Abstract
In everyday life, we make simple visual judgments about object properties, e.g., how big or wide is a certain object? When judging such properties haptically, there are specific exploratory routines for different tasks. Our goal is to test whether there are also task-specific oculomotor routines which support perceptual judgments. In a first study, observers saw different scenes with two objects presented in a photorealistic virtual reality environment. Observers were asked to judge which of the two objects was taller or wider while gaze was tracked. As all tasks were performed with the same set of virtual objects in the same scenes, we can compare spatial characteristics of exploratory gaze behavior to quantify oculomotor routines for each task. Width judgments showed fixations around the center of the object with larger horizontal spread. For height judgments, gaze was shifted towards the top of the object. These results suggest there are different routines in gaze behavior and that they presumably are used for perceptual judgments. To test the causal link between oculomotor behavior and perception, in a second study, observers memorized a standard object, and compared the width and height of other objects to this standard. Height and width of the compared object was varied relative to the standard. In one block, observers could use their routines to freely gaze at the object. In another block, a gaze contingent set up forced observers to fixate the center of the object. The time objects were visible was matched across blocks. Discrimination performance, quantified as the slope of psychometric functions, was worse for the height task in gaze contingent blocks, but was not impaired for the width task where central fixation was not very different from free viewing. These results suggest that restricted gaze can interfere with natural oculomotor routines and impair visual performance.