Abstract
Just like other complex biological features, image vision (multi-pixel light sensing) did not evolve suddenly. Animal visual systems have a long prehistory of non-imaging light sensitivity. The first spatial vision was likely very crude with only few pixels, and evolved to improve orientation behaviors previously supported by single-channel directional photoreception. The origin of image vision was simply a switch from single to multiple spatial channels, which improved the behaviors for finding a suitable habitat and position itself within it. Orientation based on spatial vision obviously involves active guidance of behaviors but, by necessity, also assessment of habitat suitability and environmental conditions. These conditions are crucial for deciding when to forage, reproduce, seek shelter, rest, etc. When spatial resolution became good enough to see other animals and interact with them, a whole range of new visual roles emerged: pursuit, escape, communication and other interactions. All these new visual roles require entirely new types of visual processing. Objects needed to be separated from the background, identified and classified to make the correct choice of interaction. Object detection and identification can be used actively to guide behaviors but of course also to assess the over-all situation. Visual roles can thus be classified as either ancient non-object-based tasks, or object vision. Each of these two categories can also be further divided into active visual tasks and visual assessment tasks. This generates four major categories of vision into which I propose that all visual roles can be categorized.
Highlights
Imagine you have just bought a sandwich and a paper mug of coffee and are looking for a place to sit and have your lunch
There are animals that live and prosper with every imaginable intermediate from simple non-visual photoreception to the full set of visual roles found in vertebrates, arthropods and cephalopods
The roles that vision serve can be neatly divided into ancient vision and object vision, where the former must have evolved before the latter
Summary
Imagine you have just bought a sandwich and a paper mug of coffee and are looking for a place to sit and have your lunch. Apart from the obvious multiplication of directional photoreceptors, true vision requires novel neural circuits for discrimination of spatial intensity differences (contrasts) and their motion With these in place, even a small number of photoreceptors, and a very low resolution, opens for much more efficient orientation in the environment. True spatial vision replaces directional photoreception, but non-directional photoreception remains as important as before vision evolved (Figure 1) It may even acquire new roles such as controlling light-dark adaptation of visual photoreceptors (Aranda and Schmidt, 2020). In contrast to non-object based visual assessment, which informs about habitat quality and current conditions, perception provides information on the current situation and allows for the planning of actions This too is a major advance from just ancient vision. Introduction of object vision can be expected to result in major improvements of ancient vision (Figure 1)
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