Extended Data Figure 7: Orientation maps do not reflect fisheye distortion.
a, Grating patches were presented at the foot point (FP), the point at which a line from the eye is perpendicular to the tangent screen, and at locations on the screen displaced from the FP along radial orientations of 0, 45, and 90°. b, Predicted map if fisheye distortion caused orientation tuning to be biased towards the radial orientation with respect to the FP. c, Projective field of foot point (black, indicated with white star) and patch at 0° (directly lateral on screen) from foot point (white patch, black star). d, As in c for patches at 90 and 45° with respect to foot point. e, Orientation map for this animal. Blue areas prefer horizontal bars, red areas prefer vertical bars, and arrows indicate lines from projective field of foot point to projective fields of patches. f, Expected orientation map according to distortion hypothesis. Note that the area at the projective field of the foot point should be untuned, and a line from the projective fields of the FP and a spot located at 0° relative elevation should pass from untuned areas to progressively more horizontal-preferring areas. Instead, it passes from a horizontal-preferring area at the FP to vertical-preferring areas as it moves to greater eccentricity. Trajectories along other projections of radial orientations (45 and 90°) are similarly poor fits to prediction. g, h, As in b and c for another animal. Orientation map for this animal in o also does not match prediction of fisheye distortion hypothesis. Arrow indicates shadow of blood vessel. i, j, Checkerboard pattern before and after ‘pre-distortion’ to offset fisheye effect. This pre-distortion was applied to change bar width by 1/cosine(θ), with θ the eccentricity from the FP, for both vertical and horizontal bar stimuli. k, l, Orientation maps for an animal in response to standard (k) and ‘pre-distorted’ (l) bar stimuli. In this animal the transverse sinus was not fully retracted and partially obscures the field of view. Note similarity of patterns in k and l. m, n, As in k, l, for the animal in c–e imaged on a different day. Comparison of maps in e and m reveals inter-trial variability, which is comparable to variability between standard and pre-distorted stimuli (m and n). o, p, As in k, l for a third animal. Map in o is overlaid with projective fields of points in visual field as in e. The reflectance change ΔR/R from black to white is 12 × 10−4 (c), 19 × 10−4 (d), and 18 × 10−4 (g, h). The reflectance change ΔR/R from red to blue is 4 × 10−4 (e, k, o), 5 × 10−4 (l, p), 7 × 10−4 (m), and 9 × 10−4 (n).
