Helen J. Neville

Syntactically based sentence processing classes: Evidence from event-related brain potentials

Theoretical considerations and diverse empirical data from clinical, psycholinguistic, and developmental studies suggest that language comprehension processes are decomposable into separate subsystems, including distinct systems for semantic and grammatical processing. Here we report that event-related potentials (ERPs) to syntactically well-formed but semantically anomalous sentences produced a pattern of brain activity that is distinct in timing and distribution from the patterns elicited by syntactically deviant sentences, and further, that different types of syntactic deviance produced distinct ERP patterns. Forty right-handed young adults read sentences presented at 2 words/sec while ERPs were recorded from over several positions between and within the hemispheres. Half of the sentences were semantically and grammatically acceptable and were controls for the remainder, which contained sentence medial words that violated (1) semantic expectations, (2) phrase structure rules, or (3) WH-movement constraints on Specificity and (4) Subjacency. As in prior research, the semantic anomalies produced a negative potential, N400, that was bilaterally distributed and was largest over posterior regions. The phrase structure violations enhanced the N125 response over anterior regions of the left hemisphere, and elicited a negative response (300-500 msec) over temporal and parietal regions of the left hemisphere. Violations of Specificity constraints produced a slow negative potential, evident by 125 msec, that was also largest over anterior regions of the left hemisphere. Violations of Subjacency constraints elicited a broadly and symmetrically distributed positivity that onset around 200 msec. The distinct timing and distribution of these effects provide biological support for theories that distinguish between these types of grammatical rules and constraints and more generally for the proposal that semantic and grammatical processes are distinct subsystems within the language faculty.

CROSS-MODAL PLASTICITY: WHERE AND HOW?

Animal studies have shown that sensory deprivation in one modality can have striking effects on the development of the remaining modalities. Although recent studies of deaf and blind humans have also provided convincing behavioural, electrophysiological and neuroimaging evidence of increased capabilities and altered organization of spared modalities, there is still much debate about the identity of the brain systems that are changed and the mechanisms that mediate these changes. Plastic changes across brain systems and related behaviours vary as a function of the timing and the nature of changes in experience. This specificity must be understood in the context of differences in the maturation rates and timing of the associated critical periods, differences in patterns of transiently existing connections, and differences in molecular factors across brain systems.

Maturational constraints on functional specializations for language processing: Erp and behavioral evidence in bilingual speakers

Changes in several postnatal maturational processes during neural development have been implicated as potential mechanisms underlying critical period phenomena. Lenneberg hypothesized that maturational processes similar to those that govern sensory and motor development may also constrain capabilities for normal language acquisition. Our goal, using a bilingual model, was to investigate the hypothesis that maturational constraints may have different effects upon the development of the functional specializations of distinct sub within language. Subjects were 61 adult Chinese/English bilinguals who were exposed to English at different points in development: 13, 46, 710, 1113, and after 16 years of age. Event-related brain potentials (ERPs) and behavioral responses were obtained as subjects read sentences that included semantic anomalies, three types of syntactic violations (phrase structure, specificity constraint, and subjacency constraint), and their controls. The accuracy in judging the grammaticality for the different types of syntactic rules and their associated ERPs was affected by delays in second language exposure as short as 13 years. By comparison the N400 response and the judgment accuracies in detecting semantic anomalies were altered only in subjects who were exposed to English after 1113 and 16 years of age, respectively. Further, the type of changes occurring in ERPs with delays in exposure were qualitatively different for semantic and syntactic processing. All groups displayed a significant N400 effect in response to semantic anomalies, however, the peak latencies of the N400 elicited in bilinguals who were exposed to English between 1113 and >16 years occurred later, suggesting a slight slowing in processing. For syntactic processing. the ERP differences associated with delays in exposure to English were observed in the morphology and distribution of components. Our findings are consistent with the view that maturational changes significantly constrain the development of the neural systems that are relevant for language and, further, that subsystems specialized for processing different aspects of language display different sensitive periods.

Auditory and Visual Semantic Priming in Lexical Decision: A Comparison Using Event-related Brain Potentials

Abstract This study compared and contrasted semantic priming in the visual and auditory modalities using event-related brain potentials (ERPs) and behavioural measures (errors and reaction time). Subjects participated in two runs (one visual, one auditory) of a lexical decision task where stimuli were word pairs consisting of “prime” words followed by equal numbers of words semantically related to the primes, words unrelated to the primes, pseudo-words, and nonwords. Subjects made slower responses, made more errors, and their ERPs had larger negative components (N400) to unrelated words than to related words in both modalities. However, the ERP priming effect began earlier, was larger in size, and lasted longer in the auditory modality than in the visual modality. In addition, the lateral distribution of N400 over the scalp differed in the two modalities. It is suggested that there may be overlap in the priming processes that occur in each modality but that these processes are not identical. The results a...

Improved auditory spatial tuning in blind humans

Despite reports of improved auditory discrimination capabilities in blind humans and visually deprived animals, there is no general agreement as to the nature or pervasiveness of such compensatory sensory enhancements. Neuroimaging studies have pointed out differences in cerebral organization between blind and sighted humans, but the relationship between these altered cortical activation patterns and auditory sensory acuity remains unclear. Here we compare behavioural and electrophysiological indices of spatial tuning within central and peripheral auditory space in congenitally blind and normally sighted but blindfolded adults to test the hypothesis (raised by earlier studies of the effects of auditory deprivation on visual processing,) that the effects of visual deprivation might be more pronounced for processing peripheral sounds. We find that blind participants displayed localization abilities that were superior to those of sighted controls, but only when attending to sounds in peripheral auditory space. Electrophysiological recordings obtained at the same time revealed sharper tuning of early spatial attention mechanisms in the blind subjects. Differences in the scalp distribution of brain electrical activity between the two groups suggest a compensatory reorganization of brain areas in the blind that may contribute to the improved spatial resolution for peripheral sound sources.

