Does a bilingual speaker representeach language in different areas of the brain?

• Brain lesions that affect one language and not the otherwould lead to the conclusion that languages are represented in different areas of the brain.

• Extreme cases have shown postoperative impairment in one language with spontaneous recovery after eight months (Paradis and Goldblum 1989).

• Ojemann and Whitaker (1978) found that electrical stimulation of certain areas in the cortex interrupted naming in both languages, whereas stimulation of other areas interrupted naming in only one language.

• Klein et al. (1994), using PET, found that naming pictures in second language vs naming pictures in a first language resulted in activation in the putamen, a sub cortical area that has been associated with phonological processing.

• Other studies have found that bilinguals show activity in left frontal areas of the brain for semantic and phonological analyses of words in both their languages (Klein et al. 1995; Wagner et al. 1996).

• A recent study by Hernandez et al. (1997) was designed to look at this issue using functional MAGNETIC RESONANCE IMAGING (fMRI)for Spanish–English bilinguals.

• Participants were asked to name a picture in their first language, second language, or to alternate between each language on successive trials.

• Results revealed slower reaction times and an increase in the number of cross-language errors in the alternating condition relative to the single-language condition.

• In the fMRI study, there was no difference when comparing activation for naming in the first and second language. However, activation in the prefrontal cortex increased significantly when participants were asked to alternate between languages.

• Thus it appears that the left prefrontal cortex may also act to reduce the amount of interference between languages (as indexed by slower reaction times and increased cross-language errors

Cortical Organization For Language

• Recent work using event-related potentials (ERP) supports previous behavioral findings suggesting that second language learning is better in those who learn their second language early.

• Mclaughlin and Osterhout (1997) found that college students learning French progressively improve from chance to near-native performance on lexical decision

What effects does age of second language acquisition

have on brain representation?

• However, electrophysiological indices revealed sensitivity to French words after only a few weeks of instruction.

• An increased N400 (a waveform that indexes lexical-semantic processing) for words preceded by semantically unrelated words (coffee-dog) was found as the number of years of exposure to French increased, but it never approached the levels seen in native French speakers.

• Weber-Fox and Neville (1996) have found differences in the N400 to semantic violations, but only for those who learned a second language after the age of eleven.

• Changes in ERPs to grammatical violations, however, appeared even for those who learned their second language before the age of four. Perani et al. (1996), using POSITRON EMISSION TOMOGRAPHY (a measure of localizedbrain activity), have found that listening to passages in a first language results in an activation of areas that is not apparent in the second language for late second language learners.

• Example: increased activation in the left and right temporal pole, the left inferior frontal gyrus, and the left inferior parietal lobe).

• Thus age of acquisition has an effect on electrophysiological measures of brain activity as well as on the neuroanatomical areas that are involved in second language processing.

Bilingual Brain: Sharper, More Focused

• The ability to speak two languages can make bilingual people better able to pay attention than those who can only speak one language.

• Scientists have long suspected that some enhanced mental abilities might be tied to structural differences in brain networks shaped by learning more than one language, just as a musician’s brain can be altered by the long hours of practice needed to master an instrument.

Bilingual Brain: Sharper, More Focused

• A study published in the Proceedings of the National Academy of Sciences, researchers at Northwestern University for the first time have documented differences in how the bilingual brain processes the sounds of speech, compared with those who speak a single language, in ways that make it better at picking out a spoken syllable, even when it is buried in a babble of voices.

Bilingual Brain: Sharper, More Focused

• Dr. Nina Kraus, the head of the research team stated the research conducted has shown that the nervous system of a bilingual person responds to sound in a way that is distinctive from a person who speaks only one language.

• Through this fine-tuning of the nervous system, people who can master more than one language are building a more resilient brain, one more proficient at multitasking, setting priorities.

Bilingual Brain: Sharper, More Focused

• Researchers from the Center for Health Studies in Luxembourg reported that the ability to speak more than one language also may help protect memory.

• After studying older people who spoke multiple languages, they concluded that the more languages someone could speak, the better: People who spoke three languages were three times less likely to have cognitive problems compared to bilingual people. Those who spoke four or more languages were five times less likely to develop cognitive problems.

Bilingual Brain: Sharper, More Focused

• Researchers at the University of British Columbia’s Infant Studies Centre reported that babies being raised in a bilingual family show from birth a preference for each of the native languages they heard while still in the womb and can readily distinguish between them.

• Moreover, bilingual infants appear to learn the grammars of their two languages as well as babies learning a single language, even when the two languages are as different from one another as English and Japanese, or English and Punjabi.

Nina Kraus is a Professor at Northwestern University, investigating the neural

encoding of speech and music and its plasticity. Her research examines the

neural encoding of sound in the normal system, how it is disrupted in clinical

populations, and how it reacts to differing levels of expertise. For individuals with

speech and language disorders (reading, auditory processing disorder, autism), the neural encoding of speech can provide a

biological marker of deficient sound encoding, while the musician’s brain

illustrates how extensive auditory expertise can enhance sensory-cognitive

interactions. Investigations on brain plasticity are aimed at improving speech

perception and auditory learning in normal and clinical populations.