Insect optomotor experiments in the dark using virtual reality
1University of Oulu, Faculty of Science, Department of Physics and Chemistry
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|Academic dissertation to be presented, with the permission of the Doctoral Training Committee for Technology and Natural Science of the University of Oulu, for public discussion in the Auditorium YB210, Linnanmaa, on 15th December, 2014, at 12 o’clock noon.
Associate Professor Marie Dacke
Doctor Rafael Kurtz
Professor David O’Carroll
Professor Matti Weckström
Vision is capable of providing an animal with a wealth of information very fast. Visually guided behaviours are numerous, ranging from foraging to navigation. Vision can be quite reliable in bright light, but the signals produced by the photoreceptors become progressively more unreliable with falling light intensities.
In this thesis the usefulness of a novel virtual reality-based environment for insect vision research is reviewed, and the low-light vision of the American cockroach, Periplaneta americana, is assessed using the optomotor behavioural paradigm and intracellular photoreceptor recordings. The optomotor reaction is visual behaviour where an animal responds to a rotation of its environment by following the movement of its surroundings with its eyes or — like insects — by rotating its body in the direction of the movement. Placing the cockroach on a trackball in the middle of the virtual reality apparatus and projecting a rotating pattern of vertical stripes around it invariably causes an optomotor reaction if the cockroach is able to see the moving pattern. Presenting the cockroaches with the stimulus pattern at different low light levels and observing their abilities to follow the movement reveal the lowest light intensity at which they are able to use vision in guiding their behaviour. The compound eye photoreceptor signals at this behavioural threshold consist of singlephoton absorption events called ‘bumps’ at the extremely low rate of one bump every ten seconds.
Furthermore, the role of the simple eyes or ocelli in the low-light vision of the cockroach is studied in the virtual reality by covering the compound eyes, the ocelli, or both. The ocelli seem to measure the light intensity and communicate this information to the compound eyes, and also have a direct effect on the general activity level of the cockroach.
Report series in physical sciences
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