Language processing in bilingual aphasia: a new insight into the problem.

There is increasing evidence that a bilingual person should not be considered as two monolinguals in a single body, a view that has gradually been adopted in the diagnosis and treatment of bilingual aphasia. However, its investigation is complicated due to the large variety in possible language combinations, pre- and postmorbid language proficiencies, and age of second language acquisition. Furthermore, the tests and tasks used to assess linguistic capabilities differ in almost every study, hindering a direct comparison of their outcomes. Behavioral, electrophysiological, and neuroimaging data from healthy population show that the processing of second language domains (semantics, syntax, morphology) depends on factors such as age and method of acquisition, proficiency level and environment in which the second language was acquired. A number of single and multiple case reports that rely on behavioral testing of bilingual aphasics replicate these results. Additionally, they show that the patient's performance depends on the size and location of the lesion, as well as language typology and morphological characteristics. Furthermore, the impairment and recovery patterns and recovery generalization from treated to untreated language depend on the lexical and orthographic distances between the two languages. For healthy bilinguals, language processing is usually studied in comparison to monolinguals. We advocate that a good starting point for identifying patterns specific for bilingual aphasia is to compare patient studies of bilinguals and monolinguals.

Sentence Context Prevails Over Word Association in Aphasia Patients with Spared Comprehension: Evidence from N400 Event-Related Potential.

Behavioral and event-related potential (ERP) studies on aphasia patients showed that lexical information is not lost but rather its integration into the working context is hampered. Studies have been conducted on the processing of sentence-level information (meaningful versus meaningless) and of word-level information (related versus unrelated) in aphasia patients, but we are not aware of any study that assesses the relationship between the two. In healthy subjects the processing of a single word in a sentence context has been studied using the N400 ERP. It was shown that, even when there is only a weak expectation of a final word in a sentence, this expectation will dominate word relatedness. In order to study the effect of semantic relatedness between words in sentence processing in aphasia patients, we conducted a crossed-design ERP study, crossing the factors of word relatedness and sentence congruity. We tested aphasia patients with mild to minimum comprehension deficit and healthy young and older (age-matched with our patients) controls on a semantic anomaly judgment task when simultaneously recording EEG. Our results show that our aphasia patient's N400 amplitudes in response to the sentences of our crossed-design study were similar to those of our age-matched healthy subjects. However, we detected an increase in the N400 ERP latency in those patients, indicating a delay in the integration of the new word into the working context. Additionally, we observed a positive correlation between comprehension level of those patients and N400 effect in response to meaningful sentences without word relatedness contrasted to meaningless sentences without word relatedness.

A comparison of two spelling Brain-Computer Interfaces based on visual P3 and SSVEP in Locked-In Syndrome.

OBJECTIVES: We study the applicability of a visual P3-based and a Steady State Visually Evoked Potentials (SSVEP)-based Brain-Computer Interfaces (BCIs) for mental text spelling on a cohort of patients with incomplete Locked-In Syndrome (LIS). METHODS: Seven patients performed repeated sessions with each BCI. We assessed BCI performance, mental workload and overall satisfaction for both systems. We also investigated the effect of the quality of life and level of motor impairment on the performance. RESULTS: All seven patients were able to achieve an accuracy of 70% or more with the SSVEP-based BCI, compared to 3 patients with the P3-based BCI, showing a better performance with the SSVEP BCI than with the P3 BCI in the studied cohort. Moreover, the better performance of the SSVEP-based BCI was accompanied by a lower mental workload and a higher overall satisfaction. No relationship was found between BCI performance and level of motor impairment or quality of life. CONCLUSION: Our results show a better usability of the SSVEP-based BCI than the P3-based one for the sessions performed by the tested population of locked-in patients with respect to all the criteria considered. The study shows the advantage of developing alternative BCIs with respect to the traditional matrix-based P3 speller using different designs and signal modalities such as SSVEPs to build a faster, more accurate, less mentally demanding and more satisfying BCI by testing both types of BCIs on a convenience sample of LIS patients.