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Master of Science (M.S.)

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distribution, fixation durations, frequency, predictability, reading


The most important predictors of fixation durations in reading are a word’s frequency of occurrence (as measured by counts in large corpora) and its predictability in context (as measured by cloze probability). Two recent eye-tracking studies investigated distributional effects of word frequency (Staub et al, 2010) and word predictability (Staub, 2011) separately. The present study investigates the distributions associated with these two variables when they are manipulated in the same experiment. When considering the overall means, frequency and predictability showed significant main effects (LF>HF; LP>HP), with no interaction. In addition, we found evidence supporting the previous distributional findings where frequency and predictability affect all fixations (causing a shift in the distribution), but frequency also has a special influence on the longest fixations. Interestingly, the model fits suggested that there was an interaction between the predictors in first fixation duration. However, this effect was not visible in the vincentiles (which are plots of the actual data) and it appeared to be conditional on four particular subjects. Since we did not find convincing evidence of an interaction in our distributional analysis, the present findings provide support for theories of fixation durations whereby frequency and predictability combine additively.


First Advisor

Adrian Staub