Active Research Projects
We conduct experiments examining the neural underpinnings of aspects of language and cognitive processing, in typically developing children and adults as well as those exhibiting atypical or pathological development utilizing combinations of behavioral and electrophysiological techniques. This page provides short summaries of our current and recent research projects.
If you would like to participate in any of these studies, please visit the volunteer page.
EEG 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.
Effects of diglossic codeswitching and semantic coherence in speakers of Modern Arabic
This study uses EEG to investigate 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)). Study participants are presented with 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. Participants are asked to judge whether the final word is in the same language as the rest of each sentence. Brain responses 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. These results for the first time provide insight into the organization of diglossic languages in the brain; even though the speakers of such languages experience them as being closely related, this evidence suggests that diglossic languages are separate from one another but might differ in the strength of their connections at different levels of representation (phonological, lexical, semantic and syntactic).
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.
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.
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.
Biomarkers for early intervention with children at-risk for Autism.
Children with autism spectrum disorders (ASD) have many challenges to overcome, and those who also have a communication impairment are at even greater risk for being unable to learn basic social and educational skills. However, identifying language problems is very difficult in young children, and current methods require that a child have language or be “of language age” in order to participate. Finding an early and objective way to identify language problems in ASD could help lead to earlier intervention and hence better outcomes. Some studies have attempted to find a brain signature of language processing that could be used to identify which children at risk for ASD might benefit from early language intervention, but the methods used are expensive and difficult to interpret. Using EEG, which is readily available and much easier for young children to tolerate, we propose an investigation of the Mismatch Negativity (MMN), a brain response that is related to speech sound identification. We will record EEG in children aged 6-10 years who have ASD, with and without commuication impairment. The children will listen to various sounds, including pure tones, speech sounds and complex non-speech sounds. We predict that children with ASD and language imapirment will show differences in their brain responses to the speech sounds, and this will help us to establish whether the same measure can be used to predict language probelms in much younger children, even infants, who are at risk for ASD. In trun, this information will help us to establish a new set of criteria for accessing early language intervention and support, potentially leading to much more positive outcomes for children and families affected by ASD,
Moving toward a neurophysiological understanding of dialectal variation: African American English and Standard American English syntax
Speakers of non-standard American English comprise a large majority of the speech therapy caseloads in public schools, and this study seeks to shed some light on our neurophysiological understanding of dialectal language differences - often misjudged as indicators of a language disorder. This experiment seeks to compare ERP responses to sentences in African American English (AAE) and Standard American English (SAE) between monolingual and bidialectal speakers. Adult participants in both groups will listen to sentences with the inclusion or omission of 3rd person present tense ‘-s’ marker, the absence of which is a syntactic violation to only SAE monolingual speakers (e.g., The black cat lap/s the milk). Preliminary findings from pilot research (Garcia, Froud & Khamis-Dakwar, 2013) indicate SAE speakers’ brains respond to the syntactic violation, while AAE/SAE speakers demonstrate no statistically significant difference between conditions. This suggests that AAE is represented in the brain as a linguistic system distinct from AAE - not simply as a different or less formal “register”. This perspective could help us to a better understanding of the difficulties encountered by children who are exposed to an English language variety at home that is syntactically and semantically different from the Standard American English used in school curriculums.
Exploring early visual sensory differences in dyslexia
Once referred to as “word blindness,” dyslexia is now understood to involve more than visual perception and for decades has been viewed as a linguistic problem relating to a phonological deficit. Described as an inability to achieve reading competency despite adequate motivation, cognition and sensory levels, and appropriate educational input, dyslexia affects 5-17% of the population. The characteristic deficits of the disorder are not clearly homogeneous and hence an underlying explanation continues to elude researchers, evaluators and remediation specialists, though various proposals are emerging.
One such proposal, the Magnocellular Theory of Developmental Dyslexia, posits deficits in magnocellular neurons in the brain as the underlying basis for developmental dyslexia. These “large cells” support the transmission of fast temporal, low-contrast sensory information. Although magnocellular neurons can be found in sensory and motor systems throughout the central nervous system, only the visual system has a distinct magnocellular pathway. Studies of the magnocellular pathway in the visual system suggest that this pathway follows a protracted course of development, raising the possibility that it is more vulnerable to pathological change during development as well as having greater potential for plasticity. These observations led to the suggestion that the magnocellular pathway might be implicated in developmental dyslexia.
In contrast to the magnocellular pathway, the visual system employs parvocellular systems (that have “small cells”) to process high frequency stimuli, such as color. In this study, we aim to establish whether magnocellular brain responses are compromised in people with dyslexia, in contrast to stimuli that are typically processed by the parvocellular pathways. Because the stimuli are “basic” in the sense of being pure visual (not alphabetic) percepts, this line of research may lead to procedures that are useful for very early (in infancy) identification of magnocellular changes. Such early identification could lead to pre-linguistic intervention - and hence perhaps prevention - for those at risk of developmental dyslexia.
Effects of mindfulness practices on executive function in school children
Research has supported the effectiveness of mindfulness training among adults on anxiety, attention, working memory, and executive function, a suite of skills used in the service of goal-directed behavior, which includes selective attention and inhibition. However there have been few investigations of the effects of mindfulness in young children. In the light of recent findings demonstrating the deleterious effects of poverty on educational attainment, cognitive development, attention and executive function, this study undertakes to evaluate the effects of mindfulness in kindergarten children. Using a Go/No-Go task designed to detect the ability to attend only to specified stimuli, we will record and analyze the brain responses of kindergarten children who have undertaken mindfulness training and compare them with their age-matched peers who have not had such experience. In keeping with our overall commitment to multi-modal investigations of cognitive processes, we will correlate the ERP findings related to executive function and attention with measures of stress hormones in saliva (cortisol and alpha amylase). It is hoped that these preliminary studies will provide a foundation for a larger-scale investigation that will focus on the effects of meditation on stress and language development in children of varying socioeconomic status.