When phonology fails: orthographic neighbourhood effects in dyslexia

Both cerebral hemispheres contain phonological, orthographic and semantic representations of words, however there are between-hemisphere differences in the relative engagement and specialization of the different representations. Taking orthographic processing for example, previous studies suggest that orthographic neighbourhood size (N) has facilitatory effects in the right but not the left hemispheres. To pursue the nature of this asymmetric N effect, in particular whether there are individual differences in such specialisation, we examined N in a case of developmental dyslexia, FM. We first describe the nature of his difficulties, which are mainly severe phonological deficits. Employing the divided visual field paradigm with FM revealed a greater sensitivity in the right than in the left hemisphere to orthographic variables, with a significant inhibitory N effect in the left, but not right hemisphere. Such inhibition, to a lesser degree, was found among a group of adults with dyslexia but not among age-matched normal readers. We argue that enhanced sensitivity to orthographic cues is developed in some cases of dyslexia when a normal, phonology-based left hemisphere word recognition processing is not achieved. The interpretation presented here is cast in terms of differences between people with dyslexia and typical readers that originate in the atypical way in which orthographic representations are initially set up.     

Reading without phonology?

Responses to items such as brane are slower and/or more error prone than responses to items such as slint in lexical decision (is this string spelt like a real word?). The received view is that this “pseudohomophone” effect is attributable to phonological receding. Taft (1982) has challenged this view, offering instead a grapheme-grapheme account which assumes that graphemes that map onto a common phoneme develop the ability to activate each other without reference to phonological mediation.

Taft's grapheme-grapheme account is tested in two experiments. Experiment 1 shows that the presentation of a pseudohomophone facilitates the response to a subsequently presented word (e.g., groce-gross). Experiment 2 shows that nonword letter strings that are translatable into words by the application of putative grapheme-grapheme rules (e.g., gloce-gloss) produce no facilitation. These results are consistent with the notion of a phonological influence but inconsistent with the grapheme-grapheme account. Loci for this pseudohomophone priming effect are discussed.     

Deficient implicit phonological representations in children with dyslexia

This study tested the segmentation hypothesis of dyslexia by measuring implicit phonological representations in reading-disabled 11- to 13-year-olds. Implicit measures included lexical gating, priming, and syllable similarity tasks designed to reduce metalinguistic demands. Children with dyslexia performed consistently worse than CA and RA controls when more segmental representations were required across all three tasks. Implicit phonological representations were correlated with measures of speech perception, phoneme awareness, and phonological short-term memory, but not rapid automatized naming, and accounted for unique variance in predicting reading ability. Results provide strong support for less mature implicit phonological representations in children with dyslexia.     

Reading without phonology: Evidence from aphasia

This study of an aphasic dyslexic supports the view that there are separate visual and phonological pathways in reading. The patient retained a reading vocabulary of at least 16 500 words although she was unable to perform operations that critically depend on grapheme-to-phoneme conversion; these included reading nonsense words, recognizing rhymes and homophones, and accessing lexical entries from homophonic spellings such as “kote”. Typographical variation, such as mixed case presentation, did not interfere with her reading performance, which suggests that it is mediated by letter identification rather than by a wholistic method of word recognition. The total performance pattern strongly suggests that this patient identifies words by matching particular letter-strings with their corresponding meanings.     

Speech perception deficits by Chinese children with phonological dyslexia

Findings concerning the relation between dyslexia and speech perception deficits are inconsistent in the literature. This study examined the relation in Chinese children using a more homogeneous sample—children with phonological dyslexia. Two experimental tasks were administered to a group of Chinese children with phonological dyslexia, a group of age-matched control children, and a group of adults. In addition to a categorical perception task, a selective adaptation task was carried out. The results indicated that Chinese children with phonological dyslexia were less consistent than both the child and adult control groups in identifying stimuli within a given phonetic category. Furthermore, they did not show any significant adaptation effects in the selective adaptation task even when the adapting stimulus was identical to an endpoint stimulus in the test continuum. It seems that children with phonological dyslexia have a general deficiency in representing and processing speech stimuli.     

