The "temporal processing deficit" hypothesis in dyslexia: new experimental evidence

The notion that developmental dyslexia may result from a general, nonspecific, defect in perceiving rapidly changing auditory signals is a current subject of debate (so-called "temporal processing deficit" hypothesis). Thirteen phonological dyslexics (age 10-13 years) and 10 controls matched for chronological and reading age were compared on a temporal order judgment (TOJ) task using the succession of two consonants (/p/-/s/) within a cluster. In order to test the relevance of the temporal deficit hypothesis, the task also included two additional conditions where either the two stimuli were artificially slowed or the interstimulus interval was expanded. As expected, the TOJ performance was significantly poorer in dyslexics than in controls. Moreover, in the "slowed speech" condition dyslexics' performance improved to reach the normal controls' level, whereas no significant improvement occurred when increasing the interstimulus interval. Finally dyslexics' performances, especially on the slowed condition, were found correlated with several tests of phonological processing (phoneme deletion, rhyme judgment, and nonword spelling tasks). These results lend support to the general temporal deficit theory of dyslexia.     

Spanish developmental dyslexia: Prevalence, cognitive profile, and home literacy experiences

This study was designed to examine the prevalence, cognitive profile, and home literacy experiences in subtypes of Spanish developmental dyslexia. The subtyping procedure used comparison with chronological-age-matched and reading-level controls on reaction times and accuracy responses to high-frequency words and pseudowords. Using regression-based procedures, 8 phonological dyslexics and 16 surface dyslexics were identified from a sample of 35 dyslexic fourth graders by comparing them with chronological-age-matched controls on reaction times to high-frequency word and pseudoword reading. However, when the dyslexic subtypes were defined by reference to reading-level controls, 12 phonological dyslexics were defined but only 5 surface dyslexics were identified. Both dyslexic subtypes showed a deficit in phonological awareness, but children with surface dyslexia also showed a deficit in orthographical processing assessed by a homophone comprehension task. This deficit was associated with poor home literacy experiences, with the group of parents with children matched in reading age, in comparison with the group of parents with children with surface dyslexia, reporting more literacy home experiences.     

Picture Naming Deficits in Developmental Dyslexia: The Phonological Representations Hypothesis

The picture and word naming performance of developmental dyslexics was compared to the picture and word naming performance of non-dyslexic (“garden variety”) poor readers, reading age, and chronological age-matched controls. The stimulus list used for both tasks was systematically manipulated for word length and word frequency. In order to examine picture naming errors in more depth, an object name recognition test assessed each subject's vocabulary knowledge of those names which they were unable to spontaneously label in the picture naming task. Findings indicated that the dyslexic and the garden variety poor readers exhibited a picture naming deficit relative to both chronological and reading age-matched controls. Findings also indicated that both groups of impaired readers obtained superior scores in the word naming task than in the picture naming task, while both groups of controls showed no difference in performance across tasks. The dyslexics' picture naming errors, but not those of the garden variety poor readers, were particularly marked on polysyllabic and/or low frequency words, indicating a possible phonological basis to the picture naming deficit of the dyslexic children. These children also recognized significantly more unnamed target words than all comparison groups, suggesting a particular difficulty inretrievingthe phonological codes of known picture names rather than a vocabulary deficit. Results are discussed in terms of dyslexics' difficulty in encoding full segmental phonological representations of names in long-term memory and/or in processing these representations in order to generate required names on demand.     

汉语发展性阅读障碍亚类型的初步探讨

以阅读水平匹配组为参照对29名汉语发展性阅读障碍儿童的认知缺陷模式进行了分析,并考察了不同亚类型阅读障碍儿童的汉字识别模式。结果表明汉语发展性阅读障碍存在不同的亚类型,以语音缺陷型、快速命名缺陷型及两者结合的双重缺陷型为主,与英语国家研究中的双重缺陷假设一致。语音缺陷型儿童汉字识别时有更多的语义错误,对声旁中的部分语音线索不敏感;快速命名缺陷型儿童汉字识别时依赖声旁语音线索,表现出阅读发展的一般延迟;双重或多重认知缺陷型是阅读损伤最严重的亚类型     

