harnad@mind.UUCP (02/15/87)
Adam V. Reed (adam@mtund.UUCP) at AT&T ISL, Middletown NJ USA, wrote in support of the following position: Psychophysicists measure conscious experience in the same sense that physicists measure ordinary physical properties. Our senses and central nervous systems are analogous to the physicist's measuring equipment. If we can assume that this "mental" equipment is similar in all of us, then reports of psychophysical "measurements" of private, conscious experiences are just as objective as reports of physical measurements of physical phenomena, and objective in the same sense (observer-independence). I will attempt to show why this is incorrect. But first let me say that there is really no reason for a psychophysicist to get embroiled in the mind/body problem (or its "other-minds" variant). In cog-sci there is a real empirical question about what processes and performances are justifiably and relevantly mind-like, because it is mental capacity (or at least its performance manifestations) that one is attempting to capture and model. It MATTERS in cognitive modeling whether you've really captured intelligence, or just a clever toy (partial) look-alike. There is no corresponding problem in psychophysics. The input/output charactersitics, detection sensitivities, etc., of human observers have face validity as displayed in their performance data. There is no empirical question affecting the validity (as opposed to the interpretation) of the data that depends on their being a measure of conscious experience rather than merely human receiver I/O characteristics. For simplicity I will focus on detection performance only, although the same arguments could be applied to discrimination, magnitude judgment, identification, etc. If a subject reports when he detects the presence of a signal, and this relation (signal/detection-report) displays interesting I/O regularities (thresholds, detectabilities, criterial biases, etc.), those regularities are indisputably objective in the same sense that the physicist's (or engineer's) regularities are. The sticky part comes when one wants to interpret the measurements and their regularities, not as they are objectively -- namely input/output performance regularities of human subjects under certain experimental conditions -- but as measurements of and regularities in conscious experience. Adam has an "intuition pump" in support of the latter interpretation: He suggests that a subject can compute his own (say) detection thresholds if he receives detection trials plus feedback as to whether or not a stimulus was present. His only performance would be to report, after a long series of trials and private calculations, what his detection threshold was. Since everyone can in principle do this for himself, it is observer-independent, and hence objective. Yet it involves no overt behavior other than the final threshold report; otherwise, it is exactly like a physicist performing an experiment in the privacy of his lab, and then reporting the results, which anyone else can then replicate in the privacy of his own lab. So surely the measurement is not merely of behavioral regularities, but of conscious experience. There are many directions from which one can attack this argument: (i) One could call into question the "lab" analogy, pointing out that, in principle, two physicists could check each other's measurements in the same "lab," whereas this is not possible in one-man psychophysics. (ii) One could question the objectivity of being both subject and experimenter. (iii) One could question whether the subject is performing a "measurement" at all, in the objective sense of measurement; only the psychophysicist is measuring, with the subject's receiver characteristics under various input conditions being the object of measurement. The subject is detecting and reporting. (iv) One could point out that one subject's report of his threshold is not subject-independently tested by another subject's report of his own threshold. (v) One could point out that intersubjective consensus hardly amounts to objectivity, since all subjects could simply share the same subjective bias. (and so on) These objections would all trade (validly) on what we really MEAN by the objective/subjective distinction, which is considerably more than consensus among observers. I will focus my rebuttal, however, on Adam's argument, taken more or less on its own terms; I will try to show that it cannot lead to the interpretation he believes it supports. First, what work are the "covert calculations" really doing in Adam's thought-experiment? What (other than the time taken and the complexity of the task) differentiates a simple, one-trial detection-response from the complex report of a threshold after a series of trials with feedback and internal calculations? My reply is: nothing. Objectively speaking, the normal trial-by-trial method and the long-calculation-with-feedback method are just two different ways of making the same measurement of a given subject's threshold. (And the only one doing the measuring in both cases is the psychophysicist, with the data being the subject's input and output. Not even the subject himself can wear both hats -- objective and subjective -- at one time.) So let's just talk about a simple one-trial detection, because it shares all the critical features at issue, and is not complicated by irrelevant ones. The question then becomes "What is the objectivity-status of reports of single stimulus-detections from individual subjects?" rather than "How observer-independent is the calculation of detection thresholds after a series of trials with feedback?" The two questions are equivalent in the relevant respects, and they share the same weaknesses. When a subject reports that he has detected a stimulus, and there was in fact a stimulus presented, that's ALL there is, by way of data: Input was the stimulus, output was a positive detection report. (When I say "behavioral" or "performance" data, I am always referring to such input/output regularities.) Of course, if I'm the subject, I know that there's something it's "like" to detect a stimulus, and that the presence of that sensation is what I'm really reporting. But that's not