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In natural scene viewing, participants tend to direct their gaze towards the image center, the "central bias". Unless the head is fixed, gaze shifts to peripheral targets are accomplished by a combination of eye and head movements, but there are substantial individual differences in the propensity to use the head. Here, we address whether inter-individual differences in central bias and head movement propensity are related. In one part of the experiment, participants freely viewed natural scenes of two different sizes under laboratory conditions (limited screen size, sitting with head fixed by chin and forehead rest). In the second part, participants stood in the center of a cylindrical, 240° panoramic screen and were free to move their eyes, head and upper body. In each trial, they directed their gaze from the screen's vertical midline (0°) to a peripheral target that was located at 5 to 70 degrees eccentricity on either side. Two different conditions were used - an exogenous mode (vertical bar appearing at target position) and an endogenous mode (target position verbally instructed at screen center). The central bias was quantified by the median Euclidian distance of fixations to the image center. Across participants, we found a strong correlation in central bias between the two image sizes; this is, central bias scaled with image size. In the peripheral target task, we found a strong correlation between the exogenous and the endogenous mode, indicating that the tasks were a robust measure of head movement propensity. Despite substantial inter-individual variability in both tasks, no significant correlation was found between head movement propensity and central bias. Taken together, our results suggest that central bias in scene viewing on typical screen sizes is predominately determined by visual properties, and individual differences in central bias are not explained by head movement propensity.
Acknowledgements: The work was funded in part by the German Research Foundation (DFG), SFB/TRR135 – project ID 222641018.