Naturalistic time-based delayed task

The results from the mixed measures ANOVA conducted for initial investigation of the effect of memory load on the two participant groups, revealed that individuals with dyslexia were less able to remember prospectively compared to controls, regardless of the memory load condition.

This finding supports the hypothesis that individuals with dyslexia have problems with PM and is in line with the self-reported PM deficits in dyslexia found in Study 1. This result also supports previous literature discussed in Chapter 3, which pointed towards PM difficulties in dyslexia (e.g. Smith-Spark et al., 2004). The main effect of PM load condition supported Basso et al. (2010) who found that PM load has a negative effect on PM performance. Nevertheless, there was no interaction between participant group and PM load condition and this was not in line with the literature regarding WM problems in dyslexia (e.g. Smith-Spark & Fisk, 2007) which was used to argue that individuals with dyslexia would have PM problems in high PM load condition. This finding was also not in line with the reasoning that insufficient WM

resources prevent individuals with dyslexia from consciously compensating for their PM deficit, as argued by Nicolson and Fawcett (1990) DAD/CC hypothesis. Nicolson and Fawcett found that individuals with dyslexia were impaired at more difficult tasks compared to easier tasks and thus, the lack of interaction between the PM load and participant group is not in line with these results. PM tasks requiring a greater number of PM actions to be held in memory during the retention interval did not result in greater PM decline in individuals with dyslexia compared to controls (and relative to items involving low PM load). Nevertheless, the CC hypothesis was established on the basis of a study employing children with dyslexia whereas, in the current investigation an adult sample was used. Therefore, it is possible that these adults with dyslexia are more able to consciously compensate compared to children and thus, the PM load

manipulation was not cognitively demanding enough. Furthermore, as the high PM load conditions included a mixture of event-based and time-based PM tasks, which varied in task difficulty; it is difficult to make this assumption.

5.1.4.2. Naturalistic time-based delayed task

The results showed that individuals with dyslexia were significantly less able to remember prospectively on a naturalistic time-based task, involving a 24 hour time interval between intention formation and intention execution phases. These results are consistent with the argument that memory decay processes which also apply to PM (Tobias, 2009), are more prevalent in PM tasks involving longer time intervals. This in turn could result in worse PM performance, as longer time intervals may provide more opportunities to forget to perform the

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PM activity or one may be more likely to forget to monitor the time when there are longer time intervals. Nevertheless, this by itself does not explain why dyslexic individuals performed worse on this task compared to controls. It could be reasoned that distractible attention

(Nicolson & Fawcett, 1990) or difficulties with inhibition of distracters (Palladino et al., 2001) played a part in the PM deficit found in dyslexia in this experiment. Namely, one can suggest that in tasks involving longer time intervals it is possible that distractibility may have a negative effect on maintaining the PM intention in memory, with the dyslexic group being more likely to forget.

There are several other theoretical possibilities that could account for these results. As this task took place in naturalistic everyday settings, it is more likely that there were many more

distractions in the environment compared to a laboratory controlled setting. Therefore, one could be distracted from the PM intention and thus stop monitoring the time, leading to failure of PM. Another issue is that due to increased involvement in everyday life activities (compared to a laboratory setting) and difficulty with automatisation of some of the real life tasks, this could have resulted in a lack of available cognitive resources (e.g. WM capacity). Additionally, inhibition and task switching difficulties in dyslexia (e.g. Hari & Renvall, 2001) could be relevant in explaining the PM deficit found on the basis of this naturalistic task. That is to say, participants with dyslexia could have difficulties with inhibiting their current ongoing tasks in order to switch between the ongoing tasks and time monitoring activity/performance on the PM task.

On the other hand one may argue that dyslexic individuals have difficulties with spontaneous retrieval processes. Namely, tasks involving long time intervals are more likely to rely on spontaneous retrieval processes (McDaniel & Einstein, 2007). Since the PM task involving long time intervals may be too taxing for attentional resources to constantly monitor the environment for the appropriate time to perform the task (hold the PM intention in conscious awareness) and perform other daily tasks. Thus, individuals with dyslexia whose spontaneous retrieval

processes fail would also fail to retrieve the PM intention at the appropriate time. The explanations of the naturalistic results provided briefly within this section will be expanded upon in the following chapters when considering other naturalistic and semi-naturalistic tasks.

139 5.1.5. Summary

The results from the MIST indicated that individuals with dyslexia may have problems with PM even though the multivariate analysis of variance was not significant. The lack of statistically significant effects may be because the MIST has been designed for use with clinical samples and thus, is not sensitive enough for more subtle difficulties with PM. Nevertheless, the two-way ANOVA results conducted on participant group and cognitive load indicated that

individuals with dyslexia performed significantly worse on PM task regardless of PM task load.

These results are in line with the data from questionnaires used in Studies 1 and 2, which showed that individuals with dyslexia perceive themselves as having PM problems. The MIST also indicated that there may be a problem with time-based PM in adults with developmental dyslexia. Individuals with dyslexia were found to have significantly worse performance compared to controls on the time-based PM task involving a 24 hour time interval between intention formation and execution.

The next stage of this thesis which developed organically, was to investigate both event- and time-based PM under laboratory controlled conditions in order to have a closer look at the processes that may underlie PM deficits in dyslexia. Laboratory investigation was employed with the aim of seeing if a range of different PM tasks coupled with differential processes results in identifying any PM deficits in dyslexia. The next chapter (Chapter 6) probed into an event-based PM (focal and non-focal), followed by a chapter (Chapter 7), which investigated time-based PM. These investigations were accompanied by field experiments in order to see whether there are any group differences on the different PM types under real life conditions.

140 Chapter 6: Event-based prospective memory

Einstein and McDaniel (1990) developed an experimental paradigm allowing the investigation of event-based PM. Einstein et al. (1995) used this basic event-based PM paradigm to

investigate PM in adults. In this study participants had to answer general knowledge questions as the ongoing task (e.g. “How many hours will it take a person to walk 24 miles at the rate of three miles per hour?”). Participants were told before they started that when they saw a question with the word president in it they needed to press the F8 key. Then, before participants began the general knowledge questions task they were presented with a distractor task based on vocabulary. The PM cue was used six times in the ongoing activity and participants were required to respond to it by pressing the F8 key each time they saw it. PM performance was measured by the proportion of PM trials in which participants remembered to perform this PM task. Participants were generally able to remember well to perform the intended activity when encountering the PM cue (average 90% correct PM responses).

The relationship between the ongoing task and the PM cue can differ. This can depend on the characteristics of the ongoing task and PM cue (McDaniel & Einstein, 2007). Depending on the relationship between the ongoing task and PM cue, the PM cue may be characterised as being focal or non-focal (see Chapter 1). Study 4 investigated an event-based PM with focal PM cue whereas Study 5 employed a non-focal PM cue.