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From: adam@mtund.UUCP
Newsgroups: comp.cog-eng,comp.ai
Subject: Objective measurement of subjective variables
Message-ID: <842@mtund.UUCP>
Date: Sun, 25-Jan-87 10:15:06 EST
Article-I.D.: mtund.842
Posted: Sun Jan 25 10:15:06 1987
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John Cugini:
>>	                        .... to explain, or at least discuss, private
>>	subjective events.  If it be objected that the latter are outside the
>>	proper realm of science, so be it, call it schmience or philosophy or
>>	whatever you like. - but surely anything that is REAL, even if
>>	subjective, can be the proper object for some sort of rational
>>	study, no?
Stevan Harnad:
>   Some sort, no doubt. But not an objective sort, and that's the point.
>   Empirical psychology, neuroscience and artificial intelligence are
>   all, I presume, branches of objective inquiry.
>          ....   Let's leave the subjective discussion of private events
>   to lit-crit, where it belongs.

Stevan Harnad makes an unstated assumption here, namely, that subjective
variables are not amenable to objective measurement. But if by
"objective" Steve means, as I think he does, "observer-invariant", than
this assumption is demonstrably false. I shall proceed to demonstrate
this in two parts: (1) private events are amenable to parametric
measurement; and (2) relevant results of such measurement can be
observer-invariant.

(1) Whether or not a stimulus is experienced as belonging to some target
category is clearly a private event. Now data for the measurement of d',
the detection-theoretic measure of discriminability, are usually
gathered using overt behavior, such as pressing "target" and
"non-target" buttons. But in principle, d' can be measured without any
resort to externally observable behavior. Suppose I program a computer
to present a sequence of stimuli and, following enough time after
each stimulus to allow the observer to mentally classify the experience
as target or non-target, display the actual category of the preceding
stimulus. The observer would use this information to maintain a mental
count of hits and false alarms. The category feedback for the last
stimulus could be followed by a display of a table for the conversion of
hit and false alarm rates into d'. Thus, the observer would be able to
mentally compute d' without engaging in any externally observable
behavior whatever.

(2) In some well-defined contexts, the variation of d' with an
independent variable is as lawful as anything in the "known to be
objective" sciences such as physics (see Reed, Memory and Cognition
1976, 4(4), 453-458, equation 5 and bottom panel of figure 1, for an
example of this). The parameters of such lawful relationships will
differ from observer to observer, but their form is observer-invariant.
In principle, two investigators could perform the experiment as in (1)
above, 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*.

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.
										   Adam Reed
										   mtund!adam,attmail!adamreed