part of the psychophysical data, at least not an objective part. Because whereas someone else can certainly look at the same stimulus, and experience the sensation for himself, he's not experiencing MY sensation. I believe that he's experiencing the same KIND of sensation. The belief is surely right. But there's certainly no objective basis for it. Consider that no matter how many times the same stimulus is presented to different subjects, and all report detecting it, there is still no objective evidence that they're having the same sensation -- or even that they're having any sensation at all. It is the everyday, informal solution to this "other-minds" problem -- based on the similarity of other subjects' behavior to our own -- that confers on us the conviction that they're experiencing similar things with "similar equipment." But that's no objective basis either. Contrast this psychophysical detection experiment with a PHYSICAL detection experiment. Suppose we're trying to detect an astronomic effect (say, an "alpha") through a telescope. If an astronomer reports detecting an alpha, there is the presumption -- and it can be tested, and confirmed -- that another astronomer could, with similar equipment and under similar conditions, detect an alpha. Not his OWN alpha, but an objective, observer-independent alpha. This would not necessarily be the self-same alpha -- only a token of the same type. Even establishing that it was indeed an instance of the same generic type could be done objectively. But none of this carries over to the case of psychophysical detection, where all the weight of our confidence that the sensation exists and is of the same type is borne by our individual, subjective, intuitive solutions to the every-day other-minds problem -- the "common"-sense-experience we all share, if you will. I'm not, of course, claiming that this "common sense" is likely to be wrong; just that it's unique to subjective phenomena and does not amount to objectivity. Nor can it be used as a basis for claiming that psychophysics "measures" conscious experience. Yes, we all have subjective experience of the same kind. Yes, that's what we're reporting when we are subjects in a psychophysical experiment. But, no, that does not make psychophysical data into objective measures of conscious experience. (In fact, "an objective measure of a subjective phenomenon" is probably a contradiction in terms. Think about it.) A third case is worth considering, because it's midway between the physical and the psychophysical detection situation, and more like the latter in the relevant respects: Unlike cognitive science, which is concerned with active information-processing -- learning, memory, language, etc. -- psychophysics is in many ways a calibration science: It's concerned with determining our sensitivities for detection, discrimination, etc. As such, it is really considering us in our capacity as sensory devices -- measuring instruments. So the best analogy would probably be the equivalent kind of investigation on physical measuring devices. If what was at issue was not the astronomer's objectivity in alpha detection but the telescope's, then once again observer-independent conclusions could be drawn. Comparisons between the telescope's sensitivity and that of other alpha-detection devices could be made, etc. Here it would clearly be the device's input/output behavior that was at issue, nothing more. The same seems true of psychophysical detection. For although we all know we're having sensations in a detection experiment, the only thing that is being, or can be, objectively measured under such conditions is our sensitivity as detection devices. Nor is more AT ISSUE in psychophysics. In cog-sci, one can say of an input/output device that purports to model our behavior: "But how do you know that's really how I did it? After all, I can do much more (and I do it all consciously), whereas all you have there is a few dumb processes and performances." This is a real issue in cognitive modeling. (The buck stops at the TTT, however, according to my account.) In psychophysics, on the other hand, nobody is going to question the validity of a detection threshold because there's no way to show that it's based on measuring consciousness rather than mere input/output performance characteristics. Before turning to Adam Reed's specific comments, let me reiterate that this analysis is just as applicable, mutatis mutandis, to the more complicated case of threshold calculation after a series of trials with feedback. It's still a matter of input/output characteristics -- this time with a long series of inputs, with instructions -- rather than any "direct, objective measurement of experience." There's just no such thing as the latter, according to the arguments I'm making. [And I haven't even brought up the vexed issue of psycho-physical "incommensurability," namely, that no matter how reliable our psychophysical judgments, and how strong our conviction that they're veridical in our own case, there is no OBJECTIVE measure on which to equate and check the validity of the relation between physical stimulation and sensation. Correlations between input and output are one thing -- but between physical intensity and "experiential intensity"...?] Adam writes: > I don't buy the assumption that two must *observe the same > instance of a phenomenon* in order to perform an *observer-independent > measurement of the same (generic) phenomenon*. The two physicists can > agree that they are studying the same generic phenomenon because they > know they are doing similar things to similar equipment, and getting > similar results. But there is nothing to prevent two psychologists from > doing similar (mental) things to similar (mental) equipment and getting > similar results, even if neither engages in any overt behavior apart > from reporting the results of his measurements to the other. My point is > that this constitutes objective (observer-independent) measurement of > private (no behavior observable by others) mental processes. Apart from the objections I've already made about the "similar equipment" argument [what, by the way, is "mental equipment"? sounds figurative], about the experimenter as subject, about