and that the dolphin's cortex is so peculiarly organized with respect to the cell types described by Morgane. For the present, it may be heuristic to continue to accept simple quantitative measures and to disregard the differences in organization. It is consistent with evolutionary thinking that the processing done by a brain will be appropriate to the analytic problems that it must solve. For example, a bird's forebrain areas that are functionally equivalent to the mammalian visual cortex are structurally peculiar. They are nonlayered and are similar in appearance to the basal ganglia in mammals, and yet birds are primate-like in their capacities to use visual information. There is no clue about other differences between birds and mammals that might be related to this gross difference in the structural organization of their brains. The peculiarly arranged dolphin cortex might handle the same kinds and amounts of neural information as is handled by the normally layered neocortex of other mammals, but the best guess is that fundamental differences in processing will be discovered that are correlated with the structural differences.
In these speculations I have treated experienced reality as a construction of the brain and the self as part of experienced reality. This implies that our idea of self may be a species-typical feature of our perceptual world. Among the implications of this view in a reconstruction of the Umwelt of dolphins is that although something analogous to self as we know it may occur in dolphins its expression is likely to be different from ours. The self as an object can presumably be made only by large amounts of brain tissue, as required by the "second constraint" mentioned at the beginning of this chapter. The self is the center and point of reference in the perceptual world.
When knowledge of the external world is based on echolocation, the sensory data as enhanced in a large-brained species may generate an especially unusual self. Information from echolocation can be sensed at the same time by several individuals, and if dolphins were to construct their realities from such data the perceptual worlds of a group of dolphins would be much more nearly the same than ever occurs in human groups. I suggested the analogy to the way we would know the external world if we could share neural data actually processed in the visual system. In this sense a group of dolphins could occasionally share an immediate experience of "self" in their perceptual worlds.
There is no reason to assume that individual dolphins do not distinguish themselves from other individuals or cannot distinguish between self and notself But if their reality is built partly from the analysis of data generated by echolocation, the analysis, enhanced, could at least occasionally take the form of a communal model of reality rather than the kind of model that our brain generates and which we know as private experience. An extended self could be constructed