by Paul Pietsch
Gabor was no ordinary person. And in the early 1960s. in Michigan, two other extraordinary persons entered the scene--Emmett Leith and Juris Upatnieks. A small amount of work had been done in this field after Gabor's research; but Leith and Upatnieks turned Gabor's rudimentary discovery into holography as it is practiced today. And among their long string of remarkable inventions and discoveries was one that precipitated nothing less than hologramic memory theory itself.
***
The germ of hologramic memory is unmistakable in Gabor's original discoveries--in retrospect. A physicist named van Heerden actually proposed an optical theory of memory in 1963; but his work went as unnoticed as Gabor's had. As in the case of the acorn and the oak, it is difficult to see the connection, a priori. Leith and Upatnieks did for the hologram what Gabor had done for interference in general: they extended it to its fullest dimensions.
Leith had worked on sophisticated radar, was a mathematical thinker, and thoroughly understood waves; and in 1955 he had become intrigued by the hologram. Upatnieks was a bench wizard, the kind of person who when you let him loose in a laboratory makes the impossible experiment work.
Gabor's so-called "in-line" method (because object lies between plate and source) put several restrictions on optical holograms. For instance, the object had to be transparent. This posed the problem of what to do about dense objects. Besides, we actually see most things in reflected light. Leith and Upatnieks applied an elaborate version of Fresnel's old trick: they used mirrors. Mirrors allowed them to invent "off-line" holograms, and to use reflected light. The light came from a point source. The beam passed through a special partially coated mirror, which produced two beams from the original; and other mirrors deflected the two beams along different paths. One beam, aimed at the object, supplied the object waves. The other beam furnished the reference waves. They by-passed the scene but intersected and interfered with the reflected object waves at the hologram plate.
Leith and Upatnieks used a narrow beam from an arc lamp to make their early holograms. But there was a problem. The holographed scene was still very small. To make holograms interesting, they needed a broad, diffuse light. But with ordinary light, a broad beam wouldn't be coherent.
So Leith and Upatnieks turned to the laser. The laser had been invented in 1960, shortly before Leith and Upatnieks tooled up to work on holograms. The laser is a source of extremely coherent light, not because it disobeys the uncertainty principle but because each burst of light involves a twin emission--two wave trains of identical phase and amplitude.
The insight Leigh and Upatnieks brought to their work was profound. Back when holograms were very new, I had seen physicists wince at what Leith and Upatnieks did to advance their work. What they did was put a diffuser on the laser light source. A diffuser scatters light, which would seem to throw the waves into random cadence and total incoherence. Leith's theoretical insight said otherwise: the diffuser would add another order of complexity to the changes in the phase spectrum but would not cancel the coherent phase relationship between object and reference waves. Not if he was right, anyway! And Leith and Upatnieks went on to make a
diffuse-light hologram
, in spite of all the conventional reasons why it couldn't be done.
***
Gabor had tried to make his object act like a single point source. The encoded message spread out over the medium. But each point in the scene illuminated by diffuse light acts as though it is a source in itself; and the consequence of all points acting as light sources is truly startling. Each point in the hologram plate ends up with the phase and amplitude warp of every point in the scene, which is the same as saying that every part of the exposed plate contains a complete record of the entire object. This may sound preposterous. Therefore, let me repeat: Each point within a diffuse hologram bears a complete code for the entire scene. If that seems strange, consider something else Leith and Upatneiks found: "The plate can be broken down into small fragments, and each piece will reconstruct the entire object."[9]
How can this be? We'll have to defer the complete answer until later. But recall the sizeless nature of relative phase, of angles and degrees. The uncanny character of the diffuse hologram follows from the relative nature of phase information. In theory, a hologram's codes may be of any size, ranging from the proportions of a geometric point up to the magnitude of the entire universe.[10]
Leith and Upatnieks found that as fragments of holograms became small, "resolution is, of course, lost, since the hologram constitutes the limiting aperture of the imaging process."[11] They were saying that tiny pieces of a hologram will only accommodate a narrow beam of decoding light. As any signal carrier becomes very tiny, and thus very weak, "noise" erodes the image. But vibrations, chatter, static, snow--noise--have to do with the carrier, not the stored message, which is total at every point in the diffuse hologram. Even the blurred image, reconstructed from the tiny chip, is still an image of the whole scene.
Not a word about mind or brain appeared in Leith and Upatnieks's articles. But to anyone even remotely familiar with Karl Lashley's work, their descriptions had a very familiar ring. Indeed, substitute the term
brain
for
diffuse hologram
. and Leith and Upatnieks's observations would aptly summarize Lashley's lifelong assertions. Fragments of a diffuse hologram reconstruct whole, if badly faded, images. Correspondingly, a damaged brain still clings to whole, if blurred, memories. Sharpness of the reconstructed image depends not on the specific fragment of hologram but upon the fragment's size. Likewise, the efficiency with which Lashley's subjects remembered their tasks depended not on which parts of the brain survived but on how much brain the animal retained. "Mass action and equipotentiality!" Lashley might have shouted had he lived another six years.
