Resting-state functional connectivity and reading subskills in children.

Individual differences in reading ability have been linked to characteristics of functional connectivity in the brain in both children and adults. However, many previous studies have used single or composite measures of reading, leading to difficulty characterizing the role of functional connectivity in discrete subskills of reading. The present study addresses this issue using resting-state fMRI to examine how resting-state functional connectivity (RSFC) related to individual differences in children's reading subskills, including decoding, sight word reading, reading comprehension, and rapid automatized naming (RAN). Findings showed both positive and negative RSFC-behaviour relationships that diverged across different reading subskills. Positive relationships included increasing RSFC among left dorsal and anterior regions with increasing decoding proficiency, and increasing RSFC between the left thalamus and right fusiform gyrus with increasing sight word reading, RAN, and reading comprehension abilities. In contrast, negative relationships suggested greater functional segregation of attentional and reading networks with improved performance on RAN, decoding, and reading comprehension tasks. Importantly, the results suggest that although reading subskills rely to some extent on shared functional networks, there are also distinct functional connections supporting different components of reading ability in children.

Music as a scaffold for listening to speech: Better neural phase-locking to song than speech.

Neural activity synchronizes with the rhythmic input of many environmental signals, but the capacity of neural activity to entrain to the slow rhythms of speech is particularly important for successful communication. Compared to speech, song has greater rhythmic regularity, a more stable fundamental frequency, discrete pitch movements, and a metrical structure, this may provide a temporal framework that helps listeners neurally track information better than the rhythmically irregular rhythms of speech. The current study used EEG to examine whether entrainment to the syllable rate of linguistic utterances, as indexed by cerebro-acoustic phase coherence, was greater when listeners heard sung than spoken sentences. We assessed listeners phase-locking in both easy (no time compression) and hard (50% time-compression) utterance conditions. Adults phase-locked equally well to speech and song in the easy listening condition. However, in the time-compressed condition, phase-locking was greater for sung than spoken utterances in the theta band (3.67-5 â€‹Hz). Thus, the musical temporal and spectral characteristics of song related to better phase-locking to the slow phrasal and syllable information (4-7 â€‹Hz) in the speech stream. These results highlight the possibility of using song as a tool for improving speech processing in individuals with language processing deficits, such as dyslexia.

ERPs reveal the temporal dynamics of auditory word recognition in specific language impairment.

We used event-related potentials (ERPs) to compare auditory word recognition in children with specific language impairment (SLI group; N=14) to a group of typically developing children (TD group; N=14). Subjects were presented with pictures of items and heard auditory words that either matched or mismatched the pictures. Mismatches overlapped expected words in word-onset (cohort mismatches; see: DOLL, hear: dog), rhyme (CONE -bone), or were unrelated (SHELL -mug). In match trials, the SLI group showed a different pattern of N100 responses to auditory stimuli compared to the TD group, indicative of early auditory processing differences in SLI. However, the phonological mapping negativity (PMN) response to mismatching items was comparable across groups, suggesting that just like TD children, children with SLI are capable of establishing phonological expectations and detecting violations of these expectations in an online fashion. Perhaps most importantly, we observed a lack of attenuation of the N400 for rhyming words in the SLI group, which suggests that either these children were not as sensitive to rhyme similarity as their typically developing peers, or did not suppress lexical alternatives to the same extent. These findings help shed light on the underlying deficits responsible for SLI.

Electrophysiological indices of phonological impairments in dyslexia.

PURPOSE: A range of studies have shown difficulties in perceiving acoustic and phonetic information in dyslexia; however, much less is known about how such difficulties relate to the perception of individual words. The authors present data from event-related potentials (ERPs) examining the hypothesis that children with dyslexia have difficulties with processing phonemic information within spoken words compared to age-matched readers with typical development. METHOD: The authors monitored ERPs to auditory words during a simple picture-word matching task. The key manipulation was the inclusion of both matching stimuli and three types of mismatches (cohort, CONE-comb; rhyme, CONE-bone; and unrelated, CONE-fox). RESULTS: Children with dyslexia showed atypical N400 ERP waveforms to both types of phonological mismatches, but not to phonologically unrelated mismatches, reflecting a relative insensitivity to phonological overlap among auditory words. CONCLUSION: The data suggest that children with dyslexia have impairments in integrating phonological information into word-level representations. The results suggest that speech perception difficulties in dyslexia might have consequences for processing auditory words.

Atypical neural responses to phonological detail in children with developmental language impairments.

Specific Language Impairment (SLI) is a developmental disorder affecting language learning across a number of domains. These difficulties are thought to be related to difficulties processing auditory speech, given findings of imperfect auditory processing across nonspeech tones, individual speech sounds and syllables. However the relationship of auditory difficulties to language development remains unclear. Perceiving connected speech involves resolving coarticulation, the imperceptible blending of speech movements across adjacent sounds, which gives rise to subtle variations in speech sounds. The present study used event-related potentials (ERPs) to examine neural responses to coarticulation in school age children with and without SLI. Atypical neural responses were observed for the SLI group in ERP indices of prelexical-phonological but not lexical stages of processing. Specifically, incongruent coarticulatory information resulted in a modulation of the N100 in the SLI but not typically developing group while a Phonological Mapping Negativity was elicited in the typically developing but not SLI group, unless additional cues were present. Neural responses to unexpected lexical mismatches indexed by the N400 ERP component were the same for both groups. The results demonstrate a relative insensitivity to important subphonemic features in SLI.

