Despite minuscule eyes and tiny brains, flying insects successfully perform remarkable behaviours with their limited visual system. In this thesis, I have investigated how the fruit fly (Drosophila melanogaster) responds to visual stimuli of different sizes and depths in a virtual environment. For tethered flying Drosophila, I analyse the orientation and robustness of perception to small objects and square gratings during innate, voluntary, and conditioned behaviours. My research aims to understand whether fruit flies respond behaviourally to objects smaller than their optical resolution limit and whether binocularity is used for small object detection.
Recent work has highlighted that ultrafast photomechanical photoreceptor microsaccades beneath the lens may enhance the spatial resolution limit of the fly below the optical limit. Therefore, I investigated how fruit flies respond to extremely small singular objects and dark and light stripes (gratings) within their visual field. My results reveal that fruit flies respond behaviourally to stimuli smaller than the interommatidial angle (the angular separation between neighbouring lenses). Additionally, flies respond robustly to close and small patterns when the pattern subtends the same size on the retina but are presented as either close-small or far-big. Furthermore, flies show an innate attraction for a singular feature when presented with distinct 2D or 3D small objects (ranging between 1-4°). Finally, learning experiments confirm that they can discriminate between these objects, although they fail to learn when one eye is occluded. Taken together, this supports the theory that fruit flies possess higher spatial resolution than predicted by their optics and use binocularity in close range.
In summary, the results gathered in this thesis contribute to a new insight into the visually guided behaviours of insects in virtual environments. Among other findings, my results emphasise the importance of both eyes contribution to vision, enhancing the animals’ ability to see their world.
