Chapter 13 - Dynamic coding of saccade length in reading

Abstract

It is commonly assumed that eye movements in reading are determined with respect to word entities, and that the distribution of initial landing sites in words derives from a strategy of aiming at specific parts of peripherally located target words. The chapter investigates the oculomotor processes responsible for the determination of saccade length and initial landing sites. Distributions of saccade length during pseudo-reading and normal reading were analyzed. Strategy-based, visually guided, and corrective saccades were qualitatively identified after examining the influence of launch site, word length, and saccade latency. Gaussian mixture models were implemented to approximate the frequency of the three groups of saccades. The distributions of saccade length in pseudoreading and normal reading were simulated; the percentages of saccade frequency for the three groups varied in relation to saccade latency, word length, and launch distance. Both simulated and empirical data showed that strategy-based saccades of a relatively constant length were favored at early time intervals whereas visually guided saccades became more likely later during a fixation; the former were more frequent in reading compared with pseudo-reading. The chapter concludes that eye guidance in reading is the result of dynamic coding of saccade length instead of cognitively based aiming strategies.