Is dyslexia a visual perceptive disorder? New empirical data

Several studies have shown that a phonological deficit is the origin of developmental dyslexia, because dyslexics have important difficulties in mapping orthographic to phonological codes. However, visual criteria are still used for the diagnosis of dyslexia and to develop methods of intervention. This study attempts to determine whether there are visual problems in dyslexic children. To this aim, dyslexic children and children without reading difficulties, matched by chronological age, participated in two experiments. One study was based on the Reversal test and the other was a visual decision task in which participants had to decide whether two letters were the same or different. There were 40 pairs of letters, to measure reaction times and mistakes. The results showed that dyslexics had similar performance to controls in the detection of different visual stimuli. Developmental dyslexics do not appear to have visual perceptual problems, but a particular difficulty to retrieve the phonological code of graphemes.     

英语发展性阅读障碍的训练程序

英语发展性阅读障碍的成因解释有三种倾向：基于语言的,非语言的,以及二者兼有的。语言学取向者认为障碍发生在语言学层次上,尤其是语音障碍;非语言学取向者认为有着更基本的视听知觉障碍,尤其是听觉时间加工缺陷;基于流畅性的双重障碍假说则认为二者兼有。根据这三类假设,研究者们开发了与之相应的基于语音意识缺陷、听觉时间加工缺陷和双重障碍的训练方案,其设计思路、材料选择和程序安排,对中文发展性阅读障碍的训练研究,有一定参考价值     

Picture naming deficits in developmental dyslexia in German

Recent research with English developmental dyslexics comparing the picture naming performance of these children to the picture naming performance of non-dyslexic (‘garden variety’) poor readers, reading age matched controls and chronological age matched controls has suggested that a selective difficulty in retrieving the phonological codes of known names on demand underlies the picture naming deficit found in developmental dyslexia (Swan & Goswami, Picture naming deficits in developmental dyslexia: the phonological representations hypothesis, Brain and Language, 56 (1997), 334–353). If the underlying causal factors in dyslexia are independent of the orthography that the child is learning to read, then a difficulty in retrieving the phonological codes of known names on demand should also be found in developmental dyslexics who are learning to read other languages. We therefore set out to replicate Swan and Goswami’s study with a group of German developmental dyslexics. We were interested to see whether a phonological deficit is characteristic of dyslexia in all orthographies, even those, such as German, in which high orthographic transparency means that dyslexic children read with considerable accuracy.     

Neural correlates of temporal auditory processing in developmental dyslexia during German vowel length discrimination: an fMRI study

This fMRI study investigated phonological vs. auditory temporal processing in developmental dyslexia by means of a German vowel length discrimination paradigm (Groth, Lachmann, Riecker, Muthmann, & Steinbrink, 2011). Behavioral and fMRI data were collected from dyslexics and controls while performing same-different judgments of vowel duration in two experimental conditions. In the temporal, but not in the phonological condition, hemodynamic brain activation was observed bilaterally within the anterior insular cortices in both groups and within the left inferior frontal gyrus (IFG) in controls, indicating that the left IFG and the anterior insular cortices are part of a neural network involved in temporal auditory processing. Group subtraction analyses did not demonstrate significant effects. However, in a subgroup analysis, participants performing low in the temporal condition (all dyslexic) showed decreased activation of the insular cortices and the left IFG, suggesting that this processing network might form the neural basis of temporal auditory processing deficits in 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.     

Temporal order and processing acuity of visual,auditory, and tactile perception in developmentally dyslexic young adults

We studied the temporal acuity of 16 developmentally dyslexic young adults in three perceptual modalities. The control group consisted of 16 age- and IQ-matched normal readers. Two methods were used. In the temporal order judgment (TOJ) method, the stimuli were spatially separate fingertip indentations in the tactile system, tone bursts of different pitches in audition, and light flashes in vision. Participants indicated which one of two stimuli appeared first. To test temporal processing acuity (TPA), the same 8-msec nonspeech stimuli were presented as two parallel sequences of three stimulus pulses. Participants indicated, without order judgments, whether the pulses of the two sequences were simultaneous or nonsimultaneous. The dyslexic readers were somewhat inferior to the normal readers in all six temporal acuity tasks on average. Thus, our results agreed with the existence of a pansensory temporal processing deficit associated with dyslexia in a language with shallow orthography (Finnish) and in well-educated adults. The dyslexic and normal readers' temporal acuities overlapped so much, however, that acuity deficits alone would not allow dyslexia diagnoses. It was irrelevant whether or not the acuity task required order judgments. The groups did not differ in the nontemporal aspects of our experiments. Correlations between temporal acuity and reading-related tasks suggested that temporal acuity is associated with phonological awareness.     

