Fig. 5.

Natural disparity statistics. The data from refs. 25 and 26 have been averaged across subjects and subjected to a weighted combination across tasks as in ref. 24. (A) Distributions of cyclovergence from ref. 25, weighted across tasks, for $\lambda$ = 0.6 to 1 (Eq. 1). Negative cyclovergence is extorsion. When $\lambda$ = 1, Listing’s Extended Law is precisely obeyed so all cyclovergence values are zero. (B) Median horizontal disparity at each position in the central $30^{○}$ of the visual field assuming $\lambda =0.8$. The abscissa and ordinate represent azimuth and elevation, respectively. Disparity values are indicated by color: darker blue corresponds to larger uncrossed disparity; darker yellow corresponds to larger crossed disparity. The white curve indicates where the median disparity changes sign from crossed to uncrossed. (C) Distributions of naturally occurring horizontal disparity along the horizontal and vertical meridians. Upper plots the normalized probability of different disparities along the horizontal meridian, and Lower plots those probabilities along the vertical meridian. The thick blue curves represent the median disparities at each eccentricity, while the thin curves represent the 25th and the 75th percentiles of the distribution.