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It is possible that the findings of Experiments 3 and 4 are not as discrepant as they appear. Rather, the relationship between working memory and the interaction effect in Experiment 4 may be weaker than that shown in Experiment 3. To test for this, the correlation coefficients between working memory and the interaction effect in studies 3 and 4 were compared using Fisher’s Z transformation (Fisher, 1915). This analysis revealed that the two correlation coefficients did not differ to a statistically significant degree (z = 1.18, p = .24). As a consequence, the datasets were combined and analysed as a whole. These analyses are presented below.

Table 18. Descriptive statistics for the individual difference variables across subjects in Experiments 3 and 4 (n = 115) Mean SD ND Comprehension 235.52 14.33 ND Vocabulary 242.60 11.74 Working Memory 4.47 0.98 Decoding composite(z-scores) 0.00 0.84

Figure 10. Mean percentage error rates for all conditions (n = 115). Error bars represent one standard error above and below the mean

The accuracy data were subjected to a 2 x 2 analysis of variance. There was a main effect of coherence (F (1, 114) = 46.13, p<.001). Participants were more accurate on incoherent trials than they were on coherent trials (see Figure 10). There was a main effect of cohesion (F(1, 114) = 10.27, p =.001), showing that participants’ judgements of coherence were, overall, more accurate for sentence pairs that were bound with cohesive ties. There was also an interaction between coherence and cohesion (F(1, 114) = 26.50, p<.001). This interaction was mainly driven by

0 2 4 6 8 10 12 14 16 Coherent Incoherent Cohesive Incohesive Table 19. Accuracy and reading times for all participants in all conditions (mean(sd); n=115)

Coherent Incoherent

Cohesive Incohesive Cohesive Incohesive Percent error: 8.44(6.95) 12.74(8.55) 6.07 (6.08) 4.94(6.04) Target sentence RTs (ms): 1981(510) 1858(488) 2056(510) 1805(466) Std. Residuals of target sentence RTs: -.0372(.220) .0357(.277) .1026(.228) -.0329(.325)

differences in the coherent condition (t(114) = 5.19, p<.001), although the differences in the incoherent condition approached statistical significance (t(113) = 1.89, p =.062).

For the analysis of RTs, incorrect trials were excluded (872/10860; 8.3%). Mean reading times for each participant were then calculated for each participant across conditions. Trials that were 2.5 standard deviations above their mean RT were replaced with a cut off value (i.e. 2.5SD above their mean reading time). In total, 9975 trials were used for the analysis of reading times, 277 of which had been replaced with each individual’s 2.5SD cutoff (2.8% in total). Just under ninety two percent of trials were retained for analysis.

As cohesive target sentences were longer than incohesive target sentences, it was necessary to factor-out sentence length for these analyses. For each participant separately, the reading times for target sentences were regressed on the number of characters (including spaces) in each sentence (i.e. sentence length). The standardised residuals that resulted from this

procedure were then used for the following analyses. A graphical representation of the mean reading time residuals in the 4 conditions is presented in Figure 11.

Figure 11. Mean standardised residuals of target sentence reading times. Error bars represent one standard error above or below the mean (n = 115).

The mean standardised residuals were then used in a 2 (coherence) x 2 (cohesion) ANOVA. The interaction between coherence and cohesion depicted in Figure 11 was significant (F(1, 114) = 28.94, p <.001). Again, cohesive ties facilitated participant’s comprehension of coherent sentence pairs, whereas their presence in incoherent sentence pairs impeded their comprehension. This impedance may stem from the fact that the coherence gap was contradicted by the presence of a coherence marker, causing readers to consider these cases in more depth and read them for relatively longer.

The intention of this combined analysis was to ascertain whether the interaction between coherence, cohesion and working memory group shown in Experiment 3 would hold once those data were combined with data from Experiment 4. Based on performance on the sentence span task, the participants were placed into ‘low’ and ‘high’ working memory groups. Those who

-0.1 -0.05 0 0.05 0.1 0.15 Coherent Incoherent Cohesive Incohesive

recalled 4 or fewer items in the sentence span task were placed into the ‘low working memory’ group, and those who recalled either 5 or 6 items were placed in the ‘high working memory’ group. The component reading characteristics of these two groups are presented in Table 20. Significant differences between the groups (as assed by independent samples t-tests) are highlighted with asterisks.

