Saccade length consistency during reading and shape-scanning.

Human gaze behaviour provides insights into the mental processes underlying the execution of a task. As reading involves visual sampling and language processing, various studies investigate how the linguistic information of texts influences visual behaviour. However, established measures of human visual behaviour are dependent on the exact configuration of the text stimuli and the nonlinguistic stimuli used for comparison, leaving systematic stimulus-independent differences largely unknown. Here, we show that relative saccade length distributions reveal similarities and differences in gaze dynamics during reading and shape-scanning. In a within-subject design, participants read texts and scanned a spatially matched array of geometric shapes. We find that the lengths of consecutive saccades in target direction are more consistent during reading than during shape-scanning, suggesting that saccadic planning is more constrained during reading. The consistency of eye movements opposite to the target direction does not differ for the experimental conditions. These results consolidate findings from neurocognitive studies on the vision-language interface and suggest how underlying neural structures manifest themselves in observable visual behaviour. Furthermore, the results indicate that relative saccade lengths could present a new measure for investigating how linguistic processing influences human visual behaviour during reading. More broadly, the results suggest that analysing gaze behaviour dynamics via relative saccade lengths might provide novel insights into similarities and differences across tasks.