Binocular Depth Cues
1. Convergence Angles of Optical Axes of the Two Eyes
When our eyes attempt to focus on a single point, they must rotate inwards or outwards, depending on the distance of the point from our eyes. Consider the example on the left which is similar to the one we studied for motion parallax. Here we imagine the red and green dots at the bottom correspond to our left and right eye, respectively. When our eyes attempt to focus on the middle red teapot, they must rotate strongly inwards. By contrast, when they try to focus on the more distant middle blue teapot, they rotate farther outwards. This effect is most pronounced in extreme cases, such as focusing on an object a few inches from our eyes as opposed to something several feet or more away.
