Most visual scientists would immediately dismiss this simple model as a model of human stereopsis. They would point to the mountain of psychophysical evidence demonstrating that vertical disparity profoundly influences both eye movements and depth perception. These effects are of two main types: (1) Appropriate patterns of vertical disparity influence the depth perception caused by horizontal disparity (Backus, Banks, van Ee, & Crowell,
1999; Banks & Backus,
1998; Banks, Hooge, & Backus,
2001; Berends & Erkelens,
2001; Berends, van Ee, & Erkelens,
2002; Brenner, Smeets, & Landy,
2001; Clement,
1992; Duke & Howard,
2005; Friedman, Kaye, & Richards,
1978; Frisby et al.,
1999; Gillam, Chambers, & Lawergren,
1988; Gillam & Lawergren,
1983; Helmholtz,
1925; Ito,
2005; Kaneko & Howard,
1996; Ogle,
1952,
1953; Pettet,
1997; Pierce & Howard,
1997; Pierce, Howard, & Feresin,
1998; Rogers & Bradshaw,
1993,
1995; Stenton, Frisby, & Mayhew,
1984; Wei, DeAngelis, & Angelaki,
2003; Westheimer,
1984; Westheimer & Pettet,
1992; Williams,
1970). (2) Uniform vertical disparity evokes corrective vertical vergence movements, even at short latencies, in the direction that reduces the vertical disparity (Allison, Howard, & Fang,
2000; Busettini, Fitzgibbon, & Miles,
2001; Howard, Allison, & Zacher,
1997; Howard, Fang, Allison, & Zacher,
2000; Yang, Fitzgibbon, & Miles,
2003). Such phenomena are evidence that vertical disparity is not simply “tolerated” because of the finite width of horizontal epipolar bands; it is actively detected and used in perception. To all previous workers, it has seemed obvious that the stereo system must therefore include true vertical-disparity detectors: That is, the early visual system must contain neurons tuned to a range of vertical disparities, and the vertical-disparity tuning of each detector must be taken into account when decoding its population activity. This expectation has motivated several physiological studies that have looked for disparity-tuned neurons with vertical-disparity tuning clearly different from zero (Durand, Zhu, Celebrini, & Trotter,
2002; Gonzalez et al.,
2003; Trotter, Celebrini, & Durand,
2004).