Perception of illusory shift of gaze direction by infants.

Detection of others' gaze direction is an essential tool in everyday communication. As the gaze direction is analyzed rapidly and automatically, we hardly notice how we are performing this task. Wollaston's illusion [Wollaston, W. H. (1824). On the apparent direction of eye in a portrait. Philosophical Transactions of the Royal Society of London Series B, 114, 247-256] provides us the chance to understand an aspect of this problem, in which the change in orientation of the face results in the shift of the perceived gaze direction. This illusion suggests that we analyze others' gaze directions by integrating information from eyes and that from face. By using Wollaston's illusion, we examined how 6- to 8-month-old infants process gaze direction in upright and inverted faces. Our results suggest that 8-month-olds process gaze direction in terms of the orientation of the face, and perceive an illusory shift of the gaze direction in Wollaston's illusion when the face was shown in an upright orientation.