[From Rick Marken (2000.02.14.1300)]
Bruce Nevin (2000.02.13.2037)--
"Encoding" is a metaphor that implies discrete bits of
Martin Taylor (20000214 09:42) --
Is that your point (Rick and Bill?).
I don't think so. I think encoding is a real process, not a
metaphor; and it can be applied to discrete or analog data.
Here the distinction I'm trying to make. Take (for simplicity)
a 16 bit digital array, analogous to the retinal array:
I think of encoding as a process that maps an input array
like this into an encoded version of the array, like this
10 bit string:
If you know the input array is going to consist mainly of
certain patterns (like the 8 bit ASCII letter codes) then
you can _encode_ 8 bit patterns of the input array into
a 5 bit code (enough bits to identify the 26 possible 8
bit patterns plus some codes indicating non-letter ASCII
strings) and reduce the amount of data you send to 62% of
that in the original array. Of course, the destination has
to know your coding scheme so that it can decode the ten
bits you sent (0000100010) into the original 16 bit message
Neither the encoding nor the decoding is a perceptual
process from my point of view; the result of the encoding
is just the input in a new form; the result of the decoding
is the original input.
I think of a perception as a function that maps some _aspect_
of the input array into an output whose value indicates the
state of that aspect of the input. One aspect of the input
array that could be perceived is the ASCII letter code found
in the first 8 bits of the input array. A perceptual function
would transform this 8 bit string into a number (possibly a
five bit binary number like the encoding scheme above) whose
value indicates the ASCII state of the first 8 bits of the
input array (1-26, say, with a value of 27 meaning a non-letter
ASCII state of the array).
I wouldn't call this 5 bit output of the perceptual function
a _coded_ representation of the input array because it's not
going to be _decoded_; it's just what it is; a value. In PCT,
that value _is_ a perception. If that value is the controlled
input to a control system then it's that value (and, as a side
effect, the input bit string to which it corresponds) that is
I think this distinction, between a value that functions as
a code and a value that functions as a perceptual variable, is
important to understand. It could be just a verbal problem; I
think the word "code" is sometimes used to mean the same thing
as we, in PCT, mean by "represent". After all, the perceptual
signal is just blips in a neuron which represent ("code"), in
terms of firing rate, some aspect of the input to the system.
But I think it's best to try to avoid using "code" to mean
"represent" because I think it confuses the issue. "Code"
implies decoding; "represent" implies no decoding; you just
deal with (control) the representation (perception) as is.
I admit that the distinction is subtle; but I think it's very
important in terms of communicating (and using) PCT.