Summary: 840 nature neuroscience · volume 2 no 9 · september 1999
Because the left and right eyes are set apart, points in the scene
are projected to slightly different locations on the two eyes' reti-
nal images. Disparity is defined as the vector difference in posi-
tions of identified corresponding points in the left and right eyes,
each measured with respect to the point of fixation as origin. The
geometrical relationship between disparity and depth has been
extensively analyzed by researchers in vision and in photogram-
metry1, the engineering field of measuring three-dimensional
scene structure from multiple views.
In the context of this analysis, a key experimental question is
whether the human visual system actually uses the information in
the disparity field to infer three-dimensional depth. Wheatstone2
demonstrated this for horizontal disparity in the 1830s.
Helmholtz3 and Ogle4 suggested that the vertical component of
the disparity field is also used; this was more convincingly estab-
lished only recently5,6.
Disparity is based critically on measurements on corresponding
points--retinal projections of a three-dimensional point visible in