6 Imperfect Communication
Defining communication as the output of two complementary informative processes
describes communication in an ideal noiseless environment where the second
function is a perfect inverse of the other. Here, the second function perfectly
“undoes” what the first function “does” and there is no noise introduced into the
system.
In the real world, however, there is almost always noise present and communication
is imperfect, except in the presence of error correcting codes that allow the
recipient of a message other than the message that was sent to recover the original
message [Ham86, Los90].
We refer to the output of a noisy communication channel as noise modified
communication. Communications received that have been noise modified but
can be understood accurately or used by a human, even given the noise induced
changes in it, are acceptable noisy communications. These errors or noise may
be induced by external processes and events, causing the informative processes to
function differently than they would without the error producing process. Noise or
errors in the information may be viewed as additive if the operations of each process
are independent of the operations of the other processes and these processes
are in series.
In many cases, the inversion provided by a process or is imperfect, that
is, for some ? it will be the case that "4 $A@ For example, consider
the case where the author who grew up in the northern United States refers to
snow when talking with his daughter, who has spent her life in the southern half
of the country. The author’s hierarchy encodes a certain set of meanings as snow
while his daughter decodes the term snow as a rather different phenomenon. Here
the daughter’s receiving function isn’t the exact inverse of her father’s encoding
function.