An eye-movement analysis of the word-predictability effect

  • Shirley-Anne, S. Paul

    Student thesis: Doctoral ThesisDoctor of Philosophy


    The primary aim of this thesis was to identify the mechanism under-pinning the word-predictability effect, while a secondary aim was to investigate whether words are processed in serial or parallel. In five experiments, adults’ eye-movements were monitored as they read sentences for comprehension on a computer screen. In Experiments 1 and 2, a critical target-word that was either of high- or low-frequency and either predictable or unpredictable was embedded in experimental sentences. The nature of the preview of the target word was manipulated such that it was either identical to the target or was misspelled (the misspelling was more severe in Experiment 2). Predictability effects were apparent in the identical preview condition in both experiments, whilst they were only apparent in the misspelled condition of Experiment 1. This outcome is compatible with early Guessing Game type models of reading which propose that readers predictions about up-coming words using contextual parafoveal information. When taken together, the results of Experiments 1 and 2 also suggested that frequency and predictability exert additive effects on fixation durations.In Experiment 3, four levels of word-predictability were employed. The function relating word-predictability and word-processing time was strictly monotonic: word-processing time decreased as predictability increased. This outcome was consistent with a word-prediction account of predictability in which there is no penalty for incorrect guessing. Experiment 3 also showed that processing time on the pre-target word increased as the predictability of the up-coming increased. This outcome replicated an effect obtained by Kliegl, Nuthmann and Engbert (2006) who claim that it arises as a result of memory retrieval processes cued by prior sentence context Experiment 4 replicated the manipulation in Experiment 3 but included additional condition in which the preview of the target word was masked while in parafoveal vision, using a pixel scrambling technique. The target-predictability effect was again a graded one, and did not depend upon the availability of initial information, providing evidence against the word-prediction theory. Additionally, there was no pre-target predictability effect in the unmasked condition. There was a pre-target effect in an direction in the masked condition, although this appeared to be a consequence of the mask. Experiment 5 replicated Experiment 4, but replaced the masked condition with a non-predictable but semantically related word, and the results showed no pre-target effects at all. It was concluded that inverted pre-predictability effects are more likely to be related to higher-level sentential processing.
    Date of Award2010
    Original languageEnglish
    SponsorsEconomic and Social Research Council, UK
    SupervisorWayne Murray (Supervisor)


    • Eye-movements
    • Reading
    • Word-predictability

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