load on both presentation modes. Better memory performance is a typical observation in case of an integrated maintenance of the features (which was derived from the differences in accuracy and reaction times on intact and recombined probes, or cross-domain interference that would not occur in case of an isolated maintenance, e.g., Prabhakaran et al., 2000; Morey, 2009, 2011). The results of Experiment 3 seemed thus to point to an integrated maintenance in case of an integrated presentation and a separate feature maintenance in case of an isolated feature presentation. However, we wanted to test an alternative explanation for our results: presentation time. This alternative explanation was based on two findings. First of all, it has been suggested that an integrated feature presentation gives rise to a simultaneous processing of its constituent features while an isolated feature presentation results in

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sequential processing of the features (e.g., Ceraso, 1985; Duncan, 1984; Woodman & Vogel, 2008). In Experiment 3, the letters in locations in the integrated feature condition were shown for 1500 ms. Due to simultaneous processing, this gives rise to a feature processing time of 1500 ms per feature. In the isolated feature presentation, participants had only 750 ms to process each separate feature for further maintenance. This difference in

encoding/consolidation time leads us to our second claim. It has been shown in a number of studies that longer encoding/consolidation time results in better memory performance (e.g., Barrouillet, Plancher, Guida, & Camos, 2013; Bayliss, Bogdanovs, & Jarrold, 2015; Karlsen et al., 2010; Oberauer & Eichenberger, 2013). Could the better memory performance we have observed in Experiment 3 be due to a longer encoding/consolidation time per feature in the integrated condition instead of due to an integrated maintenance? This was tested in

Experiments 6 and 7. We replicated Experiment 3 with modified presentation times. In Experiment 3, the integrated and isolated conditions were characterized by an equal total presentation time of the memory items (see Figure 4.4). In Experiments 6, we equalized the feature presentation time instead of the total presentation time (see Figure 4.4) and in Experiment 7 we equalized both the feature presentation and the total presentation time in several conditions. Both experiments were run under different cognitive loads. In order to exclude an explanation in terms of encoding/consolidation time and favor an interpretation in terms of integrated maintenance in the integrated presentation condition, we should observe higher memory performance in the integrated than in the isolated presentation condition when the feature presentation times are equalized. Additionally, observing this pattern in all

different cognitive load conditions would mean that an integrated maintenance is not particularly dependent on attentional resources.

Figure 4.4: Schematic representation of an equal total presentation time and an equal feature presentation time.

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If on the other hand, we observe equal memory performance in the integrated and isolated presentation condition under equal feature presentation times, this could still be the result of an integrated object-based maintenance as well as an isolated feature-based

maintenance of the feature associations. In case of an object-based maintenance this would mean that this kind of object-based maintenance does not necessarily result in better memory performance over and above the encoding/consolidation time. In case of a feature-based maintenance, it would then be logical that an isolated maintenance of the features results in the same memory performance if the encoding/consolidation time are equalized. Based on the existing evidence of integrated maintenance for cross-domain associations, we predict that the increase of the feature presentation time in the isolated presentation condition in Experiments 6 and 7 would increase memory performance, but that the integrated presentation mode would nevertheless result in better memory performance. The difference observed in Experiment 3 between an integrated and an isolated presentation would hence be reduced, but still present.

The results of Experiments 6 and 7 (in the conditions with equal feature presentation times) would thus favor the idea that maintenance of the associations is done integrated if memory performance is indeed better in the integrated than in the isolated presentation condition. However, conclusive evidence on the underlying representation can at this point of research most prominently be supplied by the comparison of exact and recombined probes in a recognition paradigm. In Experiment 8, we replicated Experiment 6 but combining the recall paradigm with the classical recognition paradigm (Prabhakaran et al., 2000). The results of the recall paradigm should not be novel as compared to Experiment 6, but this experiment has the advantage that it can directly link memory performance to the underlying

representations. Concerning the recognition task, a higher accuracy score and/or shorter reaction times for exact than for recombined probes would indicate an integrated

maintenance. We expect to observe this pattern of results in the integrated presentation mode, independently of the cognitive load. In the isolated presentation condition, we do not expect to observe this pattern. As for Experiment 6, we predict that the integrated presentation condition will result in better memory performance, based on the supposed integrated underlying representations of the cross-domain associations.

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Based on the literature discussed in the first three chapters, we have in the current chapter summarized the main lacunas and issues of discussion concerning the capacity limits, the resources and the representations for the maintenance of cross-domain associations. We have explained as well how we count to contribute to these ongoing discussions and provide additional information on the subject. This will be done in a series of eight experiments, for which we have detailed the main hypothesis and the accompanying predictions. The next three chapters will briefly resume the rationale for each experiment, followed by an exhaustive description of the methodology, the results and a preliminary discussion of the findings.

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CHAPTER 5:

WORKING MEMORY CAPACITY FOR