Leith and Upatnieks published an account of the diffuse hologram in the November 1964 issue of the Journal of the Optical Society of America. The following spring, ink scarcely dry on the journal pages, Bela Julesz and K. S. Pennington explicitly proposed that memory in the living brain maps like information in the diffuse hologram. Hologramic theory had made a formal entry into scientific discourse.
***
Whom should we credit then for the idea of the hologramic mind? Lashley? He had forecast it in pointing to interference patterns. Van Heerden? He saw the connection. Pribram? The idea might not have made it into biology without his daring. The cyberneticist Philip Westlake, who wrote a doctoral dissertation to show that electrophysiological data fit the equations of holograms? Julesz and Pennington, for the courage to come right out and say so? I've spent many years unsuccessfully trying to decide just who and when. And I'm not really the person to say. But I am thoroughly convinced of this: subtract Leith and Upatnieks from the scene, and a thousand years could have slipped by with only an occasional van Heerden observing, unnoticed, how closely the hologram mimics the living brain. For the genesis of the theory recapitulates virtually the history of human thought: only after Pythagoras's earth became Columbus's world did it become perfectly obvious to everyone else that our planet was a sphere. And only after Gabor's principle became Leith and Upatnieks's diffuse hologram did science enter the age of the hologramic mind.
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chapter four
Mimics of Mind
THEORY, ABSTRACTION, AND ANALOGY are words used pejoratively by many writers, editors, and publishers, even in an age alternately sustained and menaced by the yield of theoretical physics. Yet theories provide a matrix for much of scientific knowledge. And whatever less committal synonym we may choose (principle, explanation, concept, generalization, for instance), theory is what we really demand of science when we apply
why
to our questions about Nature.
Abstractions, in turn, are what theories really deal in: when we compare six apples with six oranges, we divide or square or multipl
y the numbers, the abstractions-- not the pits or rinds. The old cliché about not comparing apples and oranges is (to tweak if not mix a metaphor) a lot boloney if we're talking about numbers. "How many apples will you give me for two or oranges?" A good test of a valid abstraction is to ask: does it survive if we shift it to a new set of parochial conditions? The ninety-degree angle-- the abstraction-- made by the edges of a table top does not depend on oak or maple; it can be formed of brass, or asphalt, or two streaks of chalk.
The analogy has its intellectual justification in the first axiom of geometry: things equal to the same things are equal to each other. Things dependent upon the same abstractions are analogs of each other!
Analogy can show us what a theory does , but not what a theory is . Nor does analogy provide a rigorous test of a theory's applicability to a problem. Analogy can't serve as substitutes for the experiment, in other words. Nonetheless, analogies often reveal a theory's implications. They also help connect abstractions to some concrete reality; they often put us in a position to grasp the main idea of a theory with our intuition. The analogy can also expose a subject and show important consequences of a theory, even to those who do not know the strange language of the theory. The analogy can put the theory to work on a human being's familiar ground-- experience. It is by way of the analogy that I shall introduce the reader to hologramic theory.
***
The hologram is not a phenomenon of light, per se, but of waves; in theory, any waves or wavelike events. I've already mentioned acoustical holograms. X-ray holograms, microwave holograms, and electron holograms also exist, as do "computer" holograms, which are holograms constructed from mathematical equations and reconstructed by the computer; holograms, in other words, of objects comprised of pure thought.
The same kinds of equations can describe holograms of all sorts. And the very same phase code can exist simultaneously in several different media. Take acoustical holograms, for instance. The acoustical holographer produces his hologram by transmitting sound waves through an object. (Solids transmit sound as shock vibrations, as, for example, knocks on a door.) He records the interference patterns with a microphone and displays his hologram on a television tube. Sound waves cannot stimulate the light receptors in our retinas. Thus we would not be able to "see" what a sonic wave would reconstruct. But the acoustical holographer can still present the scene to us by making a photograph of the hologram on the TV tube. Then, by shining a laser through the photograph, he reconstructs optically-- and therefore visibly-- the images he originally holographed by sound.
Sound is not light, nor is it the electronic signals in the television set. But information carried in the phase and amplitude of sound or electronic waves can be an analog of the same message or image in a light beam, and vice versa. It is the code-- the abstract logic--that the different media must share, not the chemistry. For holograms are encoded, stored information. They are memories in the most exacting sense of the word--the mathematical sense. They are abstractable relationships between the constituents of the medium, not the constituents themselves. And abstract information is what hologramic theory is about.
As I said in the preceding chapter, the inherent logic in waves shows up in many activities, motions, and geometric patterns. For example, the equations of waves can describe a swinging pendulum; a vibrating drum head; flapping butterfly wings; cycling hands of a clock; beating hearts; planets orbiting the sun, or electrons circling an atom's nucleus; the thrust and return of an auto engine's pistons; the spacing of atoms in a crystal; the rise and fall of the tide; the recurrence of the seasons. The terms harmonic motion, periodic motion, and wave motion are interchangeable. The to-and-fro activity of an oscillating crystal, the pulsation in an artery, and the rhythm in a song are analogs of the rise and fall of waves. Under the electron microscope, the fibers of our connective tissues (collagen fibers) show what anatomists call periodicity, meaning a banded, repeated pattern occurring along the fiber's length. The pattern is also an analog of waves.
