Abstract
Half of the global population can be considered bilingual. Nevertheless when faced with patients with aphasia, clinicians and therapists usually ignore the patient’s second language (L2) albeit its interference in first language (L1) processing has been shown. The excellent temporal resolution by which each individual linguistic component can be gaged during word-processing, promoted the event-related potential (ERP) technique for studying language processing in healthy bilinguals and monolingual aphasia patients. However, this technique has not yet been applied in the context of bilingual aphasia. In the current study, we report on L2 interference in L1 processing using the ERP technique in bilingual aphasia. We tested four bilingual- and one trilingual patients with aphasia, as well as several young and older (age-matched with patients) healthy subjects as controls. We recorded ERPs when subjects were engaged in a semantic association judgment task on 122 related and 122 unrelated Dutch word-pairs (prime and target words). In 61 related and 61 unrelated word-pairs, an inter-lingual homograph was used as prime. In these word-pairs, when the target was unrelated to the prime in Dutch (L1), it was associated to the English (L2) meaning of the homograph. Results showed a significant effect of homograph use as a prime on early and/or late ERPs in response to word-pairs related in Dutch or English. Each patient presented a unique pattern of L2 interference in L1 processing as reflected by his/her ERP image. These interferences depended on the patient’s pre- and post-morbid L2 proficiency. When the proficiency was high, the L2 interference in L1 processing was higher. Furthermore, the mechanism of interference in patients that were pre-morbidly highly proficient in L2 additionally depended on the frequency of pre-morbid L2 exposure. In summary, we showed that the mechanism behind L2 interference in L1 processing in bilingual patients with aphasia depends on a complex interaction between pre- and post-morbid L2 proficiency, pre- and post-morbid L2 exposure, impairment and the presented stimulus (inter-lingual homographs). Our ERP study complements the usually adopted behavioral approach by providing new insights into language interactions on the level of individual linguistic components in bilingual patients with aphasia.
Highlights
The incidence rate of bilingual aphasia is keeping pace with the increase in bilingualism which is currently exceeding 50% of the global population (Grosjean, 1994)
When running repeated measure analysis of variance (ANOVA) on performance accuracy of English word-pairs with relatedness as independent effect, we observed a significant effect of relatedness for all three groups: young healthy F(1,8) = 8.69, p = 0.018, older healthy group F(1,12) = 17.14, p = 0.001, and patients (4 bilingual patients) F(1,6) = 56.5, p = 0.0003)
A repeated measure ANOVA on performance accuracies for the Dutch stimulus list with homograph prime, relatedness, and their (RxH) interaction as independent factors showed a significant effect of homograph prime for young controls [F(1,16) = 16.18, p = 0.001], older controls [F(1,24) = 11.35, p = 0.0025] and patients [F(1,12) = 25.34, p = 0.0003]
Summary
The incidence rate of bilingual aphasia is keeping pace with the increase in bilingualism which is currently exceeding 50% of the global population (Grosjean, 1994). The interference of L2 in L1 processing was studied repetitively for healthy bilinguals using both electrophysiological (EEG, MEG) and behavioral methods (Caramazza and Brones, 1979; Midgley et al, 2008; Martin et al, 2009). For bilingual patients with aphasia this issue was studied using behavioral methods only (Kiran and Iakupova, 2011; Siyambalapitiya et al, 2013; Kiran et al, 2014). According to these studies, L2 interference and language interaction in general depends on a complex interaction between pre- and post-morbid proficiency levels, impairment location, severity level and type of developed aphasia. We will report here on results obtained from patients who were less proficient in their L2 both before and after the development of aphasia (L1 dominant) and acquired their L2 when they were around 10 – 12 years old (late bilinguals)
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