Cosmos #11 Persistence of Memory

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
First-time Visitors: Please visit Site Map and Disclaimer. Use "Back" to return here.


Information

Bits and Bytes

The fundamental unit of information is a bit, a single unambiguous question that can be answered in terms of yes and no. With one bit, you can specify one of two possiblities, two bits specify one of four (yes-yes, yes-no, no-yes or no-no) and in general n bits specify one of 2n possibilities

Counting a space as a letter, it takes 5 bits to specify a letter (2 to the fifth power, 32, is the smallest power of two larger than 26.) Computers typically store information in bytes, or clusters of 8 bits. One byte will specify one of 256 possibilities, enough to account for all our letters, numbers, and punctuation marks. If we package information in clumps of two bytes, each unit specifies one of 256 x 256 = 65,536 possibilities. That's enough to encode all the world's writing systems, including Chinese.

Bits and bytes were pretty specialized pieces of information when Cosmos was produced. Now everyone with a home computer has some idea what they are. It's easy to identify how much space something takes up in a computer. Identifying how much of that information is necessary to extract the full meaning of something is harder; identifying how much of that meaning is significant is harder yet. A written page contains a few thousand bits of information; we can probably eliminate all the a's, an's and the's and most of the vowels without sacrificing any real information content. Excess information above what we really need to recover meaning is termed redundancy.

The brute-force way to encode pictorial information is in terms of pixels, or small dots. This means of storage is extremely redundant and space-consuming. Using this mode of storage a picture really is worth a thousand words. We can simplify pictorial information by identifying large blocks that are all the same color; images stored this way take only a few per cent of the space of pixel-stored images. Line drawings can be described in terms of the beginnings and ends of line segments and can be encoded in even more compact terms.

Genes and Information

The information content of genes is easy to calculate. Each rung on the DNA ladder consists of a pair of nucleotides: cytosine (C) paired with guanine (G) or adenine (A) paired with tyrosine (T). Thus each rung can be one of four possibilities: A-T, T-A, C-G or G-C; it makes a difference which end is which. Thus each rung on a DNA chain contains two bits of information.

A virus contains 104 bits of information in its DNA or about one printed page. A bacterium contains 106 bits or about 100 printed pages. A one-celled animal, an amoeba, contains 4 x 108 bits; 80 volumes at 500 pages each. Mammals contain 5 x 109 bits or 1500 volumes at 500 pages each.

What if even genes cannot cope with the data flow? Then we have brains. Incidentally, this is the fundamental fallacy of eugenics; once brains become the principal repository of information for a species, genes become less important. In fact it is perfectly possible to select for good genes but bad brains. George Bernard Shaw was once asked semi-seriously by a famous beauty if he would be interested in a love affair. "Just think," she said "imagine a child with my looks and your brains." To which Shaw replied "Yes, but what if it had my looks and your brains?

The Human Brain

Structure of the Brain

Many biologists believe that the brain evolved from the inside out and consists of several levels or shells. From oldest to youngest they are:

In addition, the brain has two halves, one of which seems to be connected with intuition,the other with critical analysis. In effect, we have two parallel computers programmed for different tasks.

How the Brain Stores Information

It's natural to suppose that different brain functions occupy different places. We know sensory and motor functions do, and people with brain damage often undergo personality changes. In the 19th century there was a widespread theory, called phrenology, that claimed to be able to read personality from the exterior shape of a person's skull, based on the idea that the skull conformed to areas of growth in the brain. The idea deserves to be treated a bit more charitably than histories of science typically do; in the total absence of understanding of the brain it was at least a plausible hypothesis. However, we now know it's wrong; the brain stores information in a radically different way.

In a computer, a bit of information has a specific location in space; a transistor conducts current or not; a dot on a diskette is magnetized or not. In the brain, each neural connection represents one bit: the cell is either transmitting to its neighbor or not. But in the brain the bits don't stay static; they are constantly moving. Also, it appears that every time a memory is accessed, it is copied. One copy is used for some application, say taking a test, and the other keeps on circulating. Thus old or frequently-accessed memories seem to be stored as multiple copies in many places.

How Much Information Can The Brain Contain?

We often hear that even Albert Einstein never used more than a tiny fraction of his brain capacity. There are two things wrong with that idea:

Chances are that the data you have created occupies only a tiny part of your computer's active memory or disk space. Most of the rest, termed overhead in computer parlance, is the operating system and other software. Similarly, a large part of your cerebral cortex is used for processing sensory data, especially vision. Also, if you filled every byte of your computer memory or disk drive with data and software, you couldn't do anything. You need a large amount of free space for working. In the brain, where information is constantly in motion, this is even more true.

