Book Summary: The Bilingual Brain by Albert Costa

A book summary of the key ideas from The Bilingual Brain: And What It Tells Us About the Science of Language by Albert Costa, along with informal notes and the view from the blog.

Book Summary: The Key Ideas

#1: Phonological differentiation and the sound inventory: Babies can differentiate phonologically a long time before they can speak, building a “sound inventory” in their brains. If not exposed to two languages, this ability to differentiate deteriorates with age.

#2: Disassociational deficits and switching costs: Brain damage can affect grammatical processing differently, but rarely different languages. We exert more cognitive effort in using our second language and therefore it is generally harder to switch to our dominant language.

#3: Impaired recall, empathy, and brain structure: Studies suggest bilinguals are better are putting themselves in others’ shoes. Neuroimaging studies suggest learning a second language may alter brain structure, increasing grey matter and white matter.

#4: Bilingualism and the attention system: Studies suggest bilinguals handle “task switching” more proficiently than monolinguals, indicating that there may be a benefit for cognitive flexibility.

#5: The effect of bilingualism on decisions and logic: Studies suggest that taking decisions in our second language may reduce some cognitive biases and alter our moral perspective on dilemmas.

Book Notes: The Key Ideas in Detail

Premise of the Book

Albert Costa was one of the leading researchers in the field of neurolinguistics, specialising in research on the cognitive and neurological implications of bilingualism. The book explores how two (or more) languages can coexist in the brain and the implications of that coexistence.

Costa believed that understanding the bilingual brain could help us to understand other cognitive domains like attention, learning and decision making. As he puts it in his opening words, “bilingualism is a window into the study of human cognition.”

Key Idea #1: Phonological differentiation and the sound inventory

In all human language, the probability that two syllables follow one another (known as transitional probability) is higher within words than between words.

Researchers tested this idea with babies to see if they made associations between syllables according to probability. Babies appeared to pay more attention to stimuli that did not meet their expectations. In other words, despite not being able to speak yet, babies compute clear patterns in the sounds of languages, as well as intonation and accentuation. All of this helps babies to build a lexicon.

Decoding speech signals becomes harder, of course, for babies exposed to two languages. Rules on the sequences of sound are not necessarily consistent between languages. “Contrastive properties” such as tone and stress can create even more complexity between languages.

From studies that measure brain activity, it appears that babies can differentiate between different sounding languages just hours after birth. Even for phonologically similar languages, babies exposed to languages have shown an ability to differentiate in just 4 months.

Bilingual babies also seem to pay more attention to lip movement than monolingual babies. Studies suggest they can even differentiate two languages that they haven’t been exposed to by visual context alone.

As babies grow, they build up what Costa calls a “sound inventory”. But if not exposed to two languages, the ability to differentiate phonetically deteriorates as they get older.

Key Idea #2: Disassociational deficits and switching costs

Studies on the impact of brain damage on language processing offer some interesting insights. Brain damage deficits can be “associational” – language dysfunctions that appear together – or “disassociational” – e.g. showing certain language dysfunction in one language but not in another. It is the latter type of deficit that can tell us more about bilingualism in the brain.

In most cases of bilingual brain damage, two languages are impaired equally – though Costa accepts there are exceptions. Instead, the evidence points to differences in grammatical processing. For example, studies have highlighted brain damage cases that affect one grammatical category (e.g. nouns) but not another (e.g. verbs).

While disassociational deficits between languages aren’t common, studies do show wider-ranging brain activity when processing second languages. Costa suggests the higher cognitive effort required is the likely explanation.

Interestingly, the evidence also suggests that both languages are active regardless of the one that gets used. It seems bilinguals cannot “switch off” the other language while processing another.

Much of the research on bilingualism therefore looks at the idea of “linguistic control” by measuring “switching costs” between languages. Generally, it is harder for people to switch to their dominant language in switching tasks, unless they well-balanced bilinguals. As Costa puts it, “the most balanced bilinguals should show the same amount of switching cost for both languages.”

Finally, studies also demonstrate that if languages are left unused over time, they can be forgotten completely. These provides useful context on brain plasticity.

Key Idea #3: Impaired recall, empathy, and brain structure

When looking at the cognitive impact of bilingualism, Costa begins with a clear assertion:

“The bilingual experience does not seem to have dramatic effects on the linguistic capacity or any other cognitive domain of individuals.”

In other words, bilingualism doesn’t make us smarter. In fact, studies show that access to the lexicon is less efficient in bilinguals. Costa suggests this might be due to the mental interference of competing languages. This is why bilinguals tend to find themselves in tip-of-the-tongue moments more often than monolinguals.

There is also some evidence that bilinguals have a slightly lower vocabulary than monolinguals, which Costa suggests is likely related to exposure.

There is an upside, however. Bilinguals appear to be more adept at learning new languages, and not just because of similarities between languages and the shortcuts that might create. (Studies eliminated this effect by inventing a language and found that bilinguals were more proficient in learning and remembering it.) Bilingualism also appears to reduce the “ego-centric bias”, with bilinguals more capable of putting themselves in others’ shoes at an earlier age.

As for the brain itself, neuroimaging studies have found that bilinguals exhibit activity in more brain regions when processing language. What’s more, studies also suggest bilingualism can change the structure of the brain. Several studies have reported increased grey and white matter in the brain region associated with phonological processing, as well as deeper brain regions such as the basal ganglia.

Key Idea #4: Bilingualism and the attention system

Some studies suggest that regular use of a second language improves mental conflict resolution. That basically means the response to a main target when confronted with incongruous stimuli (think being told to turn left by somebody pointing with their right hand).

Similarly, studies have looked at “task switching”, with results showing bilinguals consistently handle task switching better than monolinguals. This suggests bilingualism might foster greater cognitive flexibility.

Costa accepts there is still widespread debate over the effects of bilingualism on the executive control system. He points to the risk of publication bias (i.e. journals only being published if they produce positive results) and a couple of contradictory studies.

Some of these doubts, Costa suggests, are countered by neuroimaging studies that point to a potential benefit for executive control. Studies have shown higher grey matter and white matter in regions associated with domain-general executive control after completing spells of immersion in new languages.

Moreover, some studies suggest bilingualism may even delay the onset of dementia symptoms. While other studies muddy the waters, Costa suggests there is enough evidence to prove an effect on cognitive deterioration.

Key Idea #5: The effect of bilingualism on decisions and logic

We have more emotional connection to emotive words in our dominant language. Studies suggest that the emotional value of words is smaller in a foreign language and therefore grabs our attention less. Similarly, studies of the psycho-physiological and neural responses echo these findings, showing heightened emotional responses in the dominant language.

Emotional intensity is associated with heuristics and cognitive biases, which has led academics to explore the hypothesis that using a foreign language might reduce these biases. Indeed, a range of studies suggest that our lower emotional connection to foreign languages reduces cognitive biases such as loss aversion, risk aversion and mental accounting.

It seems that the cognitive effort of thinking in a second language can drive us to consider problems more logically. This could have economic impacts, but it also stretches into the moral domain.

Bilingual participants in one study responded to a moral dilemma (in this case, the idea of killing a man to prevent certain death for 5 others). When presented in a foreign language, they found that people were twice as likely to choose the utilitarian response.

The book concludes with a focus on social categorisation. Several studies have found that accent/language can be a bigger determinant in grouping of people than other characteristics such as skin colour.

You can buy the book here or you find more of our book notes here. For further interesting health/science reads, check out How to Change Your Mind by Michael Pollan and Lifespan by David Sinclair.

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