Characterizing the morphosyntactic processing deficit and its relationship to phonology in developmental dyslexia.

This study explores the morphosyntactic processing deficit in developmental dyslexia, addressing the on-going debate on the linguistic nature of the disorder, and directly testing the hypothesis that the deficit is based on underlying processing difficulties, such as acoustic and/or phonological impairments. Short German sentences consisting of a pronoun and a verb, either correct or containing a morphosyntactic violation, were auditorily presented to 17 German-speaking adults with dyslexia, and 17 matched control participants, while an EEG was recorded. In order to investigate the interaction between low-level phonological processing and morphosyntactic processing, the verbal inflections were manipulated to consist of different levels of acoustic salience. The event-related potential (ERP) results confirm altered morphosyntactic processing in participants with dyslexia, especially when morphosyntactic violations are expressed by both lexical and inflectional changes. Moreover, ERP data on phoneme discrimination and behavioural data on phonemic awareness and verbal short-term memory reveal phonological deficits in dyslexic participants. However, a causal relationship between phonological and morphosyntactic processing was not conclusive, because anomalous morphosyntactic processing in dyslexia is not directly mediated by acoustic salience, rather it correlates with high-level phonological skills and is mediated by lexical cues.

Psychophysical estimates of frequency discrimination: more than just limitations of auditory processing.

Efficient auditory processing is hypothesized to support language and literacy development. However, behavioral tasks used to assess this hypothesis need to be robust to non-auditory specific individual differences. This study compared frequency discrimination abilities in a heterogeneous sample of adults using two different psychoacoustic task designs, referred to here as: 2I_6A_X and 3I_2AFC designs. The role of individual differences in nonverbal IQ (NVIQ), socioeconomic status (SES) and musical experience in predicting frequency discrimination thresholds on each task were assessed using multiple regression analyses. The 2I_6A_X task was more cognitively demanding and hence more susceptible to differences specifically in SES and musical training. Performance on this task did not, however, relate to nonword repetition ability (a measure of language learning capacity). The 3I_2AFC task, by contrast, was only susceptible to musical training. Moreover, thresholds measured using it predicted some variance in nonword repetition performance. This design thus seems suitable for use in studies addressing questions regarding the role of auditory processing in supporting language and literacy development.

Sensitivity to lexical stress in dyslexia: a case of cognitive not perceptual stress.

Sensitivity to lexical stress in adult German-speaking students with reading difficulty was investigated using minimal pair prepositional verbs whose meaning and syntax depend on the location of the stressed syllable. Two tests of stress perception were used: (i) a stress location task, where listeners indicated the location of the perceptually most prominent syllable, and (ii) a stress pattern identification task, where listeners indicated if the stress pattern was appropriate for its semantic frame. The students with reading difficulties performed worse than the normally reading students on both tasks. Their poorer performance did not reflect the lack of a percept for lexical stress rather patterns of performance across the two tasks suggested that each loaded onto different underlying cognitive abilities. Deficits in these, rather than perceptual difficulties, explained observed group differences. Students with reading difficulties have a normal implicit knowledge of lexical stress usage but lack the necessary cognitive resources for developing an explicit metalinguistic awareness of it. Deficits in these skills not deficiencies in lexical stress perception are implicated in their reading difficulties.

Encoding: the keystone to efficient functioning of verbal short-term memory.

Verbal short-term memory (VSTM) is thought to play a critical role in language learning. It is indexed by the nonword repetition task where listeners are asked to repeat meaningless words like 'blonterstaping'. The present study investigated the effect on nonword repetition performance of differences in efficiency of functioning of some part of the neural architecture mediating VSTM. Hypotheses were stated within Baddeley and Hitch's (1974) multicomponent model of VSTM, with respect to regions of the brain known to be active during tasks tapping into VSTM. We were specifically interested in activations associated with the posterior planum temporale (Spt) which emerge during rehearsal since this region is hypothesized to be central to VTSM (Buchsbaum, Olsen, Koch, & Berman, 2005a). Participants performed a delayed reaction time task in the scanner which explicitly mimicked the three main stages of information-processing involved in VSTM (encoding, rehearsal, recall (here recognition)). The data for each stage were then convolved with scores from a separately measured nonword repetition task. Rather than observing a pattern of individual differences located to specific regions specialized for supporting VSTM, a dissociation in direction of correlation in overlapping regions of the brain was observed during encoding and recognition. Larger hemodynamic responses during encoding were associated with better nonword repetition, and vice versa during recognition. There was little evidence for a network of activations specialized for VSTM. Instead, the main correlations were observed in regions also known to be involved in long-term memory. It seems that individuals who are better at nonword repetition and hence at language learning, activate these regions more efficiently than poorer nonword-repeaters early after stimulus input. These observations are discussed with respect to various models proposed for explaining the phenomenon of VSTM.

Children with specific language impairment: the role of prosodic processes in explaining difficulties in processing syntactic information.

Children with specific language impairment (SLI) experience great difficulties in language comprehension and/or production whereby the majority of these children have particular problems in acquiring syntactic rules. In the speech stream boundaries of major syntactic constituents are reliably marked by prosodic cues. Therefore, prosodic information provides an important cue for discovering the syntactic structure of a language [Jusczyk, P.W., 2002. How infants adapt speech-processing capacities to native language structure. Curr. Dir. Psychol. Sci. 11, 15-18.]. Following this, the question is, whether children with SLI differ in the processing of syntactic information from normally developing children and to what extent this is related to the processing of the inherent prosodic information. Children heard either correct sentences or sentences with a word category violation (syntactic level) and a joined prosodic incongruity (prosodic level) while event-related brain potentials (ERPs) were recorded. Judging the sentence's correctness, control children performed better than children with SLI for all types of sentences. With respect to the ERPs, control children showed a bilateral early starting anterior negativity sustaining into a late anterior negativity and a P600 in posterior regions in response to incorrect sentences. Children with SLI showed a comparable P600 but unlike the control children there was only a late, clearly left lateralized anterior negativity. The complete absence of a right anterior negativity in children with SLI suggests that they may not access prosodic information in the same way normal children do. The differences in prosodic processing may in turn hamper the development of syntactic processing skills as indicated by the absence of the syntax-related early left anterior negativity.

Lexical-semantic processes in children with specific language impairment.

The current study used event-related brain potentials to investigate lexical-semantic processing of words in sentences spoken by children with specific language impairment and children with normal language development. Children heard correct sentences and sentences with a violation of the selectional restriction of the verb. Control children showed an N400 effect followed by a late positivity for the incorrect sentences. In contrast, children with specific language impairment showed no N400 effect but did show a late, broadly distributed positivity. This absence of the N400 effect is due to a relatively large negativity for correct sentences, suggesting weaker lexical-semantic representations of the verbs and their selectional restrictions in children with specific language impairment.