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adam@mtund.UUCP (Adam V. Reed), of AT&T ISL Middletown NJ USA, wrote:

>	Stevan Harnad makes an unstated assumption... that subjective
>	variables are not amenable to objective measurement. But if by
>	"objective" Steve means, as I think he does, "observer-invariant", then
>	this assumption is demonstrably false.

I do make the assumption (let me state it boldly) that subjective
variables are not objectively measurable (nor are they objectively
explainable) and that that's the mind/body problem. I don't know what
"observer-invariant" means, but if it means the same thing as in
physics -- which is that the very same physical phenomenon can
occur independently of any particular observation, and can in
principle be measured by any observer, then individuals' private events
certainly are not such, since the only eligible observer is the
subject of the experience himself (and without an observer there is no
experience -- I'll return to this below). I can't observe yours and you
can't observe mine. That's one of the definitive features of the
subjective/objective distinction itself, and it's intimately related to
the nature of experience, i.e., of subjectivity, of consciousness.

>	Whether or not a stimulus is experienced as belonging to some target
>	category is clearly a private event...[This is followed by an
>	interesting thought-experiment in which the signal detection parameter
>	d' could be calculated for himself by a subject after an appropriate
>	series of trials with feedback and no overt response.]... the observer
>	would be able to mentally compute d' without engaging in any externally
>	observable behavior whatever.

Unfortunately, this in no way refutes the claim that subjective experience
cannot be objectively measured or explained. Not only is there (1) no way
of objectively testing whether the subject's covert calculations on
that series of trials were correct, not only is there (2) no way of
getting any data AT ALL without his overt mega-response at the end
(unless, of course, the subject is the experimenter, which makes the
whole exercise solipsistic), but, worst of all, (3) the very same
performance data could be generated by presenting inputs to a
computer's transducer, and no matter how accurately it reported its
d', we presumably wouldn't want to conclude that it had experienced anything
at all. So what's OBJECTIVELY different about the human case?

At best, what's being objectively measured happens to correlate
reliably with subjective experience (as we can each confirm in our own
cases only -- privately and subjectively). What we are actually measuring
objectively is merely behavior (and, if we know what to look for, also
its neural substrate). By the usual objective techniques of scientific
inference on these data we can then go on to formulate (again objective)
hypotheses about underlying functional (causal) mechanisms. These should
be testable and may even be valid (all likewise objectively). But the
testability and validity of these hypotheses will always be objectively
independent of any experiential correlations (i.e., the presence or
absence of consciousness).

To put it my standard stark way: The psychophysics of a conscious
organism (or device) will always be objectively identical to that
of a turing-indistinguishable unconscious organism (or device) that
merely BEHAVES EXACTLY AS IF it were conscious. (It is irrelevant whether
there are or could be such organisms or devices; what's at issue here is
objectivity. Moreover, the "reliability" of the correlations is of
course objectively untestable.) This leaves subjective experience a
mere "nomological dangler" (as the old identity theorists used to call
it) in a lawful psychophysical account. We each (presumably) know it's
there from our respective subjective observations. But, objectively speaking,
psychophysics is only the study of, say, the detecting and discriminating
capacity (i.e., behavior) of our trandsucer systems, NOT the qualities of our
conscious experience, no matter how tight the subjective correlation.
That's no limit on psychophysics. We can do it as if it were the study
of our conscious experience, and the correlations may all be real,
even causal. But the mind/body problem and the problem of objective
measurement and explanation remain completely untouched by our findings,
both in practise and in principle.

So even in psychophysics, the appropriate research strategy seems to
be methodological epiphenomenalism. If you disagree, answer this: What
MORE is added to our empirical mission in doing psychophysics if we
insist that we are not "merely" trying to account for the underlying
regularities and causal mechanisms of detection, discrimination,
categorization (etc.) PERFORMANCE, but of the qualitative experience
accompanying and "mediating" it? How would someone who wanted to 
undertake the latter rather than merely the former go about things any
differently, and how would his methods and findings differ (apart from
being embellished with a subjective interpretation)? Would there be any
OBJECTIVE difference?

