Saturday, November 19, 2005

Considering how we know ...

Today I begin an experiment. And it shall be a modest beginning. I mentioned awhile back two books by the late British neurophysiologist W. Russell Brain -- Mind, Perception and Science and Tea with Walter de la Mare. What I plan to do over the next few days -- even weeks, if necessary -- is go over each in some detail, a bit at a time. I begin with a passage from the first chapter of Mind, Perception and Science:

A tuning fork is struck or a whistle is blown, or in some other way the air is made to vibrate, and a series of waves with a frequency of, say, 4,000 vibrations a second is propagated through the air. It strikes the observer's ear and a portion of the cochlea, attuned to this particular frequency, is caused to vibrate at the same rate. So far the subject has heard nothing. The vibration of this part of the cochlea starts a series of nerve-impulses in a certain fibre or fibres of the auditory nerve. No nerve-fibre in the body can carry impulses at so fast a rate. The frequency with which nerve-impulses can follow one another along a nerve depends upon the electrochemical structure of nervous tissue and is never more than 1,500 a second, and often much less. ... The auditory nerve-fibre therefore conducts impulses at its accustomed rate, and, by a series of relay paths, the impulses reach the auditory area of the cerebral cortex in the temporal lobe. Electro-encephalography enables us to detect its arrival there and in the experimental animal we can record simultaneously the frequency of the sound-stimulus, and the electrical response which it evokes in the auditory cortex. These are entirely dissimilar. (Emphasis mine.)

Brain goes on to note that "the difference in pitch of two sounds is correlated with a difference in their frequencies, but no such difference is to be found in the events in the nervous system upon which the discrimination of their respective sense-data depends. These have neither the frequencies of the stimuli nor do they differ from each other in frequency (emphasis mine). They differ only in that the nervous impulses travel by different paths and reach different destinations in the cerebral cortex; and this seems to be true not only of the difference between one sound and another, but also of that between nervous impulses evoked by auditory, visual and olfactory stimuli."

I think it will be obvious that the "facts" of the matter indicate, as Brain puts it, "that sense-data are 'really' located in the cerevral cortex or in the mind of the observer." The question is why they appear to be located outside the observer. Presumably, it's because that's where the original stimulus is located. But the absolute dissimilarity of the stimulus and the response makes the whole matter problematic, to say the least.

I throw this out and invite comment. I'm certainly going to be thinking about it -- and this is only the beginning of what is a very interesting little book.

No comments:

Post a Comment