The eyes have it: the evolution of complex vision as a precondition for the emergence of consciousnessEdelman, D.B. (2008) The eyes have it: the evolution of complex vision as a precondition for the emergence of consciousness. In: 12th annual meeting of the Association for the Scientific Study of Consciousness, 17-22 June 2008, Taipei, Taiwan. Full text available as:
AbstractGiven increasing evidence for consciousness in a number of mammals, the strong possibility of consciousness in birds, and the documentation of sophisticated cognitive abilities suggesting at least the possibility of a form of awareness in some invertebrates, it is conceivable that consciousness appeared independently a number of times during animal evolution. If this is so, it is likely that, in some radically different animals, conscious states are based, not on neural homologies, but rather on functionally analogous neural architectures. Were there convergent conditions that favored the independent elaboration of neural substrates for consciousness a number of times? I suggest that the emergence of camera eyes with focusing lenses, as well as neural substrates for rapid cross-modal integration of visual input, provided the basis for just the sort of unified perceptual scenes that are believed to underlie conscious states in mammals. Among the senses, arguably it is vision that involves the fastest processing of the largest amount of input. Moreover, with some possible exceptions (i.e., sonar in bats and cetaceans), vision is unique in its wide spatial range; many mammals and birds can see distant objects in great detail, but can’t necessarily hear distant sounds as acutely. Finally, visual acuity over distance allows the tracking of a far-off moving object and, presumably, the time to plan an appropriate response. The visual systems of mammals and birds are well characterized in terms of the architecture of the eyes (a focusing lens projecting an image onto a retina populated by different rhodopsin-based receptors), as well as the specialization of brain regions processing different aspects of the visual scene. However, although the structure of the eye is well documented in invertebrates such as coleoid cephalopods and spiders, the neural substrate for vision in these animals is not well understood. Nevertheless, the clear behavioral sophistication and visual abilities of certain invertebrates suggest the possibility of a kind of cross-modal integration akin to that found in many vertebrates. I discuss the possible evolution of conscious states in different animal lines in the context of complex ecologies that may have engendered selection for animals with complex vision. Comments/DiscussionThis work suggests that the emergence of single compartment, camera eyes during animal evolution was a critical precondition for the emergence of consciousness. Moreover, on this basis, it introduces the possibility of conscious states in certain invertebrate species, i.e., cephalopods such as the octopus and perhaps some arachnids, most notably, the jumping spider.
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