Eye movement control during visual object processing: effects of initial fixation position and semantic constraint.

Eye movement patterns were recorded while subjects viewed arrays of line drawings of objects. The initial landing position of the eyes on an object was found to be normally distributed around the center of the object, with the modal landing position at the center. Landing variability was greater in the direction of the eye movement vector than in the direction perpendicular to the movement, and there was more of a tendency to undershoot the center of the object than to overshoot it. Landing position was found to influence other aspects of eye movement behaviour. The duration of the first fixation on an object decreased and the probability of refixating an object increased as the deviation of the initial landing position from the center of the object increased. The effect of a cognitive factor, semantic constraint, was also examined. Landing position and semantic constraint were found to interact such that semantic constraint had a greater effect the further the eyes landed from the center of the object. The results are discussed in terms of their implications for the use of eye movement behaviour as an indicator of perceptual and cognitive processing.