24 January 2014

A new discovery by Queensland Brain Institute (QBI) scientists at The University of Queensland (UQ) published by eminent journal Science has shattered illusions that more complex eyes with more colour channels necessarily result in better colour vision.

The Ishihara test for shrimp - Mantis shrimp trained to respond to different colours reveal how surprisingly poor their colour sense is

A new discovery by Queensland Brain Institute (QBI) scientists at The University of Queensland (UQ) published by eminent journal Science has shattered illusions that more complex eyes with more colour channels necessarily result in better colour vision.

Lead author Ms Hanne Thoen found that Haptosquilla trispinosa (mantis shrimp), which process twelve colour channels compared to three in humans, actually perform worse in differentiating between colours.

“Theoretically mantis shrimp should be far better at distinguishing colours than we are,” Ms Thoen said.

“Human brains – and all other animals including birds, monkeys, frogs and fish – determine the colours of objects by comparing the relative excitation of inputs. For instance, in humans this is red, green and blue,” she said.

“The critical finding is that mantis shrimp do not, and this means their way of encoding colour is different to all other animals known.”

A number of tests were conducted, including training the animals to respond to certain colours and using a two-way choice test with food as a reward.

By receiving food when choosing one particular colour and not any other, the animals quickly learned which choice to make and also revealed how they encode colour.

“We tested their ability to discriminate between colours that differ a lot – such as red and blue, and then changed to colours that got closer and closer together along the spectrum – red-green, red-yellow, red-orange – and noted when they started to make mistakes,” Ms Thoen said.

“Results were also compared to a number of other animals including humans, bees, fish and butterflies, and although theoretically they should be better than all of them, they are far worse.”

Professor Justin Marshall runs the Sensory Neurobiology Group at QBI, and says finding an animal that processes colour vision in a new way is remarkable and totally unexpected.

“It solves a long standing problem of why mantis shrimp have 12 colour receptors – because they process colours and the contrast they provide in a totally different way to anything we have previously seen in an animal,” Professor Marshall said.

“This is the first time since the original descriptions of colour vision in the 1800s that we are able to say that there is another way of colour processing out there.”

The findings demonstrate how evolution pushed the design of nervous system towards a simple arrangement, rather than trying to fully interpret all the information from a very complex colour vision at the retinal level.

“This has the potential to teach us more about humans’ more simplistic perceptions of colour and about bio-inspired machine-vision solutions that might borrow ideas from the evolutionary process,” Professor Marshall said.

The importance and implications of the finding is highlighted by Science running a commentary on the article.

“We have no doubt that this new discovery will stimulate and inspire the advancement of new and innovative technologies within the applied sciences,” Ms Thoen said.

“Modern cameras struggle with the amount of data they take in due to increased pixel numbers; maybe there is a more efficient way and the bio-inspiration provided by stomatopods could be the answer.”

“In fact, mantis shrimp sample their world in a way more similar to a satellite than other animals,” Professor Marshall concluded.

The project was supported by grants from the Asian Office of Aerospace Research and Development, Air Force Office of Scientific Research, Australian Research Council and Doctoral Fellowship (2013) from Lizard Island Research Station – a facility of the Australian Museum.

The study can be accessed here.

Media: Mikaeli Costello, Director Advancement and Communications, Queensland Brain Institute, +61 401 580 685 or mikaeli.costello@uq.edu.au; Professor Justin Marshall, Queensland Brain Institute, +61 7 3345 1397, +61 423 024 162, or justin.marshall@uq.edu.au