Eye-tracker data

6.1.2.3.5.1. Noticing failure analysis

Dyslexics (M = 2.88, SD = 5.37) did not differ significantly compared to controls (M = 3.65, SD

= 6.88) in terms of the percentage of total PM cues on which they did not fixate their eyes and to which they did not respond correctly, t (48) = .438, p = .663. However, controls (M = 9.38, SD = 11.80) differed compared to dyslexics (M = 3.37, SD = 8.33) in terms of the percentage of total PM cues on which they have not fixated their eyes but still responded to them correctly, t (41.05) = 2.06, p = .045. Even though this difference was not significant when a Bonferroni corrected alpha level of .025 was applied, it still indicated that there was a difference in eye fixation patterns between the two participant groups with controls fixating eyes their less on the PM cues in trials to which correct PM responses were provided compared to dyslexics who tended to fixate their eyes on these PM cues more.

6.1.2.3.5.2. Number of fixations and dwell time

6.1.2.3.5.2.1. Prospective memory stimuli

Group differences regarding the total number of fixations and mean dwell time (ms) on PM stimuli were analysed using independent samples t-test. The results showed that dyslexics (M =

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25.69, SD = 9.11) fixated significantly more on PM cues compared to controls (M = 18.88, SD

= 5.90), t (43.20) = 3.17, p = .003. The mean dwell time data revealed that dyslexics (M = 396.38, SD = 143.12) dwelled longer on PM cues compared to controls (M = 288.83, SD = 91.73), t (48) = 3.13, p = .003. In both cases, a Bonferroni corrected alpha level of .025 was applied.

6.1.2.3.5.2.2. Ongoing stimuli

The results in Table 13 show the descriptive statistics for number of fixations and mean dwell time data for ongoing stimuli responses in Block 1 and Block 2.

Table 13: Descriptive statistics for the number of eye fixations and dwell times for ongoing stimuli in Blocks 1 and 2.

Means Number of fixations Mean dwell time (ms)

Controls Dyslexics Controls Dyslexics

Type of Trial M SD M SD M SD M SD

Ongoing (Block 1)

502.75 144.37 700.46 242.30 385.13 114.46 583.85 257.19

Ongoing (Block 2)

494.13 118.62 679.50 234.93 378.34 85.12 573.23 245.30

A mixed measures ANOVA was used in order to compare the number of eye fixations made by dyslexics and controls on the ongoing stimuli in Blocks 1 and 2 (determined by interest areas related to the ongoing stimuli). The results showed a significant main effect of participant group, F (1, 48) = 13.05, p = .001, ηp

2 = .214. After the inspection of means, it could be stated that dyslexics fixated their eyes on the ongoing stimuli in Blocks 1 and 2 significantly more than controls. The effect of block type was not significant, F (1, 48) = .932, p = .339, ηp

2 = .019.

There was no significant interaction between participant group and block type, F (1, 48) = .162, p = .689, ηp

2 = .003.

The results from a mixed measures ANOVA conducted on mean dwell time (ms) data revealed a significant main effect of participant group, F (1, 48) = 13.65, p < .001, ηp

2 = .221. Inspection of the means indicated that dyslexics dwelled significantly longer on the ongoing stimuli in

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Blocks 1 and 2 compared to controls. The effect of block type was not significant, F (1, 48) = .401, p = .529, ηp

2 = .008. This indicated that both participant groups did not differ significantly in the length of dwell time on the ongoing stimuli in Block 1 compared to Block 2. There was no significant interaction between participant group and block type, F (1, 48) = .019, p = .890, ηp

2 < .001.

6.1.2.4. Discussion

The PM accuracy data from this experiment did not indicate that participants with dyslexia have a deficit with PM and, thus, the results did not support the hypothesis. The effect of block type found in the ongoing task RT data was approaching significance (.054). This could indicate that there was a cost related to performing the PM task which revealed itself in the RTs to the ongoing trials irrespective of participant group. As the results approached significance this does not provide robust support for the multiprocess view of PM (McDaniel & Einstein, 2000), which states that PM tasks employing focal PM cues rely on automatic spontaneous retrieval processes (see Einstein et al., 2005, for empirical support) and thus, would predict that there should be no cost related to performing PM task visible on the ongoing trials.