Developmental letter position dyslexia

Letter position dyslexia (LPD) is a peripheral dyslexia that causes errors of letter order within words. So far, only cases of acquired LPD have been reported. This study presents selective LPD in its developmental form, via the testing of 11 Hebrew‐speaking individuals with developmental dyslexia. The study explores the types of errors and effects on reading in this dyslexia, using a variety of tests: reading aloud, lexical decision, same‐different decision, definition and letter naming. The findings indicate that individuals with developmental LPD have a deficit in the letter position encoding function of the orthographic visual analyser, which leads to underspecification of letter position within words. Letter position errors occur mainly in adjacent middle letters, when the error creates another existing word. The participants did not show an output deficit or phonemic awareness deficit. The selectivity of the deficit, causing letter position errors but no letter identity errors and no migrations between words, supports the existence of letter position encoding function as separate from letter identification and letter‐to‐word binding.     

Developmental and acquired dyslexia: A comparison

Jorm (1979a) has drawn attention to similarities between developmental dyslexia and acquired deep dyslexia, an analogy which has been criticized by A. W. Ellis (1979). A series of three experiments compared the two syndromes, using the techniques applied by Patterson and Marcel (1977) to adult deep dyslexics, to study a group of 15 boys suffering from developmental dyslexia. Patterson and Marcel's patients were able to perform a lexical decision task but showed no evidence of phonemic encoding of nonwords; our dyslexic children performed this task very slowly and with reduced accuracy but showed clear evidence of phonemic coding of the nonword items. Patterson and Marcel observed that their patients could not read out orthographically regular nonwords; our dyslexic children were able to do this task, although more slowly and somewhat less accurately than their chronological age or reading age controls. Finally, Patterson and Marcel observed that highly imageable words were more likely to be read correctly than words of equal frequency but low imageability; we observed a similar effect in both our dyslexic group and in their reading age controls. This implies that the imageability effect may not be peculiar to dyslexics but may be characteristic of normal reading under certain conditions. It is concluded that developmental dyslexics differ from the patients studied by Patterson and Marcel in demonstrating a pattern of reading which, though slow, is qualitatively similar to the reading of normal readers of a younger age. As such, our results do not support Jorm's position.     

Speech prosody and developmental dyslexia: Reduced phonological awareness in the context of intact phonological representations

Recent research indicates that awareness of the rhythmic patterns present in spoken language (i.e., prosody) may be an important and relatively overlooked predictor of reading ability. Two studies investigated the prosodic processing abilities of skilled adult readers and adults with developmental dyslexia. Participants with dyslexia showed reduced awareness of lexical and metrical stress and these skills were found to be significantly associated with, and predictive of, phonological decoding ability. In contrast, the same individuals showed normal patterns of stress based priming at magnitudes similar to controls. These results—suggesting reduced phonological awareness in the context of intact phonological representations—are consistent with recent findings reported in the domain of phonemic processing. Implications for the phonological deficit theory of dyslexia are discussed.     

Specific phonological impairments in dyslexia revealed by eyetracking

Phonological deficits in dyslexia are typically assessed using metalinguistic tasks vulnerable to extraneous factors such as attention and memory. The present work takes the novel approach of measuring phonology using eyetracking. Eye movements of dyslexic children were monitored during an auditory word recognition task in which target items in a display (e.g., candle) were accompanied by distractors sharing a cohort (candy) or rhyme (sandal). Like controls, dyslexics showed slower recognition times when a cohort distractor was present than in a baseline condition with only phonologically unrelated distractors. However, unlike controls, dyslexic children did not show slowed recognition of targets with a rhyme distractor, suggesting they had not encoded rhyme relationships. This was further explored in an overt phonological awareness test of cohort and rhyme. Surprisingly, dyslexics showed normal rhyme performance but poorer judgment of initial sounds on these overt tests. The results implicate impaired knowledge of rhyme information in dyslexia; however they also indicate that testing methodology plays a critical role in how such problems are identified.     

