Although I think the hypothesis y'all propose in the abstract is on the right track, I wasn't sure whether the following two facts were problematic:
1. phonotactic learning studies in babies often seem to mimic complementary distribution (e.g. Amanda's coronal stops before high vowels and labial beforemid); yet learning relies on babies still being able to discriminate coronal and labial before both types of vowel in order to treat legal and illegal trials differently. So complementary distribution (at least with this short exposure) cannot influence babies' ability to discriminate between sounds. [ac]
mm, two thoughts on this, one slightly out on a limb and the other well out on a limb. first thought: in my opinion, there is not a good theory of the relationship between category formation and discrimination. most models are designed for one or the other task, and attempts to model both generally involve taking a model of categorization and adding on an ad hoc mechanism for predicting discrimination. there is no apparent reason why discrimination has to decline when categories form, and in some cases it appears not to. my co-authors may disagree with me on this point, but i feel like our model does not specifically address discrimination. second thought: i have not seen any compelling evidence that 9-month-olds "know" that there is such a thing as "coronal" that encompasses multiple phones. on the other hand, there is abundant evidence that they can discriminate pretty much anything that is meaningfuly different. that's not really in opposition to your point, i guess. more a caveat that we should be careful what generalizations we assume the baby is assigning to her stimuli. [RD]
Ditto to what Robert said -- it's not clear that infants haven't learned about native phonetic categories prior to the loss of sensitivity to foreign contrasts. And b) It sounds like what you're saying is that infants can learn phonotactic dependencies at 4 months -- not that they know native language phonotactics at 4 months. So I'm not sure how that bears on the issue of what they have learned about the native language. Certainly being able to learn that sort of pattern indicates that they're likely doing that sort of processing in the real world. But real language almost certainly takes longer to learn than our miniature artificial ones. For example, 6 month olds (and that's the youngest we've tested) show consonant learning in my phonetic learning studies, although there's no evidence that they know native language consonant categories yet. [JM]
It seems to me that this sort of data is also problematic for the segments-then-phonotactics view that we're criticizing in our work. Under a strong version of that hypothesis, I think we'd expect that infants would be incapable of learning anything about phonotactics until they were totally done learning about segments (either in their native language, or in the context of the experiment). I think these data are good news for us, actually. [MG]
2. Phonotactic learning occurs long before babies start converging on their languages inventory. For instance, we've had babies learn a V-C dependency at 4 and 6 months, and a #C dependency at 7 months. [Incidentally, we found that constraints on allophones are hard to learn at later ages; so the VC dependency was on nasal vowels, and 4 and 6-mo could learn it, 11mo babies couldn't if they were learning English, but were ok with it if learning French.] [ac]
i don't think there's very clear evidence that infants haven't converged on their language's inventory by 4-6 months. the evidence we have is that by 6 months, their within-category discrimination DECREASES relative to across-category discrimination. which is certain proof that there is a category there. however, this does not mean there is no category there before: absence of evidence is not unequivocal evidence of absence. it is entirely possible that the category onset occurs before the decline in discrimination. this goes back to the point i was mentioning before -- until we have a better theory of why discrimination declines with categorization, we have to be careful about how we interpret the presence/absence of categories. there is one really interesting study by nobuo masataka that speaks to this point -- he found that japanese learning infants' vowel productions were significantly influenced by the most recent vowel their mother had produced. in particular, if mother produced /a/, the next vowel baby produces is, on average, spectrally shifted toward /a/, and the same holds true for the other point vowels. if i recall correctly, this was 4-month-olds! seen from a certain theoretical lens, this could be evidence of extremely early category formation. alternatively, it could be viewed as a means by which categories are learned. in either case, though, it is clear evidence that infants have already discovered aspects of the forward mapping from articulation to acoustics. [RD]
I haven't read that Masataka study but from your description I'm not sure why you would take it to be evidence for phonetic categories. A simpler explanation would be the latter one you mentioned -- the babies are starting to figure out how articulation relates to acoustics. [JM]
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