Individuals with dyslexia had significantly slower RTs compared to individuals without dyslexia when responding to PM cues and ongoing trials. This is in line with the double-deficit hypothesis of dyslexia (e.g. Wolf and Bowers, 1999; see Chapter 2 for more details) which states that there is a processing speed deficit in individuals with dyslexia. Also, the results revealed that individuals with dyslexia focally fixated on the stimuli significantly more compared to controls. This could mean that individuals with dyslexia tried to compensate for their attentional deficit by monitoring the screen significantly more compared to controls, and this could have resulted in there being no PM deficit found. Since larger number of eye-fixations could be indicative of a greater allocation of attentional resources by individuals with dyslexia in order to compensate for an attentional deficit. However, this is debatable, as PM tasks with focal cues strongly encourage spontaneous retrieval processes which rely on the PM cue for the retrieval of the PM intention (McDaniel & Einstein, 2007). This type of retrieval has been argued to be automatic (McDaniel, Einstein & Rendell, 2008) and thus, it is less likely for participants to rely on conscious monitoring under focal task conditions. Thus, if this is the case, why were there more eye fixations recorded in the dyslexic group? It may be possible that individuals with dyslexia relied more on monitoring processes compared to controls, who relied

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more on spontaneous retrieval resulting in fewer eye fixations. This could be a form of coping strategy employed by individuals with dyslexia in order to avoid PM failure. This type of strategy is in line with the proposed by Nicolson and Fawcett (1990) conscious compensation (CC) used by individuals with dyslexia.

Moreover, Marsh, Cook and Hicks (2006) suggested that each participant decides, before starting the task the level of attentional resources to allocate on the basis of the perceived difficulty of the task. Thus, it is also possible that individuals with dyslexia perceived this task as more difficult than controls. As a result, they may have decided to allocate more attentional resources, by employing monitoring processes as a coping strategy in order to perform well on this task and mask a PM deficit. Nevertheless, if participants with dyslexia relied more on monitoring processes, then one could argue that individuals with dyslexia should have a poorer performance on either the PM or ongoing task (or both tasks), as they have been reported to struggle in cognitively demanding tasks (e.g. Nicolson and Fawcett, 1990; for a discussion see Chapter 2), but no interaction effects were found. Performing an ongoing task and monitoring for PM cues could be argued to be cognitively demanding. According to Marsh, Hicks & Cook (2005) if both tasks (ongoing and PM) use the same domain (e.g. semantic as it was the case in this experiment) the cognitive resources available for this type of processing have to be shared and this will result in a poorer performance showing either on the ongoing, PM or both tasks. In addition, if one was employing monitoring processes to perform this PM task, it would add to the cognitive demand and would require additional attentional resources and WM capacity.

Both of these types of capacities have been found to be deficient in dyslexia (e.g. Smith-Spark, Fisk, Fawcett & Nicolson, 2003; Smith-Spark & Fisk, 2007; Varvara et al., 2014; see Chapter 2).

Nevertheless, the results of this study did not show that there were any performance related differences between dyslexics and controls on either the PM or ongoing tasks. Thus, it is possible that individuals with dyslexia generally took significantly longer to perform the ongoing and PM tasks, in order to compensate for the capacity related deficit. It might be argued that if there was a time limit to perform the ongoing task, PM failures could become visible in individuals with dyslexia. This seems to be a more plausible explanation of the results in contrast to previously suggested problem with processing speed of the stimuli. Since

individuals with dyslexia had slower processing speed, they should have similar numbers of eye fixations in comparison to control participants, but show longer dwell times. Supposing that it takes longer for participants with dyslexia to process the stimuli cognitively, they would not

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necessarily need to fixate their eyes significantly more times compared to controls, but could just fixate them in a specific point and dwell on it while cognitive processing takes place.

However, this was not the case. Individuals with dyslexia were found to have significantly more eye fixations as well as longer mean dwell times. Thus, it is possible that participants with dyslexia generally took longer to respond to the tasks, not only due to slower processing speed but that they also tried to consciously compensate for their PM deficits (this is in line with CC hypothesis; Nicolson & Fawcett, 1990). Namely, a greater amount of monitoring was performed by dyslexic individuals to compensate for PM deficit resulting in similar to controls PM

performance. Since greater monitoring of the stimuli provides greater chances of PM intention retrieval as the embedded in the ongoing task PM cue is more likely to be recognised as associated with the intended action.