[ASC-media] Media release: Crabs reveal how we recognise danger

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Sun Nov 22 23:07:23 CET 2009

:: The Vision Centre
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Crabs reveal how we recognise danger

November 23, 2009 – for immediate release

Research into how fiddler crabs see danger is helping scientists to understand how all animals, including humans, recognise which objects are a threat – and could one day help robots learn to do the same.

The research throws new light on the complex process that enables animals to learn which objects they can ignore and which they need to pay attention to.

This process, called habituation, occurs in all animals - but how it happens in natural situations is still poorly understood says Dr Jan Hemmi from The Vision Centre and the Australian National University (ANU), who conducted the study with his colleague at ANU, Dr Tobias Merkle.

“For animals, accurately learning which objects are threats and which aren’t is crucial to their survival. If they accidently ignore a predator they will be killed.”

“Humans have the same issue – everything is constantly moving around us and we need to learn to ignore events that are not important. This study may help us find out how that’s done.”

Understanding how animals learn which objects they need to be wary of could be used in the future to improve robots and unmanned aerial vehicles (UAVs), he adds.

“A big difference between robots and animals is that animals are constantly learning about their surroundings – more and more, scientists are trying to incorporate this learning process into robots.”

According to Dr Hemmi, the fiddler crab was an ideal model animal with which to test the process of habituation in a natural situation, as it is possible to accurately work out what the animals are able to see while making a decision. 

The crabs are constantly threatened by birds flying overhead and people visiting the beach. After around ten minutes crabs can become accustomed to people near them, but will still run to their burrows when birds fly overhead, he adds.

In order to test how the crabs distinguish threatening birds from harmless objects, Dr Hemmi and Dr Merkle made dummy predators fly overhead every two to three minutes, but not attack.

The crabs initially ran away from this stimulus, but after a dummy predator approached the crabs from a close by position around ten times, the crabs adjusted to its presence and stopped heading for their burrows.
However, as soon as the dummy predator was moved farther away to outside their field of vision and then approached, they reacted as if it was a threat once more - and ran for home.

This suggests that identifying whether an object is a predator or harmless not only depends on what the object looks like and what it’s doing at a certain point in time, but also its history, says Dr Hemmi.
“How much of a threat they feel an object poses depends on where the stimulus came from and what it’s doing now.”

The crabs never became accustomed to dummy predators flying in from outside their field of vision, suggesting that if they don’t know an object’s history they will assume it’s dangerous, he adds.

“If an object remains in their field of vision, then they know where it’s been and it appears they assume it won’t hurt them as it hasn’t done this before. When it comes from somewhere they can’t see, they have no idea of its past and can’t tell whether it’s a threat or not, so will always head for home.” 

The crabs displayed an advanced ability to filter threats from harmless objects, and became accustomed to the dummy predator while still running from real bird predators that were flying overhead during the experiment.
Dr Hemmi and Dr Merkle hope to use the fiddler crab to understand the detailed mechanisms and pathways that control the process of habituation.

“Seeing how crabs respond to objects that remain in their field of vision, but are moving around, will give us more insight into how this learning process works.”

The paper ‘High stimulus specificity characterizes anti-predator habituation under natural conditions’ by Jan M. Hemmi and Tobias Merkle was published early online on 23 September 2009 in the Proceedings of the Royal Society B: Biological Studies.

The Vision Centre is funded by the Australian Research Council as the ARC Centre of Excellence in Vision Science, T. Merkle is a Fellow of the German Research Foundation. 

More information:

Dr Jan Hemmi, the Australian National University and The Vision Centre, ph +61 (0)2 6125 8561 or 0403 660 221
Dr Tobias Merkle, Centre for Visual Sciences, the Australian National University, ph +61 (0)2 6125 5576 
Professor Trevor Lamb, The Vision Centre, ph +61 (0)2 61258929 or 0434022375
Professor Julian Cribb, The Vision Centre media contact, 0418 639 245
Martyn Pearce, ANU media, ph +61 (0)2 6125 5575 or 0416 249 245

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