Disparity-evoked vergence is directed towards average depth

Disparity-evoked vergence is studied in stereograms showing one or two depth planes which are defined by isolated dots of varying density and contrast. Vergence position immediately after stimulus presentation was measured using a psychophysical technique (dichoptic nonius lines). In the unequivocal stimuli (one depth plane), elicited vergence was in accordance with earlier findings. If two depth planes are presented, elicited vergence lies between the two planes, approaching the plane with higher dot density and/or dot contrast. In quantitative measurements, we show that the involved depth averaging mechanism uses signal power per depth plane as a weight. Therefore, the relative pulling strength of dot density as compared to dot contrast follows a power law with exponent 2. We propose a population code for vergence control based on disparity-tuned pools of units