The effects of word frequency, text case, and contextual predictability on binocular fixation during reading

Properties of text which affect binocular coordination during reading have received little attention compared to other areas of eye movement research. The evidence, to date, has been equivocal, with some suggesting that the visual system tolerates less binocular fixation disparity (BFD) under conditions which make reading difficult and others reporting no such effect. Two eye movement experiments were conducted to investigate this issue further. In Experiment 1, participants read sentences containing high and low frequency words. Half of sentences were presented in normal case and half in alternating case (e.g., aLtErNaTiNg cAsE), replicating Juhasz, Liversedge, White & Rayner (2006). Results showed that neither frequency nor case affected the magnitude of disparity. In Experiment 2, BFD was investigated in a more linguistically rich reading context by manipulating predictability (high vs. low) in addition to frequency and case. Results showed that BFD was significantly smaller for low frequency target words in contexts which made reading difficult. It is concluded that the linguistic and orthographic properties of the text do, in fact, influence binocular coordination. Implications of these results are discussed in relation to models of reading.