The bilingual brain: cerebral representation of languages.

The present article deals with theoretical and experimental aspects of language representation in the multilingual brain. Two general approaches were adopted in the study of the bilingual brain. The study of bilingual aphasics allows us to describe dissociations and double dissociations between the different subcomponents of the various languages. Furthermore, symptoms peculiar to bilingual aphasia were reported (pathological mixing and switching and translations disorders) which allowed the correlation of some abilities specific to bilinguals with particular neurofunctional systems. Another approach to the study of the bilingual brain is of the experimental type, such as electrophysiological investigations (electrocorticostimulation during brain surgery and event-related potentials) and functional neuroanatomy studies (positron emission tomography and functional magnetic resonance imaging). Functional neuroanatomy studies investigated the brain representation of languages when processing lexical and syntactic stimuli and short stories. Neurophysiologic and neuroimaging studies evidenced a similar cerebral representation of L1 and L2 lexicons both in early and late bilinguals. The representation of grammatical aspects of languages seems to be different between the two languages if L2 is acquired after the age of 7, with automatic processes and correctness being lower than those of the native language. These results are in line with a greater representation of the two lexicons in the declarative memory systems, whereas morphosyntactic aspects may be organized in different systems according to the acquisition vs learning modality.     

Sensitivity of event-related brain potentials to task rules

Previous studies have suggested that brain potentials evoked around 300 ms after stimulus onset index the processes underlying perceptual decision-making. However, the sensitivity of these evoked potentials to the task rules, which link sensory perception to the proper action, has not been studied previously. In this study, event-related potentials (ERPs) of the human brain were examined when subjects randomly performed delayed-matching-to-identity (DMI) and delayed-matching-to-category (DMC) tasks. The results showed that the amplitudes of the brain potentials evoked 228–328 ms after test-stimulus onset varied according to the task rules and indexed the processes responsible for decision-making. In contrast to these potentials, the preceding evoked activity (< 228 ms) did not show any sensitivity to the changes in the subjects’ responses and indexed the processes responsible for stimulus perception. These findings support the idea that the potentials evoked after 228 ms from stimulus onset are influenced by the task rules and do not index simple sensory perception.     

Two faces,two languages: An fMRI study of bilingual picture naming

This fMRI study explores how nonlinguistic cues modulate lexical activation in the bilingual brain. We examined the influence of face race on bilingual language production in a picture-naming paradigm. Chinese–English bilinguals were presented with pictures of objects and images of faces (Asian or Caucasian). Participants named the picture in their first or second language (Chinese or English) in separate blocks. Face race and naming language were either congruent (e.g., naming in Chinese when seeing an Asian face) or incongruent (e.g., naming in English when seeing an Asian face). Our results revealed that face cues facilitate naming when the socio-cultural identity of the face is congruent with the naming language. The congruence effects are reflected as effective integration of lexical and facial cues in key brain regions including IFG, MFG, ACC, and caudate. Implications of the findings in light of theories of language processing and cultural priming are discussed.     

Matching words to concepts in two languages: A test of the concept mediation model of bilingual representation

A categorization paradigm was used to investigate the relations between lexical and conceptual connections in bilingual memory. Fifty-one more fluent and less fluent English-French bilinguals viewed category names (e.g.,vegetable) and then decided whether a target word (e.g.,peas) was a member of that category. The category names and target words appeared in both English and French across experimental conditions. Because category matching requires access to conceptual memory, only relatively fluent bilinguals, who are able to directly access meaning for their second language, were expected to be able to use category information across languages. The performance of lessfluent bilinguals was expected to reflect reliance on lexical-level connections between languages, requiring translation of second-language words. The results provided evidence for concept mediation by more-fluent bilinguals, because categorization latencies were independent of the language of the category name. However, the performance of less-fluent bilinguals indicated that they did not follow a simple lexical translation strategy. Instead, these subjects were faster at categorizing words in both languages when the language of the category name matched the language of the target word, suggesting that they were able to access limited conceptual information from the second language. A model of the development of concept mediation during second language acquisition is described.     