Table 20. Component reading skills of the two working memory groups (mean(sd) Working Memory Group

High (n = 58) Low (n = 57) Mean ND comprehension scaled score: 237.72 (13.13)^ 233.28 (15.24)^ Mean ND vocabulary scaled score: 245.47 (9.79)** 239.68 (12.87)** Mean working memory (max=6): 5.31 (0.47)*** 3.61 (0.49)*** Mean decoding composite (Z-scores): .1501 (0.58)* -.1527 (1.01)* ***p<.001; **p<.01; *p=.05; ^p<.10

As shown in Table 20, the high working memory group performed marginally better than the low working memory group on the comprehension component of the Nelson Denny reading test (t(113) = 1.68, p=.097). They performed significantly better than the low working memory group on the vocabulary component of the Nelson Denny reading test (t(113) = 2.71, p=.008); the sentence span task (t(113) = 18.99, p<.001); and on the decoding composite (t(113) = 1.97, p =.052).

A 2 (coherence) x 2 (cohesion) x 2 (working memory group) mixed-design ANOVA, with working memory group as the between subjects factor, was conducted on the length-corrected residuals of the reading time data. There was no interaction between coherence and working memory group by subjects(F1(1, 113) = .235, p = .63) or by items (F2(1, 2274) = 0.16, p = .69), and there was no interaction between cohesion and working memory group by subjects (F1(1, 113) =

.019, p=.89) or by items (F2(1, 2274) = 0.72, p = .40). The analysis did reveal, however, a significant 3-way interaction between coherence, cohesion and working memory group by subjects (F1(1, 113) = 4.292, p <.04) and by items (F2(1, 2274) = 4.46, p < .04).

A 2 (coherence) x 2 (cohesion) ANOVA was conducted on the standardised reading time residuals of the two groups separately. Neither group showed main effects of coherence or cohesion (all Fs <2). The low working memory group showed a moderate interaction between coherence and cohesion by subjects (F1(1,56) = 5.09, p <.03) and a strong interaction by items

(F2(1, 1100) = 15.70, p <.001). In contrast, the high working memory group showed a very strong interaction between coherence and cohesion by subjects (F1(1, 57) = 31.05, p <.001) and by items (F2(1, 1174) = 52.01, p <.001). See Figure 12 for a graphical representation of these findings. Figure 12. Mean residuals of target sentence reading times for the high working memory group (n=58) and the low working memory group (n = 57). Error bars represent one standard error above and below the mean

-0.1 -0.05 0 0.05 0.1 0.15 0.2

Coherent Incoherent Coherent Incoherent

Low WM High WM

Cohesive Incohesive

As can be seen in Figure 12, both groups showed an interaction between coherence and cohesion, but group differences arose in the coherent condition. The residual RTs of the high WM group are significantly different between the coherent/cohesive and coherent/incohesive

conditions (t(57) = 2.70, p=.009). This effect is not demonstrated by the low WM group, however (t(56) = 1.057, p = .295). Thus, when presented with sentences that cohere but in which coherence is not reinforced by the presence of a cohesive tie, both groups of readers show a relative slowing of target sentence RT, but this effect is much more pronounced for high WM participants than it is for low WM participants.

To assess the contribution of the component variables to the size of the interaction between coherence and cohesion, a step-wise hierarchical multiple regression analysis was

conducted using the interaction value of the standardised residuals as the dependent variable. The interaction value was ascertained in the same manner as in Experiments 3 and 4.

Table 21. Pearson’s correlation coefficients between component variables and the interaction values

ND Comprehension ND Vocabulary Working

Memory Decoding Composite Interaction Value ND Comprehension 1 ND Vocabulary .54** 1 Working Memory .11 .22* 1 Decoding Composite .42** .57** .21* 1 Interaction Value .06 .-.01 .24** .15 1 **p<.01; *p<.05.

The only variable that shared a significant correlation with the interaction value was working memory. This variable was used as the sole predictor of the interaction value the regression analysis presented in Table 22.

Table 22. Regression analysis with absolute interaction value as the dependent variable

B SE B β ∆R2 Constant Working Memory -.251 .103 .178 .039 .241 .058* *p = .009

As can be seen in Table 22, working memory accounts for just under 6% of the variance in interaction effect sizes.