I think both Paul and Norbert have drawn the lines here too oversimply, and perhaps not even in the right places. I doubt that the contrast for earliest word learning is merely between “quick” essentially one-trial learning (hence, by implication, recollecting what you previously knew in Plato’s terms) triggered by a suitable (contingent) input, vs a slow incremental procedure that gathers and evaluates evidence delivered partially, across many encounters. The first problem is that the difference in expressive range between a human (even 3 year old) vocabulary and a moth-wing coloration is so large as to make analogizing between these grotesque. The 40000 or so common words really all do mean different things (pace Hume, who had a constructionist story, but alas one that doesn’t work). Second, the relation between what’s acquired and the contingent trigger is nonaccidental for wing colors and bee navigational guidance just as Paul says, whereas (as I blush even to say in present company) the sound and the meaning of a word are not only arbitrarily related but arbitrarily varying across languages (Suppose that there were something like “phonetic symbolism” such that the big animals were labeled with multisyllabic words, etc., this might be a better analogy with the wing-color situation; but alas this isn’t so either). Accordingly, contra Norbert, the learning of even first words is – perhaps paradoxically – slow (in the sense that such knowledge usually appears after, probably, many many encounters with a word-sound) but quick (in that it appears suddenly, immediately, if we are right, in the presence of the “right” encounter, which may be the first encounter or the 150th encouter). The problem is the selection of the right encounter. The usual (associationist) story is really very compelling on a commonsensical basis – it’s probably true that /dog/ occurs more systematically in the presence of dogs than does /aardvark/, etc. , so it seems reasonable that one would be collecting and comparing across successive encounters. But the problem (even leaving aside our and many other experimental demonstrations that memory won’t support such a procedure) is that the set of concepts and the set of observations are both so large – essentially open – as to make it unlikely in the extreme that a Mind could carry through the collect, contrast, compare procedure required to extract the needed generalization (/dog/ refers to a dog qua dog). Some progress may come from noting the temporal parameters within which observation of a dog, utterance of /dog/, and mutual attention to dogs (e.g., joint visual fixation) co-occur, something we’re working on (maybe this will deserve the title “representational causation”). But I think it’s premature to be happy at all about where we are in thinking about POS and word learning.
Because the next problem, really it is the real first problem, is that most words cannot be acquired at all if the procedure is limited to mapping between a sound and “the world.” For many many words, the world plays almost no role at all in constraining the potential meaning (try “think” or “probably” or “similar” or “fair”) and for most it plays a subsidiary role, with linguistic information providing the bulk of the information (information from “the world” is generally brushed off and ignored both by adults and 3 year olds when pitted against linguistic information, amazing!). How soon we forget: Because there are some suggestions now that learning is on single trials (plus a confirmation trial) one tends to forget a longer line of evidence that most words are learned via a domain-specific machinery that examines their linguistic licensing conditions. The tiny set of words that are acquired absent linguistic information is however crucial because (1) they are the very first words, and for necessary reasons; (2) they provide the enabling information for building the language-specifics of structured representations within which all subsequent meanings are learned (specifically, you have to find out where the subject of the clause is, in your language, and you do this, basically, by seeing where in sentences “dog” shows up, within dog scenarios); (3) speaking systematically, all theoretical questions are begged unless there is a NONlinguistic way of learning some ‘seed words’ (otherwise you are trapped saying you learned the syntax from the meanings and you learned the meanings from the syntax); the procedure has to be grounded by a first, domain-general, procedure for confronting the world; (4) this procedure is exceedingly limited, I believe, but attainable even by very lowly animals taught stupid tricks in the laboratory by psychologists. Call this learning. Because it is an “outside in” procedure designed by nature to work no matter how disorganized and unsystematic your present circumstances Not “acquisition,” applicable to the “inside out” procedures to follow. You need a learning procedure, linked to the world, to get into that system, which though it is UG at bottom, is well disguised at the surface (e.g., as English, vs Urdu, vs ASL…). Your mother just says blah-blah-blah instead of NP VP, there’s the rub.