Figure 4.

Cone-type specificity of receptive field structure. (A) Signs of weights of the L–M-specific unit on the lower right panel of Figure 3. Left: Positive weights are indicated by black dots; negative weights, by white dots for both L and M cones. Right: Positive weights are indicated by black dots; negative weights, by white dots for M cones and vice versa for L cones. This yields homogeneous subfields, indicating +L − M and −L + M opponency. (B) Receptive fields corresponding to the cone weight pattern imposed on the original mosaic (leftmost receptive field plot, “learned”) and on four mosaic patches where the type of each L and M cone had been reassigned randomly with the same probabilities as in the original mosaic (“randomized mosaics”). In the latter cases, the resulting receptive field structures are weak and irregular, indicating that the learned weight pattern is not only spatial but also cone-type specific.