Binocular fusion during reading

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Reading is an incredibly valuable skill in today’s society, and it is used in thousands of day-today tasks. It is, therefore, vital that we develop detailed psychological theories about this important human visuo-cognitive function. In order to accurately model eye movements during reading - and then map aspects of them onto the psychological processes underpinning human language comprehension - it is critical to know exactly what people perceive. We read with both eyes, and therefore, visual processing necessarily involves the creation of a single perceptual representation from two independent visual signals, one from each eye. One neglected aspect of occulomotor behaviour during reading is the coordination of both eyes: binocular vision requires that the vergence angle between the two visual axes is adjusted to allow for processes of fusion. Fixation disparity (slight vergence errors) and the process of fusion are core phenomena in relation to binocular coordination, yet, to date, there is no single unified theoretical account of these phenomena. Fusional processes are, very fundamentally, disparity driven. The time course of fusional processes during reading is still unclear. In the proposed research, we will systematically explore this time course by manipulating the amount of binocular information (foveally and parafoveally) present after saccade execution. Further, in order to address the question of the amount of fixation disparity that can be tolerated whilst fusion is still attained, we will manipulate the absolute disparity of the two visual inputs after saccade execution. Both experimental manipulations will be realized by means of an advanced experimental technique termed saccade contingent change methodology.