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F ig u re 7.1. Mean percentage error for the Control and Dyslexic groups in both the Short and Long conditions. All error bars indicate standard error o f the mean.

C ond itio n Dyslexies C o n tro ls % Error S.D. % Error S.D.

Short Word Pairs 4 J % (&5) 0.7% (1.9) Long Word Pairs 12.8% (11.1) 3 j % (4.9)

T ab le 7.3. Mean percentage error and standard deviations (S.D.) in the Control and Dyslexic groups as a function o f Length.

c g. a> a: 2 6 0 0 2 4 0 0 - 2 2 0 0 - 2 0 0 0 - 1 8 0 0 - 1 6 0 0 - 1 4 0 0 - 1200 1 0 0 0 ^ 8 0 0 6 0 0 C o n tr o ls D y s l e x i e s

Short W ord s Long W ords

Figure 7.2. Latency o f response (m sec) for the Control and Dyslexic groups in both the Short and Long conditions. Error bars indicate mean standard error.

2 8 0 0 2 3 0 0 £

^

F igure 7.3. Latency o f response (m sec) for the Control and Dyslexic groups with the shorter set o f tw o-syllable words (Set A) and the longer set o f two syllable words (Set B) in the spoonerism task. Error bars indicate mean standard error.

T h e r e a c tio n tim e d a ta a re s h o w n in T a b le 7 .4 a n d p lo tte d w ith r e s p e c t to le n g th in F ig u re 7 .2 . O n ly d a ta fro m c o r re c t tr ia ls w e re a n a ly s e d . In a d d itio n , m ic r o p h o n e fa ilu re s w e re e x c lu d e d (2 .7 % o f tria ls ). D a ta p o in ts g r e a te r th a n tw o s ta n d a rd d e v ia tio n s fro m th e g ro u p m e a n w e re c la s s ifie d a s o u tlie rs a n d w e re a ls o e x c lu d e d (4 .0 % f o r e a c h g ro u p ). T h e r e m a in in g d a ta w e re e n te r e d in to a r e p e a te d m e a s u re s A N D V A w ith G ro u p a s th e b e tw e e n - s u b je c t fa c to r (D y s le x ic v s. C o n tro l) a n d r e p e a te d m e a s u r e s o n L e n g th ( S h o r t v s L o n g ) in a d d itio n to a b y -ite m a n a ly s is . T h e b y - s u b je c t a n a ly s is in d ic a te d a m a in e ffe c t o f le n g th , w ith s lo w e r r e s p o n s e s in th e L o n g c o n d itio n [ F ( l,3 0 ) = 8 .6 ; p < .0 1 ]. A L e n g th x G ro u p in te r a c tio n in d ic a te d a

differential effect across groups, with a greater effect of longer stimuli in the dyslexic group [F(l,30) = 5.4; p < .05]. A comparable pattern was found in the by-item

analysis. This indicated a main effect of Group [F(l,34) = 675.6; p<.01] and a main effect of Length [F(l,34) = 31.1; p<.01] in addition to a Length x Group interaction

[F(l,34) = 31.4; p<.01].

Condition Dyslexies Mean RT S.D.

C ontrols Mean RT S.D.

Short Word Pairs Long Word Pairs

1717.0 903.5 2163.2 1275.8 718.8 770.9 256.5 278.8

T able 7.4. Mean response times (msec) and associated standard deviations (S.D.) for the Control and Dyslexic groups as a function o f Length.

In order to evaluate the effect of phoneme length, the mean reaction time was calculated for each participant for each set of bisyllabic words: Set A, consisting of spoonerism pairs less than 9 phonemes in length (Dyslexies: 2086msec, s.d.=1354.6; Controls: 750.2msec, s.d.=268.0) and Set B, consisting of spoonerism pairs greater than 10 phonemes in length (Dyslexies: 2365.8msec, s.d.=l 136.0; Controls: 788.9, s.d.=318.0). These data, plotted in Figure 7.3, were analysed in a repeated measures ANOVA, with Chroup as the between-subject factor (Dyslexic vs. Control) and repeated measures on Condition (Set A vs. Set B). This analysis indicated a main effect of Group [F(l,30) = 18.3; p < .01] with faster responses by the control participants, and a main effect of Condition [F(l,30) = 8.7; p < .01] with faster

responses with Set A (of shorter phoneme length) relative to Set B (of longer phoneme length). A significant Group x Condition interaction [F(l,30) = 5.0; p < .05] reflected the greater effect of longer stimuli in the dyslexic group.

In order to evaluate the effect o f presentation rate and the task requirements the performance o f the dyslexic participants in the current study were contrasted with a group of ten dyslexies (drawn from Brunswick et al., 1999 and the dyslexies assessed in Experiment 4) matched for performance IQ with the dyslexies in the current study (previous participant’s performance IQ: 115; current participant’s performance IQ

121 ; p>.05). For both groups errors were scored on the first word only, on those ten items used with all previous and current participants (marked with an asterisk in Table

7.2). The rate of error o f the participants in the previous studies (30%) was found to significantly greater than the error rate o f the participants in the current study (8.8%; t (24)=2.5; p<.05).

