DOES COLOUR VISION MAKE YOU NARROW-MINDED?
Bahar Eriköz, Tom FitzGibbon, Ulrike Grünert and Paul R. Martin
According to a controversial hypothesis, signals for red-green colour vision travel along an evolutionary ancient koniocellular division of the visual pathway. We tested this hypothesis by comparing the size of the koniocellular pathway in normal and red-green colour-blind marmoset monkeys.
We predicted that if red-green signals travel in the koniocellular pathway, then the koniocellular pathway should be smaller in animals which lack a functional red-green channel. But we were surprised to find that in red-green colour-blind monkeys the koniocellular pathway is even larger than normal. The difference is not great in relative volume (about 19%, see the graph), but in absolute numbers would correspond to over 20,000 cells.
We conclude that the konicellular pathway does not carry an additional red-green colour channel in trichromatic colour vision, but why this pathway is expanded in dichromatic monkeys is not clear. Perhaps these animals rely on other types of koniocellular cells to compensate for lack of red-green colour signals.
Figure: The upper panel shows schematic sections through the visual relay centre (lateral geniculate nucleus) where we measured the size of the koniocellular (konio) pathway. The lower graphs show for one animal (left) the size of the koniocellular layers. The population averages (right) showed that the konicellular layers in dichromatic "red green colour blind" monkeys are larger than in monkeys with normal colour vision.
Reference: Eriköz B, FitzGibbon T, Grunert U, Martin PR (2008). Lateral geniculate nucleus in marmosets: a comparison of dichromatic and trichromatic animals. Proceedings of the Australian Neuroscience Society 18: 67.