Materials and Procedure
5.2. Integrated versus isolated feature presentation
Experiment 2
Several experiments on cross-domain associations have compared the maintenance of features when these had been presented as integrated objects or as isolated features (e.g., Morey, 2011; Prabhakaran et al., 2000). Better memory performance has been shown for the integrated presentation mode. We replicated and extended this research by first of all putting it in a working memory context by adding a processing task and secondly by manipulating the cognitive load of the processing task. This manipulation should inform us about the
involvement of attention within this higher memory performance resulting from an integrated presentation.
A complex span paradigm was used to compare the maintenance of three letters and three locations when these had been presented integrated (letters in locations) or isolated. This limit of three verbal and three spatial features was chosen as it corresponded to the highest capacity estimate for cross-domain associations in Experiment 1. In line with literature on cross-domain maintenance, we predicted that maintenance would be better for the integrated than the isolated presentation condition. In line with Experiment 1, we did not expect to observe a different effect of the cognitive load for the integrated and the isolated presentation modes.
Method
Participants and Design
Thirty-six participants of the University of Geneva took part in this experiment (mean age = 20.54 years, SD = 1.56 years, 32 female) and were paid or given course credit for their participation. Presentation mode and cognitive load were manipulated within subjects.
Materials and Procedure
A complex span task was used combining the maintenance of letters and locations with the neutral tone discrimination task used in Experiment 1. Series of three locations and
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three letters were presented. These locations and letters were presented either integrated or isolated (see Figure 5.3).
Figure 5.3: Example of a trial in the a) integrated and b) isolated presentation mode in Experiment 2.
The integrated condition was the same as the cross-domain maintenance condition in Experiment 1 at list length three. The isolated condition differed on several points. Instead of showing a letter in location for 1500 ms followed by a blank screen of 500 ms and a
processing phase, a location was shown for 750 ms followed by a blank screen for 250 ms and half a processing phase, followed by a letter for 750 ms, a blank screen of 250 ms and the other half of the processing phase. This resulted in exactly the same total duration but a strict separation of the spatial and verbal feature. Recall in the integrated and isolated presentation condition was done similarly. In general, participants first clicked a locations and then typed a letter. In the integrated condition, the letter appeared in the clicked location which had turned grey. Participants then had to press ENTER to validate this response and clean the screen to be able to recall the next association. In the isolated presentation condition, the clicked location turned grey. Participants had to validate this response by pressing ENTER, which made the response disappear from the screen. Then they had to type a letter, which appeared in the middle of the screen. ENTER validated the response and cleaned the screen so a next location could be recalled. The answers appeared hence on screen in the same way as they had been presented at study (integrated or isolated).
During the processing phases, participants performed the neutral tone discrimination task used in Experiment 1 in which they had to discriminate the frequency of two tones. In the integrated condition, processing phases consisted of the discrimination of four tones in 8000 ms, four tones in 5172 ms or eight tones in 8000 ms in the low, medium and high cognitive
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load condition respectively. In the isolated condition, these processing phases were cut in half, resulting in the processing of two tones in 4000 ms, two tones in 2586 ms or four tones in 4000 ms in the respective conditions. The pace of the processing task was thus kept constant in the two conditions (one item every 2000 ms, one item every 1293 ms and one item every 1000 ms in the low, medium and high cognitive load condition respectively).
All participants performed the integrated and isolated presentation condition in one experimental session, in a blocked counterbalanced order. Each block started with a training on the memory task, then on the tone discrimination task and then on the combination of both, before the start of the experimental block. For the actual experiment, two lists were produced composed each of nine series of letters and locations. These had been created by randomly associating three letters to three locations without replacement. Letters always concerned consonants (except W, Y and Z) and locations were indicated by a grey square out of a grid of 16 empty white squares (see Figure 5.3 for an example of the presentation of the memory items). These lists were each as often combined with the integrated and the isolated condition and used as often for the first or the second presented condition. Both lists contained three trials of each cognitive load. These nine trials were displayed in a random order. To
counterbalance the attribution of series to cognitive load, three different versions of both lists were created. In total, each participant performed three trials per cognitive load condition, in the integrated as well as in the isolated presentation condition.
Recall performance was evaluated per domain. One point was given for each verbal series recalled in the correct order and one point was given for each spatial series recalled in the correct order. Scores were calculated per presentation mode (integrated or isolated) and per cognitive load condition (low, medium or high) for the verbal and the spatial domain separately. These scores could range between zero and three and corresponded to the number of series correctly recalled for the verbal or spatial domain.
Results
One participant did not reach the 75 % accuracy criterion for the tone discrimination task and was excluded from further analysis. 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
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number of series correctly recalled, with order as between subject factor and domain, presentation mode and cognitive load as within subject factors. The effect of presentation mode was significant, F(1, 33) = 42.87, p < .001, η2 = .57, with an integrated presentation leading to better recall performance. The effect of domain was also significant, F(1, 33) = 34.52, p < .001, η2 = .51, with verbal recall exceeding spatial recall. The effect of cognitive load, F(2, 66) = 13.80, p < .001, η2 = .30, and its linear trend, F(1, 33) = 23.76, p < .001, were highly significant as well. There was also an interaction between presentation mode and domain, F(1, 33) = 11.75, p = .002. The integrated presentation led to better recall scores in comparison to the isolated presentation for both the verbal and the spatial domain, F(1, 33) = 8.22, p = .007, η2 = .20, and F(1, 33) = 45.53, p < .001, η2 = .58, respectively, but this
difference was more pronounced for the spatial domain. There was no significant effect of order, F(1, 33) < 1, and none of the other interactions reached significance. The main results are summarized in Table 5.1.
Table 5.1: Number of series correctly recalled (and SD) as a function of domain, presentation mode and cognitive load in Experiment 2
Spatial Verbal
First of all, it was observed that an integrated feature presentation led to better memory performance than an isolated presentation. Secondly, there was a significant decrease in recall scores as the cognitive load of the processing task increased. This decrease rate was however the same for the integrated and isolated presentations. The maintenance of features presented integrated is thus to the same extent dependent on attention as the maintenance of features presented in isolation. These main results confirm our predictions. However, two remarks have to be made before drawing any firm conclusions. First, the present design contained a possible confound. In the integrated condition, a task switch from maintenance to processing appeared after each cross-domain association, hence three times per trial. In the isolated condition, this kind of task switch occurred after each feature hence six switches in total. It
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has been shown that an increase in task switches negatively affects memory performance in a working memory context (e.g., Liefooghe, Barrouillet, Vandierendonck, & Camos, 2008).
Secondly, performance was generally quite elevated, especially for verbal maintenance. In the integrated condition for example, 13 out of 35 participants obtained the maximum span score for verbal maintenance in all three cognitive load conditions. This clearly represents a ceiling effect, which might have been present to a lesser extent in other conditions as well. Our reasoning to show three letters and three locations was based on the highest capacity limit for domain associations observed in Experiment 1 (i.e., 2.99 associations). This cross-domain capacity estimate is however limited by the lower of the limits for the verbal and spatial features making up the associations. Spatial feature capacity was the limiting factor and verbal feature capacity could thus easily exceed this capacity limit of three items.
Experiment 3 was set up to neutralize these two concerns.