Developmental surface dyslexias - Naama Friedmann

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cortex 44 (2008) 1146–1160 1153 comprehension, which will be presented in the next sections. The bottom rows of Table 4 include the threshold for each task above which the number of errors of a dyslexic participant is significantly larger (Crawford and Howell’s (1998) t-test, p < .05) than the age-matched control group. (For example, the adults control group had an average of 1.0% errors in reading aloud irregular/potentiophonic words, with SD of 0.9%. For these data, given 16 participants in this control group, the lowest score that would be significantly different from the control would be 2.7% errors, using Crawford and Howell’s (1998) t-test, and this is presented in Table 2.) 2.3.2. Lexical decision The participants differed with respect to their ability to decide which of two letter strings was a word spelled correctly, as seen in Table 4. Whereas nine of the participants performed within the normal range in this task ( p > .05 for the comparison of each of them with their controls), eight performed significantly poorer than their controls (t > 6, p < .001). 2.3.3. Homophone and potentiophone comprehension The assessment of homophone/potentiophone comprehension showed that some of the participants performed well in this task, indicating preserved access to semantics, whereas others did poorly. As seen in Table 4, six of the participants performed within normal limits in the homophone selection task, whereas the other participants performed significantly poorer than their control groups ( p < .05), five of them performing at chance level on this task. Thus, the results yielded 3 patterns: impaired reading aloud, lexical decision, and comprehension; impaired reading aloud and comprehension, with intact lexical decision; and impaired reading aloud with intact lexical decision and comprehension. 2.3.4. Naming The results of the naming task are reported in Table 5. The naming performance of 16 of the 17 participants was within the normal range, with performance ranging between 92 and 100 items named correctly out of 100 items, indicating intact lexical access and retrieval. Especially relevant for surface dyslexia, in which some individuals showed impaired phonological output lexicon, the naming ability of the participants in this study indicates that they had no impairment at the phonological output lexicon. None of the participants produced a phonemic paraphasia, indicating also an intact phonemic output buffer for all the participants. One participant, AS, performed below the normal range, with 88% correct naming, which might indicate a deficit in lexical retrieval as well. Unlike previously reported individuals with acquired surface dyslexia, the pattern of his errors and other responses in the naming task did not indicate a deficit in the phonological output lexicon, which is usually manifested in phonologically related paraphasias. His errors were close semantic paraphasias, hesitations, and don’t know responses, and only one of his paraphasias was a formal paraphasia, which was not only phonologically, but also semantically, related to the target word. AS’s response pattern is not characteristic of a deficit in the phonological lexicon itself, because a deficit at this level is expected to also yield phonemic paraphasias. According to his error pattern, AS’s mild lexical retrieval difficulties stem from a deficit either in the semantic lexicon, or in the access from the semantic lexicon to the phonological output lexicon – according to Butterworth (1989) and Caramazza and Hillis (1990), when there is no access to the phonological representation of the target word, a word which is semantically related to it, whose phonological representation is available, might be produced instead. The fact that he had frequency effect on naming (r pb ¼ .2, p ¼ .03) further supports a deficit in the access to the phonological output lexicon rather than a deficit in the semantic lexicon (Jescheniak and Levelt, 1994). It might be interesting to note that AS’s reading indicated that he also had a deficit in the access from the orthographic input lexicon to the phonological output lexicon, so his deficit might be a general difficulty accessing the phonological output lexicon. (This is unlike the other eight individuals Table 5 – Performance on naming 100 objects Participant Correct responses Don’t know Paraphasia Correct naming following Semantic Formal a Long hesitation Semantic paraphasia SH 93 1 1 3 2 GL 96 1 1 1 1 OF 95 3 2 YR 92 4 1 3 OM 96 4 BZ 100 AS 88 2 5 1 3 1 OS 96 2 2 AK 95 1 2 2 0 AM 97 3 AL b 96 1 1 1 1 KR 92 5 2 1 NF 99 1 IR 100 YD 96 4 a All the formal paraphasias produced by our participants were phonologically and semantically related to the target. b AL’s don’t know response and his correct response following hesitation also included a definition of the target.
