Visual and Somatosensory Processes

The hamster is an animal not specialized for vision that curiously has captured the attention of numerous specialists in vision. Although the initial choice of the hamster for Schneider’s (1969) germinal paper was guided principally by the experimental convenience of the hamster’s insatiable appetite for sunflower seeds and the ease of the neurosurgical approach to the midbrain, unforeseen advantages have emerged in studying hamsters. The analysis of hamster vision has forced a clearer understanding of the different reasons why comparative analyses of visual systems are useful. A researcher might choose to investigate hamster vision because the goal is to understand human vision. Since the hamster visual system is less elaborate than ours, one might hope to see the fundamental organization of mammalian vision somehow laid bare in the hamster. This is decidedly the context in which most work in rodent (principally rat) vision has been done to date. Alternatively, a researcher might be interested in the general design of sensory systems and in how the visual system is evolutionarily modified to fit the requirements of particular niches. By chance, it has turned out that the hamster is markedly less trainable than the rat, former principal representative of the “simple” mammalian visual system. The rat can usually be induced to perform simple versions of primate puzzles, whereas visuomotor tasks asked of the hamster must reflect its natural behavior more directly, and have included such things as recognition of seeds, crickets and other hamsters, and the ability to find holes and avoid barriers and threats. The resulting compilation of the natural visual capacities of a granivorous, predated-upon mammal primarily active at twilight makes a new sort of comparison possible to those of other well-studied vertebrates in different visual niches, such as frogs, monkeys, and cats. Basic design features of the vertebrate visual system versus niche specific adaptations are contrasted by these two approaches.