Neurocognitive investigations in communication sciences and disorders: Breaking with tradition
Neuroscientific investigation in Communication Sciences and Disorders (CSD) is a developing field. In this presentation, we will introduce three studies of language representation in specific sociolinguistic situation or specific communication disorder utilizing EEG; an imaging technique with a high temporal resolution. We discuss how neuroscientific approaches to speech language pathology can elucidate brain processes underpinning communication, its disorders and discuss the need for more clinically oriented ERP studies in this field as part of evidence based practice framework.
The first research presentation used EEG to investigate the underlying neural representations associated with lexical and phonological levels of presentation in diglossia, a sociolinguistic phenomenon in which complementary social functions are distributed between formal and colloquial varieties of a language. The first study in this set, examines the neurofunctional bases of codeswitching between Modern Standard Arabic (MSA) and Colloquial Palestinian Arabic (PCA). Six native speakers of PCA listened to sentences from three experimental conditions: grammatical sentences in MSA or PCA, sentences with a semantically anomalous final word, and sentences with codeswitched final words. N400 amplitude increased with the presence of semantic anomaly in both MSA and PCA, whereas the codeswitching manipulation resulted in a variety of changes both earlier (N200) and later (P600) in the processing stream. The second study in this set used EEG to investigate the mismatch negativity (MMN) responses of native speakers of Levantine Arabic to switching between Spoken and Standard language varieties, while controlling for semantic, acoustic-phonetic, and phonological variables. Utilizing a passive-listening oddball paradigm, eighteen participants were presented with four real-word conditions: 1) PCA words with different meanings (PCA Ha? (right) - Had (border); 2) PCA and MSA words with the same meanings (PCA Ha?, MSA Haq (right); 3) switching between varieties and between meanings (PCA Ha?- MSA Hað (luck)); and 4) switching across languages (PCA fi:l (elephant): English feel). A significant MMN response was found in response to the phoneme category switch within language varieties. However, a significantly greater MMN response was found for variety shift (where the standard and deviant belong to two different language varieties but have the same meaning). These findings suggest that the switch between varieties has neurophysiological consequences over and above a phonemic category change.
The second research presentation used EEG to evaluate the overspecification of phonological representations hypothesis in Childhood Apraxia for Speech (CAS). We investigated auditory MMN responses from children with CAS and a group of typicallydeveloping peers (aged 6-7 years). CV syllables were presented in randomized order in two passive-listening oddball paradigms, phonemic (/ba/, /pa/) and allophonic (/pa/, / pha/), with /pa/ always representing the standard (240 trials per condition, 16% deviants). In the phonemic contrast condition increased MMN responses were associated with deviant stimuli for children in the comparison group but not children with CAS. The allophonic condition did not elicit greater MMN for the deviant in the comparison group, but in the CAS group, significant early positivity (P50) and MMN-like response to the deviant stimuli was observed. We propose that these preliminary findings are consistent with a view of CAS as a disorder affecting underlying phonological representations.
The third research study used EEG to examine neural correlates of phonological processing in internationally adopted (IA) children in the language that IA children were exposed to prior to adoption (LA) and the language of the environment (LE) .A recent meta-analytic examination of language skills in IA children, reveals that when children's language skills are examined during the toddler-preschool years, IA children appear to do well, but when language skills are examined during the school-age years (and beyond) there appears to be poorer performance in the IA children as opposed to their nonadopted peers (Scott et al., in submission). We investigated auditory MMN responses from IA participating children (3 to 5 years of age) adopted from China and exposed to LE for at least 2 years, and non-adopted monolingual participating children matched for age, under three sets of stimuli: a Cantonese only phonemic feature (/maai5/ (buy) & /maai6/(sell)) using tonal differences present in Mandarin and not in English. The second set is constructed to examine MMN responses to English features that are not represented in Cantonese (/mat/ vs. /mad). The third set represents English phonemic contrast evident in both languages (/mad/ and /man/). Based on preliminary results, enhanced MMN responses were observed for tonal differences in IA children and not for the control group.
We argue that clear understanding of language representation and processing in communication disorder or in specific sociolinguistic situation as well as the best intervention in these cases can be informed by neurophysiological investigations addressing unresolved issues in this field of research. ERP technique due to its high temporal resolution has the potential to highlight the temporal unfolding of neural events associated with different sub processes of language comprehension and production. Future directions for studies incorporating ERP in combination with other behavioral methods to examine clinical questions about assessment, intervention planning, or effects of intervention will enable a deeper understanding of language disorder, and language learning in a specific communication disorder or difference