Attention to central and peripheral visual space in a movement detection task: an event-related potential and behavioral study. I. Normal hearing adults.

The effects of focussed attention to peripherally and centrally located visual stimuli were compared via an analysis of event-related brain potentials (ERPs) while subjects detected the direction of motion of a white square in a specified location. While attention to both peripheral and foveal stimuli produced enhancements of the early ERP components, the distribution over the scalp of the attention-related changes varied according to stimulus location. The attention-related increase in the amplitude of the N1 wave (157 ms) to the peripheral stimuli was greater over the parietal region of the hemisphere contralateral to the attended visual field. By contrast, the largest effects of foveally directed attention occurred over the occipital regions where the increase was bilaterally symmetrical. Additionally, the effects of attention on the ERPs were significantly larger for moving than for stationary stimuli, and this effect was greater for peripheral than for central attention. A long-latency positive displacement component (300-600 ms) was larger over the right than the left hemisphere during attention to the lateral visual fields, but was symmetrical in amplitude when central stimuli were attended. These results suggest that different pathways are modulated when attention is deployed to different regions of the visual fields. Further, they suggest that the special role of the right hemisphere in spatial attention may be limited to analysis of information in the visual periphery.

Event-related brain potentials during initial encoding and recognition memory of congruous and incongruous words

Abstract Event-related brain potentials (ERPs) were recorded while subjects read statements followed by words that were either semantically congruous or incongruous with the preceding phrase, and during a subsequent recognition test. Congruous words yielded smaller N400s and better memory than did incongruous statements. In addition, the ERPs to correctly recognized old words were characterized by an enhanced late positivity (P650) relative to those elicited by correctly identified new words. A second experiment essentially replicated the results of the first. In addition, the amplitude of the late positive component (P650) elicited by final words on initial exposure was predictive of subsequent recognition; words that would be later recognized were associated with a larger P650 (whether they were incongruous or not) than were words that would not be recognized. These ERP data provide evidence that within 250 ms of the presentation of a congruous word and within 450 ms of an incongruous word, a significant portion of the brain processes which determine whether a word will or will not be recognized some time in the future have taken place.

The neurobiology of sensory and language processing in language-impaired children

Clinical, behavioral, and neurophysiological studies of developmental language impairment (LI), including reading disability (RD), have variously emphasized different factors that may contribute to this disorder. These include abnormal sensory processing within both the auditory and visual modalities and deficits in linguistic skills and in general cognitive abilities. In this study we employed the event-related brain potential (ERP) technique in a series of studies to probe and compare Merent aspects of functioning within the same sample of LI/RD children. Within the group multiple aspects of processing were affected, but heterogeneously across the sample. ERP components linked to processing within the superior temporal gyrus were abnormal in a subset of children that displayed abnormal performance on an auditory temporal discrimination task. An early component of the visual ERP was reduced in amplitude in the group as a whole. The relevance of this effect to current conceptions of substreams within the visual system is discussed. During a sentence processing task abnormal hemispheric specialization was observed in a subset of children who scored poorly on tests of grammar. By contrast the group as a whole displayed abnormally large responses to words requiring contextual integration. The results imply that multiple factors can contribute to the profile of language impairment and that different and specific deficits occur heterogeneously across populations of LI/RD children.

Speech processing activates visual cortex in congenitally blind humans

Neurophysiological recordings and neuroimaging data in blind and deaf animals and humans suggest that perceptual functions may be organized differently after sensory deprivation. It has been argued that neural plasticity contributes to compensatory performance in blind humans, such as faster speech processing. The present study employed functional magnetic resonance imaging (fMRI) to map language‐related brain activity in congenitally blind adults. Participants listened to sentences, with either an easy or a more difficult syntactic structure, which were either semantically meaningful or meaningless. Results show that blind adults not only activate classical left‐hemispheric perisylvian language areas during speech comprehension, as did a group of sighted adults, but that they additionally display an activation in the homologueous right‐hemispheric structures and in extrastriate and striate cortex. Both the perisylvian and occipital activity varied as a function of syntactic difficulty and semantic content. The results demonstrate that the cerebral organization of complex cognitive systems such as the language system is significantly shaped by the input available.

Visual and auditory sentence processing: A developmental analysis using event‐related brain potentials

Subjects aged 5 to 26 years listened to and read (7 to 26 years) sentences that ended either with a highly expected (best completion) or a semantically inappropriate (anomalous completion) word. Event‐related potentials (ERPs) to sentence final words displayed effects of contextual priming in both modalities in all age groups. Early and late ERP components displayed large decreases in amplitude and latency with age. These changes necessitated normalization procedures so that overall changes in amplitude with age could be assessed separately from changes in the amplitude of the differences between best‐completion and anomalous‐completion words. There were significant reductions in the contextual priming effects with age. Moreover, these age‐related changes were different for the auditory and visual modalities, and for the early and later phases of the priming effect. These results suggest that nonidentical systems, with different developmental time courses, generate the early and late priming effects in th...