Completed Research Projects
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.