Seeing in the dark: Vision and visual behaviour in nocturnal and deep-sea animals.

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Vision and visual navigation in nocturnal animals The most basic research into how nocturnal animals see well in very dim light has led to surprising applications in digital imaging techology. We spoke to Professor Eric Warrant about his work exploring how insects and other animals see in the dark “Most people think of insects as lower life-forms, but they’re not. They are really sophisticated and have amazing brains. The brain of an insect is divided into many sub-regions. There’s a whole area devoted entirely to vision, and this visual area alone is broken down into even more sub-structures, each of which has hundreds of thousands of neurons connected in every possible combination.”

number of questions about how exactly their visual systems work. It is this quest for discovery which has driven Professor Warrant’s work. The project itself has a four pronged approach to the study. In order to investigate just how well insects can see, and testing the extent of their visual performance, Professor Warrant will be carrying out behavioural studies. In

Professor Eric Warrant has had an active interest in the study of nocturnal insects for many years; his research stems from a desire to discover how nocturnal insects see so well in an environment where there is very little light. “Nocturnal insects can see a lot better than we can,” Professor Warrant says, “and my research is not just about trying to determine the kind of visual power these insects have in dim light, but also trying to work out exactly how it is that they see so well.” The Seeing in the Dark project is not just looking at the physical properties of insect eyes, but is taking a closer look at the neural processes that occur within the brains of the insects as they navigate in dim light. “I wanted to find out what special tricks these creatures have,” says Professor Warrant. “How can they see colour? How are they able to fly through a dark forest at night without crashing into trees? How do they learn visual landmarks and recall them to find their homes in what can be a visually complicated environment, where we ourselves would have great difficulties finding our way in bright light?” When we consider the relative size of an insect, and therefore the size of their eyes and brains, the fact that they have such sophisticated optical abilities poses a

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recent studies, he and his colleagues have shown that it is possible to train a nocturnal hawk moth to associate the colour blue with food; from this, it is then possible to introduce further stimuli, such as striped patterns or different shapes, to test spatial resolution. “What we have learned from this,” Professor Warrant says, “is that they can see colours at night, whereas we and nearly all other vertebrates cannot.” Some insects have the innate ability to see very faint patterns of polarised light, which are produced around the moon; it is this

ability which allows them to navigate in the dark. The second approach is to study the neural performance of the insects with electrophysiology, using electrodes to investigate specific neurons that have been identified in the visual system. “Traditionally, we have been working mainly in the retina,” says Professor Warrant. “We have been recording from photoreceptors and looking at what specific properties of the photoreceptors suit them for life in very dim light.” Following this, the aim is to look further into the brain and investigate different circuits of neurons; the hope is to discover how these circuits improve and enhance the visual signal as it passes from the retina to the brain. “Its not a trivial task at all to get to the bottom of this, but the higher you get in the visual system in terms of finding circuits of cells within the brain that deal with vision, the more you can learn. The hope is that we can build a picture of the strategies that these insects use neurally. I would hope that within five to ten years, we will be able to do this, but whether we can actually pin down the exact circuitry and know which cells are involved and how they are connected and exactly what they do, I will be very pleased if we can do that before I retire.” Thirdly is the study of the eye itself, looking at the optics and structure of the eye. “We are trying to work out exactly how sensitive to light the optics and morphology of the eye are and determining what exactly this adds to the nocturnal visual system,” Professor Warrant says. The fourth approach is to compile a theoretical understanding of the insect nocturnal visual system, based upon the

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Seeing in the dark: Vision and visual behaviour in nocturnal and deep-sea animals. by Blazon Publishing and Media Ltd - Issuu