170mm x 244mm Collerton c10. tex V3-11/21/2014 5:28 P. M. Page 246 246 CH10 GEOMETRIC VISUAL HALLUCINATIONS (a) (b) Figure 10. 25 (a) Binocular pressure phosphene. Source: Redrawn from Tyler (1978). (b) Lattice tunnel hallucination. Source: Reproduced from Siegel (1977), with permission from Alan D. Iselin. is a more complex form of the imagery. Figure 10. 25b shows an artistic rendering of many reports describing tunnelimagery. It shows contours varying in thickness, colour, and even a suggestion of depth(although this may be an optical illusion). It is evident that such complex imagery requires a deeper and more comprehensive theory than that presented here. In particular, it requires a theory that has a random element, and covers the remaining visual features, that is, preferences for colour, depth and motion. [A paper on such a theory is in preparation. ] There is another source of data concerning more complex visual hallucinations, and that source is cave art. Figure 10. 26 shows a painting from the Peche-Merle cave, and Figure 10. 27 shows one from the older Chauvet cave. It will be seen that both paintings contain elements of some of the imagery seen in the Klüver form constants. A study of such paintings led Clottes and Lewis-Williams (1998) to propose that they were the creation of Shamans who painted what they saw on the cave walls deep underground, (perhaps triggered by flickering light from torches). Thus they could be the earliest known examples of the generation of flicker phosphenes in Homo sapiens. But the cave paintings, and other imagery painted or carved on rocksin South Africa,led Lewis-Williamstoproposeaclassificationoftheimagery as hallucinogenic in origin and comprising three stages of increasing complexity (Lewis-Williamsand Dowson,1988). Figure10. 28showsdetailsofthethreestages in the evolution of complexity inthe observed imagery. 10. 4. 7 In which neocortical areas is the imagery located? It seems clear that the Turing mechanism that generates the Klüver form constants is first triggered in V1, but then it moves progressively forward from V1 to higher