170mm x 244mm Collerton c10. tex V3-11/21/2014 5:28 P. M. Page 228 228 CH10 GEOMETRIC VISUAL HALLUCINATIONS a planar array. However, the theory can account for only two of the four Klüver formconstants. Thusitcanaccountverywellforformconstants(c)tunnel,funnel, alley, cone or vessel, and (d) spiral; and partially for form constant (a) grating, and chessboard, but not for the other forms classed as (a) lattice, fretwork, filigree or honeycomb, and not for class (b) cobweb. In other words it works for thickbars or spots, butnotfor thinlineimagery. Itwasnotuntil1993that Ibegantounderstand how to obtain the thin line form constants classed as (a) or (b). 10. 2 A new mathematical formulation of V1 circuitry The Ermentrout-Cowan model essentially treats V1 as a cortical retina. But Hubel and Wiesel's Nobel Prize-winning discovery that most V1 neurons have a definite preferencefor orientated stimuliintheformofmovinggratingsorbars(Hubeland Wiesel, 1959, 1962) showed that V1 is functionally considerably more complex thantheretina. Theirsubsequentdiscoveryoftheregularityandspatialhomogene-ityof V1anditsmodulararchitecture(Hubeland Wiesel,1974a)indicatedahighly organized almost crystalline structure. However, it was not until the techniques of optical imaging were applied to V1 (Blasdel, 1992) that the real structure of V1 became apparent. Figure 10. 10a shows an optical image of a small patch of Macaque V1, and Figure 10. 10b shows another optical image of a smaller patch of Cat V1 combined with the image of a stained inhibitory neuron and its local connections. Similarly Figure 10. 11a shows an optical image of a patch of Owl Monkey V1, in which connections between iso-orientation patches have been stained. These connections are the longer-ranged horizontal patchy connections of V1 (Gilbert, (a) (b) Figure 10. 10 (a) Distribution of orientation preferences in Macaque V1 obtained via optical imaging. Differentorientationpreferencepatchesarepseudo-coloured. (b)Connectionsmadeby aninhibitoryinterneuronin Cat V1. Theinjectionsiteisdenotedbythesmallwhitestar. Thecell body of the inhibitory neuron is shown in white. Source: Reproduced with permission of Nature Publishing Group. ( Seeinsertforcolourrepresentationofthisfigure. )