Criteria for consciousness in humans and other mammals
Section snippets
The limits of behavioral criteria
“Accurate report” (AR) is the standard behavioral index for consciousness in humans. Accurate report is extremely useful and sensitive in people with intact brains. For example, we can report the light of a star on a dark night, involving a flow of single photons to a single retinal receptor. This conscious event corresponds to the lower limit of physical energy. Similarly subtle percepts are reportable in audition and touch. AR can thus be highly sensitive and accurate.
Accurate report in
Consciousness and the brain
Physiologically, three basic facts stand out about consciousness.
Putting it all together
How, in practice, can these properties be used to test comparative predictions about consciousness? Considering this question raises the issue that the foregoing properties vary considerably in their testability. Those that have to do with structural homologies of neuroanatomy are relatively easy to test; it is not difficult to identify a thalamocortical complex in a monkey or in a dog (criterion #2).
Conclusions
Contrary to widespread belief, the question of animal consciousness is not unapproachable. Human consciousness depends on well-established properties of the thalamocortical complex, a structure that is shared with other mammals. While a great deal remains to be discovered, there are at least 17 properties that can also be tested, with varying degrees of precision, in other species.
Acknowledgments
This work was supported by The Neuroscience Institute and the Neuroscience Research Foundation, which are gratefully acknowledged. We thank Drs. Gerald M. Edelman and Bjorn Merker for constructive comments.
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