This stimulus is a sparse random dot stereogram (RDS) that approximates motion in depth (MID) and that can be modulated randomly (or moved smoothly) along the toward-away axis.

The stimulus, when fused binocularly, appears to be a field of dots with random placement in x, y and z (depth). The dots move coherently in depth (z) over time. When dots move too far or too close, based on a disparity limit, they disappear and eventually wrap around (between near and far).

The dots in the right eye can be made to have opposite sign compared to those in the left eye, or to be spatially unrelated to those in the left eye (see the dotcorr parameter below).

Currently, the random dot field is centered at zero disparity.




FIGURE 1. Conceptual model underlying the generation of images for the left and right eyes. A fixed number of dots (black circles) are descibed by an (x,y,z) position, where z is depth. The dots may change their z-coordinate according to a random walk. The left and right stimulus images are created by drawing the dots with a horizontal (x) offset determined by their depth (z). The diagram shows the positions of four example dots in the left (green) and right (red) stimulus images.

The inset plot at the right shows the contrast of dots as a function of z for three example envelope shapes: square (black), tent (red) and circle (green).