On the specificities of the inverted-optimal viewing position effect and their implications on models of eye movement control during reading

During reading, the probability of refixations increases and the duration of first fixations decreases with growing distance of the initial fixation position from a word's center (i.e., the optimal viewing position, OVP). The question, whether or not refixation-OVP and first-fixation duration inverted-OVP curves are modulated by the lexical characteristics of the actually fixated stimulus is still a matter of debate. The aim of the present study is to investigate the relative temporal succession of the availability of lexical information and the preparation of saccadic motor programs. For that purpose, the lexicality effect in event-related brain potentials and the onset of saccadic eye movements (as an observable indicator for the preparation of saccadic motor programs) were recorded simultaneously. Initial fixation position on a stimulus was experimentally varied by means of the variable viewing position paradigm. The observed first-fixation duration inverted-OVP curve was not modulated by lexical characteristics and an effect of initial fixation position on the onset of the lexicality effect in event-related brain potentials (i.e., a lexicality-OVP effect) could be observed. An analysis of the time-course of both effects revealed that it is highly unlikely that refixations as observed by the variable viewing position paradigm can be modulated by lexical characteristics. An interpretation in terms of an early cohort of refixations that corrects for suboptimal initial fixation positions and that is not influenced by lexical characteristics of the stimulus material is favored. Subsequently, it is analyzed how current models of eye movement control can account for the present study's results.