I really like that M&B are looking at a learning problem that would be interesting to both nativists and non-nativists (a lot of the time, it seems like the different sides are talking past each other on what problems they're trying to solve). I also really like that they're exploring a variety of different probabilistic learning models. It does seem that M&B are still approaching the learning problem from a strongly nativist perspective, given the way they've described the actual problem: the learner knows there are two classes of behavior that link syntactic structure to semantic interpretation (raising vs. control), and that there are specific cues the learner should use to figure out which behavior a given verb has (animacy & eventivity). Importantly, only those cues (and their distribution) are relevant. There also seems to be an implicit assumption (at least initially) that unambiguous data are required to distinguish the behavior of any given verb, and the learning problem results because unambiguous data aren't always available (this is a common way learnability problems are framed in a nativist perspective). One thing I wondered while reading this is what would happen if the behavior of these verbs was taken in the context of a larger system - that is, would it possibly be easier to recognize these distinct classes of verbs if other information were deemed relevant besides the two cues M&B look at? I believe they hint at this themselves in the paper - that it might be possible to look at the syntactic distribution of these verbs over all frames, rather than just the ambiguous frame that signals either raising or control (She VERBed to laugh). This doesn't solve the problem of knowing what the different linking rules are between structure and interpretation, but maybe it makes the classification problem (that there are distinct classes of verbs) easier.
Some more targeted thoughts:
- Footnote 2 talks about the issues of homophony, and I can certainly see that tend's meanings are pretty distinct between raising and regular transitive verb. However, happens looks like it means very similar things whether it's raising or regular transitive, so I wonder how children would make this distinction - or if they would at all. If not, then this looks like an additional class of verb that involves mixed behavior.
- The end of section 2 talks about how 3- and 4-year-olds are very sensitive to animacy when they interpret verbs in the ambiguous raising/control frame. I can completely believe that animacy might generally be a cue children use to help them figure out what things should mean (e.g., if a verb takes an agent or not).
- I really like the discussion/caveat that M&B do in the intro of section 4 about biological plausibility.
- I also really liked the discussion of the linear reward penalty (LRP) learner's issues in section 4.2.1. Not having an intermediate state equilibrium is problematic if you need there to be mixed behavior (e.g., something is ambiguous between raising and control). I admit, I was surprised by the saturating accumulator model M&B chose to implement to correct that problem. I had some trouble connecting the various pieces of it to the process in a child's mind - the intuitive mapping didn't work for me the way it does for the LRP learner. For example, the index they talk about right at the end of section 4.2.2 seems fairly ad-hoc and requires children to do abstracting over patterns of frames defined by these different semantic cues.