Of course, a periodically patterned connective-tissue fiber is not literally a wave. It is a piece of protein. A pendulum is not a wave, either, but brass or wood or ivory. And the vibrating head of a tom-tom isn't the stormy sea, but the erstwhile hide of an unlucky jackass. Motions, activities, patterns, and waves all obey a common set of abstract rules. And any wavy wave or wavelike event can be defined, described, or, given the engineering wherewithal, reproduced if one knows amplitude and phase. A crystallographer who calculates the phase and amplitude spectra of a crystal's x-ray diffraction pattern knows the internal anatomy of that crystal in minute detail. An astronomer who knows the phase and amplitude of a planet's moon knows precisely where and when he can take its picture. But let me repeat: the theorist's emphasis is not on the nominalistic fact: It is on logic, which is the basis of the hologram.
Nor, in theory, does the hologram necessarily depend on the literal interference of wavy waves. In the acoustical hologram, for example, where is the information? Is it in the interferences of the sonic wave fronts? In the microphone? In the voltage fluctuations initiated by the vibrating microphone? In oscillations among particles within the electronic components of the television set? On the television screen? In the photograph? The answer is that the code-- the relationships-- and therefore the hologram itself, exists-- or once existed-- in all these places, sometimes in a form we can readily appreciate as wavy information, and in other instances as motion or activity, in forms that don't even remotely resemble what we usually think of as waves.
***
Lashley's experiments can be applied to diffuse holograms, as I have pointed out. His results depended not on where he injured the brain but on how much . Likewise, cropping a corner from a diffuse hologram does not amputate parts from the regenerated scene. Nor does cutting a hole in the center or anywhere else. The remaining hologram still produces an entire scene. In fact, even the amputated pieces reconstruct a whole scene-- the same whole scene. What Lashley had inferred about the memory trace is true for the diffuse hologram as well: the code in a diffuse hologram is equipotentially represented throughout the diffuse hologram.
***
The loss of detail that occurs when we decode a small piece of diffuse hologram is not a property of the code itself. Blurring is a result mainly of noise, not the signal. How seriously noise affects the quality of an incoming message depends on the ratio of noise to signal. If the signal is powerful, we may dampen noise by reducing volume or brightness. But with very weak signals, as short-wave radio buffs can testify, a small amount of noise (static) severely impedes reception. In optical holograms, the relative level of noise increases as the size of the hologram decreases. And in a small enough piece of hologram, noise can disperse the image.
We have already made the analogy between the survival of memory in a damaged brain and the survival of image in a marred hologram. Signal-to-noise ratio is really an analog of the decline in efficiency found in Lashley's subjects. In other words, the less brain, the weaker the signal and the greater the deleterious consequence of "neural noise."
***
Loss of detail in an image produced from a small chip of hologram is a function of decoding, not of the code itself. An infinitesimally small code still exists at every point in the diffuse hologram. Like a single geometric point, the individual code is a theoretical, not a physical, entity. As with geometric points, we deal with codes physically in groups, not as individuals. But the presence of a code at every location is what accounts for the demonstrable fact that any arbitrarily chosen sector of the hologram produces the same scene as any other sector. Granted, this property may not be easy to fathom; for nothing in our everyday experience is like a diffuse hologram. Otherwise, the mind would have been the subject of scientific inquiry long before Leith and Upatnieks.
***
If a single holographic code is so very, very tiny, any physical area should be able to contain many codes-- infinitely many, in theory.[1] Nor
would the codes all have to resemble each other. Leith and Upatnieks recognized these properties early in their work. Then, turning theory into practice, they went on to invent the "multiple hologram"-- several totally different holograms actually stacked together within the same film.
With several holograms in the same film, how could reconstruction proceed without producing utter chaos? How might individual scenes be reconstructed, one at a time? Leith and Upatnieks extended the basic operating rules of holography they themselves had developed. During reconstruction, the beam must pass through the film at a critical angle-- an angle approximating the one at which the construction beam originally met the film. During multiple constructions, Leith and Upatnieks set up each hologram at a different angle. Then, during reconstruction, a tilt of the film in the beam was sufficient for one scene instantly to be forgotten and the other remembered.
One of Leith and Upatnieks' most famous multiple holograms is of a little toy chick on wheels. The toy dips over to peck the surface when it's dragged along. Leith and Upatnieks holographed the toy in various positions, tilting the film at each step. Then, during reconstruction, by rotating the film at the correct tempo, they produced images of the little chick, in motion, pecking away at the surface as though going after cracked corn. Some variant of their basic idea could become the cinema and TV or tomorrow.
***
Multiple holograms let us conceptualize something neither Lashley nor anyone else had ever satisfactorily explained: how one brain can house more than one memory. If the engram is reduplicated and also equally represented throughout the brain, how can enough room remain for the next thing the animal learns--and the next...and the next? Multiple holograms illustrate the fact that many codes can be packed together in the same space.