Code-switching effects in bilingual word recognition: a masked priming study with event-related potentials

Two experiments tested language switching effects with bilingual participants in a priming paradigm with masked primes (duration of 50 ms in Experiment 1 and 100 ms in Experiment 2). Participants had to monitor target words for animal names, and ERPs were recorded to critical (non-animal) words in L1 and L2 primed by unrelated words from the same or the other language. Both experiments revealed language priming (switching) effects that depended on target language. For target words in L1, most of the language switch effect appeared in the N400 ERP component, with L2 primes generating a more negative going wave than L1 primes. For L2 target words, on the other hand, the effects of a language switch appeared mainly in an earlier ERP component (N250) peaking at approximately 250 ms post-target onset, and showing greater negativity following an L1 prime than an L2 prime. This is the first evidence for fast-acting language-switching effects occurring in the absence of overt task switching.     

On the automaticity of emotion processing in words and faces: event-related brain potentials evidence from a superficial task

The degree to which emotional aspects of stimuli are processed automatically is controversial. Here, we assessed the automatic elicitation of emotion-related brain potentials (ERPs) to positive, negative, and neutral words and facial expressions in an easy and superficial face-word discrimination task, for which the emotional valence was irrelevant. Both emotional words and facial expressions impacted ERPs already between 50 and 100 ms after stimulus onset, possibly reflecting rapid relevance detection. Following this initial processing stage only emotionality in faces but not in words was associated with an early posterior negativity (EPN). Therefore, when emotion is irrelevant in a task which requires superficial stimulus analysis, automatically enhanced sensory encoding of emotional content appears to occur only for evolutionary prepared emotional stimuli, as reflected in larger EPN amplitudes to faces, but not to symbolic word stimuli.     

Semantic processing of words, cognitive resources and N400: an event-related potentials study

The specificity of the right hemisphere (RH) contribution to the semantic processing of words is still debated. Indeed, the semantic impairments of right hemisphere damaged (RHD) subjects may be the expression of limited general cognitive resources rather than a specific impairment of semantic processing ([Monetta et al., 2001]; [Murray, 2000]). The purpose of this study was to evaluate the possibility that the N400 reflect the availability of cognitive resources through an analysis of its different amplitudes according to different semantic complexity level. Ten young adults without any history of neurological damage participated in a semantic categorization task with two different levels of difficulty based on prototypicality. Event related potential (ERP) signals from 64 electrodes were recorded. An N400 was observed during the processing of difficult words and distractors. The results show that the greatest N400 activation was observed during the processing of difficult words, thus reflecting a possible increase in the amount of required cognitive resources.     

Self-esteem modulates attentional responses to rejection: Evidence from event-related brain potentials

Individuals with low self-esteem have been shown to exhibit an attentional bias for social rejection cues. The present study investigated whether individuals with low self-esteem would demonstrate greater reactivity to rejection-related stimuli during an attention shifting task than was exhibited by those with high self-esteem. Individuals with low self-esteem showed higher amplitude event-related potentials (ERPs) in response to rejection cues than was observed for those with high self-esteem. These results suggest that individuals with low self-esteem allocate more attentional resources to rejection cues than those with high self-esteem. Discussion will focus on the implications of these findings for understanding the connection between low self-esteem and social rejection.     

Age-related differences in semantic priming: evidence from event-related brain potentials

Hasher and Zacks (1988) suggested that aging may affect processes involved in the inhibition of irrelevant information during language processing. Our experiment tested this hypothesis using the N400 event-related brain potential in a priming paradigm and assessed whether older subjects could benefit from the constraints of a sentence context. Twenty older (63 to 88 years) and 20 young (19 to 29 years) subjects read sentences and word pairs. Each final word varied on the degree of relatedness to the preceding context, with some being highly related (BC), moderately related (R), or unrelated (U). Younger subjects showed the expected N400 effect gradient (U > R > BC) in both the sentence and word-pair contexts, while older adults showed no discrimination between the conditions (U = R = BC) for the sentence and limited discrimination (U > BC) for the word pairs. These results support the inhibition-deficit hypothesis, whereby older adults fail to inhibit related items in working memory, and suggest that older adults do not benefit from the constraints of a sentence context.     

