Integrated versus isolated feature presentation, a change of paradigm

Dans le document The maintenance of cross-domain associations in working memory (Page 143-152)

Materials and Procedure

5.3. Integrated versus isolated feature presentation, a change of paradigm

Experiment 3

In order to counter the different number of task switches in the two presentation modes in Experiment 2, two options seemed feasible. According to the first option, the isolated presentation mode could show a location followed by a letter and followed by an entire processing phase (instead of separating each feature by half a processing phase). The

difference between the integrated and isolated condition would then concern the presentation of a letter in location or a sequential presentation of a location and a letter. However, due to the processing phases separating the letter and location presentation, we reasoned that this rhythm might anyhow strongly incite a binding process in the isolated condition. We chose hence the second option: a Brown-Peterson paradigm. All items to be maintained are shown before a single processing phase is initiated. In the integrated condition, all letters in locations are presented sequentially. In the isolated condition, the presentation of locations and letters is alternated sequentially until all features have been presented. Using this paradigm stresses less the unity of the locations and letters in the isolated condition. In order to avoid the second concern of Experiment 2, i.e., ceiling effects, we used a span procedure ranging from two to six features pairs. This led to an increase in the duration of the experiment and the isolated

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and integrated presentation modes were administered in two different sessions for each participant.

This third experiment compared thus anew the capacity limits of an integrated with an isolated feature presentation. As in the previous experiments, we were also interested in the impact a decrease in attentional availability might have on these capacity limits. We

manipulated hence the cognitive load of the tone discrimination task in a similar way as in the two previous experiments.

Method

Participants and Design

Twenty-five students from the University of Geneva (mean age = 21.76 years, SD = 6.51, 20 female) completed the two sessions of this experiment for the integrated and isolated presentation respectively. They were paid or given course credit for participation. The

cognitive load was manipulated within subjects.

Materials and Procedure

A Brown Peterson paradigm was used, combining the maintenance of letters and locations with the neutral tone discrimination task used in both previous experiments.

Participants were presented with a series of letters and locations. Once all the items to be maintained had been presented the tone discrimination task started for 12 s. At the end participants had to recall all the letters and locations in the correct order. As in Experiment 2, letters and locations could be presented integrated, i.e. a letter displayed within a certain location, or isolated, i.e. first a location and on the next screen a centrally displayed letter (see Figure 5.3). The cognitive load of the tone distraction task was manipulated and consisted of six tones at a rate of one tone every 2000 ms, nine tones at a rate of one tone every 1293 ms8 or 12 tones at a rate of one tone every 1000 ms for the low, medium and high cognitive load

8 The attentive reader might have noticed that nine tones at a rate of 1293 ms results in a retention interval of 11637 ms and not 12000 ms. A human mistake is at its origin. The resulting difference in retention interval is however small (363 ms) and cannot account for the obtained results. This shorter retention interval appeared in the medium cognitive load. If a shorter retention interval resulted in better memory performance, then we should have observed higher memory performance in the medium as compared to the low and high cognitive load. This was however not the case and this small difference will hence be considered negligible.

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condition. At the end of the tone discrimination task the word recall (“rappel”) appeared on screen and participants were incited to recall all the letters and locations in the correct order.

Series of ascending length from two to six letters and two to six locations were created as in Experiment 2. We created again two different lists as participants performed two

sessions for the integrated and isolated condition. Nine series per list length were created and attributed in a counterbalanced way to a cognitive load condition as in Experiment 2. Series were presented in ascending order, and randomly presented within a given list length.

Each participant performed a block of the integrated and a block of the isolated condition in two different sessions. The order of the sessions was counterbalanced. All

participants saw the items of list one in the first session and list two in the second session. The different versions of these lists (as a result the attribution of cognitive load conditions) were counterbalanced over participants.