The human record for learning foreign languages is about 40. If we assume a vocabulary of 10,000 words per language (extremely literate) and an average of 10 characters per word, one byte per character, we get 4 megabytes of information. In modern software terms that's a small file. Even if we assume that ten times as much space is needed to store grammar, we are still only up to 40 megabytes. In one story, Sherlock Holmes admitted he had never heard of the Solar System and didn't want to know, on the grounds that it might crowd out more useful information. He needn't have worried. Textbook learned information will never fill more than a tiny fraction of anyone's brain capacity.

How much information would be needed to record your life completely? Visual information would probably account for the vast majority of information recorded. Assume you store visual information at movie speed, 32 frames per second, and that your brain is as good at compressing this information as a good computer algorithm. A photograph can be compressed to about 50,000 bytes without losing much content. If you live 100 years, that's 100 x 365 x 24 x 60 x 60 or 3.1 x 109 seconds. At 32 frames per second and 50,000 bytes per frame, that's 5 x 1015 bytes or 4 x 1016 bits, about 400 times the number of neural connections in the brain. But this is still pretty inefficient data storage. Most visual scenes don't change very much from one moment to the next. Good video compression schemes record only the changes from one scene to the next and can compress some video data by 100 times or more. In reality, of course, your brain deems only a tiny fraction of the information it receives as worthy of recording. A lot of information is recorded in terms of patterns or templates rather than actual images. This complicates things like eyewitness testimony enormously since memories of witnesses are only as good as the patterns their brains use.

Non-Human Intelligence on Earth?

The life form most often suspected of being a non-human terrestrial intelligence is whales. Whale "songs" are 15-30 min. long, comparable in complexity to short pieces of classical music, and with about the information content of the Iliad or Odyssey.    Whale sounds are rich in 20 hertz frequencies, about at the lower threshold of human hearing. A "Deep Sound channel" in the oceans that conducts low frequencies efficiently means that whales effectively had worldwide communication. Ship propellers also emit at 20 Hz and may interfere with whale communication. Since the episode was filmed commercial whaling by Norway, Japan, and the former USSR has diminished still further.

Cities and Brains

Evolution of cities, like that of organs and organisms, is conservative. Vestiges of the past are contained in present. Each new addition must mesh with past structures, and it is common to see restructuring and adaptation of existing systems for new uses. Humans are the only known species to have devised information storage outside of brains - Libraries (and now the Internet) are a communal memory that permits communication across time.

Doubters of evolution pose a good question when they ask "what good is half a wing, or half an eye?" The utility of half an eye is obvious - any light detection and imaging ability is better than none. How wings evolved is more contentious. Feathers probably evolved as insulating materials that were only later adapted for flight. Small creatures don't need much to improve their aerodynamic capabilities - a mouse dropped off a cliff would bounce and walk away - so a small creature with feathers purely for insulation might well find improved gliding ability as a fringe benefit. So it's indeed true that organs need to be useful at every stage of their evolution. The problem is that most critics of evolution who raise this issue are looking for any pretext at all to reject evolution, and they rarely spend any effort trying to figure out alternative uses for partial features.

Would-be devisers of alternative technologies forget the conservative nature of evolution. New technologies must mesh with pre-existing systems. This conservatism often causes undesirable or obsolete features to persist long after their utility is lost. 35-mm cameras initially used movie film because it was easily available. 35-mm cameras had sprockets because movie cameras did. Now 35-mm film continues to be made with sprocket holes even though it has long been possible to abandon them, because 35-mm cameras have to be made to make use of the film, which means the film has to have sprocket holes ..... Any new automotive technology will have to be compatible with existing autos. Nobody is going to by an electric or hydrogen-burning auto without a promise that it will be easily refueled. The alternative is to create and install a completely new technology all at once. It has been done, but it's a huge task.

Also, new technologies have to be a distinct enough improvement on the old system to be perceived as a real improvement. A ten per cent improvement in performance rarely compensates for the trouble of replacing an old system with a new one, and an eventual payoff in the future has to be very large to compensate for additional costs now.


Return to Explorations of the Universe Index
Return to Professor Dutch's Home Page

Created 13 January 1998, Last Update 12 April 2000

Not an official UW Green Bay site