A review on the electroencephalography markers of Stroop executive control processes

The present article on executive control addresses the issue of the locus of the Stroop effect by examining neurophysiological components marking conflict monitoring, interference suppression, and conflict resolution. Our goal was to provide an overview of a series of determining neurophysiological findings including neural source reconstruction data on distinct executive control processes and sub-processes involved in the Stroop task. Consistently, a fronto-central N2 component is found to reflect conflict monitoring processes, with its main neural generator being the anterior cingulate cortex (ACC). Then, for cognitive control tasks that involve a linguistic component like the Stroop task, the N2 is followed by a centro-posterior N400 and subsequently a late sustained potential (LSP). The N400 is mainly generated by the ACC and the prefrontal cortex (PFC) and is thought to reflect interference suppression, whereas the LSP plausibly reflects conflict resolution processes. The present overview shows that ERP constitute a reliable methodological tool for tracing with precision the time course of different executive processes and sub-processes involved in experimental tasks involving a cognitive conflict. Future research should shed light on the fine-grained mechanisms of control respectively involved in linguistic and non-linguistic tasks

The neural underpinnings of shared meaning between speakers and listeners of naturalistic language

Speakers and listeners usually interact in larger discourses than single words or even single sentences. The goal of the present study was to identify the neural bases reflecting how the mental representation of the situation denoted in a multi-sentence discourse (situation model) is constructed and shared between speakers and listeners. An fMRI study using a variant of the ambiguous text paradigm was designed. Speakers (n=15) produced ambiguous texts in the scanner and listeners (n=27) subsequently listened to these texts in different states of ambiguity: preceded by a highly informative, intermediately informative or no title at all. Conventional BOLD activation analyses in listeners, as well as inter-subject correlation analyses between the speakers’ and the listeners’ hemodynamic time courses were performed. Critically, only the processing of disambiguated, coherent discourse with an intelligible situation model representation involved (shared) activation in bilateral lateral parietal and medial prefrontal regions. This shared spatiotemporal pattern of brain activation between the speaker and the listener suggests that the process of memory retrieval in medial prefrontal regions and the binding of retrieved information in the lateral parietal cortex constitutes a core mechanism underlying the communication of complex conceptual representations

Perception of non-native sounds in a second language: Electrophysiological evidence of neuroplasticity in the phonological system

Second language learners frequently encounter difficulty in perceiving specific non-native sound contrasts. This phenomenon called phonological deafness rather occurs if the second language (L2) is learned after early childhood and is quite persistent even when high L2 proficiency is attained (Dupoux et al., 2008). However, if the neuronal underpinnings of phonological processing are plastic to a certain degree, late L2 learners should be able to reach the capacity to distinguish non-native phonemic contrasts (Best & Strange, 1992; Flege et al., 1997; Iverson et al., 2012). In the present study, our goal was to examine the extent to which the phonological system in late L2 learners is adaptable. We designed an ERP experiment in which the capacity to discriminate second language phonemic contrasts mediated lexical access. We used a semantic violation paradigm in which the difference between semantically congruent and incongruent items was implemented by a phonemic contrast that was unique to the second language, English, but absent in the first language, French (e.g., /ɪ/ - /i/: ship – sheep). Twelve young adult native speakers of French with intermediate proficiency in English participated in the ERP experiment. Participants heard sentences that contained either a semantically congruent item (e.g., The anchor of the ship was let down) or an incongruent one (e.g., *The anchor of the sheep was let down) and were asked to perform a grammaticality judgement. Preliminary results reveal that second language learners of English showed a larger centro-parietal negativity between 300-500 ms after the onset of semantically incongruent words as compared to congruent target words, i.e. an N400 effect. This finding indicates that L2 learners were sensitive to the semantic incongruency mediated by a phonemic contrast. Critically, the N400 effect size varied as a function of L2 proficiency, i.e. the more proficient the participants, the larger the N400 effect size. Thus, the sensitivity to phonemic contrasts of a second language seems to play a significant role in lexical access. With an increasing capacity to discriminate second language phonemic contrasts, the access to lexical information is facilitated. These findings show that even late learners of a second language can develop a perceptual sensitivity to discriminate non-native sound contrasts, at least at the segmental phonological level, which also indicates that neuroplasticity in the phonological system allows for a certain adaptation to linguistic environmental constraints. Further investigations should explore how targeted training can improve the sensitivity to second language phonemic contrasts