Each trial followed the same temporal design. Participants were first informed about the cognitive load condition for the upcoming trial during 750 ms. This was followed by an asterisk for 750 ms and the first item to be maintained. In the integrated condition, a letter in location was displayed during 1500 ms, followed by a blank screen for 500 ms. Hereafter the next letter in location appeared followed by a blank screen and so on until the end of the series. In the isolated condition, first a location was shown for 750 ms, followed by a blank screen for 250 ms. Then a letter was shown in the middle of the screen for 750 ms, followed by a blank screen for 250 ms. After this a new location appeared and this procedure continued until the end of the series. After the last memory item had been followed by a blank screen, the tone discrimination task started for 12000 ms, followed by the word recall (“rappel”).

Then participants could start recalling all of the letters and locations in the correct order.

Recall was done in the same way as in Experiment 2 by clicking locations and typing letters.

These appeared on screen in the same way as at study, i.e. as integrated objects in the integrated presentation mode and as isolated features on sequential displays in the isolated presentation condition. Each session had first of all started with a training phase. This

included training on the memory task, the tone discrimination task and a combination of both.

As in the previous experiments, an accuracy score of 80 % on the processing task was a requisite to continue to the actual experiment.

A verbal and a spatial span score were calculated per presentation mode (integrated or isolated) and per cognitive load condition (low, medium or high) according to the

all-or-117

nothing unit scoring. When all of the verbal features of a series were recalled in the correct order, this added 1/3 of a point to the verbal span score for the integrated or the isolated presentation mode. When all of the spatial features of a series were recalled in the correct order, this added 1/3 of a point to the spatial span score in the respective condition.These points were added to a basis score of one as series of one were not presented. Span scores per domain ranged thus between one and six.

Additionally, cross-domain span scores were calculated. These scores are based on the correct recall of the feature pairs. If feature associations are maintained as integrated objects, then it makes sense to evaluate how many objects can be maintained, as we have previously done in Experiment 1. Theoretically, this measure only makes sense for the integrated presentation condition as in this case letters and locations are suggested to be maintained integrated. Expressing the amount of isolated features in terms of a number of objects items that can be maintained is rather senseless, as these are not assumed to be maintained as an ensemble. For the sake of comparison, we calculated this cross-domain span score for the integrated as well as the isolated feature condition anyway. If all of the feature pairs

(composed of a verbal and a spatial feature) were recalled in the correct order, then 1/3 of a point was added to the basis cross-domain span score of one. These cross-domain span scores ranged thus also between one and six.

Results

All participants reached the predetermined criterion of 75 % on the tone discrimination task. First of all, 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 mean verbal and spatial span scores with order as between subject factor and domain, presentation mode and cognitive load as within subject factors. There was a significant effect of presentation mode, F(1, 23) = 26.49, p < .001, η2 = .54, with the integrated presentation (M = 4.26) leading to better

memory performance (M = 3.76, see Figure 5.4). There was also a significant effect of domain, F(1, 23) = 89.73, p < .001, η2 = .80, with verbal recall (M = 4.76) being better than spatial recall (M = 3.25). The general effect of cognitive load was not significant, although the linear trend was, F(1, 23) = 5.11, p = .03. The interaction between presentation mode and domain was significant, F(1, 23) = 10.46, p = .004. For both the verbal and the spatial

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domain, the integrated presentation mode led to better recall performance (M = 4.90 versus 4.63 for the verbal spans and M = 3.62 versus 2.88 for the spatial spans), F(1, 23) = 5.58, p = .03, η2 = .20 and F(1, 23) = 34.52, p < .001, η2 = .60, but this difference was more

pronounced for the spatial domain. The effect of order was not significant, F(1, 23) < 1 and none of the other interactions was significant either.

Additionally, we analyzed the cross-domain span scores9. A (Order: integrated – isolated or isolated - integrated) X 2 (Presentation mode: integrated or isolated) X 3 (Cognitive load: low, medium or high) repeated measure ANOVA was performed on the mean cross-domain span scores with order as between subject factor and presentation mode and cognitive load as within subject factors. There was a significant effect of presentation mode, F(1, 23) = 41,87, p < .001, η2 = .65, with the integrated presentation mode (M = 3.45) leading to better recall than the isolated presentation mode (M = 2.70). The effect of cognitive load was significant as well, F(1, 23) = 3.30, p = .046, η2 = .13. Increasing the cognitive load resulted in lower recall performance (M = 3.19, 3.12 and 2.91 in the low, medium and high cognitive load condition respectively). There was also a triple interaction between

presentation mode, cognitive load and order, F(1, 23) = 3.95, p = .026. The effect of cognitive load in the second session was always less pronounced than in the first session. As the order of the presentation modes was counterbalanced, this resulted in the present interaction.

