Vision

Introduction. When a fly moves through space in its environment, the animal processes information from optic flow to stay on course while in flight, or it fixates objects during its search for food. When startled, flies move towards the light. This chapter attempts to describe the anatomy of the Drosophila retina and the processing of visual information in the photoreceptors, or how a visual stimulus is transformed into a neuronal correlate. We also focus on a behavior dependent on all photoreceptors, the innate spectral preference. Some of the properties of a visual stimulus that can be detected by the visual system of Drosophila are intensity, contrast, motion, wavelength, and polarization (Borst, 2009; Heisenberg and Wolf, 1984). The efficiency of a light stimulus depends on the sensitivity curves of the photoreceptors involved in the visual task. For Drosophila, the wavelengths of visible light range from around 250 nm to 650 nm, and thus from UV to orange (Hardie, 1985). Depending on the visual task, different types of photoreceptors might be involved, therefore the effective range of light might vary.