An electrophysiological study of task demands on concreteness effects: evidence for dual coding theory.

We examined ERP responses during the generation of word associates or mental images in response to concrete and abstract concepts. Of interest were the predictions of dual coding theory (DCT), which proposes that processing lexical concepts depends on functionally independent but interconnected verbal and nonverbal systems. ERP responses were time-locked to either stimulus onset or response to compensate for potential latency differences across conditions. During word associate generation, but not mental imagery, concrete items elicited a greater N400 than abstract items. A concreteness effect emerged at a later time point during the mental imagery task. Data were also analyzed using time-frequency analysis that investigated synchronization of neuronal populations over time during processing. Concrete words elicited an enhanced late going desynchronization of theta-band power (723-938 ms post stimulus onset) during associate generation. During mental imagery, abstract items elicited greater delta-band power from 800 to 1,000 ms following stimulus onset, theta-band power from 350 to 205 ms before response, and alpha-band power from 900 to 800 ms before response. Overall, the findings support DCT in suggesting that lexical concepts are not amodal and that concreteness effects are modulated by tasks that focus participants on verbal versus nonverbal, imagery-based knowledge.

Speech perception, rapid temporal processing, and the left hemisphere: a case study of unilateral pure word deafness.

The mechanisms and functional anatomy underlying the early stages of speech perception are still not well understood. One way to investigate the cognitive and neural underpinnings of speech perception is by investigating patients with speech perception deficits but with preserved ability in other domains of language. One such case is reported here: patient NL shows highly impaired speech perception despite normal hearing ability and preserved semantic knowledge, speaking, and reading ability, and is thus classified as a case of pure word deafness (PWD). NL has a left temporoparietal lesion without right hemisphere damage and DTI imaging suggests that he has preserved cross-hemispheric connectivity, arguing against an account of PWD as a disconnection of left lateralized language areas from auditory input. Two experiments investigated whether NL's speech perception deficit could instead result from an underlying problem with rapid temporal processing. Experiment 1 showed that NL has particular difficulty discriminating sounds that differ in terms of rapid temporal changes, be they speech or non-speech sounds. Experiment 2 employed an intensive training program designed to improve rapid temporal processing in language impaired children (Fast ForWord; Scientific Learning Corporation, Oakland, CA) and found that NL was able to improve his ability to discriminate rapid temporal differences in non-speech sounds, but not in speech sounds. Overall, these data suggest that patients with unilateral PWD may, in fact, have a deficit in (left lateralized) temporal processing ability, however they also show that a rapid temporal processing deficit is, by itself, unable to account for this patient's speech perception deficit.

Congruency of auditory sounds and visual letters modulates mismatch negativity and P300 event-related potentials.

A key determinant of skilled reading is the ability to integrate the orthographic and auditory forms of language. A number of prior studies have identified neural markers in adult readers corresponding to audio-visual integration of letters and their corresponding sounds. However, there remains some controversy as to the stage of processing at which this occurs. In the present study, we examined this issue using event-related potentials (ERPs), due to their sensitivity to the timing of perceptual and cognitive processes. Letter sounds were presented auditorily in an unattended mismatch negativity (MMN) paradigm, which is argued to be indicative of auditory sensory memory. Concurrently, participants performed a visual letter identification task. On critical trials, the auditory stimulus was played concurrently with the visual letters. We observed significant MMNs both when the visual letter was congruent with the auditory stimulus, and when it was incongruent. However, the magnitude and scalp distribution of this effect was attenuated in incongruent trials. We also observed a later-going effect of congruency on P300 trials, marked by increased amplitudes and latencies for incongruent compared to congruent trials. The results suggest audiovisual integration of letters and sounds can and does occur during relatively early pre-attentive stages of sensory processing, and that these effects extend to later-going attentional phases of processing as well.

Graded effects of regularity in language revealed by N400 indices of morphological priming.

Differential electrophysiological effects for regular and irregular linguistic forms have been used to support the theory that grammatical rules are encoded using a dedicated cognitive mechanism. The alternative hypothesis is that language systematicities are encoded probabilistically in a way that does not categorically distinguish rule-like and irregular forms. In the present study, this matter was investigated more closely by focusing specifically on whether the regular-irregular distinction in English past tenses is categorical or graded. We compared the ERP priming effects of regulars (baked-bake), vowel-change irregulars (sang-sing), and "suffixed" irregulars that display a partial regularity (suffixed irregular verbs, e.g., slept-sleep), as well as forms that are related strictly along formal or semantic dimensions. Participants performed a visual lexical decision task with either visual (Experiment 1) or auditory prime (Experiment 2). Stronger N400 priming effects were observed for regular than vowel-change irregular verbs, whereas suffixed irregulars tended to group with regular verbs. Subsequent analyses decomposed early versus late-going N400 priming, and suggested that differences among forms can be attributed to the orthographic similarity of prime and target. Effects of morphological relatedness were observed in the later-going time period, however, we failed to observe true regular-irregular dissociations in either experiment. The results indicate that morphological effects emerge from the interaction of orthographic, phonological, and semantic overlap between words.

