Researchers widely agree that first and second languages are handled similarly in the brain. According to previous research, proficient bilinguals’ brain activity is broadly quite similar when accessing their first and second languages.
However, the literature exploring this until now has relied on imaging methods that can tell us where in the brain there is activity, but not how languages are represented in those areas. Distinct patterns of activation may have differentiated first and second languages in those same regions all this time, and by relying on traditional forms of imaging analysis alone, we could have been none the wiser.
Thanks to new imaging methods, however, we’re finally able to take a look at activation in these areas in a much more detailed way. Now, newly published work from Emily Nichols at The University of Western Ontario and colleagues suggests that languages are represented more distinctly than we thought.
For this study, the researchers gathered a sample of 32 bilingual English and Mandarin speakers living in Beijing. All participants spoke English as their first language, and Mandarin as their second. As might be expected, the age of acquisition (AoA) and proficiency of Mandarin — as measured by self-report and pre-testing, respectively — varied from person to person.
During their fMRI scans, participants were presented with a picture-word matching task in both English and Mandarin. For each trial of this task, they were shown a picture for 2.5 seconds, while an audio clip of a common two-syllable word, which either matched or didn’t match the image shown, was played. These audio clips alternated between English and Mandarin for all 160 trials, and participants were asked to indicate as quickly as possible via button press whether or not the audio given matched the contents of the image.
The team then used a technique known as representational similarity analysis (RSA) on imaging data collected during correct trials, in order to see which brain areas reliably showed different patterns of activation between languages. This fMRI technique is relatively new, and can reveal differences in similar activation patterns which were previously unmeasurable. For example, a previous study looking at reading in bilingual individuals used RSA to show distinct activation patterns in regions which handle visual word recognition when participants read text in each language. Here, the team hoped to apply this same method to probe brain activity during auditory, rather than visual, word recognition.
As expected, both English and Mandarin produced activity in an extensive network of language-related regions. When the team looked within those regions that were active for both languages, there were no overall significant differences in activation depending on language. However, the story changed when the team looked in more detail at the effects of AoA and proficiency on the levels of activation.
These analyses revealed that there were differences in how the two languages were represented, which could be predicted by AoA and proficiency. For example, people with a wider difference in first and second language proficiency showed more dissimilar patterns of activation in areas such as the left inferior fusiform gyrus and bilateral supramarginal gyrus, which are involved in articulation and auditory-motor integration, respectively. The more similar the proficiency between the two languages, the more similar the activation pattern. Likewise, the older the AoA, the more distinct the patterns of activation between first and second languages were.
In addition, results showed several areas that were more active in those with younger AoAs — the right insula, the left anterior intraparietal sulcus, and the area prostriata of the calcarine sulcus. However, the relationship between these regions and bilingual auditory word recognition is less clear. It’s likely that differences in activation in these areas, at least in part, represent differences in the ability to inhibit other language responses. But, further research is needed to disentangle exactly what these differences mean, and how they relate to AoA.
Interestingly, there was also a distinct dissimilarity between participants with lower second language proficiency and those who acquired their second language later in ventral visual areas, which handle object recognition and concept representation. This, the authors suggest, is indicative that language can likely affect our perceptions of what we’re looking at. This idea isn’t totally unheard of, either — previous research outlining the label-feedback hypothesis also highlighted that variations in language can alter our ability to categorise, discriminate between, and even detect objects.
These findings not only support the current model of an integrated language system in bilinguals, but they extend our understanding of how individual differences dictate language representations within the brain. Future research to verify that these patterns are consistent across languages, or whether they vary by language similarity, are likely to give us a greater understanding of whether these results are in part due to the large differences between English and Mandarin. Research using RSA which looks into the effect grammar may have on differences in brain activation is also a topic for investigation. As it stands, this study represents a new and exciting approach for disentangling finer differences in how the brain represents and utilises first and second languages.
Emma L. Barratt (@E_Barratt) is a staff writer at BPS Research Digest