170mm x 244mm Collerton c10. tex V3-11/21/2014 5:28 P. M. Page 236 236 CH10 GEOMETRIC VISUAL HALLUCINATIONS π/2π/2 3π/2 π/2 3π/2π/2-π/2π/2 x x-π/2 Single map Double map Striate cortex Visual fieldyy 3π/2 Figure 10. 16 Actionoftheretino-corticalpoint(single)andvector-field(double)Mapsonlog-arithmic spiralcontours inthevisual field. (a) (b) Figure 10. 17 (a)Non-contouredrollpatternonthesquarelattice. (b)Non-contouredhexagonal pattern onthehexagonal lattice. spirals in the visual field, measured in such relative terms, all lie along the cortical images of such forms, as shown in figure 10. 16 Given such a double map we can now compute the appearance in the visual field of the doubly periodic even V1 planforms shown in figures 10. 14 and 10. 15. The results are shown in figures 10. 17and 10. 18.