How are eye fixation durations controlled during scene viewing? Further evidence from a scene onset delay paradigm

Recent research on eye movements during scene viewing has focused on where the eyes fixate. But eye fixations also differ in their durations. Here we investigated whether fixation durations in scene viewing are under the direct and immediate control of the current visual input. In two scene memorization and one visual search experiments, the scene was removed from view during critical fixations for a predetermined delay, and then restored following the delay. Experiment 1 compared filled (pattern mask) and unfilled (grey field) delays. Experiment 2 compared random to blocked delays. Experiment 3 extended the results to a visual search task. The results demonstrate that fixation durations in scene viewing comprise two fixation populations. One population remains relatively constant across delay, and the second population increases with scene onset delay. The results are consistent with a mixed eye movement control model that incorporates an autonomous control mechanism with process monitoring. The results suggest that a complete gaze control model will have to account for both fixation location and fixation duration.