Science 343, 411–413 (2014)

The mantis shrimp possesses one of the most complex eyes of all animals, having 12 photoreceptor types — more than any other animal. This ocular complexity has mystified scientists, as theoretical analysis indicates that this level of sophistication is far greater than that required to distinguish the colours of the visible spectrum. Researchers in Australia and Taiwan have recently gained new insight into the reason why. They first trained mantis shrimps to respond to light of a particular wavelength by offering them a food reward. They then presented individual animals with light from two optical fibres — one emitting light of the trained wavelength and the other light at a slightly different wavelength — to test whether they were able to distinguish the two colours. Surprisingly, the mantis shrimps exhibited poorer spectral discrimination (∼25 nm) than other animals with only three types of photoreceptors. The researchers postulate that the mantis shrimp employs a different mechanism for processing visual sensory data — one that favours processing speed over wavelength discrimination ability. Instead of performing multiple dichromatic comparisons like other animals, the mantis shrimp appears to bin colours into 12 separate channels.