Idem, págs. 32 y 33

To explore whether inhibition and updating impairments associated with dyslexia and comorbid dyslexia-ADHD manifest more severely as a function of disorder specific processing rule -visual based versus phoneme based- separate 2 (Group: dyslexia and control; comorbid and control) x 2 (Rule: Visual and Phoneme) mixed ANCOVAs controlling for speed were conducted (see Table 7).

Post Hoc between differences on disorder specific cost variables in error or RT scale (𝑃ℎ𝑜𝑛𝑒𝑚𝑒𝑁𝑏𝑎𝑐𝑘𝐸𝑟𝑟𝑜𝑟/𝑅𝑇 − 𝑃𝑖𝑐𝑡𝑢𝑟𝑒𝑁𝑏𝑎𝑐𝑘𝐸𝑟𝑟𝑜𝑟/𝑅𝑇), and one sample t-tests were employed to further explore any significant effects or trends from ANCOVA analysis.

Response Inhibition

Dyslexia: for commission errors, there was no main effect of processing rule (visual only or phoneme only); a trend for a main effect of group (F(1,52)=7.15, p<.05) but no interaction effect. Dyslexia participants made more errors than control participants regardless of whether they processed visual or phoneme content (collapsed across rule). For reaction time, there was a significant main effect of rule type (F(1,52)=9.76, p<.004), no main effect of group and no interaction effect. When group was collapsed, all participants took

significantly longer to successfully complete the phoneme-based rule compared to the visual-based rule.

Comorbid dyslexia-ADHD: for commission errors, there was a trend for a main effect of rule (F(1,40)=5.77, p<.05) and group (F(1,40)=8.84, p<.05), but no interaction effect. When group was collapsed, all groups made more errors for the phoneme based rule than for the visual based rule. When rule was collapsed, comorbid participants had more errors than control participants. For reaction time, no main effect of rule and group, and no interaction effect were observed.

113 Updating

Dyslexia: for errors, there was no main effect of rule or group, but there was a trend for an interaction effect (F(1,53)=5.21, p<.05). For reaction time, there was no main effect of rule and group, and no interaction effect. Post-Hoc differences on a phoneme error cost (controlling for speed) and independent samples t-test (50% error rate) were conducted to further explore the trend for a significant group x rule error interaction effect (see Table 8). Control participants demonstrated a greater phoneme error cost than dyslexia

participants (F(1,53)=5.21, p<.05, control: M=31.14, SD=11.07; dyslexia: M=20.70,

SD=15.06). Independent sample t-tests (compared to chance performance 50% error rate) suggest that this may be due to task difficulty, both groups performed significantly worse than chance on the phoneme rule based task (dyslexia: T(26)=-7.29, p<.004; control:

T(28)=-6.6, p<.004); while both groups performed similar to or better than chance on the visual rule based task (dyslexia: T(26)=.77, p>.05; control: T(28)=5.7, p<.004). This

suggests that the phoneme rule based task may have been too difficult to sensitively profile between group updating differences, floor effects in this task are further depicted in figure 24.

Comorbid dyslexia-ADHD: for errors, there was no main effect of rule, a trend for a main effect of group (F(1,41)=6.52, p<.05) and a significant interaction effect (F(1,41)=29.48, p<.004). When rule was collapsed, the comorbid group demonstrated more errors than the control group. For reaction time, there was no main effect of rule, a significant main effect of group (F(1,41)=14.10, p<.004) and a trend for an interaction effect (F(1,41)=6.88, p<.05). When rule was collapsed, the comorbid group had lower reaction time than the control group. Post-Hoc differences on a phoneme error/RT cost (controlling for speed) and independent samples t-test (50% error rate) were conducted to further explore the group x rule interaction effects (see Table 8). Control participants demonstrated greater phoneme error (F(1,41)=29.47, p<.004, control: M=31.14, SD=11.07, comorbid: M=5.07, SD=15.38) and reaction time cost (F(1,41)=6.88, p<.05, control: M=33.82, SD=72.99, comorbid: M=-43.55, SD=70.57) than comorbid participants. Independent sample t-tests (compared to chance performance 50% error rate) suggest again that this may be due to task difficulty: Both groups performed significantly worse than chance on the phoneme

rule based task (comorbid: T(14)=-4.56, p<.004; control: T(28)=-6.6, p<.004); while the comorbid group performed worse than chance on the visual rule based task (T(14)=-3.62, p<.004) and the control group performed significantly better than chance on the visual rule based task (T(28)=5.7, p<.004). Again, this suggests that the phoneme rule based task may have been too difficult to sensitively profile between group updating differences, floor effects in this task are further depicted in figure 24.