Selective attention to color and location: An analysis with event-related brain potentials

Event-related brain potentials (ERPs) were recorded from subjects as they attended to colored bars that were flashed in random order to the left or right of fixation. The task was to detect slightly smaller target bars having a specified color (red or blue) and location (left or right). The ERP elicited by stimuli at an attended location contained a sequence of phasic components (P122/N168/N264) that was highly distinct from the sequence associated with selection on the basis of color (N150-350/P199/P400-500). These findings suggested that spatially focused attention involves a gating or modulation of evoked neural activity in the visual pathways, whereas color selection is manifested by an endogenous ERP complex. When the stimulus locations were widely separated, the ERP signs of color selection were hierarchically dependent upon the prior selection for spatial location. In contrast, when the stimulus locations were adjacent to one another, the ERP signs of color selection predominated over those of location selection. These results are viewed as supporting “early selection” theories of attention that specify the rejection of irrelevant inputs prior to the completion of perceptual processing. The implications of ERP data for theories of multidimensional stimulus processing are considered.     

Evaluative priming from subliminal emotional words: Insights from event-related potentials and individual differences related to anxiety

The present ERP study investigated effects of subliminal emotional words on preference judgments about subsequent visual target stimuli (paintings, portraits). Each target was preceded by a masked 17-ms emotional adjective. Four classes of prime words were distinguished according to the combinations of positive/negative valence and high/low arousal. Targets were liked significantly more after positive-arousing primes (e.g., happy), relative to negative-arousing (brutal), positive-nonarousing (mild), and negative-nonarousing primes (lazy). In the target ERP, amplitude of right-hemisphere positive slow wave was increased after positive-arousing compared to negative-arousing primes. Evaluative priming effects on judgments and ERPs were more pronounced in high state-anxious participants. The results suggest that (1) there is indeed affective/semantic processing of unconscious words, (2) evaluative priming operates relatively late during target processing, (3) to be effective, prime words need to score high on the arousal dimension, and (4) individual differences in state anxiety modulate the susceptibility to subliminal evaluative priming.     

Individual differences in concept learning and brain event-related potentials

An irrelevant auditory probe procedure was employed to evoke brain event-related potentials (ERPs) in 56 males while they learned concepts presented to them in study booklets. A mastery test was administered to assess concept acquisition. Ss were divided into two groups according to whether or not their achievement test results were above or below the average score for all learners. A one-way multivariate analysis of variance (MANOVA) was computed for each presentation page employing as multiple dependent measures ERP amplitudes which corresponded to specific concepts. MANOVAs and their subsequent statistics revealed that, as theorized, ERPs evoked at the right frontal, temporal and parietal, as well as the left parietal, regions, significantly distinguished below-from above-average concept learners. As hypothesized, poorer concept learners engaged these hemispheric sites less, and manifested more variability at them, than better learners. It was established that the frontal, temporal and parietal areas which are chiefly implicated in crystallized intelligence are engaged during the actual process of concept learning itself.     

Neuroaffective processing in criminal psychopaths: brain event-related potentials reveal task-specific anomalies

This study aimed to confirm neuroaffective processing deficits in psychopaths by measuring late brain event-related potential (ERP) components and behavior in groups of psychopathic and nonpsychopathic inmates of a Singaporean prison while they performed two tasks. In a Categorization task, affective stimuli were task-relevant and required focused attention, while in a Vigilance task, affective pictures were presented in the background while participants discriminated vertical from oblique lines. Psychopaths showed differences in late positive ERPs that were sensitive to affective stimulus properties (valence and arousal) in the Categorization, but not in the Vigilance task, suggesting that only under conditions of focused attention did psychopaths show a neuroaffective processing deficit. In the Categorization task, psychopaths also showed a significantly larger prefrontal negative ERP (N350) whose amplitude correlated positively with the behavioral facet of psychopathy. In the Vigilance task, psychopaths both missed more targets and showed significantly smaller target-evoked parietal ERPs when viewing arousing pictures, suggesting their attentional focus was disrupted by the affective background.     

