So far we've talked about, this plasticity that exists, right? The fact that speech sounds can be reacquired. The fact that that bilingual infants who have 2 native languages not only appear able to learn those two speech contrasts, but may actually remain open to speech contrast past the normal window seen in monolinguals. And we can now ask about phonology in a second language. Now, there's a very longstanding literature and I don't want anyone to come away with the idea that I think that speaking two languages, or that the window is open forever in the same way for someone who's older, let's say 10, 12, 15, 18 years of age. For the vast majority of people when a second language is learned later in life in general it has a stronger accent. There have been studies in the past. A very seminal study done by Asher and Garcia on Cuban immigrants who arrived into the US and essentially found that as the age of arrival increased as they were older when they arrived in the US, they had a stronger accent in English. One study that's been done to look at the difference between when a language is learned and the accent was performed by Susan Guillaume. In the study, she looked at Spanish Quichua bilinguals. Quichua is an Indian Language spoken near Quito, Ecuador and what she wanted to do was to compare these two languages and they're interesting because Quichua has a reduced vowel space, so it actually has fewer vowels than Spanish. Remember, I told you Spanish has the A, E, I, O, U. Catalan has a larger vowel space and English has an even larger vowel space, many more vowels than Spanish. Well Quichua has a smaller vowel space, so what we would find with this is if we compare it we would observe in space these five Spanish vowels. With the space being restricted in Quichua with three vowels. And what we would see is that essentially, something like a Spanish accent would feel like a slurring of those boundaries in Quichua, and a Quichua accent would feel like a restriction on the boundaries in Spanish. So Guillaume looked at age of acquisition and Quichua Spanish bilinguals. And she found that those who learned Quichua and Spanish early in life were able to go between these two different vowel spaces. Not exactly like a monolingual but much more close to a monolingual when they learned it early in life. So what Guillaume found was that early bilinguals were able to go between the Quichua and Spanish vowel space quite well, close to a monolingual. But those who learned a second language later in life would have an accent. Right? In either one of those languages. And it was essentially either a restriction of the vowel space or an over expansion of the vowel space. But they were not able to go between these two vowel spaces as well if they were later learners. The question you're wondering is what is that age? What is the difference between early and late? And of course, this differs across studies. In this study, Guillaume was looking at simultaneous filing with those who acquire both languages before the age of three and sequential bilinguals, those who had acquired a second language after age five. And what she found was that, the simultaneous bilinguals could adapt to each of these vowel spaces as adults, right? So, those who had learned a second language before age three, as adults, could adapt between these two vowel spaces. And those adults who had learned a second language after age five could not adapt as well. So, they had an accent in their production. Now this suggests again that the ability to sound more like a native is dependent on age. There's a bit of controversy in this area because it does seem to differ across individuals. Some individuals can learn a second language later in life and have less of an accent or no perceptible accent, and some individuals can learn it earlier in life and have more of a perceptible accent. But in this particular study the difference between three and five seemed to indicate a clear differentiation between the ages at which a more native like or non-native like accent could be achieved in both languages. The difference between early and late learning has been considered extensively in the literature by Jim Flege who did a lot of seminal work looking at the differences in age and how those affected the perception of sounds. And the question you might ask is well, if I have a non-native language, how do I perceive those sounds? How is it that even though I might have learned the language late in life, I can still hear those sound differences, and I can still approximate the pronunciation between those differences? How do I do that? And so one study that was conducted by Pilar Archila-Suerte looked at this particular question. In her study what she wanted to do was look at the difference in saf, sef, sof and suf. Those are nonwords, those are not words in English, right? And they have the saf, sef, sof, suf, I don't want to sound like Spanish because they are, sof and suf, specifically are not Spanish like, but it would saf, sef, sof, suf in Spanish. But it's saf, sef, sof, suf in English. And by picking these sounds, she could ask a couple of questions. One was, how do monolinguals look on this task, how do bilinguals look on this task, and does age matter? Now specifically in this task they were asked to hear two sounds. So they would hear something like saf saf or saf sof, and they had to say how similar or different were and they were rating this from one to four. It wasn't particularly fun. Often times Pilar reported to me that subjects by the end didn't know what they were hearing. They did know what they were hearing, because they could clearly indicate the sounds, but it is a bit of a long task, and it took awhile for them to go through all these different sound combinations and decide between one and four. Is it really similar, not so similar, somewhat dissimilar, or really dissimilar? Now, interestingly, when we look at the data, one way to represent the data would be to look at these four clusters, right? Saf, sof, sef, suf, that's four different clusters. And when we look at the visual of the monolinguals they appear really like four clusters. Now there's a little bit of variation in how these sounds were presented. They were recorded by Jay Zeven, a researcher