For many decades, speech scientists have marveled at the complexity of speech sounds. In English, a relatively simple task of distinguishing “bat” from “pat” can involve as many as 16 different sound cues. Also, English vowels are pronounced so differently across speakers that one person’s “Dan” can sound like another’s “done”. Despite all this, most adult native English speakers are able to understand English speech sounds rapidly, effortlessly, and accurately. In contrast, learning a new language is not an easy task, partly because the characteristics of foreign speech sounds are unfamiliar to us. For instance, Mandarin Chinese is a tonal language, which means that the pitch pattern used to produce each syllable can change the meaning of the word. Therefore, the word “ma” can mean “mother”, “hemp”, “horse”, or “to scold,” depending on whether the word was produced with a flat, rising, dipping, or a falling pitch pattern. It is no surprise that many native English speakers struggle in learning Mandarin Chinese. At the same time, some seem to master these new speech sounds with relative ease. With our research, we seek to discover the neural and genetic bases of this individual variability in language learning success. In this paper, we are focusing on genes that target activity of two distinct neural regions: prefrontal cortex and striatum.

Recent advances in speech science research strongly suggest that for adults, learning speech sounds for the first time is a cognitively challenging task. What this means is that every time you hear a new speech sound, a region of your brain called the prefrontal cortex – the part of the cerebral cortex that sits right under your forehead –¬ must do extra work to extract relevant sound patterns and parse them according to learned rules. Such activity in the prefrontal cortex is driven by dopamine, which is one of the many chemicals that the cells in your brain use to communicate with each other. In general, higher dopamine activity in the prefrontal cortex means better performance in complex and difficult tasks.

Interestingly, there is a well-studied gene called COMT that affects the dopamine activity level in the prefrontal cortex. Everybody has a COMT gene, although with different subtypes. Individuals with a subtype of the COMT gene that promotes dopamine activity perform hard tasks better than do those with other subtypes. In our study, we found that the native English speakers with the dopamine-promoting subtype of the COMT gene (40 out of 169 participants) learned Mandarin Chinese speech sounds better than those with different subtypes. This means that, by assessing your COMT gene profile, you might be able to predict how well you will learn a new language.

However, this is only half the story. While new learners may initially use their prefrontal cortex to discern foreign speech sound contrasts, expert learners are less likely to do so. As with any other skill, speech perception becomes more rapid, effortless, and accurate with practice. At this stage, your brain can bypass all that burdensome cognitive reasoning in the prefrontal cortex. Instead, it can use the striatum – a deep structure within the brain¬¬ – to directly decode the speech sounds. We find that the striatum is more active for expert learners of new speech sounds. Furthermore, individuals with a subtype of a gene called FOXP2 that promotes flexibility of the striatum to new experiences (31 out of 204 participants) were found to learn Mandarin Chinese speech sounds better than those with other subtypes.

Our research suggests that learning speech sounds in a foreign language involves multiple neural regions, and that genetic variations which affect the activity within those regions lead to better or worse learning. In other words, your genetic framework may be contributing to how well you learn to understand a new language. What we do not know at this point is how these variables interact with other sources of variability, such as prior experience. Previous studies have shown that extensive musical training, for example, can enhance learning speech sounds of a foreign language. We are a long way from cracking the code of how the brain, a highly complex organism, functions. We hope that a neurocognitive genetic approach may help bridge the gap between biology and language.

 

Han-Gyol Yi – gyol@utexas.edu
W. Todd Maddox ¬– maddox@psy.utexas.edu
The University of Texas at Austin
2504A Whitis Ave. (A1100)
Austin, TX 78712

Valerie S. Knopik – valerie_knopik@brown.edu
Rhode Island Hospital
593 Eddy Street
Providence, RI 02093

John E. McGeary – john_mcgeary@brown.edu
Providence Veterans Affairs Medical Center
830 Chalkstone Avenue
Providence, RI 02098

Bharath Chandrasekaran – bchandra@utexas.edu
The University of Texas at Austin
2504A Whitis Ave. (A1100)
Austin, TX 78712

Popular version of paper 4aSCb16
Presented Thursday morning, October 30, 2014
168th ASA Meeting, Indianapolis

 

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