Are learning phonotactics and learning segments codependent?

Robert, Matt, Jessica and I have been having a discussion on this topic over email. Look out! Comments are interspersed.

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]

probabilities

Hi all,
I have been rereading Matt's recent article on phonotactic learning with phonotactic probabilities and thinking about the upcoming workshop on cues in phonological learning and I am just wondering about the different weightings of cues in infants than adults and the different kinds of cues that we will discuss at the workshop: distributional, articulatory, acoustic, etc... In Matt's paper he found that adults were pretty insensitive to the probability variation of /s/ in onset position and I am wondering whether we might not expect different things from infants. Let me see what you all think of my predictions. While infants are clearly *very* sensitive to probabilities in the input they also might be less sensitive to articulatory ease since they don't really articulate yet (this would not be true for toddlers of course), so they might show a different performance pattern here than adults. This also begs the the question of why adults show a lack of sensitivity (perhaps something that Matt can help me with). Is it because they are less sensitive to probabilities over time or because they show a heightened sensitivity to ease of articulation?
-Amanda

Some questions on the ideas put forward by y'all

Hello everyone,

I was re-reading everyone's abstracts and thought that there were some interesting coincidences and intriguing mismatches.

For example, I might be reading Susan's wrong, but it seems that she predicts that, with a 1-to-1 mapping from articulation to acoustics, the magnitude of the change in the articulation predicts basically two levels of structure: one corresponding to slower and larger movements and one to more abrupt changes. Only the latter would, according to my interpretation of her abstract, provide acoustic cues. This matches Ying and Jeff's finding that an automatic feature extractor operating on the raw acoustic signal is good at finding manner features, but not so good with place features. On the contrary, motor cues are most useful for place of articulation, but not so great with manner.

Susan also suggests that it is not only the level of fine acoustic cues that affects speech perception, but also the other level. May this be related to Jessica, Robert and Matt (JRM)'s learner of phonotactic constraints and segments? If I get their point right, both infants and adults would rely on acoustic cues in context to discover/perceive phonological categories, and this process may go from a holistic chunk (perhaps syllable-based?) to phone-sized elements. In relation to this, I was thinking that while one may expect that articulatory experience would aid the formation of prosodic categories (like syllabic/word templates), it was at first surprising for me that it is also important for learning of segments. Now I see that this fits really well with JRM's proposal that we may learn phonotactics and segments at the same time, don't you think?

Further, this learning strategy (of phonotactics+segments) must be flexible and still active in adulthood, given that Lisa D's adults are able to learn a minimal pair of words that relies on a non-native phonotactic contrast, but her results also suggest that the presence of a minimal pair (which, through semantic cues, forces listeners to focus on the relevant acoustic cues) is a necessary condition for learning in adults. On the other hand, the presence of minimal pairs cannot be a necessary condition in toddlers (cf. Pater et al. 2004), as Ying and Jeff point out, while already in childhood semantic information is actually helpful, according to Lisa G's results. Is there a developmental trend here? May it be geared by a difference in processing abilities? (If so, would we predict that adults in a high-processing load task would behave like Pater's toddlers and have a *harder* time with the minimal pair than with the non-minimal pair?)

Another question that follows from Susan's hypothesis that these two levels interact in perception is how language experience affects this interaction. Grant's paper seems to suggest that this interaction is mediated by specific experience, such that sheer experience with one of the categories (AmEng speakers must have experience with retroflex sounds, and even with the retroflex fricative in words like 'shrill') is not enough, but speakers must have been exposed to the particular contrast that relies on the acoustic/higher level features under study. This is particularly important for early category formation: Chandan's corpus analysis looks at the correlation of pitch and VOT, which could be interpreted as respective examples of the larger and finer categories proposed by Susan. If IDS takes advantage of the apparent predilection of infants for pitch, will it have its voiced segments be primarily marked with pitch? However, given young infants' very limited articulatory abilities, we'd expect them to rely primarily on acoustic-feature based contrasts, which -now following Ying and Jeff - would predict a primacy of VOT.