Stochastic Context-free Grammar - Linguistics and Psycholinguistics

Linguistics and Psycholinguistics

With the publication of Gold's Theorem 1967 it was claimed that grammars for natural languages governed by deterministic rules could not be learned based on positive instances alone. This was part of the argument from the poverty of stimulus, presented in 1980 and implicit since the early works by Chomsky of the 1950s. Among other arguments, this led to the nativist (but still unproven) view, that a form of grammar, including a complete conceptual lexicon in certain versions, were hardwired from birth. However, Gold's learnability result can easily be circumvented, if we either assume the learner learns a near-perfect approximation to the correct language or that the learner learns from typical input rather than arbitrarily devious input. In fact, it has been proved that simply receiving input from a speaker who produces positive instances randomly rather than according to a pre-specified devious plan leads to identifiability in the limit with probability 1.

Recently, probabilistic grammars appear to have gained some cognitive plausibility. It is well known that there are degrees of difficulty in accessing different syntactic structures (e.g. the Accessibility Hierarchy for relative clauses). Probabilistic versions of Minimalist Grammars have been used to compute information-theoretic entropy values which appear to correlate well with psycholinguistic data on understandability and production difficulty.