Pseudoname learning by German-speaking children with dyslexia: evidence for a phonological learning deficit

In 2 experiments, German-speaking dyslexic children (9-year-olds) showed impaired learning of new phonological forms (pseudonames) in a variety of visual-verbal learning tasks. The dyslexic deficit was also found when phonological retrieval cues were provided and when the to-be-learned pseudonames were presented in spoken as well as printed form. However, the dyslexic children showed no name-learning deficit when short, familiar words were used and they also had no difficulty with immediate repetition of the pseudowords. The dyslexic children's difficulty in learning new phonological forms was associated with pseudoword-repetition and naming-speed deficits assessed at the beginning of school, but not with phonological awareness and visual-motor impairments. We propose that the difficulty in learning new phonological forms may affect reading and spelling acquisition via impaired storage of new phonological forms, which serve as phonological underpinnings of the letter patterns of words or parts of words.     

Developmental dyslexia: Electrophysiological evidence of clinical subgroups

Event-related potentials (ERPs) to word and to musical-chord stimuli were recorded in 13 dyslexic boys and 13 age-matched normal readers. Normal readers and dyslexics whose reading handicaps involved visual-spatial processing deficits had greater word versus musical-chord ERP waveform differences over the left as compared to the right hemisphere. Dyslexics whose reading difficulties were related to auditory-verbal processing deficits did not exhibit this asymmetry. These results are interpreted as supportive of the hypothesis that the latter group of dyslexics has failed to develop normal left hemisphere specialization for processing of auditory-linguistic material.     

The simultaneous activation hypothesis: explaining recovery from deep to phonological dyslexia

Deep dyslexia evolved into phonological dyslexia in one patient. Semantic errors resolved while phonological and derivational errors persisted in reading. Nonword reading improved but remained inferior to word reading. Despite a residual semantic deficit naming improved. The Simultaneous Activation Hypothesis explains recovery from deep to phonological dyslexia and the continued dissociation between reading and naming errors. Partial recovery to all three reading routes increased constraints for word selection at the phonological output lexicon (POL) improving word reading. With recovery, the POL receives additional supportive information from the partially recovered direct oral reading route and grapheme-to-phoneme conversion (GPC) eliminating semantic errors in oral reading. Nonword reading also improved because of partial recovery to all three routes. Semantic errors in naming persisted because additional constraints were unavailable at the POL to activate a phonological entry. Phonological and derivational errors were more frequent in reading than in naming the result of incomplete GPC recovery. Residual nonword reading deficits resulted from incomplete GPC recovery, indicated by the persistence of neologisms in nonwords. The Simultaneous Activation Hypothesis readily accounts for the evolution from deep to phonological dyslexia.     

Developmental dyslexia and word retrieval deficits

Developmental dyslexics, selected on the basis of very slow naming rates on the Rapid Automatic Naming Tasks (RAN), were compared to normal readers on oral language, picture categorization, and reading tasks. Findings indicated that the dyslexics' word retrieval deficits were one symptom of a more generalized, however subtle, oral language deficit which involved both receptive and expressive oral language functioning. The dyslexics' word retrieval problem also seemed chiefly related to language processing and not to deficits in semantic memory as there were no significant differences between dyslexics and controls on a nonverbal semantic memory task (picture categorization). In naming and identifying printed words, the dyslexics appeared to rely considerably upon the "indirect" or "assembly-of-phonology" route; they were slower in naming irregularly spelled words compared to regularly spelled words and on a lexical decision task, the dyslexics were slower in making negative decisions for "pseudohomophones" (e.g., "braik") than for other matched nonwords. Results are discussed in terms of the logogen model with some consideration of a developmental model as well.     

Developmental dyslexia: the visual attention span deficit hypothesis

The visual attention (VA) span is defined as the amount of distinct visual elements which can be processed in parallel in a multi-element array. Both recent empirical data and theoretical accounts suggest that a VA span deficit might contribute to developmental dyslexia, independently of a phonological disorder. In this study, this hypothesis was assessed in two large samples of French and British dyslexic children whose performance was compared to that of chronological-age matched control children. Results of the French study show that the VA span capacities account for a substantial amount of unique variance in reading, as do phonological skills. The British study replicates this finding and further reveals that the contribution of the VA span to reading performance remains even after controlling IQ, verbal fluency, vocabulary and single letter identification skills, in addition to phoneme awareness. In both studies, most dyslexic children exhibit a selective phonological or VA span disorder. Overall, these findings support a multi-factorial view of developmental dyslexia. In many cases, developmental reading disorders do not seem to be due to phonological disorders. We propose that a VA span deficit is a likely alternative underlying cognitive deficit in dyslexia.     