发展性阅读障碍亚类型研究进展

发展性阅读障碍是一种特殊的学习障碍,伴有多种认知缺陷并且存在不同的亚类型。依据相关的阅读模型理论,阅读障碍可划分为语音型和表层型。从认知缺陷角度出发,语音加工缺陷是主要的缺陷表现,以此为特征形成一种主要的阅读障碍的亚类型,同时还有以正字法加工缺陷和快速命名缺陷为主的其他亚类型。而以基本感知觉缺陷为标准,主要有以视觉加工缺陷和以听觉加工缺陷为主的两种亚类型。在汉语条件下,依据同样的阅读模型理论,语音型阅读障碍亚类型比例明显低于拼音文字条件下的。汉语阅读障碍也具有分别以语音加工缺陷、快速命名缺陷和正字法加工缺陷为主要认知缺陷的亚类型。未来有必要从神经机制角度进一步明确不同亚类型的神经基础。     

Is the impaired N170 print tuning specific to developmental dyslexia? A matched reading-level study with poor readers and dyslexics

Left N170 print tuning has been associated with visual expertise for print and has been reported to be impaired in dyslexics, using age matched designs. This is the first time N170 print tuning has been compared in adult dyslexics and adult poor readers, matched in reading level. Participants performed a lexical decision task using both word-like stimuli and symbol strings. In contrast to dyslexics, poor readers displayed similar N170 tuning to control expert readers, suggesting that impaired N170 specialization is a hallmark of developmental dyslexia. Our findings provide electrophysiological support for dyslexia being the result of abnormal specialization of the left occipito-temporal areas involved in the expert processing of print. Furthermore, as shown by correlations data and in accordance with the phonological mapping deficit theory, the impaired visual expertise for print described in dyslexics may have been caused by their core phonological deficits.     

汉语发展性阅读障碍儿童的主要亚类型分析*

采用语音意识测验、语素意识测验、正字法意识测验和快速命名测验对发展性阅读障碍儿童和阅读水平匹配组儿童进行测验。采用标准差切分法对阅读障碍的主要亚类型进行分析。结果发现,具有语音意识缺陷的人数比例最大,其次是正字法意识缺陷。结论:汉语发展性阅读障碍的主要亚类型为语音意识缺陷和正字法意识缺陷,快速命名缺陷和语素意识缺陷在汉语阅读障碍儿童中存在,但只是次要缺陷。     

Global and local pitch perception in children with developmental dyslexia

This study investigated global versus local pitch pattern perception in children with dyslexia aged between 8 and 11 years. Children listened to two consecutive 4-tone pitch sequences while performing a same/different task. On the different trials, sequences either preserved the contour (local condition) or they violated the contour (global condition). Compared to normally developing children, dyslexics showed robust pitch perception deficits in the local but not the global condition. This finding was replicated in a simple pitch direction task, which minimizes sequencing and short term memory. Results are consistent with a left-hemisphere deficit in dyslexia because local pitch changes are supposedly processed by the left hemisphere, whereas global pitch changes are processed by the right hemisphere. The present data suggest a link between impaired pitch processing and abnormal phonological development in children with dyslexia, which makes pitch pattern processing a potent tool for early diagnosis and remediation of dyslexia.     

