What are you looking at? Acuity for triadic eye gaze.

The authors measured observers' ability to determine direction of gaze toward an object in space. In Experiment 1, they determined the difference threshold for determining whether a live "looker" was looking to the left or right of a target point. Acuity for eye direction was quite high (approximately 30 s arc). Viewing the movement of the looker's eyes did not improve acuity. When one of the looker's eyes was occluded, the observers' acuity was disrupted and their point of subjective equality was shifted away from the exposed eye. Experiment 2 was a replication of Experiment 1, but digitized gaze displays were used. The results of Experiment 3 showed that the acuity for direction of gaze depended on the position of the looker's target. Overall, the results indicated that humans are highly sensitive to gaze direction and that information from both eyes is used to determine direction of regard.