The nature of phonological processing in oral reading: Evidence from surface dyslexia

Investigation of a neurological patient (PT) who presents with a relatively pure disorder of reading was carried out. His performance on a number of oral reading tasks was very similar to that of the surface dyslexic patient (HTR) reported by Shallice, Warrington and McCarthy (1983). Both patients showed an effect of “degree” of regularity in terms of accuracy of reading response. PT did not, however, show an effect of “typicality of divergence”, which was considered by Shallice and his colleagues to be responsible for the former effect. The size of orthographic-phonological unit operational in PT's oral reading was experimentally determined. PT appeared to rely on grapheme-phoneme correspondences that were assigned in a probabilistic rather than an “all-or-none” manner. No evidence for the existence of the sub-syllable as an independent unit was found. In contrast, this unit apparently mediated the performance of skilled adult readers. Implications of these results for models of the phonological route are discussed.     

Residual ability to use grapheme-phoneme conversion rules in phonological dyslexia

A case of acquired phonological dyslexia is described (P.M.). The patient was encouraged to read nonwords by analogy with real words, i.e., by changing phonemes in real words to produce pronounceable nonwords. P.M. was able to perform this task suggesting that he retained some ability to use grapheme-phoneme conversion rules. On the basis of P.M.'s performance an additional connection in Morton's logogen model is postulated.     

Aphasia, dyslexia and the phonological coding of written words

A possible account of the reading difficulty of certain aphasic-dyslexic patients includes the notion that they are impaired in translating the written word into a phonological code via grapheme-phoneme conversion rules. This notion was tested in two experiments, both utilizing orthographically regular non-words (like dake) as stimuli. The first experiment provides an analysis of two patients' (largely successful) attempts to repeat non-words, and their (almost totally unsuccessful) attempts to read them. Second, in a lexical decision task (is this written letter-string a word or not?), the finding that normals are slowed by non-words homophonic with real words (like flore) was replicated using a modified technique. This effect, attributable to phonological coding, was not shown by the patients. At the same time, their ability to discriminate between words and non-words was essentially intact. Consideration was given to mechanisms which might underlie such patients' correct and erroneous readings of words and non-words.     

Speed of phonological and orthographic processing as factors in dyslexia: electrophysiological evidence

The author investigated the hypothesis that speed of processing in the phonological and orthographic systems is one of the underlying variables of word-reading effectiveness. Speed of processing was assessed using measures of behavioral reaction time and electrophysiological latencies during phonological and orthographic task performance. Participants were 20 dyslexic and 20 normal-reading, male college students. An electrophysiological component complex (N1-P2-N2), as well as 2 other components (P3 and N4), was identified in both groups on each of the experimental tasks. Significant group differences were obtained only on the phonological tasks. Speed of processing during phonological judgment tasks was significantly prolonged among the dyslexic readers compared with the controls as reflected by P2, P3, and N4 latencies and reaction time. Between-task comparisons revealed significantly prolonged P2, P3, and N4 latencies on phonological compared with orthographic tasks in both dyslexic and normal readers, indicating that phonological classification of words may demand more time than orthographic classification. However, the gap score between speed of processing on the phonological and orthographic tasks was larger among the dyslexic readers and was observed mainly in P3 latency and reaction time. The highest correlation between word-reading accuracy score and the experimental measures was obtained in the dyslexic group with P3 latency gap score and in the control group with P2 latency gap score. The author proposes that slow phonological processing may cause "asynchrony" between the processing speeds within and between phonological and orthographic systems and may lead to a lack of efficient integration among the various subprocesses activated in reading, may slow down reading rate, and may impair word-reading effectiveness.