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by John Michael Williams, 1999. Placed in public domain.
Some past studies have seemed to show that stereoacuity becomes poorer as observation distance is decreased from one meter, and that single-cell receptive field size in the visual system is not the reason for it. The geometric theory of stereopsis does not predict such a decrease.
This JOSA Letter reports unpublished, reanalyzed control data from the Lit and Hyman (1951) Pulfrich Effect experiment. The variance of settings was used as a measure of stereoacuity for fixed and moving targets with no Pulfrich filter in place.
One of the observers showed a mild degradation in stereoacuity with decreasing distance, both for fixed and moving (19 degrees visual angle per second) targets; the other observer showed no consistent change.
Reanalysis of available old data has left the problem unsolved. The literature of stereoacuity as a function of observation distance remains at best equivocal, and if there is an effect of decreased stereoacuity with decreased observation distance, it must be small or perhaps observer-specific.
The Pulfrich Effect, SIU-C. Last updated 2000-07-23