Executive functioning, prospective memory and dyslexia

3.2.1. Supervisory attentional system, working memory link to prospective memory and dyslexia

Varvara et al. (2014) argued that task complexity is responsible for poor task performance in dyslexia. Smith-Spark et al. (2003) explained that EF deficits argued in dyslexia and more specifically the domain general CE, results in significant drop of performance (compared to controls) if a task places a high demand on executive resources. Furthermore, Fawcett and Nicolson (1994) argued that complex skills which require fluency in component sub-skills, multi-modality skills involving the monitoring of various modalities/sources of information, skills which depend on time (and require fast speed of processing) and vigilance tasks which require concentration over time, are all vulnerable to disruption in individuals with dyslexia.

Tasks involving these skills have been argued to create demands which prevent individuals with dyslexia from using CC to direct performance. These complex task conditions which are

reported to result in performance deficits in dyslexia rely strongly on SAS/CE component of WM.

Prospective memory tasks have also been suggested to depend strongly on WM (e.g. Einstein et al., 2000). Marsh et al. (2002) found that PM performance dropped when ongoing tasks

involved more WM. Martin et al. (2003) found that EF predicted time- and event-based PM performance. Burgess and Shallice (1997) stated that PM tasks involve SAS and that this is especially the case in tasks involving monitoring, as these tasks are argued to involve more cognitive resources compared to tasks relying on spontaneous retrieval. Thus complex PM paradigms which involve WM or SAS/CE (i.e. non-focal event-based, time-based or PM paradigms involving cognitively demanding ongoing tasks) could be argued to result in a poorer PM performance for individual with dyslexia than for controls. Since Smith-Spark et al. (2003) and Smith-Spark and Fisk (2007) argued that when task complexity is high, the CE or SAS of dyslexic individuals is unable to allocate extra resources to the task in order to consciously compensate for their EF deficit. This results in individuals with dyslexia performing worse

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compared to controls as their executive resources have been fully allocated to the task in hand.

Thus, if a complex PM paradigm is used, one can expect a drop of performance visible either on the ongoing or the PM tasks in individuals with dyslexia compared to controls. Furthermore, one may argue that the switching of attention and inhibition of responses involved in event-based, as well as in the time-based PM tasks could adversely impact upon PM performance in individuals with dyslexia. This is in line with the argument that the SAS or the CE component of WM is responsible for attention switching and inhibition of responses (e.g. Norman &

Shallice, 1986).

Moreover, one could argue that if a PM task involving monitoring (i.e. non-focal event-based or time-based PM) is combined with a cognitively demanding ongoing task, one could expect even more adverse effects on PM performance in individuals with dyslexia as these tasks would draw strongly on cognitive resources. This is hypothesised on the basis of WM/CE/SAS deficits in dyslexia (Smith-Spark et al., 2003; Smith-Spark & Fisk, 2007). Additionally, global deficits in higher-order cognitive processes (EF) in developmental dyslexia (Smith-Spark & Fisk, 2007;

Varvara et al., 2014) also support this hypothesis. Generally, it could be argued that the more complex the PM tasks, the greater the PM deficit will be as individuals with dyslexia would be less able to mask their performance deficits due to insufficient cognitive capacity (Nicolson &

Fawcett, 1990).

3.2.2. Inhibition, switching involvement in prospective memory and its relevance to dyslexia

Another characteristic of PM tasks is that they require one to inhibit the performance on the ongoing task, in order to switch to the performance of PM task. This is an important aspect when considering possible PM deficits in dyslexia. Gonneaud et al. (2011) investigated the relationships between event- and time-based PM measures and a wide array of cognitive functions, including executive functions, processing speed, sustained attention, retrospective episodic memory, metamemory, and binding in healthy adults. This study found that regardless of whether the task used an event- or time-based PM paradigm, PM performance was dependent on inhibition abilities and processing speed. Furthermore, it was found that event-based PM was strongly reliant on binding and retrospective episodic memory and, to a lesser extent, on

shifting, while time-based PM depended largely on inhibition.

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Individuals with reading difficulties have been found to have problems with inhibition (e.g.

Palladino et al., 2001; Swanson, 2006). In addition, Varvara et al. (2014) found that many tasks used in their research revealed poorer performance of dyslexics, due to deficits in inhibition which is one of the skills required for completion of these tasks e.g. their spoonerism task.

