Growing up my dominant language was Italian. However, thanks to my dad's sabbaticals, on more than one occasions we lived in English-speaking countries for long periods of time. My brain would reset to Italian as soon as we returned, but I never forgot English, and it was definitely easier to transition again when, as an adult, I moved to the US. However, to this day, I have yet to get rid of that feeling of inadequateness that sticks to me in many situations, whether here or back in Italy. You have no idea how many times I've said the wrong thing at the wrong time and, even worse, I had no idea what I'd said but could only guess from the snickers and smirks around me. Well, it turns out, being bilingual is no easy task, but it has its advantages, too.
"With improved juggling ability, novice jugglers demonstrate structural enhancements in a cortical region associated with processing and storage of complex visual motion. Similarly, the bilingual, a mental juggler of two languages, shows structural and functional enhancements in cortical regions involved in language use and executive control, likely resulting from a lifetime of communicating in two languages. [. . .] The need to constantly control two languages confers advantages in the executive system, the system that directs cognitive processing .""Mental juggler of two languages" . . . I love it, I can totally relate to this metaphor. BTW, I never felt truly bilingual until I started mixing up it's and its, your and you're... !
Krizman et al.  reasoned that since musical training enhances cognitive and sensory processing, a similar neural enhancement would be noticed in bilinguals.
"To test this prediction, performance on a task of integrated visual and auditory sustained selective attention was compared between highly-proficient Spanish-English bilinguals and English monolinguals."The researchers tested differences between bilinguals and monolinguals in the auditory system. I'm not at all surprised that you would find a difference. For example, I've noticed on more than one occasion that because Italian is a phonetic language (words are pronounced as they are written), many Italians who learn English as adults tend to pronounce English words as they'd read them in Italian. To me, this bias introduced by knowing the written word, or better, the inability to pronounce a word unless you see it written, attests to the fact that while growing up a language is a set of sounds one learns to reproduce, once an adult, this ability is somehow lost. Since the sound is per se "unrecognizable," the brain switches to a visual stimulus instead (the written word).
Back to the paper: as specific auditory stimulus, the researchers used the syllable "da" presented in the context of "multitalker babble relative to a quiet acoustic background." The results:
"Bilinguals, relative to monolinguals, showed enhanced sub-cortical representation of the fundamental frequency of the speech sound as well as improved sustained selective attention."Like music training, language learning impacts subcortical sound processing. The evidence collected by Krizman et al. suggests that because bilinguals constantly juggle sounds between two languages, they possess a neural enhancement in the way sound is encoded in their brains. Like with musicians, the researchers claim, their auditory system is highly efficient, flexible, and better focused in the sound processing.
I just want to add a personal note: we tend to think of language as a way to convey our thoughts, but would we have thoughts at all without a language? I didn't realize how lucky I've been to have learned English in my childhood until, as an adult, I tried to learn German. Languages do shape the way you think, and in order to learn a new language you truly have to change the way you're thinking. I still can't quite grasp the meaning of German dependent clauses until you get to the end of the sentence (a verb!!! please give me a verb!). It feels like one of those super-high stacks where I'm longing for a "pop operation" to happen. . . And once I have a verb I have to stop and reconstruct the sentence. It's not until you learn to think that way that you truly master the language.
I'm fascinated by the intrinsic relationship between thought, consciousness, and language. Feel free to chip in with your thoughts. In English, please. ;-)
Krizman, J., Marian, V., Shook, A., Skoe, E., & Kraus, N. (2012). From the Cover: Subcortical encoding of sound is enhanced in bilinguals and relates to executive function advantages Proceedings of the National Academy of Sciences, 109 (20), 7877-7881 DOI: 10.1073/pnas.1201575109