Prediction, Error, and Adaptation During Online Sentence Comprehension

A fundamental challenge for human cognition is perceiving and acting in a world in which the statistics that characterize available sensory data are non-stationary. This thesis focuses on this problem specifically in the domain of sentence comprehension, where linguistic variability poses computational challenges to the processes underlying sentence comprehension. We begin by framing the problem of linguistic variation, especially in syntax, and then propose that humans respond to this variability by continuously adapting to and learning the statistical regularities of novel linguistic environments. Experiments 1-6 provide evidence that, in the face of a novel environment whose statistics violate subjects' expectations, subjects adjust their linguistic expectations in order to allow their expectations to converge towards the statistics of the current environment. These experiments tacitly assume that adaptation is error-sensitive: subjects adapt when their expectations are violated. Experiment 7 explicitly addresses and tests this tacit assumption. In that experiment, we provide a quantitative operationalization of the syntactic "error signal" in language comprehension, and ask how the magnitude of this error signal correlates with immediate changes in linguistic expectations. This experiment also provides the context for a more in-depth discussion of what type of cognitive mechanism might give rise to the experimental results reported in this thesis. Experiment 8 attempts to more directly address the presumed environment-specificity of adaptation by asking whether distributional information indexed to a particular environment and to particular verbs can be retained over multiple days. The work reported here takes a step toward synthesizing three lines of research in psycholinguistics that have previously proceeded largely in parallel: (1) experience- or expectation-based processing, (2) syntactic priming, and (3) statistical learning in language. The work here also suggests an intriguing if somewhat tentative link between adaptation in syntactic comprehension on the one hand and adaptation in lower-level speech perception and non-linguistic perception, where adaptation phenomena have previously been more thoroughly examined.