Figure 5.4: Span scores as a function of maintenance domain, presentation mode, and cognitive load for Experiment 3. Panel a represents the verbal and spatial span scores, panel b represents the cross-domain span scores. Error bars represent the standard error of the mean.

9 A comparison between the span scores for cross-domain associations of Experiment 1 (complex span task) and Experiment 3 (Peterson task) revealed higher cross-domain span scores when using the Brown-Peterson task in Experiment 3, F(1, 50) = 6.28, p = .015, η2 = .14. The effect of cognitive load did not interact with the nature of the task, F(2, 100) < 1. This difference will be discussed in the discussion on capacity limits.

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Discussion

Experiment 3 nicely replicated the results obtained in Experiment 2 while using a different paradigm and confining ceiling effects. We can thus confirm that in terms of features, an integrated feature presentation leads to better memory performance than an isolated feature presentation. As in Experiment 2, span scores decreased as the cognitive load increased, but no interaction between cognitive load and presentation mode was observed.

Memory performance for features relies thus to the same extent on attentional resources in the integrated and isolated presentation mode.

Could the lower memory performance in the isolated condition be an artefact of the use of span scores? Points are added to the verbal and spatial span scores only if the total verbal or spatial series is recalled correctly. Imagine one can maintain four features. All trials of list length two (two verbal and two spatial features) should be correct and a verbal and spatial span score of two items would hence be the minimum. Participants who prioritize verbal maintenance could continue to increase their span scores by maintaining three verbal features and one spatial feature at list length three, and maintaining four verbal features and no spatial features a list length four. This would result in span scores of four verbal features and two spatial features. Or participants could prioritize on some trials verbal maintenance and on other trials spatial maintenance. This would increase both span scores, although to a lesser extent. Participants who attribute equal importance to both features would not increase their span scores above the minimum span scores of two for the verbal and two for the spatial features. At list length three, they would still maintain two verbal and two spatial features, as well as at list length four. The all or nothing scoring does though not attribute any points for this maintenance. Participants had however no idea about the scoring methods of the

experiment and a deliberate decision to use this strategy to gain extra points can hence be excluded. If a priorization strategy had been used anyway in one of the both conditions, then it should have been in the integrated condition as span scores are higher in this condition. The use of a priorization strategy in the integrated condition and a non-priorization strategy in the integrated condition seems however the opposite pattern of what would be expected if a strategy had been used in one of the two conditions. We would rather expect participants to maintain the associations as a whole in the integrated presentation mode and this corresponds to non-priorization. We verified this possibility anyhow by calculating the cross-domain span scores. These cross-domain span scores reflect the basic score participants would obtain, independently of the use of any further strategy. It stops to increase when the capacity limit

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for the ensemble of the features is attained and the use of any kind of strategy cannot surpass this limit. The use of these cross-domain span scores confirmed the higher memory

performance in the integrated than in the isolated presentation mode.

5.4. Discussion

The experiments run within the context of the capacity limits for cross-domain associations have allowed us to confirm two main hypotheses concerning the maintenance of cross-domain feature associations. First of all, less cross-domain associations can be

maintained than single features. Secondly, more features could be maintained when these are presented as cross-domain associations than as isolated features.