1154 cortex 44 (2008) 1146–1160 in the current study who had a deficit in the connection of the orthographic input lexicon to the phonological output lexicon, whose access to the phonological output lexicon from semantics was unimpaired.) 2.3.5. Input surface dyslexia: a deficit at the lexicon or in the access to it? In the Introduction ascribed the deficit of individuals with impaired reading aloud, lexical decision, and comprehension to an impairment in the orthographic input lexicon or in the access to it. In order to decide which of these two possibilities apply for our participants, we further tested the ability of one of the participants with this reading pattern, BZ, to perform a lexical decision task for both written and orally spelled sequences. If it is only the access from the orthographic–visual analysis system to the orthographic input lexicon that is impaired, whereas the orthographic input lexicon is intact, we would expect failure in lexical decision for written words but success in the orally spelled words because orally spelled words access the orthographic input lexicon from another route and not through the visual analyzer. However, if the lexicon itself is impaired, both modalities should yield impaired performance. 7 The written lexical decision task administered to BZ included 108 sequences, 54 words and 54 pseudohomophones. The orally spelled lexical decision comprised 34 words, including 17 existing words and 17 pseudohomophones. The results showed that BZ performed poorly on both tasks. He accepted 65% and 33% of the pseudohomophones as existing words in the oral and written task respectively, and rejected 18% and 4% of the existing words, respectively. This suggests that BZ’s orthographic input lexicon was impaired. Another factor that might speak to a deficit in the orthographic input lexicon rather than impaired access to it, is the effect of frequency. We expect that the orthographic input lexicon would be affected by frequency, with higher probability of retrieving frequent written words, whereas a pre-lexical impairment of access to the orthographic input lexicon should not be affected by lexical factors such as frequency. For this reason we analyzed the effect of frequency on the reading aloud of all participants with input surface dyslexia. This was done in two ways: First, we estimated the written frequency of the irregular words in the 340 word list using Google search, and compared the accuracy in reading the 20 most frequent irregular words to the reading of the 20 irregular words with the lowest frequency on the list. For each of the individuals, an effect of frequency was found with higher accuracy in reading the more frequent words. The second way in which we assessed frequency effect was via examination of the relative frequency of a target word and its potentiophone. We asked 50 individuals without reading disorder to evaluate the relative frequency of the 160 target words with potentiophones from the 340 words list, compared to their 7 It is, of course, possible that both access routes to the lexicon are impaired, in which case no differential diagnosis can be made between impaired lexicon and impaired access to the lexicon from all access routes. potentiophones. We then selected the 89 potentiophone pairs which yielded a significant preference for one of the potentiophones. 8 The analysis of reading accuracy showed that each of the participants made more errors on the 37 target words which were less frequent than their potentiophones, compared to the number of errors on the 52 target words which were more frequent than their potentiophones. These two analyses, which point to the effect of frequency on reading aloud of each of the individuals with input surface dyslexia, indicate a deficit in the lexicon rather than the access to it. 2.3.6. Summary – subtypes and functional localization of the deficits The results reported above indicate that the participants can be classified into three groups, each with a different subtype of developmental surface dyslexia. The first group, which includes SH, GL, OF, YR, TM, NT, OM, and BZ, showed impaired reading aloud, impaired lexical decision, and impaired homophone and potentiophone comprehension. We suggest that the participants in this group have an impairment that relates to the orthographic input lexicon, most probably in the lexicon itself. The individuals in the second group, AS, OS, and AK, had impaired reading aloud, impaired homophone/potentiophone comprehension, and good lexical decision. This pattern suggests a functioning and accessible orthographic input lexicon, with impaired output from it to semantics and to the phonological output lexicon. The third group, which included AM, AL, KR, NF, IR, and YD, showed impaired oral reading of irregular words and potentiophones, but at the same time had normal performance in lexical decision and in homophone/potentiophone comprehension. This pattern can be ascribed to intact orthographic input lexicon, which also has intact access to the semantic system, but impaired access to the phonological output lexicon. Importantly, there were no participants with good homophone comprehension who showed impaired lexical decision. The naming assessment suggests that the marked tendency to read via grapheme-to-phoneme conversion does not result from a deficit at the phonological lexicon, at least for 16 of the 17 participants, who did not have lexical retrieval deficits or phonemic paraphasias. 3. Discussion The main finding of the current study is the identification of three subtypes of developmental surface dyslexia. These subtypes differ with respect to the locus on the lexical reading route that is impaired, all leading to reading via the sublexical route, but with different performance pattern with respect to orthographic–lexical knowledge and comprehension. 8 We counted a potentiophone as significantly more frequent than its counterpart when the number of judges who chose it as the more frequent was larger than twice the number of judges who chose the counterpart plus the number of judges who said they were equi-frequent.
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Developmental surface dyslexias - Naama Friedmann

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