Psychometric functions for observer XMP. Each panel shows the responses for one vertical eccentricity (+8°, +5°, +2°, −2°, −5°, and −8°). The abscissas are the horizontal separation between the lines shown to the left and right eyes. Negative separations indicate uncrossed disparities, and positive separations indicate crossed disparities. The ordinates are the proportion of observer responses indicating that the line presented to the left eye was perceived to the right of the line presented to the right eye (i.e., indicating the lines had crossed disparity). The data were fit with cumulative Gaussians. The means of the Gaussians (indicated by the red vertical lines) were defined as the disparities between corresponding points at each eccentricity.