detection as "measurement," and about the irrelevance of the behavioral covertness to the basic input/output issue, the "generic" question seems problematic. With the alphas, above, we didn't have to oberve the same alpha, but we did have to observe the same kind of alpha. Now the "alpha" in the private case is MY sensations, not sensations simpliciter. So you needn't verify, for objectivity's sake, the specific detection sensation I had on trial N, or on any of my trials when I was subject, if you like -- just as long as the generic sensation you do check on is MINE not YOURS. Because otherwise, you see, there's this observer-dependence... > This objection [that there's no way of checking the correctness of a > subject's covert calculations] applies with equal force to the > observation, recording and calculations of externally observable > behavior. So what? What I meant here was that, after a long series of detection trials with feedback and covert calculations, there's no way you can check that I calculated MY threshold right except by running the trials on yourself and checking YOUR threshold. But what has that to do with the validity of MY threshold, or its status as a measure of my experience, rather than just my input/output sensitivity after a series of trials with complex instructions? I agree that there is validity-problem with all behavior, by the way, but I think that favors my argument rather than yours. One way to check the covert calculation is to have a subject do both -- overt detecting AND covert calculations on subsequent feedback. The two thresholds -- one calculated covertly by the subject, the other by the experimenter -- may well agree, but all that shows is that they get the same result when wearing their respctive (objective) psychophysicist's hats. What the agreement does not -- and cannot -- show is that the subject was "measuring experience" when he was detecting. It can't even show he was HAVING experience when he was detecting. But that's the whole point about behavioral measures and objectivity. If we're lucky, they'll swing together with conscious experience, but there's no objective basis for counting on it, or checking it. (And, equally important: It makes no methodological difference at all.) > Yes [there {is} no way of getting any data AT ALL without the subject's > overt mega-response at the end], but *this is not what is being > measured*. Or is the subject matter of physics the communication > behavior of physicists? The subject may be silent till trial N, but the input/output performance that is being measured is the presentation of N trials followed by a report that stands in a certain relation to the inputs. This is no different from the case of a simple trial, with a single stimulus input, and the simple report "I saw it." That's not scientific testimony, that's subjective report. The only one who can ever see THAT kind of "it" (namely, yours), is you. (And, as I mentioned, the subject is really switching hats here too.) > What is objectively different about the human case is that not only is > the other human doing similar (mental) things, he is doing those > things to similar (human mind implemented on a human brain) equipment. > If we obtain similar results, Occam's razor suggests that we explain > them similarly: if my results come from measurement of subjectively > experienced events, it is reasonable for me to suppose that another > human's similar results come from the same source. But a computer's > "mental" equipment is (at this point in time) sufficiently dissimilar > [to] a human's that the above reasoning would break down at the point > of "doing similar things to similar equipment with similar results", > even if the procedures and results somehow did turn out to be identical. First, I of course agree that people have similar experiences and similar brains, and that computers differ in both respects. But I don't consider an experience, or the report of an experience, to be a "measurement." If anything, all of me -- rather than part of me, used and experimented on by another part -- is the measuring device when I'm detecting a stimulus. After all, what's happening when I'm detecting an (astronomic) alpha: a measurement of a measurement? (The point about the computer was just meant to remind you that psychophysicists are just doing input/output sensitivity measurements, and that the same data could be generated by a computer-plus-transducer. But the difference between current computer and ourselves touches on more complex issues related to the TTT that needn't be raised here.) The relevant factors are all there in simple one-trial detection: If I report a detection, there's absolutely no objective test of whether (1) I had a sensation at all, (2) I "measured" it accurately, or even (3) whether it's measurable at all (i.e., whether experience and phsyical magnitude are commensurable). My detection sensitivity in the face of inputs, on the other hand, is indeed objectively testable. No number of private experiments by experimenter/subjects can make a dent in this epistemic barrier (called the mind/body problem). > Not true [that what we are actually measuring objectively is merely > behavior]. As I have shown in my original posting, d' can be measured > without there *being* any behavior prior to measurement. There is > nothing in Harnad's reply to refute this. It can't be done without presenting stimuli and feedback. And "behavior" refers to input/output relations. So there's a long string of real-time input involved in the covert experiment, followed by the report of a d' value. From that we can formulate the following behavioral description: That after so-and-so-many trials of such-and-such stimuli with such-and-such instructions, the subject reports X. Even when I'm myself the subject in such an experiment, that's how I would describe my findings, and those data are behavioral. This is no different, as I suggested, from a single detection trial. And the subject, of course, is switching hats during such an experiment; there's nothing magic about his behavioral silence during the covert calculations, any more than there is in the astronomer's, after he's gotten his telescope reading and performs