Completed Research ProjectsEEG studies of Childhood Apraxia of Speech
Following up on published pilot research (Froud and Khamis-Dakwar, 2012) this study investigates the hypothesis that childhood apraxia of speech (CAS) results, in part, from phonological overspecification. This hypothesis challenges current approaches to diagnosis and intervention for this speech disorder, which is widely thought to affect only motor aspects of production. For this experiment, high-density EEG is used to record the brain responses of children with CAS and age-matched controls, ages 5-7 years, as they listen to randomized sequences of sounds in four oddball paradigms: phonemic (/ba/, /pa/), allophonic (/pa/, /pha/), nonspeech complex sounds (modified lemur calls) and pure tones. In our pilot study, mismatch negativity (MMN) responses to oddball sounds in the phonemic contrast condition (/ba /, /pa/ ), were observed for the typically developing (comparison) group but not the CAS group, although a component similar to an immature mismatch response was apparent. The allophonic contrast (/pa/, /pha/) did not elicit MMN responses in the comparison group, but in the CAS group, an MMN-like response was observed. These preliminary findings are consistent with a view of CAS as aEEG studies of Childhood Apraxia of Speech Following up on published pilot research (Froud and Khamis-Dakwar, 2012) this study investigates the hypothesis that childhood apraxia of speech (CAS) results, in part, from phonological overspecification. This hypothesis challenges current approaches to diagnosis and intervention for this speech disorder, which is widely thought to affect only motor aspects of production. For this experiment, high-density EEG is used to record the brain responses of children with CAS and age-matched controls, ages 5-7 years, as they listen to randomized sequences of sounds in four oddball paradigms: phonemic (/ba/, /pa/), allophonic (/pa/, /pha/), nonspeech complex sounds (modified lemur calls) and pure tones. In our pilot study, mismatch negativity (MMN) responses to oddball sounds in the phonemic contrast condition (/ba /, /pa/ ), were observed for the typically developing (comparison) group but not the CAS group, although a component similar to an immature mismatch response was apparent. The allophonic contrast (/pa/, /pha/) did not elicit MMN responses in the comparison group, but in the CAS group, an MMN-like response was observed. These preliminary findings are consistent with a view of CAS as a disorder that not only affects motor planning but also has a phonological component. Explorations like these, that shed light on the underlying causes of speech sound disorders, could be relevant to the development of new diagnostic and therapeutic approaches to these populations.
Neurophysiology of Scientific Reasoning and Concept Formation
In this study, EEG was used to record the brain activity of adults while they engaged in problem solving using model-based and rule-based reasoning strategies. Event-Related Potentials (ERPs) known to be associated with semantic (N400) and syntactic (P600) processing in language (Kutas & Hillyard, 1980a; Osterhout & Holcomb, 1992) were shown to be elicited by the specific, but different mental representational systems thought to underpin model-based and rule-based reasoning, respectively. Examination of these ERPs yielded information about the scalp topography and mental timeline of the representational systems underlying problem solving, offering insight into the sub-processes that make up the complex tasks underpinning reasoning. Our ongoing investigation of the N400 and P600 as neurophysiological markers of these two different modes of reasoning is important because other research has shown that the human ability to form and switch between multiple representations is paramount in scientific concept formation and discovery (Neressian, 2008).
We are now building on this study with the aims to: 1) Examine the neuronal sources and spatial properties of the ERP signatures of different modes of reasoning; and 2) Investigate the same responses for children and adolescents as they process scientific problems. The intended outcome is a developmental trajectory of scientific reasoning from childhood to adulthood, that will allow us to develop an understanding of some of the interactions between brain maturation and education level. This information will provide education leaders, researchers and teachers with crucial information about the developing neural substrates of scientific reasoning and problem solving, better preparing them to shape educational experiences to support the acquisition of competencies in this domain.
