Our testing of the demonstrations indicated that the threshold for concomitant motion (the upper limit of stability) is lower for the demonstrations with the two bars and the square wave surface. For these two demonstrations, head movements that produce l min. of arc equivalent disparity or smaller is recommended.  For the two other demonstrations (sine wave and sawtooth surfaces), we recommend doubling the equivalent disparity defined by the fastest moving dots. We have programmed these two demonstrations to produce the doubling of equivalent disparity with the same size head movement. The head movement sizes that produce these equivalent disparity values are listed below. (The values in parentheses are those for the sine wave and the sawtooth surfaces.)

1. With a computer monitor: When the horizontal dimension of the QuickTime Movie Window is 10 cm* and the observer is 50 cm away, the head movements of 19 cm and 38 cm produce equivalent disparities of 2 (4) min. of arc and 1 (2) min. of arc, respectively. With the same size of head movement, doubling the window size doubles the parallax magnitude and doubling the viewing distance halves the parallax magnitude.
   
   
2. With a projector in a classroom: When the horizontal dimension of the QuickTime Movie Window is 1 m* wide, the head movement sizes required to produce equivalent disparities of 2 (4) min. of arc and 1 (2) min. of arc for viewing distances of 5 m, 10 m, and 15 m are shown in the table below. With the same size of head movement, doubling the window size doubles the parallax magnitude.

2 (4)

1 (2)

5 m

19.0

37.9

10 m

9.5

19.0

15 m

6.3

12.6