Vision did not arise and evolve to just "see" things, but rather to act on and interact with the habitat. Thus it might be misleading to study vision without its natural coupling to vital action. Here we investigate this problem in a simulation study of the simplest kind of visually-guided foraging by a species of 2D hypothetical animal called the (diurnal) paddler. In a previous study, we developed a hypothetical animal called the archaepaddler, which used positive phototaxis to forage for autoluminescent prey in a totally dark environment (the deep-sea). Here we discuss possible visual mechanisms that allow (diurnal) paddlers to live in shallower water, foraging for light-reflecting prey in ambient light. The modification consists of two stages. In the first stage Weber adaptation compresses the retinal illumination into an acceptable range of neural firing frequencies. In the second stage highpass filtering with lateral inhibition separates background responses from foreground responses. We report on a number of parameter-studies conducted with the foraging diurnal paddler, in which the influence of dark/light adaptation and lateral inhibition on foreground/background segregation and foraging performance ("fitness") are quantified. It is shown that the paddler can survive adequately for a substantial range of parameters that compromises between discarding as much unwanted visual (background) information as possible, whilst retaining as much information on potential prey as possible. Parameter values that optimise purely visual performance like foreground/background segregation are not always optimal for foraging performance and vice versa. This shows that studies of vision might indeed require more serious consideration of the goals of vision and the ethogram of the studied organisms than has been customary
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