Investigating the time course of spoken word recognition: electrophysiological evidence for the influences of phonological similarity.

Behavioral and modeling evidence suggests that words compete for recognition during auditory word identification, and that phonological similarity is a driving factor in this competition. The present study used event-related potentials (ERPs) to examine the temporal dynamics of different types of phonological competition (i.e., cohort and rhyme). ERPs were recorded during a novel picture-word matching task, where a target picture was followed by an auditory word that either matched the target (CONE-cone), or mismatched in one of three ways: rhyme (CONE-bone), cohort (CONE-comb), and unrelated (CONE-fox). Rhymes and cohorts differentially modulated two distinct ERP components, the phonological mismatch negativity and the N400, revealing the influences of prelexical and lexical processing components in speech recognition. Cohort mismatches resulted in late increased negativity in the N400, reflecting disambiguation of the later point of miscue and the combined influences of top-down expectations and misleading bottom-up phonological information on processing. In contrast, we observed a reduction in the N400 for rhyme mismatches, reflecting lexical activation of rhyme competitors. Moreover, the observed rhyme effects suggest that there is an interaction between phoneme-level and lexical-level information in the recognition of spoken words. The results support the theory that both levels of information are engaged in parallel during auditory word recognition in a way that permits both bottom-up and top-down competition effects.

Brain mechanisms implicated in the preattentive categorization of speech sounds revealed using FMRI and a short-interval habituation trial paradigm.

A hallmark of categorical perception is better discrimination of stimulus tokens from 2 different categories compared with token pairs that are equally dissimilar but drawn from the same category. This effect is well studied in speech perception and represents an important characteristic of how the phonetic form of speech is processed. We investigated the brain mechanisms of categorical perception of stop consonants using functional magnetic resonance imaging and a passive short-interval habituation trial design (Zevin and McCandliss 2005). The paradigm takes advantage of neural adaptation effects to identify specific regions sensitive to an oddball stimulus presented in the context of a repeated item. These effects were compared for changes in stimulus characteristics that result in either a between-category (phonetic and acoustic) or a within-category (acoustic only) stimulus shift. Significantly greater activation for between-category than within-category stimuli was observed in left superior sulcus and middle temporal gyrus as well as in inferior parietal cortex. In contrast, only a subcortical region specifically responded to within-category changes. The data suggest that these habituation effects are due to the unattended detection of a phonetic stimulus feature.

Imaging the past: neural activation in frontal and temporal regions during regular and irregular past-tense processing.

This article presents fMRI evidence bearing on dual-mechanism versus connectionist theories of inflectional morphology. Ten participants were scanned at 4 Tesla as they covertly generated the past tenses of real and nonce (nonword) verbs presented auditorily. Regular past tenses (e.g., walked, wugged) and irregular past tenses (e.g., took, slept) produced similar patterns of activation in the posterior temporal lobe in both hemispheres. In contrast, there was greater activation in left and right inferior frontal gyrus for regular past tenses than for irregular past tenses. Similar previous results have been taken as evidence for the dual-mechanism theory of the past tense (Pinker & Ullman, 2002). However, additional analyses indicated that irregulars that were phonologically similar to regulars (e.g., slept, fled, sold) produced the same level of activation as did regulars, and significantly more activation than did irregulars that were not phonologically similar to regulars (e.g., took, gave). Thus, activation patterns were predicted by phonological characteristics of the past tense rather than by the rule-governed versus exception distinction that is central to the dual-mechanism framework. The results are consistent with a constraint satisfaction model in which phonological, semantic, and other probabilistic constraints jointly determine the past tense, with different degrees of involvement for different verbs.

Overlapping neural regions for processing rapid temporal cues in speech and nonspeech signals.

Speech perception involves recovering the phonetic form of speech from a dynamic auditory signal containing both time-varying and steady-state cues. We examined the roles of inferior frontal and superior temporal cortex in processing these aspects of auditory speech and nonspeech signals. Event-related functional magnetic resonance imaging was used to record activation in superior temporal gyrus (STG) and inferior frontal gyrus (IFG) while participants discriminated pairs of either speech syllables or nonspeech tones. Speech stimuli differed in either the consonant or the vowel portion of the syllable, whereas the nonspeech signals consisted of sinewave tones differing along either a dynamic or a spectral dimension. Analyses failed to identify regions of activation that clearly contrasted the speech and nonspeech conditions. However, we did identify regions in the posterior portion of left and right STG and left IFG yielding greater activation for both speech and nonspeech conditions that involved rapid temporal discrimination, compared to speech and nonspeech conditions involving spectral discrimination. The results suggest that, when semantic and lexical factors are adequately ruled out, there is significant overlap in the brain regions involved in processing the rapid temporal characteristics of both speech and nonspeech signals.