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• K. Obermayer and G. G. Blasdel. Singularities in Primate Orientation Maps. . Neural Comput., 9:555-576, 1997.
  (FTP Gzipped PostScript, 19 pages, 150 kb)

  We report the results of an analysis of orientation maps in primate striate cortex with focus on singularities and their distribution. Data were obtained from squirrel monkeys and from macaque monkeys of different age. We find that approximately 80 percent of singularities which are nearest neighbors have opposite sign and that the spatial distribution of singularities differs significantly from a random distribution of points. We do not find, however, evidence for consistent geometric patterns which singularities may form across cortex. Except for a different overall alignment of orientation bands and different periods of repetition, maps obtained from different animals and different ages are found similar with respect to the measures used. Orientation maps are then compared with two different pattern models whic hare currently discussed in the literature: Bandpass-filtered white noise, which very well accounts for the overall map structure, and the FAM-model, which specifies the orientation map by the location of singularities and their properties. The bandpass-filtered noise approach to orientation patterns correctly predicts the sign correlations between singularities and accounts for the deviations in the spatial distribution of singularities away from a random dot pattern. The FAM-model can account for the structure of certain local patches of the orien tation map but not for the whole map. None of the models is completely satisfactory and the structure of the orientation map remains to be fully explained.