Environmental Determinants of Lexical Processing Effort
A central concern of psycholinguistic research is explaining the relative ease or difficulty involved in processing words. In this thesis, we explore the connection between lexical processing effort and measurable properties of the linguistic environment. Distributional information (information about a word’s contexts of use) is easily extracted from large language corpora in the form of co-occurrence statistics. We claim that such simple distributional statistics can form the basis of a parsimonious model of lexical processing effort. Adopting the purposive style of explanation advocated by the recent rational analysis approach to understanding cognition, we propose that the primary function of the human language processor is to recover meaning from an utterance. We assume that for this task to be efficient, a useful processing strategy is to use prior knowledge in order to build expectations about the meaning of upcoming words. Processing effort can then be seen as reflecting the difference between ‘expected’ meaning and ‘actual’ meaning. Applying the tools of information theory to lexical representations constructed from simple distributional statistics, we show how this quantity can be estimated as the amount of information conveyed by a word about its contexts of use. The hypothesis that properties of the linguistic environment are relevant to lexical processing effort is evaluated against a wide range of empirical data, including both new experimental studies and computational reanalyses of published behavioural data. Phenomena accounted for using the current approach include: both singleword and multiple-word lexical priming, isolated word recognition, the effect of contextual constraint on eye movements during reading, sentence and ‘feature’ priming, and picture naming performance by Alzheimer’s patients. Besides explaining a broad range of empirical findings, our model provides an integrated account of both context-dependent and context-independent processing behaviour, offers an objective alternative to the influential spreading activation model of contextual facilitation, and invites reinterpretation of a number of controversial issues in the literature, such as the word frequency effect and the need for distinct mechanisms to explain semantic and associative priming. We conclude by emphasising the important role of distributional information in explanations of lexical processing effort, and suggest that environmental factors in general should given a more prominent place in theories of human language processing.