image can also appear slightly behind or in front of the horopter. Jodi Krol (1982) shows that the latter happens when the eyes are unconsciously directed slightly in front of or behind the intended fixation point due to certain reflexes and the fixation point is therefore not on the horopter.

Finally, nerve cells have been found in the visual cortex that are tuned to a certain disparity. These cells form the basis for neural models for binocular depth vision and for the solution of the correspondence problem to be discussed. These cells