Rough Theory

Rather than doing something rational like reading the works the reading group will actually discuss this week, I’ve been drawn off onto a tangent, looking at works on what is called the “poverty of the stimulus” argument. Unfortunately, most of the key pieces I want to read are temporarily unavailable – needing to be recalled from other students, or in journals I’ll need to request via interlibrary loan – making the attempt to trace the intellectual history of this argument more frustrating than it otherwise ought to be. The discussion that follows is therefore unlikely to reflect the best possible presentation of the poverty of the stimulus argument – a better understanding of which might well obviate most or all of my questions.

As I understand it, the “cash value” of the poverty of the stimulus argument is to establish that nativist theories of language acquisition, which posit that children possess an innate predilection for grasping key grammatical principles, are more plausible than empiricist theories, which posit that children decode grammatical principles via exposure to speech in practical situations.

The argument relies on the counter-factual notion of how an “unbiased” learner might conceivably approach language acquisition – where an unbiased learner is understood as something like a computer, tackling the problem of language acquisition by brute computational force, without any organising principles at its disposal other than its own observational analysis of statistical patterns: capable of hypothesising all the various ways in which words might conceivably be combined, and having no particular a priori conditioning to organise words in any particular order. (There are prior issues about how an unbiased learner gets to the point that they understand the difference between a meaningful and unmeaningful sound, how an unbiased learner develops an understanding that streams of meaningful sounds can be chunked down into words, etc. – I’ll leave these issues aside for the moment, although they can also be brought into the nativist-empiricist debate.)

The poverty of stimulus argument maintains that the number of hypothetically-conceivable principles that could motivate the observed regularities in any given language is much greater than the number of principles that children appear to entertain, when their process of language acquisition is studied empirically: there are certain hypothetically plausible interpretive errors that children never seem to make, even though, in some cases, these errors might involve simpler “hypotheses” about how language works than the hypotheses that seem to inform children’s linguistic practice. The theory further argues that environmental stimulus is inadequate to account for children’s linguistic practice: that children do not receive sufficient reinforcement, particularly negative reinforcement, to account for their “correct” interpretations of the principles underlying spoken language. The theory can also point to a range of empirical evidence – for example, the observation that children tend to learn their native language (including sign languages) in consistent stages, with characteristic errors and achievements at each stage – that is highly suggestive that children’s language acquisition is not sensitive solely to environmental conditioning. The conclusion is therefore that nativist explanations for language acquisition are more plausible than empiricist ones.

I have a few questions about this argument, but I should perhaps indicate at the outset that I don’t have a dog in this fight – I’m not completely certain that I even understand, at this point, why this fight draws such strong emotions from the opposing positions (I’m sure I’ll learn…). I find empirically persuasive certain key claims about children’s language acquisition (that it progresses in clearly observable stages, with characteristic errors, etc.) because I’ve worked professionally in roles where these sorts of observations could be easily confirmed. To that extent, I suppose I’d be claimed by the nativist side – but only because, and this is where my questions begin, this argument seems to assume that the key opposition is between something like the following positions:

– a form of empiricism that views humans as unbiased learners, with no inbuilt predilection for making sense of their world in one direction, rather than another, and for whom environmental stimulus must therefore account for any regularities we observe in language acquisition;

vs.

– a form of nativism that argues that, because humans can empirically be observed not to be unbiased learners of language, we can therefore draw the conclusion that humans possess an innate, domain-specific facilty for language acquisition.

My curiosity – and I should stress that, at this point, my position is nothing more than a curiosity – is whether these two positions exhaust our options? The version of empiricism presented here seems somewhat straw-mannish to me – and I worry that this straw man element may have the result of obscuring an overbroad conclusion on the nativist side. It sounds superficially impressive to note, for example, that there might be a statistically enormous number of ways that an unbiased learner might choose to order English auxiliary verbs (“50,000 times the number of seconds since the beginning of the universe, and about a hundred billion times the number of neurons in the human brain”, according to one source), but that children somehow manage to hit on precisely the 99 combinations that are grammatically possible in English. But this assumes that the “real odds” of children’s performance can validly be calculated by comparing them to a hypothetical unbiased learner who can freely select any of a number of equally-weighted options from a universe of choices.

While this might sound plausible on first glance – surely you calculate odds against the universe of everything that it possible, etc. – I’m not convinced that this kind of reasoning applies in complex, interactive systems in which the actual choices available might be highly dependent on a wide variety of conditioning factors – one of which, certainly, might be some kind of nativist specialised language acquisition subsystem, but which might equally – since we’re speaking about hypothetical entities that, as I understand it, are not currently considered subject to direct empirical investigation – be hypothesised to include conditioning factors that, while not specialised to language acquisition, nevertheless have the effect, individually or in combination, of making certain kinds of linguistic interpretations more plausible than others: for example, feedback from a wide variety of environmental stimuli, not limited to the “environment” provided by spoken words, but with implications for language acquisition; neurological functions that are not specialised to language acquisition, but that shape language use; cross-fertilisations that result from the fact that children are not working only on a “problem” like auxiliary verbs in isolation, but in conjunction with other kinds of puzzles that must be also sorted during language acquisition – the combined effect of which may be to make certain grammatical extrapolations more likely than others; etc.

I don’t mind, of course, if someone wants to conclude that their preferred option among these choices is a nativist concept of a specialised language subsystem – as long as this is acknowledged as a working hypothesis for a period when we can’t yet have evidence to differentiate among a variety of possibilities. I become uncomfortable only when the argument seems to be framed as though the only conceivable alternative would be some form of hyper-Skinnerian notion of a tabula rasa, whose behaviour is determined in a very straightforward, mechanistic way by environmental stimulus. I admittedly don’t know the field of linguistics very well at all, but I have a difficult time believing that this Skinnerian fever-dream is anyone’s notion of a serious alternative. (But, yes, I’ll acknowledge that the poverty of stimulus argument offers a devastating critique of such a perspective, if anyone out there holds it…) It seems to me, though, that the actual problem is far more complex – and I’m somewhat concerned that the nativist approach might be slicing this particular gordian knot a bit too quickly: how much do we really know, at this point, about the complex array of factors that make us biased learners? About how these factors interact with one another? About how these interactions limit the plausible ranges of learning we are likely to acquire? Do we know how to interpret the empirical evidence we have about children’s language acquisition, until we have looked at these issues in more detail?

I am painfully aware that these questions may be simply naive – I am so early into this reading, and so new to this field, that I’m happy to be pointed to work of which I am all-too-likely to be unaware… These were, however, the questions that struck me, as I was reading things I wasn’t intended to read, for the discussion my reading group is about to have on something else entirely… ;-P So now back to that copy of Language and Mind…