Pulfrich stereoeffect during tracking eye movements

An experiment was conducted to compare the magnitudes of the Pulfrich stereoeffect under two viewing conditions: (a) fixating a stationary point and (b) tracking a moving target. Three different transmittances of ND filters were used for each condition. The null method was employed to estimate the magnitude of the stereoeffect, in which the apparent depth was “nulled” by adjusting the physical depth of the target moving in an elliptical path in the eye-level horizontal plane so that no depth was seen. The results obtained from two experienced subjects showed that: 1) the stereoeffect increased as the transmittance of the filter was decreased, and 2) the stereoeffect was larger in the tracking condition than in the fixating condition for all three transmittances of the filters. The results were discussed within the context of depth information available for the visual system.