The results of Experiment 1 are well in line with literature on the capacity limits. The assumption that working memory can maintain about four items has been raised by several authors and reaffirmed on several occasions (e.g., Baddeley, 2012; Baddeley et al., 2011;

Cowan, 2001, 2005; Cowan et al., 2013; Luck & Vogel, 1997; Vogel et al., 2001). We have described in chapter three that variations on the fixed capacity limit of about four items are frequently encountered due to variations in for example the cognitive load or the contribution of long-term memory. Experiment 1 was however well calibrated on these suggested fixed capacity limits. Experiment 1 showed that when the cognitive load of the processing task was low, we observed indeed that about four spatial features could be maintained. For verbal features, we observed a capacity limit of about six items under a low cognitive load. As stated before, this increase in the capacity limits is probably due to the aid of verbal rehearsal to maintain verbal information (e.g., Camos et al., 2009; Cowan, 1999). Having established this coherence with literature on this subject, we can be confident that the capacity limits for cross-domain associations we have observed make sense. We assume hence the working memory capacity limit of cross-domain associations composed of two features to be set at approximatively three.

This capacity limit is lower than suggested by Luck and Vogel (1997) and Vogel et al.

(2001). These authors had suggested the capacity limits for feature associations to be the same as for single features, and fixed at four items. We have however stated before that these studies have been the topic of controversy: several attempts to replicate the main findings have failed (e.g., Hardman & Cowan, 2015; Olson & Jiang, 2002; Wheeler & Treisman,

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2002), there was no evidence that the link between the features was maintained as well, and more recently, both the studies of Hardman and Cowan (2015) and Oberauer and

Eichenberger (2013) provided clear evidence that the capacity limits for feature associations were lower than for single features. Our study confirms this latter result and extends the scope of this result to the maintenance of cross-domain feature associations. Additionally, our study was able to quantify the amount of cross-domain associations that could be maintained, namely three. We do however acknowledge that this capacity limit might hold only for

feature associations composed of two features. Hardman and Cowan (2015) and Oberauer and Eichenberger (2013) both showed that increasing the number of features per object decreases memory performance. In their studies, the number of objects as well as the number of features per object played a dominant role within memory performance. The next step in our research on the capacity limits of cross-domain associations would then be to measure this limit for associations composed of three features. This could be accomplished by using letters in location which are additionally presented in different colors. We suppose the capacity limits of these enlarged cross-domain associations to fall beneath the limit of three items.

We will not go any further in detail on Experiment 2, as Experiment 3 replicated these results while making use of an improved methodology. We observed in Experiment 3 that the cross-domain span score in the low cognitive load condition, for those associations that had been presented integrated, was now increased up to 3.59. The number of associations maintained in Experiment 3 is clearly higher than in Experiment 1. The main difference between these two experiments concerned the paradigm used. Experiment 1 made use of a complex span task, while Experiment 3 made use of a Brown-Peterson task. This difference in capacity limits observed between the Brown-Peterson and the complex span task might be due to a higher switch cost induced by the continuous alternation of maintenance and processing in the complex span task, or to the shorter retention intervals in the

Brown-Peterson task at longer list lengths. We had observed that Experiment 1was well calibrated on the capacity limits declared in the literature. For Experiment 3, we could not affirm this synchronization with literature. We prefer hence to limit our interpretations to the relative differences observed between an integrated and an isolated feature presentation.

Experiment 3 showed that the capacity limits for cross-domain features presented integrated are higher than for these same features presented in isolation. This was clear from the cross-domain span scores as well as from the verbal and spatial span scores. This result is in line with the results of Prabhakaran et al. (2000) and Morey (2011). Both studies showed

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an integrated cross-domain features presentation to result in better memory performance than an isolated cross-domain feature presentation. At this moment, it is hence clear that there is a memory advantage of presenting features integrated. In the next chapters, we further

investigate where this advantage comes from. More specifically, in the next chapter we will elaborate on the resources involved in the maintenance of integrated cross-domain feature associations. In Experiment 1, 2 and 3, we have manipulated the cognitive load of the processing task in order to deduce the relative involvement of domain-general attentional resources in the maintenance of cross-domain associations and single features. These results

investigate where this advantage comes from. More specifically, in the next chapter we will elaborate on the resources involved in the maintenance of integrated cross-domain feature associations. In Experiment 1, 2 and 3, we have manipulated the cognitive load of the processing task in order to deduce the relative involvement of domain-general attentional resources in the maintenance of cross-domain associations and single features. These results

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