REPRESENTATIONS OF CROSS-DOMAIN ASSOCIATIONS IN WORKING MEMORY
7.1. Integrated maintenance versus feature encoding advantage
We replicated Experiment 3 with a change of the temporal parameters. Experiment 3 compared the integrated feature presentation with the isolated feature representation when each feature pair was shown within a temporal limit of 1500 ms. The total presentation time had thus been kept constant in both conditions. In Experiment 6, we kept the presentation time per feature constant instead of the total presentation time (see Figure 4.4, p. 100). In Experiment 3 and 6, features in the integrated condition were available for encoding during 1500 ms. In Experiment 6, we increased the feature presentation time in the isolated
presentation condition from 750 ms (in Experiment 3) to 1500 ms per feature. If encoding time is the main determinant for memory performance and not maintenance mode (integrated or isolated), then we should observe equal memory performance in the integrated and the isolated condition.
Participants and Design
Twenty-three students from the University of Geneva (mean age = 21.30 years, SD = 3.66, 21 female) completed the two sessions of this experiment. They were paid or given course credit for participation. The two sessions corresponded to the integrated and the isolated presentation conditions. Cognitive load (low, medium or high) was manipulated within each session.
Materials and Procedure
The task and materials were exactly the same as in Experiment 3. Participants had to maintain letters and location. In the integrated presentation condition, these were presented as letter in location objects, and at recall they were entered as objects. In the isolated
presentation conditions, the presentation of locations and letters was alternated and participants had to recall them in this alternating order. Between the presentation of the memory items and recall, a tone discrimination task had to be executed during 12 s. The cognitive load of this processing task was manipulated in a low, medium and high cognitive load condition.
The procedure was largely the same as in Experiment 3 with the following exceptions.
The most important change concerned the presentation time of the items to be remembered.
Letters in locations were shown for 1500 ms in the integrated condition (as in Experiment 3).
In the isolated condition, each location was now shown on screen for 1500 ms, followed by a letter shown for 1500 ms (in experiment 3, isolated letters and locations were shown for 750 ms each.) The total presentation time of a letter and a location in the present experiment was thus 1500 ms in the integrated condition and 3000 ms in the isolated condition.
A minor change from Experiment 3 concerned the drop of the blank screens in between the presentation of the memory items. In Experiment 3, these were inserted to make sure that in the isolated condition, participants had enough time to adequately encode the features. In Experiment 6, the presentation times in the isolated presentation condition were increased and there was no longer a need to insert these blank screens.
In the same way as in Experiment 3, we calculated first of all a verbal and a spatial span score. Additionally, a cross-domain span score was calculated.
All participants reached the predetermined criterion of 75 % on the tone discrimination task. A 2 (Order: integrated - isolated or isolated - integrated) X 2 (Domain: verbal or spatial) X 2 (Presentation mode: integrated or isolated) X 3 (Cognitive load: low, medium or high) repeated measure ANOVA was performed on the verbal and spatial span scores, with order as between subject factor and domain, presentation mode and cognitive load as within subject factors. The effect of order was not significant, F(1, 21) < 1. More important, the effect of presentation mode was not significant either, F(1, 21) < 1 (see Figure 7.1). This was confirmed by the Bayesian analysis, pBIC (H0|D) = .78. There was a significant effect of domain, F(1, 21) = 134.29, p < .001, η2 = .87, with verbal recall (M = 4.92) being better than spatial recall (M = 3.01). The effect of cognitive load was also significant, F(2, 42) = 6.08, p
= .005, η2 = .23, with a significant linear trend as well, F(1, 21) = 9.52, p = .006. Lower cognitive load resulted in higher span scores (M = 3.92, 3.68 and 3.65 in the low, medium and high cognitive load condition respectively). The three-way interaction between presentation mode, domain and order was significant, F(1, 23) = 8.96, p = .007. Memory performance for locations was always better in the second session than in the first, whatever the mode of presentation. Memory performance for letters was on the other hand always better in the first than in the second session. As the order of presentation was counterbalanced across
participants, this resulted thus in opposite patterns according to the order of presentation.
None of the other interactions was significant.
Figure 7.1: Span scores as a function of maintenance domain, presentation mode and cognitive load for Experiment 6. Error bars represent the standard error of the mean.
The principal results were confirmed in the 2 (Order: integrated - isolated or isolated - integrated) X 2 (Presentation mode: integrated or isolated) X 3 (Cognitive load: low, medium or high) repeated measure ANOVA on the cross-domain span scores. There was no effect of order, F(1, 21) < 1, and more important neither an effect of presentation mode, F(1, 21) < 1 and pBIC (H0|D) = .83. The effect of cognitive load was significant, F(2, 42) = 5.01, p = .011, η2 = .19, with a significant linear trend as well, F(1, 21) = 7.75, p = .011. Lower cognitive load resulted in higher span scores (M = 3.02, 2.75 and 2.71 in the low, medium and high cognitive load condition respectively). None of the interactions reached significance.
The similar memory performance in the integrated and isolated presentation conditions seems to suggest that feature presentation time plays indeed an important role in the
maintenance capacity for integrated or isolated features. We had predicted an effect of feature presentation time and expected the memory performance in the isolated presentation
condition to get closer to the memory performance in the integrated condition when feature presentation times were equivalent. We had however not predicted a complete matching of these performance when feature presentation times were equalized. We still assumed an integrated feature maintenance to contain an additional memory advantage. A comparison of Experiments 3 and 6 revealed however that performance in the integrated condition (which was exactly the same in both experiments except for the presence of blank intervals after the memory items in Experiment 3) was significantly better in Experiment 3 than in Experiment 6, F(1, 46) = 10.32, p = .002, η2 = .18. Performance in the isolated presentation condition (which differed in presentation time, 750 ms in Experiment 3 and 1500 in Experiment 6, and the presence of blank intervals only in Experiment 3) was however not significantly different, F(1, 46) < 1. This result was unexpected. Probably, the presence or absence of blank screens plays a major role in this pattern of results, as these add up to the presentation times. In order to be able to interpret the results of Experiments 3 and 6 in a straightforward way, we set up a replication study. Experiment 7 combined the presentation times used in Experiments 3 and 6, without the addition of blank intervals after the memory items, and in a within subject-design.