I have no lack of respect for psychophysics, and what it can tell us
about the functional basis of categorization. (I've just edited and
contributed to a book on it.) But I have no illusions about its being
in any better a position to make objective inroads on the mind/body
problem than neuroscience, cognitive psychology, artificial
intelligence or evolutionary biology -- and they're in no position at all.

>	In principle, two investigators could perform the [above] experiment
>	...and obtain objective (in the sense of observer-independent)
>	results as to the form of the resulting lawful relationships between,
>	for example, d' and memory retention time, *without engaging in any
>	externally observable behavior until it came time to compare results*.

I'd be interested in knowing how, if I were one of the experimenters
and Adam Reed were the other, he could get "objective
(observer-independent) results" on my experience and I on his. Of
course, if we make some (question-begging) assumptions about the fact
that the experience of our respective alter egos (a) exists, (b) is
similar to our own, and (c) is veridically reflected by the "form" of the
overt outcome of our respective covert calculations, then we'd have some
agreement, but I'd hardly dare to say we had objectivity.

(What, by the way, is the difference in principle between overt behavior
on every trial and overt behavior after a complex-series-of-trials?
Whether I'm detecting individual signals or calculating cumulating d's
or even more complex psychophysical functions, I'm just an
organism/device that's behaving in a certain way under certain
conditions. And you're just a theorist making inferences about the
regularities underlying my performance. Where does "experience" come
into it, objectively speaking? -- And you're surely not suggesting that
psychophyics be practiced as a solipsistic science, each experimenter
serving as his own sole subject: for from solipsistic methods you can
only arrive at solipsistic conclusions, trivially observer-invariant,
but hardly objective.)

>	The following analogy (proposed, if I remember correctly, by Robert
>	Efron) may illuminate what is happening here. Two physicists, A and B,
>	live in countries with closed borders, so that they may never visit each
>	other's laboratories and personally observe each other's experiments.
>	Relative to each other's personal perception, their experiments are
>	as private as the conscious experiences of different observers. But, by
>	replicating each other's experiments in their respective laboratories,
>	they are capable of arriving at objective knowledge. This is also true,
>	I submit, of the psychological study of private, "subjective"
>	experience.

As far as I can see, Efron's analogy casts no light at all.
It merely reminds us that even normal objectivity in science (intersubjective
repeatability) happens to be piggy-backing on the existence of
subjective experience. We are not, after all, unconscious automata. When we
perform an "observation," it is not ONLY objective, in the sense that
anyone in principle can perform the same observation and arrive at the
same result. There is also something it is "like" to observe
something -- observations are also conscious experiences.

But apart from some voodoo in certain quantum mechanical meta-theories,
the subjective aspect of objective observations in physics seems to be
nothing but an innocent fellow-traveller: The outcome of the
Michelson-Morley Experiment would presumably be the same if it were
performed by an unconscious automaton, or even if WE were unconscious automata.
This is decidely NOT true of the (untouched) subjective aspect of a
psychophysical experiment. Observer-independent "experience" is a
contradiction in terms.

(Most scientists, by the way, do not construe repeatability to require
travelling directly to one another's labs; rather, it's a matter of
recreating the same objective conditions. Unfortunately, this does not
generalize to the replication of anyone else's private events, or even
to the EXISTENCE of any private events other than one's own.)

Note that I am not denying that objective knowledge can be derived
from psychophysics; I'm only denying that this can amount to objective
knowledge about anything MORE than psychophysical performance and its
underlying causal substrate. The accompanying subjective phenomenology is
simply not part of the objective story science can tell, no matter how, and
how tightly, it happens to be coupled to it in reality. That's the
mind/body problem, and a fundamental limit on objective inquiry.
Methodological epiphenomenalism recommends we face it and live with
it, since not that much is lost. The "incompleteness" of an objective
account is, after all, just a subjective problem. But supposing away
the incompleteness -- by wishful thinking, hopeful over-interpretation,
hidden (subjective) premises or blurring of the objective/subjective
distinction -- is a logical problem.
-- 

Stevan Harnad                                  (609) - 921 7771
{allegra, bellcore, seismo, rutgers, packard}  !princeton!mind!harnad
harnad%mind@princeton.csnet