Direct control of fixation times in scene viewing: Evidence from analysis of the distribution of first fixation duration

Abstract

Participants' eye movements were monitored in two scene viewing experiments that manipulated the task-relevance of scene stimuli and their availability for extrafoveal processing. In both experiments, participants viewed arrays containing eight scenes drawn from two categories. The arrays of scenes were either viewed freely (Free Viewing) or in a gaze-contingent viewing mode where extrafoveal preview of the scenes was restricted (No Preview). In Experiment 1a, participants memorized the scenes from one category that was designated as relevant, and in Experiment 1b, participants chose their preferred scene from within the relevant category. We examined first fixations on scenes from the relevant category compared to the irrelevant category (Experiments 1a and 1b), and those on the chosen scene compared to other scenes not chosen within the relevant category (Experiment 1b). A survival analysis was used to estimate the first discernible influence of the task-relevance on the distribution of first-fixation durations. In the free viewing condition in Experiment 1a, the influence of task relevance occurred as early as 81 ms from the start of fixation. In contrast, the corresponding value in the no preview condition was 254 ms, demonstrating the crucial role of extrafoveal processing in enabling direct control of fixation durations in scene viewing. First fixation durations were also influenced by whether or not the scene was eventually chosen (Experiment 1b), but this effect occurred later and affected fewer fixations than the effect of scene category, indicating that the time course of scene processing is an important variable mediating direct control of fixation durations.