Right hemisphere sensitivity to word- and sentence-level context: evidence from event-related brain potentials

Researchers using lateralized stimuli have suggested that the left hemisphere is sensitive to sentence-level context, whereas the right hemisphere (RH) primarily processes word-level meaning. The authors investigated this message-blind RH model by measuring associative priming with event-related brain potentials (ERPs). For word pairs in isolation, associated words elicited more positive ERPs than unassociated words with similar magnitudes and onset latencies in both visual fields. Embedded in sentences, these same pairs showed large sentential context effects in both fields. Small effects of association were observed, confined to incongruous sentences after right visual hemifield presentation but present for both congruous and incongruous sentences after left visual hemifield presentation. Results do not support the message-blind RH model but do suggest hemispheric asymmetries in the use of word and sentence context during real-time processing.     

Mental rotation of mirrored letters: evidence from event-related brain potentials

Event-related brain potentials (ERPs) were recorded while participants (n=13) were presented with mirrored and normal letters at different orientations and were asked to make mirror-normal letter discriminations. As it has been suggested that a mental rotation out of the plane might be necessary to decide on mirrored letters, we wanted to determine whether this rotation occurs after the plane rotation in mirror rotated letters. The results showed that mirrored letters in the upright position elicited a negative-going waveform over the right hemisphere in the 400-500 ms window. A similar negativity was also present in mirrored letters at 30 degrees, 60 degrees, and 90 degrees, but in these cases it was delayed. Moreover, the well-known orientation effect on the amplitude of the rotation-related negativity was also found, although it was more evident for normal than for mirrored letters. These results indicate that the processing of mirrored letters differs from that of normal letters, and suggest that a rotation out of the plane after the plane rotation may be involved in the processing of mirror rotated letters.     

Accessing word meaning in two languages: an event-related brain potential study of beginning bilinguals

Twenty-eight native-English speakers enrolled in beginning and intermediate university Spanish courses participated in a mixed language semantic categorization task in which critical words were presented in English (L1) and Spanish (L2) and repetitions of these words (within- and between-languages) were presented on subsequent trials (i.e., immediate repetition). Event-related potentials were recorded to all items allowing for comparisons of the N400 component to repetitions within- and between-languages as well as to words presented for the first time. Three important findings were observed in this sample of participants during relatively early stages of acquiring a second language. First, in the typical N400 window (300-500ms), between-language repetition (translation) produced a smaller reduction in N400 amplitude than did within-language repetition. Second, the time-course of between-language repetition effects tended to be more extended in time and differed as a function of language with L2-L1 repetitions producing larger priming effects early (during the typical N400 window) and L1-L2 repetitions producing larger priming effects later (during windows after the typical N400). Third, a greater negativity in the ERP waveforms was observed when the word on the directly preceding trial was from the other language. Within the time frame of the N400, this language switch effect arose only when the target word was Spanish and the preceding word English (i.e., L1-L2). The results are discussed within the framework of current models of bilingual lexical processing.     

Age-related slowing in face and name recognition: evidence from event-related brain potentials

Age-related slowing in recognizing famous names and faces was investigated with event-related brain potentials (ERPs). In a group of young adults, item repetition induced early (220-340 ms) and late (400-700 ms) ERP modulations, apparently signaling the access to, respectively, domain-specific representations of faces and names and domain-general semantic knowledge about the persons. These repetition effects and other ERP components were then used as process-specific time markers in middle-aged and elderly participants. For both faces and names, the elderly participants' responses were slowed, but repetition priming in reaction times was not. The ERP latencies suggested that most of the age-related slowing occurred in the access to domain-specific representations and during response decision, whereas sensory and perceptual processing was largely spared.     

Working memory maintenance contributes to long-term memory formation: Evidence from slow event-related brain potentials

Behavioral research has led to conflicting views regarding the relationship between working memory (WM) maintenance and long-term memory (LTM) formation. We used slow event-related brain potentials to investigate the degree to which neural activity during WM maintenance is associated with successful LTM formation. Participants performed a WM task with objects and letter strings, followed by a surprise LTM test. Slow potentials were found to be more negative over the parietal and occipital cortex for objects and over the left frontal cortex for letter strings during WM maintenance. Within each category, they were enhanced for items that were subsequently successfully remembered. These effects were topographically distinct, with maximum effects at those electrodes that showed the maximum negativity during WM maintenance in general. Together, these results are strongly consistent with the ideas that WM maintenance contributes to LTM formation and that this may occur through strengthening of stimulus-specific cortical memory traces.