Uncertainty reduction: ambiguity resolution mechanisms in language

Ambiguity is a constant problem for any embodied cognitive agent with limited resources. Decisions need to be made, and their consequences understood, despite the probabilistic veil of uncertainty enveloping everything from sensory input to action execution.

A nice sample domain for understanding ambiguity resolution is language, where problems of uncertainty have been long appreciated. The meaning of words in general (not to mention referents like "that" or "he") can be highly ambiguous (see "the gavagai problem"). A similar problem abounds in grammar, famously in the case of garden path sentences ("the horse raced past the barn fell"), where grammatical ambiguities are often completely overlooked until a differentiating word is encountered ("fell").

Most accounts of language emphasize the distinction between semantics (the meanings of words) and syntax (the rules involved in how words are put together -- essentially, grammar). One might therefore suspect that ambiguity resolution in these two domains is separable. However, a classic Psychological Review article by MacDonald, Pearlmutter and Seidenberg describes a single ambiguity resolution mechanism which might operate both on semantics and syntax.

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