Moreover, the SAS (which has been argued to be deficient in dyslexia) has been suggested to be responsible for interruption to the ongoing activity and shifting attention to the intended action at the appropriate time or when the PM cue appears (Einstein et al., 2005). Shifting abilities have been found to be a strong predictor of PM performance (Schnitzspahn et al., 2013). Hari and Renvall (2001) postulated that individuals with dyslexia have difficulty in switching between tasks, labelling this as sluggish attentional shifting. Dyslexics have been found to take longer to switch attention between a variety of tasks with Hari and Renvall (2001) arguing that they have difficulties disengaging from one stimulus in order to engage in another stimulus in sequentially presented tasks. Thus, this evidence could suggest that individuals with dyslexia may also have a general deficit in PM, as inhibition has been found to be linked to all types of PM in adults (e.g. Schnitzspan et al., 2013; Gonneaud et al., 2011).

Other researchers (e.g. Reiter et al., 2005) found that individuals with dyslexia only show deficits in inhibition in more cognitively demanding tasks. This again could point to dyslexia related PM problems, but only in cognitively demanding PM tasks such as, non-focal event-based or time-event-based PM tasks, as these involve monitoring or PM paradigms employing cognitively demanding ongoing tasks (e.g. involving WM updating). Brosnan et al. (2002) investigated EF in adults with dyslexia and found that when task demands were high, dyslexics were not able to effectively inhibit processing of similar shapes to find a target shape within a complex visual array shapes that are slightly different. This could be argued to mirror closely the principles used in event-based PM tasks, as one needs to inhibit processing the stimuli relevant to the ongoing tasks in order to find PM target cues placed within the array of the ongoing trial stimuli. Nonetheless, an event-based PM tasks could be argued to be easier and the stimuli could be argued to be more distinctive with the PM cues more obvious and jumping out at participants. Nevertheless, this piece of research shows that inhibition problems in adults with dyslexia could be relevant to all PM tasks. However, whilst all PM tasks have been said to involve inhibition, time-based PM tasks have been argued to involve inhibition to a greater extent (Gonneaud et al., 2011).

Studies (Swanson, 2006; Palladino et al., 2001) showed that individuals with dyslexia have problems in inhibition of irrelevant information or distractors and maintenance of relevant

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information in WM. This could indicate that individuals with dyslexia will have problems with inhibiting the irrelevant information related to ongoing task in order to perform the PM task. In addition, the deficit related to maintenance of relevant information in WM in dyslexia may be important in PM tasks which strongly involve WM (e.g. PM tasks involving WM updating ongoing tasks). Individuals with dyslexia may find it difficult to maintain the relevant

information related to PM activity in WM in the presence of an ongoing activity which is highly competing for WM resources. This may stop individuals with dyslexia from recalling

information relevant to the PM tasks or from self-initiating checking of the time. Furthermore, Borella et al. (2010) has explained that the inability to inhibit irrelevant information is linked to maintenance of irrelevant information in WM and that holding unnecessary information in WM results in WM overload. This may result in insufficient amount of WM resources left for the performance of the PM task in dyslexia.

3.2.3. Processing speed, prospective memory and dyslexia

Reiter et al. (2005) found that individuals with dyslexia have slower processing speed in inhibition tasks and this could indicate that individuals with dyslexia will have slower RTs in PM tasks, as these involve inhibition of the ongoing task in order to respond to the PM task.

They also argued that individuals with dyslexia may need additional processing time in order to perform well on their EF tasks. Similar PM performance could be hypothesised in dyslexia as individuals with dyslexia may need additional time in PM tasks in order to perform well on them. Thus, if a time limit is applied to PM tasks, participants with dyslexia may respond less accurately. It is possible that individuals with dyslexia may feel the need to respond quicker than they would like to or can, and this could result in more errors in PM responses. On the other hand, if no time limit is applied, participants with dyslexia may take longer to respond correctly to the trials resulting in greater RTs.

This argument is in line with the processing speed deficit in dyslexia, which was established as a part of the double deficit hypothesis (especially when processing visual stimuli; e.g. Wolf and Bowers, 1999). Namely, if there is a processing deficit related to visual stimuli in individuals with dyslexia, one may expect individuals with dyslexia to be slower at recognising and processing PM cues in event-based PM tasks and in the ongoing tasks within all PM tasks.

Thus, slower processing speed could impact negatively on PM performance in dyslexics.

Gonneaud et al. (2011) have shown that processing speed correlated with event- and time-based PM performance in healthy adults. Namely, slower processing of the stimuli resulted in worse

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PM performance and fast processing of stimuli resulted in better PM. Therefore any deficits in processing speed reported in dyslexia could have a negative impact on their PM performance.

Furthermore, the “sluggish attentional shifting” found in dyslexia (Hari & Renvall, 2001) could be also used to support the claim that PM deficits will be found in dyslexia. It could be argued that the “sluggish attentional shifting” between the ongoing and PM tasks would result in worse PM performance. Thus, slower processing speed could be indicative of PM problems in

dyslexia.