Differential visual persistence between the two eyes: a model for the Fertsch-Pulfrich effect.

By presenting moving bars of different widths to the two eyes, an attempt was made to model the differential visual persistence produced by differential intensity filtering in the two eyes (the Fertsch-Pulfrich effect). If the phase of the two moving bars was controlled so that the thinner bar lined up with the leading edge of the wider bar, a clear depth effect was seen, which was the same as that produced by placing a filter in front of the eye seeing the wider bar. The depth effect was reversed, for example, from clockwise to anticlockwise, when the trailing edges of the targets were in alignment. These effects were additive to those produced by differential intensity filtering. When observers were permitted to control the phase relation between the two target bars in order to null the depth effect, they placed the thinner bar in alignment with the geometrical center of the wider bar. Widening the variable bar led to a reduction in its luminance, but this did not in itself seem to entail a Fertsch-Pulfrich effect. The classical latency explanation of the differential filtering effect is questioned, and a model involving spatial averaging of visual direction in conditions of differential persistence is proposed in its stead. Possible differences in the mechanisms of static and dynamic stereopsis are discussed.