Examining the influence of image features, visuomotor parameters, and task set on fixation durations in scene viewing

Scene perception requires the orchestration of visuospatial, image-related, task-related, and oculomotor processing constraints. The present study investigated how these factors influence how long the eyes remain fixated in a given location. Specifically, we tested whether local image statistics (including luminance, luminance contrast, edge density, visual clutter, and mean-shift segmentation), calculated for 1º circular regions around fixation locations, modulate fixation duration and how these effects depend on task-related control. Fixation durations and locations were recorded from 72 participants, each viewing 135 scenes under three different viewing instructions (scene search, memorization, preference judgment). Along with the image-related predictors, linear mixed models simultaneously considered a number of visuomotor and spatio-temporal covariates, including the amplitude of the previous and next saccades, and viewing time. As a key finding, local image statistics pertaining to the current fixation n predict this fixation’s duration, regardless of viewing task. For instance, greater luminance is associated with shorter fixation durations. Corresponding distributed-processing analyses investigate effects of these variables related to previous (n - 1) and next (n + 1) fixation locations. The results are in general agreement with the CRISP model of fixation durations, proposing that difficulty in moment-by-moment visual and cognitive processing of the scene modulates fixation durations.