Word Recognition Automaticity in Reading
This study examines fast word recognition process in neoliterate adults (those who recently learned to read through adult education programs), to evaluate whether they show evidence of perceptual (automatic) distinctions between linguistic and visual stimuli (words vs. symbols). Such a mechanism is thought to be the basis for effortless reading, and is known to be associated with activation in the brain's Visual Word Form Area, a region of cortex that becomes "tuned" to scripts as literacy skills are acquired (McCandliss, Cohen, & Dehaene, 2003). High density EEG was recorded from a group of neoliterate adults while they carried out two reading tasks: (1) a one-back task requiring implicit reading (available only to those who have attained automaticity), and (2) reading verification task, an explicit reading task, in which participants detected mismatches between pairs of visual and auditory words. Results were compared to recordings from a comparison group of adults who learned to read in childhood. The left-lateralized N170 ERP was targeted as an index of automaticity in reading. Participants from the comparison group showed a left-lateralized N170 to word stimuli in both the implicit and explicit reading tasks, indicating that their Visual Word Form Area is tuned in to the written script and allows them to carry out fast, automatic reading processes. Conversely, the N170 from the neoliterate group was more widespread, involving the right hemisphere of the brain as well as the left - an indication that specialization of the Visual Word Form Area has not taken place. Adult literacy training is known to be difficult in terms of teaching and maintenance (Abadzi, 2003). Our findings suggest that this could be due to a lack of brain reorganization to support automatic reading, and this experimental approach offers the potential for a new way to evaluate the effectiveness of adult literacy programs.
Perception of American English vowels by adult Spanish-English bilingual listeners
It is well known that difficulties in processing the sounds of a second language can lead to difficulties in community participation for minority populations. Some second language vowel sounds are more challenging to learn than others depending on a number of factors such as the characteristics of the first language, and how it relates to the second language, the age of acquisition of the second language, the exposure to the second language environment, among others. We looked at how the brains of Spanish-speaking learners of English handle English vowels, especially difficult contrasts that are different from the vowels in Spanish. Findings indicate that second language learners have additional challenges, because their brains are organized to respond to vowels in ways that are specific to their L1. Learning new vowel contrasts requires reorganization, which takes a lot more exposure and more focused training than has previously been understood. The ultimate goal of this project is to develop perceptual training strategies that facilitate adult second language vowel perception.
If language ability is used to categorize children with Autism Spectrum Disorders, how might we identify children at-risk earlier in language development? Current recommendations for diagnosis of Autism Spectrum Disorders rely on determining whether a concomitant language impairment is present. It is very difficult to identify specific ASD type before an age when language delays are apparent; as a result, children with ASD go without intervention until, on average, 3 years of age or older. The ability to identify language impairment earlier in development is essential for achieving more timely and specific diagnoses and interventions for at-risk children. However, in order to achieve this, methods for examining language processing in young children must go beyond the behavioral observations permitted by most current assessments.
EEG studies of Childhood Apraxia of Speech (Karen Froud, Reem Khamis-Dakwar, Melissa Randazzo)
Childhood apraxia of speech (CAS) is variously understood as a deficit of movement, motor planning or phonological representations. Underspecification theory suggests that CAS may involve abnormally specified phonological representations. In this case, simple phoneme recognition tasks should be more difficult in CAS, and this would be evident using neurophysiological indices of early auditory processing. We use EEG to compare neurophysiological responses to phonemic (/ba/, /pa/) and allophonic (/pa/, /pha/) contrasts in children with CAS and typically-developing peers. We hope that our findings will increase understanding of the underlying cause of CAS, and therefore eventually improve treatment.
Magnetoencephalographic studies of lexical processing and formal thought disorder in schizophrenia (Karen Froud)
This research, funded by the National Alliance for Research on Schizophrenia and Depression, is using MEG to examine aspects of lexical access in the brains of schizophrenic adults. Lexical access is known to be subserved by the temporal lobe, which is often impacted - anatomically as well as functionally - in schizophrenia. We can manipulate the speed of word recognition by asking people to respond to words which are more or less frequently used in the language, or which have been semantically primed (preceded by words related in meaning). We have observed that schizophrenic adults often show the same effects of lexical frequency and semantic priming as control participants, but the brain activations associated with these effects in schizophrenic brains reveal that different pathways and mechanisms may be involved. This work is being conducted in collaboration with colleagues at the KIT/MIT MEG Lab, the Psychology Research Lab at McLean Hospital, and the McGill University Language and Memory Lab.
