[From Bruce Abbott (2001.05.15.1745 EST)]
Bruce Abbott (2001.05.14.1035 EST) --
"Here's a (minor) brain-teaser to start off the week:
What are the names of all the current levels of control defined in HPCT,
beginning with the lowest?
First person to answer gets to be our PCT-person of the week, with all the
rights and privileges thereof..."
Mary Powers (2001.05.14) --
Comment from Bill: "I'm pretty sure the first level is intensity."
Hmmm -- I'm pretty sure it isn't!
Bill argued in B:CP for the first level being pure intensities devoid of any
quality. I think this was based on the fact that neural currents arising
from sensory receptors vary only in frequency, with frequency representing
the intensity of stimulation. Bill said something to the effect that the
kind of variable being represented by a given neural current depends on the
nature of the input function and not on any properties of the signal (neural
current) output by that function. The term "sensation" was then reserved
for the next higher level of perception, in which the input functions
combine intensity inputs. An example might be intensity signals from "red"
"green" and "blue" color receptors in the retina combining to produce a
range of qualitatively different perceived colors.
I would argue that there is _no_ perception of pure intensities under
ordinary circumstances, if by "perception" we mean conscious perception.
The qualitative nature of the perception depends not on the nature of the
input function (e.g., sensory receptor) but rather on the nature of the
"analyzer" whose activity gives rise (in some way nobody yet understands) to
conscious perception. A pure tone of 220 Hz is perceived as a _tone_
because its signal enters the auditory areas of the cerebral cortex, not
because it originated in the ears. (Route that same signal to the primary
visual area in the occipital lobes and the person would see flashes of light
rather than hearing a tone.) Moreover, it is perceived as a tone of 220 Hz
because the signal entered that region of the primary auditory cortex where
tones of 220 Hz are registered rather than some other region of the primary
auditory cortex. And the reason the signal enters the "right" portion of
cortex for 220 Hz sound is that it was carried by a separate pathway from a
sensory mechanism in the cochlea of the ear that was selectively stimulated
by tones of that frequency. (I recognize that the processing of sound
frequency is not this simple, but substituting the actual complex process
would make no difference to the argument.)
With respect to those "perceptual" signals that give rise to no conscious
perceptions, it makes no real difference how they are labeled;
"first-order," and "second-order" are probably just as good as "intensity"
and "sensation"; in fact they may be better as they do not connote something
belonging legitimately only to conscious perception. And even here, the
outputs of sensory receptors come already qualitatively "labeled" in the
nervous system by being carried in particular pathways that emerge from
sensory receptor mechanisms tuned to different values of some aspect of the
input energy (e.g., different frequencies). In other words, the outputs are
spacially "coded."
If anyone cares to present a different analysis or comment on this one (or
both), I'd like to hear it. (That includes you, Bill.)
Best wishes,
Bruce A.