calculations on them. > Why [will the testability and validity of these hypotheses always be > objectively independent of any experiential correlations (i.e., the > presence or absence of consciousness)]? And how can this be true in > cases when it is the conscious experience that is being measured? These input/output sensitivity characteristics of human observers would look the same whether or not human subjects were conscious. They ARE conscious, and they ARE having experiences during the measurements, but it's not their experiences we (or they) are measuring, it's their sensitivity to stimuli. It feels, when I'm the subject, as if there's a close coupling between the two. But who am I to say? That's just a feeling And feelings also seem, objectively speaking, incommensurable with physical intensities. The astronomer's detection has no such liability (except, of course, its subjective side -- "What it's like to detect an alpha," or what have you). Rather than forcing us to conclude that it's conscious experience that we're measuring in psychophysics, as Adam suggests, I think Occam's Razor (a methodological principle, after all) is dictating precisely the opposite. > I would not accept as legitimate any psychological theory > which appeared to contradict my conscious experience, and failed to > account for the apparent contradiction. As far as I can tell, Steve's > position means that he would not disqualify a psychological theory just > because it happened to be contradicted by his own conscious experience. That depends on what you mean by "contradicted conscious experience." I assume we're both willing to concede on hallucinations and illusions. I also reject radical behaviorism, which says that consciousness is just behavior. (I know that's not true.) I'd reject any theory that said I wasn't conscious, or that there was no such thing, or that it's "really" just something else that I know perfectly well it isn't. I'd also reject a theory that couldn't account for everything I can detect, discriminate, report and describe. But if a theory simply couldn't account for the fact that I have subjective experience at all, it wouldn't be contradicting my experience, it would just be missing it, bypassing it. That's just what the methodological solipsism I recommend does. It is, in a sense, epistemologically incomplete -- it can't explain everything. Whether it's also ontologically incomplete depends on the (objectively untestable) question of whether the asymptotic model that passes the TTT is or is not really conscious. If it is, then the model has "captured" conscious, even though the coupling cannot be demonstrated or explicated. If it has not, it is ontologically incomplete. But, short of BEING that model, there's no way we can ever know. (I also think that turing-indistinguishability is an EXPLANATION of why there's this incompleteness.) >>[SH:] If I were one of the [psychophysical] experimenters >>and Adam Reed were the other, how would 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. > [AR:] These assumptions are not "question-begging": they are logically > necessary consequences of applying Occam's razor to this situation (see > above). And yes, I would tend to regard the resulting agreement among > different subjective observers as evidence for the objectivity of their > measurements. I guess it'll have to be a standoff then. We disagree on what counts as objective -- perhaps even on what objective means. Also on which way Occam's Razor cuts. > For measurement to be *measurement of behavior*, the behavior must be, > in the temporal sequence, prior to measurement. But if the only overt > behavior is the communication of the results of measurement, then the > behavior occurs only after measurement has already taken place. So the > measurement in question cannot be a measurement of behavior, and must be > a measurement of something else. And the only plausible candidate for > that "something else" is conscious experience. If you're measuring, say, detection sensitivity, you're measuring input/output characteristics. It doesn't matter if these are trial-to-trial I/O/I/O etc., or just III...I/O. Only the behaviorists have made a fetish of overt performance. These days, it's safe to say that performance CAPACITY is what we're measuring, and that includes the capacity to do things covertly, as revealed in the final output, and inferrable therefrom. (Suppose you were checking a seismograph by looking at it's monthly cumulations only: Would the long behavioral silence make the end-result any less overt and "behavioral"?) As I suggested in another module, cognitive science is just behaviorism-with-a-theory, at last. The theory includes attributing covert, unobservable processes to the head -- but not conscious experiences to the mind. We know that's there those too, but for the (Occamian) reasons I've been discussing endlessly, they can't figure in our theories. > Steve seems to be saying that the mind-body problem constitutes "a > fundamental limit on objective inquiry", i.e. that this problem is *in > principle* incapable of ever being solved. I happen to think that human > consciousness is a fact of reality and, like all facts of reality, will > prove amenable to scientific explanation. And I like to think that > this explanation will constitute, in some scientifically relevant sense, > a solution to the "mind-body problem". So I don't see this problem as a > "fundamental limit". I used to have that fond hope too. Now I've seen there's a deep problem inherent in all the existing candidates, and I've gotten an idea of what the problem is in principle (that turing-indistinguishability IS objectivity), so I don't see any basis for hope in the future (unless there is a flaw in my reasoning). And, as Nagel has shown, the inductive scenario based on our long successful history in explaining objective phenomena simply fails to be generalizable to subjective ones. So I don't see the rational basis for Adam Reed's optimism. On the other hand, methodological epiphenomenalism is not all that bad -- after all, nothing OBJECTIVE is left out. -- Stevan Harnad (609) - 921 7771 {allegra, bellcore, seismo, rutgers, packard} !princeton!mind!harnad harnad%mind@princeton.csnet