It is of interest that the speed of spoonerism performance correlated significantly with spelling ability in the dyslexic group (r=0.5; p<.05) but not in the control group (r=0.1; n.s). It is possible that in some dyslexies stronger orthographic skills contribute to improved performance on the spoonerism task (Perin, 1983).

Discussion

The current study employed a novel paradigm o f spoonerism presentation that allowed measurement of both accuracy and speed of individual trial responses. According to the first prediction dyslexic participants would be slower than their peers even on those trials where their responses were entirely accurate. This was found to be the case with the dyslexic participants taking over one second longer on average per word pair. An account that postulates inefficiency in the processes of phonological access can more readily account for this slow performance even if the correct response is given. A representation account, which places the emphasis on whether or not segmentation has occurred, implies that once segmented, a given representation should be normally accessed. Secondly, it was found that the dyslexic participants were particularly sensitive to phonemic length. Increasing the mean number o f phonemes of each word in the spoonerism pair from 4 to 5 was found to impair the dyslexic participants, who were significantly slowed with the longer words. This finding supports the view that it is the number of phonological codes contemporaneously active during the task

critically influences dyslexies performance. Finally the lower rate of error in the dyslexic group under conditions o f lower task load (here in relation to presentation rate and task output requirements) is consistent with the view that the functional availability of phonological information is variable. It is not the case that a lexical item becomes fully ‘segmented’ then rendering its phonemic components available. Rather, phonological representations are dynamic entities that may be manipulated with varying degrees of efficiency depending on the level o f phonological competition.

In addition to these findings, the particularly high level of performance accuracy by the dyslexies in the current study should be noted. In the short word condition for example dyslexies had an accuracy rate of 95%. Within a representational framework this would suggest that ‘phonemic segmentation’ has occurred for these words. Adult dyslexies have also been shown to be at ceiling with comparable stimuli in a similar task o f phonological awareness (Griffiths and Frith, 2001). If it is the case that these short highly familiar words are available in segmental form then why are they accessed more slowly in reading (Experiment 1) and why are they manipulated more slowly in the spoonerism task? To postulate that the phonological representations are ‘poorly specified’ fails to reconcile this contrast between accuracy and speed of performance.

A number of arguments in defence of the representational position might be presented. For example, although phoneme segmentation can occur one might argue that the

quality of the phonological representation in dyslexies is still poorer, to the extent that access is slowed. The difficulty with such an argument is that it is too vague to provide sufficient explanatory power. It fails to explain why word reading is more impaired than picture naming; or why small differences in phoneme length can significantly affect spoonerism performance. More crucially, however, such an argument would require a clear definition of what was meant by representational ‘quality’ and how this might be experimentally assessed. If one assumes that a representation is fully

segmented, then the notion of ‘quality’ assumes a rather vague significance. A second defence o f the representational position might be to invoke a difficulty in phonological access in addition to a lack of phonological segmentation. That is, the errors made by the dyslexies would indicate that phonological segmentation has not occurred fully, while slower response times indicate impaired ‘phonological retrieval’. Such a position would be difficult to maintain if it could be shown that a process account alone would be sufficient to explain the data. Such is the claim o f the phonological competition hypothesis.

A second limitation o f the representational account is evident in its failure to predict the relationship between processing speed and phonemic length. Take for example the increased difficulty with regard to accuracy and speed of response found with long words. Longer words will inevitably increase the number of phonological codes

activated during the task - and hence the level of phonological competition. A representational account would presume that such longer words are more likely to be less well represented in dyslexic individuals, and therefore more difficult to

manipulate. However, the manipulation of phonemic length within the set of long words renders such an explanation unlikely. The phonological representation hypothesis would have to assume an intimate relation between phonological specification and word length to explain this finding. That is, an increase in word length - of even one phoneme - would lead to that word being more poorly specified. Alternatively, an additional explanation would have to be invoked (for example in terms of short-term memory load). In contrast the relationship between phoneme length and processing speed follows naturally from a competition account.

A third limitation of the representation account is its failure to explain the variability of performance accuracy. In this study the dyslexic participants made significantly fewer errors (9%) on the same items, than dyslexic participants in previous studies (30%), who had experienced a much faster rate of presentation. This comparison is limited, however, given that different participants were used in each case and different task demands were implicated. A future study might address these concerns by only varying the rate of presentation and using the same set o f stimlui. An increased rate of error at faster rates of presentation would provide strong support for the competition account, since it would demonstrate the dynamic and variable nature o f phonological representation.

The current study also aimed to address the methodological limitations of previous studies. Firstly, word pairs were recorded and digitised in a standard format, so each individual would be presented with precisely the same stimuli. Secondly, responses to individual trials were measured automatically by computer with millisecond accuracy. The advantage of such an approach is that it allows the detection of even small

differences in performance - across groups, and across experimental manipulations. Finally, concurrent scoring by the experimenter allowed error trials to be removed from any subsequent reaction time analysis.