The effects of the constancy of location and order in working memory visual–phonological binding of children with dyslexia

It has been suggested that children with dyslexia have difficulties in visual–phonological working memory (WM) binding, supporting the hypothesis that this ability is crucial in the formation of associations between written forms and phonological codes required by reading. However, research on this topic is currently scarce and has not clarified to what extent binding may be supported by spatial and temporal information. The present study examined visual–phonological WM binding performance in a group of children with dyslexia compared to a control group of typically developing children matched for age, gender, and grade. Children had to memorize ephemeral associations between meaningless shapes and nonwords, with stimuli presented in either fixed or variable spatial locations, and in either fixed or variable temporal order across trials; performance was assessed using a recognition task. Results showed that children with dyslexia have a deficit in visual–phonological WM binding in every presentation condition and that, unlike control children, they are not able to use fixed spatial locations as an aid to bind information. Crucially, however, children with dyslexia still benefit from the presentation of stimuli in a fixed temporal order. These findings support the hypothesis that a WM binding deficit is crucial in children with dyslexia, and have potential implications for treatment strategies.     

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.     

Phonological awareness and spelling in normal children and dyslexics: the case of initial consonant clusters

We investigated phonological awareness and spelling skills among normal readers and spellers in Grades 1 and 2 and among dyslexics who scored at the same level as the normals on a standardized spelling test. Both normal children and dyslexics had difficulty with consonants in word-initial clusters in a phoneme recognition task and a phoneme deletion task. Also, both groups of children had trouble producing legal spellings of syllables with initial clusters, sometimes failing to represent the second consonants of the clusters. The dyslexics' phonological awareness and spelling skills were poorer than those of the younger normal children, but the two groups showed similar patterns of performance.     

Quality of phonological representations, verbal learning, and phoneme awareness in dyslexic and normal readers

This study of dyslexia was concerned with the quality of phonological representations of lexical items. It extended the studies of verbal learning in dyslexia from learning new vocabulary items (pseudo-names) to the learning of more well-specified variants of known words. The participants were 19 dyslexic adolescents in grades 4 to 6 and 19 younger normal readers in grade 2 matched on single word decoding. The dyslexics were significantly outperformed by the reading-age controls in non-word reading and in phoneme awareness. The dyslexics also took longer time to learn to associate a set of pseudo-names with pictures of persons although the dyslexics learned to associate familiar names with pictures as quickly as the controls did. The acquisition of new phonological representations of words was studied in an imitation task with maximally distinct pronunciations of long, familiar words. The dyslexics gained less than the controls in this task. They also gained less on one measure taken from a phoneme substitution task with the same words as in the distinctness task. The results are interpreted in the light of the hypothesis that poorly specified phonological representations may be an underlying problem in dyslexia.     

Object naming in dyslexic children: more than a phonological deficit

In the present study, the authors investigate how some visual factors related to early stages of visual-object naming modulate naming performance in dyslexia. The performance of dyslexic children was compared with 2 control groups-normal readers matched for age and normal readers matched for reading level-while performing a discrete naming task in which color and dimensionality of the visually presented objects were manipulated. The results showed that 2-dimensional naming performance improved for color representations in control readers but not in dyslexics. In contrast to control readers, dyslexics were also insensitive to the stimulus's dimensionality. These findings are unlikely to be explained by a phonological processing problem related to phonological access or retrieval but suggest that dyslexics have a lower capacity for coding and decoding visual surface features of 2-dimensional representations or problems with the integration of visual information stored in long-term memory.     

Speed of processing of the visual-orthographic and auditory-phonological systems in adult dyslexics: the contribution of "asynchrony" to word recognition deficits

This study investigated whether "asynchrony" in speed of processing (SOP) between the visual-orthographic and auditory-phonological modalities contributes to word recognition deficits among adult dyslexics. Male university students with a history of diagnosed dyslexia were compared to age-matched normal readers on a variety of experimental measures while event-related potentials and reaction time data were collected. Measures were designed to evaluate auditory and visual processing for non-linguistic (tones and shapes) and linguistic (phonemes and graphemes) low-level stimuli as well as higher-level orthographic and phonological processing (in a lexical decision task). Data indicated that adult dyslexic readers had significantly slower reaction times and longer P300 latencies than control readers in most of the experimental tasks and delayed P200 latencies for the lexical decision task. Moreover, adult dyslexics revealed a systematic SOP gap in P300 latency between the auditory/phonological and visual/orthographic processing measures. Our data support and extend previous work that found SOP asynchrony to be an underlying factor of childhood dyslexia. The present data suggests, however, that among adult dyslexics the between modalities asynchrony occurs at later processing stages than in children.