Effects of diglossic codeswitching and semantic coherence in speakers of Modern Arabic (Reem Khamis-Dakwar)
Using EEG, this study is investigating lexical and syntactic processing in codeswitching between two language varieties which exist in a diglossic situation (Modern Standard Arabic (MSA) and Colloquial Palestinian Arabic (PCA)). We present sentences in PCA and MSA: grammatical sentences in the targeted variety, sentences with semantically anomalous final words, sentences with codeswitched final words, and sentences where the final word was both semantically anomalous and code-switched. We ask participants to judge whether the final word is in the same language as the rest of each sentence. Event-related potentials in response to the four conditions in each language variety, and between the two language varieties, showed that differences in N400 amplitude correlated with semantic anomaly in both languages, whereas the codeswitching manipulation resulted in a variety of changes both earlier (ELAN: 100-300 milliseconds post-onset) and later (P600: 500-700 milliseconds post-onset) in the processing stream. We need native speakers of Palestinian Arabic to participate in this study - if you're interested, please fill in the volunteer form (including information about your native language).
The Influence of L1 Properties on the Storage of L2 Parsing Knowledge in Procedural Memory: An ERP Study (J.D. Purdy)
Second-language learners may store their knowledge of target-language rules of syntax in explicit (declarative) or implicit (procedural) memory. In this study, sentences containing violations of English-language word order are presented to learners of English as a second language. The derivational suffixes of the target words indicate the words' syntactic category.Subjects consist of a group of speakers of Hungarian, a language that also signals word category through derivational morphology, and a group of speakers of Chinese, a language that does not mark syntactic category morphologically. Preliminary results indicate that both groups generate an early left anterior negativity (ELAN) in response to word-category violations in the second language. Further studies are needed to determine whether this implicit knowledge of syntactic-structure-building is integrated with other second-language knowledge, or is the result of stand-alone probabilistic classification learning.
Effects of motivation on P300 amplitude in children (Laura Sánchez)
In this research we used P300 amplitude to give an objective measure of attentional allocation in typically-developing children aged 8-12 years. P300 was elicited through two oddball paradigms: with and without explicit motivational instructions. P300 amplitude was found to be greater in the motivated condition than the not-motivated condition, suggesting recruitment of more attentional resources to the oddball detection task when children were more motivated. Interestingly, increased amplitude in the motivated condition was seen in response to both standard and deviant stimuli, possibly reflecting that children were not just paying more attention to the deviant stimuli in order to complete the task more effectively; they were also paying more attention to even irrelevant stimuli, when their levels of motivation were increased. These results have the potential to increase our understanding of the importance of motivation for engaging children in educational and therapeutic tasks.
Speech perception in late Spanish-Enlgish bilinguals - an EEG study of vowel recognition (Paula Garcia)
This study examines the perception of the English vowel contrast /i/ vs. /I/ by native Spanish speakers. Speech perception studies have revealed that perception of foreign vowels is influenced by the phoneme categories in the native language. Some native Spanish speakers find it difficult to discriminate /i/ and /I/, and they often report identifying both vowels as a single Spanish vowel. In two auditory oddball paradigms, participants were asked (a) to ignore and (b) to attend to binaurally presented English vowel sounds. Event-related potential analyses revealed a more anterior N100 response to the native than the non-native vowels in the non-attentional condition, though there was no significant amplitude difference between the two (hence, no mismatch negativity effect). This pattern of responses may be consistent with previous research showing that activation of the auditory what stream is involved in analysis of phonological features of the speech stream. In the attentional condition, the P300 showed increased amplitudes in response to the non-native vowels when compared to the native vowels; this amplitude difference was not seen in native English-speaking controls, and may provide an index of allocation of additional attentional resources to a less familiar sound. Our results suggest that there is a process of assimilation at play in L2 perception, by which non-native phonemic contrasts are assimilated to L1 contrasts. This could have implications for pedagogical approaches to second language learning, since phonemic contrasts which cannot be perceived are concomitantly more difficult to acquire.