No genuine stereo perception is possible if one has lost an eye or an ear. But as Dr. Jorgensen observed, a remarkable degree of adjustment or adaptation can occur, and this depends on a variety of factors. One of these is the increased ability to make judgments using one eye or ear, a heightened use of monocular or monaural cues. Monocular cues include perspective, occlusion, and motion parallax (the shifting appearance Of the visual world as we move through it), and monaural cues are perhaps analogous to these, though there are also special mechanisms peculiar to hearing. The diffusion of sound with distance can be perceived monoaurally as well as binaurally, and the shape of the external ear, the pinna, provides valuable cues about both the direction and the asymmetries of sound reaching it.
If one has lost stereoscopy or stereophony, one must, in effect, recalibrate one's environment, one's spatial world—and movement here is especially important, even relatively small but very informative movements of the head. Edward O. Wilson describes in his autobiography, Naturalist, how he lost an eye in childhood but nonetheless is able to judge distances and depths with great accuracy. When I met him I was struck by a curious nodding of the head, and took this to be a habit or a tic. But he said it was nothing of the sort—it was a strategy designed to give his remaining eye alternating perspectives (such as normally the two eyes would receive), and this, he felt, combined with his memories of true stereopsis, could give him a sort of simulacrum of stereo vision. He said that he adopted these head movements after observing similar movements in animals (like birds and reptiles, for instance) whose visual fields have very little overlap. Dr. Jorgensen did not mention any comparable head movements in himself—they would not be too popular in a concert hall—but such movements might well help one construct a richer, more diverse soundscape.
There are other cues that stem from the complex nature of sounds and the vicissitudes of sound waves as they bounce off objects and surfaces around one. Such reverberation can provide an enormous amount of information even to a single ear, and this, as Daniel Levitin has remarked, has an essential role in communicating emotion and pleasure. It is for this reason that acoustical engineering is a major science and art. If a concert hall or lecture hall is badly designed, sounds may be "killed," voices and music seem "dead." Through centuries of experience, the builders of churches and auditoriums have become remarkably adept at making their buildings sing.
Dr. Jorgensen says that he believes his good ear is "better than should be expected from a seventy-year-old." One's ear, one's cochlea, cannot improve as one gets older, but as Jacob L. clearly demonstrated, the brain itself can improve its ability to make use of whatever auditory information it has. This is the power of cerebral plasticity. Whether or not "hearing fibres may have crossed in the corpus callosum" to the other ear, as Jorgensen suggests, is questionable—but there most assuredly have been significant changes in his brain as he has adapted to life with one ear. New connections must have been made, new areas recruited (and a sufficiently subtle brain-imaging technique might be able to demonstrate such changes). It seems probable, too—for vision and hearing normally complement each other and tend to compensate for each other if one is impaired—that Dr. Jorgensen, consciously or unconsciously, is using vision and visual data to map the position of instruments in the orchestra and the dimensions, spaciousness, and contours of the concert hall, as a way of reinforcing a sense of auditory space.
Perception is never purely in the present - it has to draw on experience of the past; this is why Gerald M. Edelman speaks of "the remembered present." We all have detailed memories of how things have previously looked and sounded, and these memories are recalled and admired with every new perception. Such perceptions must be especially powerful in a strongly musical person, a habitual concertgoer like Dr. Jorgensen, and imagery is surely recruited to complement one's perceptions, especially if perceptual input is limited. "Every act of perception," Edelman writes, "is to some degree an act Of creation, and every act Of memory is to some degree an act of imagination." In this way the brain's experience and knowledge are called upon, as well as its adaptability and resilience. What is remarkable in Dr. Jorgensen's case, at least, is that, after such a severe loss, with no possibility of function being restored in the ordinary sense, there has nonetheless been a significant reconstruction of function, so that much Of what seemed irretrievably lost is now available to him again. Though it took some months, he has, against all expectation, been able to recover in large measure what was most important to him: the richness, the resonance, and the emotional power of music.