115

Figure 24 Floor effects on Picture rule based 2-back task compared to the phoneme rule based 2-back task across dyslexia, comorbid and control groups

Table 7 RQ3: Does EF profile of Dyslexia and Comorbid Dyslexia-ADHD differ as a function of processing rule (visual, phoneme)?

RQ Controlling for Speed A/R Controlling for Speed A/R

3 Ho: μRI-pic/phon Dys

Model 3. Response Inhibition Rule (Phoneme, Visual) Model 4. Updating Rule (Phoneme, Visual)

Dys - Con Com – Con Dys - Con Com - Con

Note: RQ= Research Question, Dys= Dyslexia, Con= Control, PS= Processing Speed, IS=Independent Sample. * p<.05 (trend), **p<.004 (significant with Bonferroni correction). Post-Hoc T-Tests explored only for significant interaction effects.

117

Table 8 Post-Hoc Tests for whether EF profile differs as a function of processing rule

RQ Post Hoc: Phoneme Updating Error Cost Post Hoc: Phoneme Updating RT Cost

3 Dys – Con Com – Con Dys - Con Com – Con

F Df P F Df P F Df P F Df P

Group 5.21 1,53 .026* 29.47 1,41 .000** 3.38 1,53 .07 6.88 1,41 .012*

PS 5.62 1,53 .021* .91 1,41 .35* .53 1,53 .47 .93 1,41 .34

Post Hoc: Independent Sample T-Test (50% error rate)

Dyslexia Comorbid Control

T Df P T Df P T Df P

Picture .77 26 .48 -3.62 14 .003** 5.70 28 .000**

Phoneme -7.29

26 .000** -4.56 14 .000** -6.6 28 .000**

Note: RQ= Research Question, Dys= Dyslexia, Con= Control, PS= Processing Speed, RT= reaction time. * p<.05 (trend), **p<.004 (significant with Bonferroni correction). Post-Hoc Tests explored only for significant interaction effects.

3.4.6 Summary

RQ1: The EF profile associated with dyslexia and comorbid dyslexia-ADHD compared to controls is overlapping as both groups are associated with impaired response inhibition and updating (trend) and unimpaired in switching abilities at the EF z-mean composite level while controlling for low-level processing speed. The profile of processing resources associated with each condition also appears to be overlapping as both groups are

associated with working memory (dyslexia-trend, comorbid- significant) and processing speed impairments (both trend, p<.05). However, the comorbid group demonstrates a trend for additional phoneme processing impairments (trend). The profile of symptoms associated with both conditions also appears to be overlapping as both groups

demonstrate significant reading impairments, socio-emotional problems and ADHD problems relative to control participants.

RQ2: EF profile does not manifest more severely in comorbid dyslexia-ADHD compared to dyslexia alone, however there is almost a trend (p < .05) for more severe response

inhibition impairments in comorbid dyslexia-ADHD. Dyslexia and comorbid dyslexia-ADHD did not differ on any processing resources. At the level of symptom expression, comorbid dyslexia-ADHD had more severe ADHD symptoms and a trend for more sever socio-emotional problems than dyslexia alone.

RQ3: Response inhibition impairments associated with dyslexia and comorbid dyslexia-ADHD did not differ as a function of processing rule (visual/phoneme based). For updating, there was a significant group x processing rule interaction where control participants experienced a phoneme rule cost compared to both dyslexia and comorbid dyslexia-ADHD. However, post-hoc analyses revealed that this cost was due to floor effects in the phoneme task compared to the visual task.