Contrary to received opinion among philosophers, psychologists, and neuroscientists, conscious duality as a principle of brain organization is neither incoherent nor demonstrably false. The present paper begins by reviewing the history of the theory and its anatomical basis and defending it against the claim that it rests upon an arbitrary decision as to what constitutes the biological substratum of mind or person.

It then moves on to provide a dynamic model for double consciousness in vertebrate brain organization, giving an evolutionary account that explains why, although each of the two cerebral hemispheres benefits from sensory input from the other for representation of the ipsilateral half of corporeal and extracorporeal space, it was important that conscious experience be confined to each rather than spanning the two. This interhemispheric duplication effect for sensory representation has been known for years but hitherto considered mysterious, or ignored on grounds that integration must be achieved at a higher level of processing.

The paper then attempts to resolve a puzzle about split-brain patients in testing situations, namely why it is that in spite of the speaking hemisphere's denial of any independent perception and agency in the mute hemisphere, which would explain its role in cross-cuing, the latter never seems to resent this, but instead continues to be cooperative and helpful. It is suggested that on the hypothesis of mental duality this is understandable, for the nonverbal hemisphere would have known prior to the surgery that it is not generating linguistic behavior.

Finally, the essay examines two kinds of bitemporal defects, one due to callosal and the other to chiasmal disruptions. On the present theory a bitemporal defect should be demonstrable in the former case when both eyes are open, because in the absence of a corpus callosum and other forebrain commissures the interhemispheric duplication effect is abolished; in the latter case interhemispheric duplication is preserved, and so the defect should be demonstrable only by testing each eye independently. This is indeed what the evidence indicates, so it appears that, contrary to the prevalent view, the function of the corpus callosum is not to integrate and unify conscious experience between the hemispheres but to duplicate this, in accord with the model of mental duality.

The general process view of learning, which guided research into learning for the first half of this century, has come under attack in recent years from several quarters. One form of criticism has come from proponents of the so-called biological boundaries approach to learning. These theorists have presented a variety of data showing that supposedly general laws of learning may in fact be limited in their applicability to different species and learning tasks, and they argue that the limitations are drawn by the nature of each species' adaptation to the particular requirements of its natural environment. The biological boundaries approach has served an important critical function in the move away from general process learning theory, but it is limited in its ability to provide an alternative to the general process approach. In particular, the biological boundaries approach lacks generality, it is in some respects subservient to the general process tradition, and its ecological content is in too many cases limited to ex post facto adaptive explanations of learning skills. A contrasting, ecological approach to learning, which can provide a true alternative to general process theory, is presented. The ecological approach begins by providing an ecological task description for naturally occurring instances of learning; this step answers the question: What does this animal learn to do? The next step is an analysis of the means by which learning occurs in the course of development, answering the question: How does the animal learn to do this? On the basis of such analyses, local principles of adaptation are formulated to account for the learning abilities of individual species. More global principles are sought by generalization among these local principles and may form the basis for a general ecological theory of learning.