Figure 2.

Control for low-level confounds. a, To exclude the possibility that low-level features of the stimuli would already lead to patterns of viewpoint mirror symmetry, a biologically realistic model of V1 simple cells was implemented (see Materials and Methods for details). As shown on an exemplary face on the right, the stimuli were spatially filtered (foveated) to account for differences in visual accuracy. The size of the face is proportional to the size of the Gabor filters used in the model. b, The V1 model responses to the standard FaceGen stimuli, as shown on the left, showed increased correlations for mirror-symmetric head orientations. This low-level confound was overcome by the addition of structured hair (shown on the right). c, The low-level similarity tuningcurves, as estimated from the model. The red “x” marks the mirror-symmetric viewpoint.