Cognitive control of eye movements in reading and visual search: Evidence from frequency-based effects

Experiments in this dissertation investigate the role of cognition in eye-movement behavior during scanning and reading. Shorter and fewer fixations on the more frequent and predictable words have been observed during reading, but not when scanning text for a target word, e.g., zebra (e.g., Rayner & Raney, 1996). Past research has employed these effects of word frequency and predictability to argue that cognition drives eye movements during reading, but not during scanning. Similarly, the present studies use effects of stimulus frequency and predictability to index cognitive control of eye-movement behavior. Experiments 1 and 2 focus on the frequency effects for non-word and word stimuli, respectively. Experiment 1 employed clusters of Landolt Cs to examine how the gap size of and frequency of exposure to clusters affected eye movements during a scanning task. The findings demonstrated that, in parallel to word frequency effects observed in reading, more frequent clusters elicited fewer and shorter fixations. Experiment 2 compared eye-movement behavior on fully-crossed high- and low-frequency adjective-noun pairs embedded in paragraphs when participants were reading vs. scanning for a target word with an asterisk (e.g., “h*rse”), a word containing the letter "q" (e.g., “quilt”), or a word rhyming with "blue" (e.g., “shoe”). The results demonstrated that eye-movement measures are affected by frequency in the tasks requiring in-depth processing, such as reading and rhyme-judgment, but not in shallow-processing tasks like asterisk-detection. Experiments 3 and 4 focus on the frequency-based predictability effects for non-word and word stimuli, respectively. Experiment 3 employed similar materials to Experiment 1 and, in addition, manipulated frequency for pairs of clusters. The more predictable clusters in the repeating pairs elicited fewer fixations, providing tentative evidence of transitional predictability effects during scanning. Experiment 4 examined the effect of transitional probability in reading by increasing the frequency of co-occurrence for pairs of words (e.g., tulip’s blossoms) in paragraphs of text. The more predictable words elicited shorter first fixation durations, suggesting that co-occurrence frequency may result in forming short-term predictions during reading. Cumulatively, the findings demonstrate that cognitive effects are not unique to reading, and afford a more sophisticated characterization of the cognitive-oculomotor coordination