[SOUND] So what metaphor could we use for the bilingual brain? Well some years ago I began, to create a circle model of Piaget's, theory of development. I like circles, I like concentric circles. And so I thought of it this way, and I created a model with the center being sensory motor. The second ring being Pre-cognitive processing. And then a later ring being Cognitive processing. And we could think of this as representing Piaget's, different stages of development. And wondered, what would happen if we took this circular model, and then looked at the brain as it develops. And in studies looking at brain development, the sensory and motor areas are the ones that develop first. Later association areas, and finally frontal cortex and as we discussed, that posterior. Part of the superior temporal gyrus being the latest. So, as we develop more and more sophisticated types of thinking, our brains transition from sensory motor processing, up to more and more complex types of processing. So, what would happen if we introduced a second language? Well, I thought about the example of late acquisition of a second language. And I imagined that one sphere, would impact a second sphere. And when I thought about that I said, well, that's kind of like a planet. But the idea that. Bilingualism might be like an asteroid belt, wasn't really appealing to me. It just didn't seem to capture, what happened. Yes, people may have some moments which are difficult when they're learning a second language, or a third, or fourth language later in life. There may be interference, but there's nothing like a, an inability to communicate at all. As I looked at these concentric circles more, I began to realize they looked like cells. And we could think of early Bilingualism as having two fused, or close to each other cells, with the rest of cognition developing around it. And late Bilingualism as involving this smaller little thing, that would attach to the bigger cell. And when I began to look at that, and think about what type of language is used, parasitism. Adaptability. And we began to think about, what the bilingual language system is like. I began to realize it's really as if there were two species in the same ecosystem. And I began to think about, bilingualism as a biological process. Not just in terms of the brain, and how the brain represents language. But in essence, in how we experience it. So the fact of learning a third language at the age of 20, led to a decrement in my first two languages. And other people have described this as well, this severe interference effect from the environment. Almost like a wave moving across the brain. People often have questions like. When should I learn a language, early or late? How does the brain process more than one language? And I think a lot of the answers to those types of questions, can be thought of and understood better, when we think about it as a biological process. And we take a biological approach. So rather than thinking that, for example, there's a Spanish, or an English, or a Portuguese, or a German place in my brain. We could think of it as my brain has a state that it's in. When I'm speaking one language or the other. So, rather than thinking about a discreet type of system, one in which we have different places for each language, we can think of language as being a brain state. So, there is no Spanish or English place in my brain. There is a Spanish state and an English state, a configuration of activity that occurs as a wave across my entire brain as I speak one language or the other. Today we can't visualize exactly what that state looks like. We don't have the technology to see in real time. All of these neurons interacting. But the day that we do, I suggest that these will be like observing weather. And looking at storms, moving across the globe. And how these different aspects of weather, interact to result in rain where we are. Or in sun, where we are. The ability to learn more than one language, is pretty incredible. And I think it helps us to think about it in a biological way, and natural system kind of way. And help for us to further explore this, area in the future.