who's done a lot of work on speech. And they were slightly different, there were things like saf, sof, suf, suf, right? So all these sounds are produced slightly differently. And the question is of course you know, what do these differences amount to. Now they shouldn't really .amount to much of anything, because there's lots of variation in how people produce the sound saf. Every speaker sounds slightly different. In fact, the amazing part is that native speakers can perceive these slight differences and essentially form a single phoneme. In studies with monolinguals, with adults, what's found is that the differences are not perceived. So, for example, I can go to like a ba ba ba, right? And a little buh buh buh, that little difference right there is a slight boundary. And what happens is that monolinguals form these phonemic boundaries, essentially these boundaries where the buh buh buh, that little difference is really small. And yet on that edge between those two sounds, monolinguals will perceive one as a p and one as a b. And there's all this variation, ba ba ba, right? All that ba ba ba is more p like, buh buh buh puh puh, it's still a b, right? So there's all this variation in the b, all this variation in the p, and this very small difference between a b and a p. And monolinguals in English would become very sensitive to this distinction. And across all languages any distinction that exists like that, that's a continuum. There is this very strict phonemic boundary that appears. When we go back to Archila-Suerte's study, what we see is that for the saf, sof, sof, and sef, there are clear differences, and the monolinguals essentially recognize them as single points. There's a little bit of variation. Now, the bilinguals who had learned English early in life, somewhere around the age of 5, they could perceive these pretty well. Almost like monolinguals, and the bilinguals who had learned English later in life, 11, 13, they perceived it in a different way. So they still had their four clusters, but the four clusters were smudged to a greater extent, so they were noisier. You could think of them as little clouds around each of these centers. What appears from these data is that early bilinguals recognize each sound so that when they hear saf they know it's saf. But for a late bilingual, in this case 11 to 13, when they here a saf, they recognize it because it's different than a sof. And it suggests that the late bilinguals are comparing sounds and using relative differences in sounds to detect what a speech sound is, and that the earlier someone learns a second language the more they can be like a monolingual, in which case they just hear that sound. It's somewhat similar to what's been studied in music, called absolute pitch. Right. In absolute pitch, what happens is those who acquire absolute pitch and learn it very early in life can detect a single musical note in isolation. And those who don't learn music early in life, and there seem to be some other restrictions on acquiring absolute pitch, those who don't learn it that way use relative pitch, they know that a musical note differs from another musical note. In a similar vein, early bilinguals seem to have an absolute phonemic perception and later bilinguals seem to be using this relative process to compare phonemes and to recognize them. After that, Archila-Suerte, Jay Zeven, and I wanted to ask a slightly different question which was, how does this process of recognizing these sounds differ in early and late bilinguals and monolinguals? So to do this A group of monolinguals, a group of early bilinguals, and a group of late bilinguals were asked to go into an FMRI scanner. Now FMRI is a measure of blood oxygenation, it is sensitive to changes in the oxygenation of the blood as people process information. And so was our hope that we would be able to observe the differences in the brains of those who had learned a language as a monolingual, as an early bilingual, or as a late bilingual once they were in adulthood. Now the interesting thing about the monolingual literature was that it essentially shows a very striking clear pattern of brain activity. So when you ask a monolingual to go into the scanner and listen to speech sounds from their native language, what you see is essentially bilateral superior temporal gyrus. Roughly about here, it's bilateral, can be more left lateralized, since it is speech. And that brain activity appears consistently, it appears early in life, even with children they show that superior temporal gyrus activity quite early and it's quite clear. And it's so clear that, in fact, oftentimes researchers will present a movie to participants just in an effort to make sure they don't fall asleep during the task. So with monolinguals we knew from the literature that there was clear bilateral superior temporal gyrus, that that's what we would observe. With the bilinguals we found again those two areas being active. Bilateral superior temporal gyrus, for the early bilinguals, there were relatively few areas that differed from the monolinguals. For the late bilinguals there were clear differences, especially when you compare the soft suf distinction. There you can really see it much more so than for the early bilinguals. This suggests again that age of acquisition plays a role in the brain activity observed. And again it expands on our idea that the reason that late bilinguals may be showing an accent, may have different perception, is because their brains have to adapt. This idea that early and late learning differ is resonant with the idea that's been proposed in the literature to consider second language learning and specifically how, when a second language is learned later in life, it has to overcome the entrenchment of the first language. This idea proposed by Brian McQueeney again, would suggest in our case for this MRI data that the second language learner who has learned a second language later in life has to invoke other brain mechanisms beyond their native language brain mechanisms in order to resolve the difference between sounds in the second language. And again we've seen this behaviorally in that they seem to be using a slightly different process of relative sound difference, now we see this also reflected in the brain.