4. Mosaic vision


Let us now enter the compound eye and see the world as viewed by an insect. Here is how the world might appear to an insect from within a single ommatidium. Each ommatidium views the visual scene
according to its position in the compound eye, and the width of its lens. The view from each ommatidia is then integrated by the nervous system to provide a view of the entire visual scene. Here is the mosaic view as
observed by an insect with this type of eye. The lens and cones of insect ommatidia are not capable of changing their focal length, so insects are probably nearsighted and distant objects appear blurry. Note that the observe scened is most distinctive when broken patterns caused by the edges of structures occur within the field of view of a single ommatidium or between adjacent ommatidia. Notice how conspicuous the pattern is when it has sharp contrasts of light and dark within the field of view of a single ommatidium. Conversely, the scene is least distinctive when a nearly similar pattern occurs within the field of a single ommatidium or between adjacent ommatidia. Likewise, movement within the field of a single ommatidium is poorly observed, but movement across the field of several ommatidia provides a high degree of sensory input. Here is how something close might appear as it moves past. Note that the most information is provided as it cuts across the fields of adjacent ommatidia. Finally, let us juxtapose a compound eye from a species such as a dragonfly that has many more ommatidia per unit area, Note that by increasing the number of ommatidia per unit area a greater number of individual ommatidia detect broken patterns within their field of view, as compared to the single larger ommatidium. Since each ommatidium acts as a visual unit, this has the effect of increasing the detail or resolution that the insect can detect in its field of view. Note how many ommatidia the flying insect crosses in this situation. this increases the sensitivity of the dragonfly’s eye to the presence of its prey. Therefore, insect vision is developed to be most sensitive to changing patterns and movement rather than to a highly resolved, detailed view of the visual scene — such as is found with the vertebrate eye.

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