Document Type

Dissertation

Date of Degree

Spring 2016

Degree Name

PhD (Doctor of Philosophy)

Degree In

Speech and Hearing Science

First Advisor

Jean K. Gordon

Abstract

This thesis explores how predictions about upcoming linguistic stimuli are generated during real-time language comprehension in younger and older adults. Previous research has shown humans' ability to use rich contextual information to compute linguistic prediction during real-time language comprehension. Research in the modulating factors of prediction has shown, first, that predictions are informed by our experience with language and second, that these predictions are modulated by cognitive factors such as working memory and processing speed. However, little is known about how these factors interact in aging in which verbal intelligence remains stable or even increases, whereas processing speed, working memory, and inhibitory control decline with age. Experience-driven models of language learning argue that learning occurs across the life span instead of terminating once representations are learned well enough to approximate a stable state. In relation to aging, these models predict that older adults are likely to possess stronger learned associations, such that the predictions they generate during on-line processing may be stronger. At the same time, however, processing speed, working memory, and inhibitory control decline as a function of age, and age-related declines in these processes may reduce the degree to which older adults can predict. Here, I explored the interplay between language and cognitive factors in the generation of predictions and hypothesized that older adults will show stronger predictability effects than younger adults likely because of their language experience. In this thesis, I provide evidence from reading eye-movements, event-related potentials (ERPs), and EEG phase synchronization, for the role of language experience and cognitive decline in prediction in younger and older English speakers. I demonstrated that the eye-movement record is influenced by linguistic factors, which produce greater predictability effects as linguistic experience advances, and cognitive factors, which produce smaller predictability effects as they decline. Similarly, the N400, an ERP response that is modulated by a word's predictability, was also moderated by cognitive factors. Most importantly, older adults were able to use context efficiently to facilitate upcoming words in the ERP study, contrary to younger adults. Further, I provide initial evidence that coherence analysis may be used as a measure of cognitive effort to illustrate the facilitation that prediction confers to language comprehenders. The results indicate that for a comprehensive account of predictive processing research needs to take into account the role of experience acquired through lifetime and the declines that aging brings.

Public Abstract

One of the major theories on how we comprehend language is based on the idea of prediction. For example, when hearing the phrase “She takes her coffee with cream and …”, you can easily predict that the next word will be “sugar”. This dissertation explored the way younger and older individuals anticipate upcoming words in context, and the role of cognitive skill and language experience in explaining predictability effects. The general hypothesis was that, if language learning continues through life span, and prediction is strongly influenced by language experience, then older adults would show stronger predictions than younger adults. However, if the generation of predictions is more strongly influenced by cognitive factors, then older adults may generate weaker predictions. To test that, I investigated the way older and younger adults move their eyes while they read predictable or less predictable words, and also younger and older adults’ brain waves in conditions that either predict a specific word or a specific semantic category. In support for our hypothesis, larger predictability effects were found as linguistic experience advanced, in the way people move their eyes as they read. In brain responses, cognitive factors influenced predictability effects in older and younger adults, in that poorer scores in cognition indicated smaller predictability effect. Most importantly, older adults were able to use context efficiently to facilitate upcoming words, evidenced by the way their brain processes semantic category information.

Keywords

publicabstract, Aging, EEG, Eye-tracking, Language processing, Prediction, Reading

Pages

xiv, 148

Bibliography

136-148

Copyright

Copyright 2016 Spyridoula Cheimariou

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