Shufflebrain

But Metherell's experiments let us go beyond the spoken word. They contain the elements of translation: translation from sound to light. Built into his system is a whole scene-shifting, from one medium to the other, with an abstract code to do the remembering. We are constantly shifting our language modalities-- writing notes at a lecture, dictating words destined for print. Consider the many forms English may take: script, sound, shorthand, print. Braille, Morse code, American Sign Language, Pig Latin. We need abstract codes-- like those in Metherell's holograms-- to move among the analogs on a whole-message basis.

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Color holography and multiple holograms also supply models for the results of split-brain research. Recall that persons who underwent the split-brain operation behaved as though their right and left cerebral hemispheres knew different things. Yet the operation did not derange them; they remained, as Gazzaniga said, "just folks." A hemisphere knew whole messages.

Suppose we decide to construct two holograms of an elephant, on the same piece of film, using two different construction angles, with, say, red at one angle and blue at the other. Remember that the reconstruction beam must contain wavelengths equal to or shorter than the original. During the reconstruction with blue light, either angle will reproduce our elephant's image; but red will work at only one angle. Still, whenever we do reconstruct the elephant's image, it is a whole image, not a tusk here, a trunk there. Wavelength manipulations, in other words, allow us to simulate the observations reported by split-brain researchers.

We can envisage another model for split-brain. Suppose we shade the left side of the film during one step of construction. Obviously, we would be able to reconstruct scenes from the right side that we would not get from the left. Gazzinga's observations hint at the possibility that humans learn to direct certain information to only one hemisphere. Active inhibition occurs on a grand scale in the nervous system, and at levels from individual cells to whole lobes. Shading in our experiment can serve as an analog of inhibition.

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A toddler I once knew went into a gleeful prance whenever her young father entered the room. Around the perimeter of her playpen she would march, damp diaper at half-mast, singing "Dadadada!" until the man rested his chin on the rail next to her little face to receive a moist kiss. One day he came home wearing new eyeglasses. The toddler began her routine but then broke off, frowning, on the first "Da," as she apprehended the change. When he bent down, she placed a wet finger on one of the curious lenses, and, maintaining the frown, continued, "dadadada!" at a puzzled pace.

No physical hologram, multiple or otherwise, matches the complexity of that toddler in action. But holograms used in the materials-testing industry suggest one feature of her behavior, namely, the instantaneous-- and simultaneous-- recognition of both the familiar and unfamiliar attributes in a scene. The technique is known as interference holography and involves looking at an object through a hologram of the object. The light waves coming from the object and from the hologram superimpose interference fringes on the object's image. Any locus where the object has changed since its hologram was made will reflect light differently than before. And in that area the interference patterns converge toward the point of change. The method is extremely sensitive. Even the pressure of a finger on a block of granite shows up immediately. The observer is immediately aware of the change but can also recognize the object in the background.

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In a splendid article in Scientific American in 1965, Leith and Upatnieks made an interesting comparison between holograms and FM signals. FM is, of course, the abbreviation for frequency modulation, and it is the form in which TV and FM radio stations broadcast. Frequency, remember, refers to the number of cycles occurring in a given period of time. In FM, the amplitudes of the radio waves stay constant while their frequencies vary, or modulate, to carry the message. As waves contract or expand, their peaks, or amplitudes, shift. Phase, remember, specifies the location of amplitudes. As many engineers describe it, and as Leith and Upatnieks point out, FM is in effect phase modulation, the generic feature of all holograms.

Physiologists have known for some time that neural signals involve frequency modulation (see Brinley), and therefore variations in phase. The reason for this has to do with the nature of the main neural signal carrier, the nerve impulse.