Discussion Following Papers by Stelmach and Stern DR. WELFORD: I think it could be misleading to equate cognitive psychology with consciousness, in the sense that cognitive psychology is implied with the processes of the treatment of information coming into the organism and, I would have thought, would go as far as deciding what to do about it. The motor side takes over when actually giving expression to decisions taken, as to what to do. I think it is meaningful to separate those two "black boxes" because there's a great wealth of evidence suggesting that this is a very important separation. What you decide to do and just how you carry it out are separable processes, in the sense that you can decide what to do and sometimes not carry it out. And in this respect possibly Dr. Stelmach has been a little "naughty" in saying that goal-directed behavior is not--perhaps I'm exaggerating-directed by feedback and is remarkably resistant to perturbation. It is, I think, fairly directed by feedback, but not by feedback that comes right away round through the sensory. It is directed by a local feedback between what happens and the orders that are given for something to happen. can see ample evidence of this quick, local feedback between actual actions produced and the "orders," so to speak, under which they are produced. Also, the fact that there is this local feedback, and that it doesn't go all the way around the loop, means that certain sorts of perturbation can exercise a profound effect. One DR. STELMACH: I think generally I would agree with those comments, but there is still remarkable evidence that whether or not you have feedback available, whether there's deafferentation in the spinal cord, you can in fact make movements that are goal oriented; you can make them very well, reproduce them very well, and never know that you made the movement. There seems to be an abundance of evidence in support of that. Secondly, if you change the "load" of the system--force the subject to make very rapid, ballistic-type movements--if you take our typical arguments that if the movements last more than forty or fifty msec, feedback is assumed not to play a role. You can find that, if again the subjects are informed as to what they have to do, as opposed to making a move and discovering feedback, you find that the outflow is remarkably robust in a sense. It doesn't mean, of course, that everything operates independent of feedback. It may be that we haven't got our notions down to a level where feedback may only take 10 msec, though it's hard to imagine that being the case, but we certainly do have some alpha-gamma coactivation which may fit the role of some localized feedback. The evidence seems to suggest that when you have a goal-oriented motor outflow (this is true in speech as well as locomotion), you have a remarkably robust system. DR. BISHOP: I'd like to change the topic for the moment and approach the question of whether the black box models are useful. I think we have no other approach except the black box approach, and I think it has obviously been useful. We can break problems down into small components. This is of course what the neurophysiologist has done, and I think we have come a long way in looking at the "output" box, the final common pathway if you will. In my own lab we've been looking at single motor unit responses in the masticatory muscles during speech and chewing, and we find that the same motor units are used in these two very different types of motor activity. However, their frequency of discharge during speech is far faster than can ever be initiated during voluntary activity, such as in swallowing and chewing. So I think that we must continue with our black boxes and I think each of us picks a different black box to wire in on or tune in on. I think when we synthesize all these black boxes we're going to begin to get some of these answers that the cognitive psychologists are so concerned with. DR. GOLDBERG: I think there is no question that there are heterarchies and there is feedback. There is no question that you can have independent programs which exist independently of the need for any feedback. That is particularly true in the oral cavity and some of the behaviors involved there. Also feedback in the normal operations of the system is important and has function--and (they) are as short as 10 msec. We have to understand this better, but they both go on at the same time. I would like to mention another important point. There've been some statements equating spinal systems and systems involving the trigeminal and other brain stem systems. I think it is critical to focus on the important differences that exist between these two systems. Of course there are similarities, but there is a tremendous range of differences that I think are critical in terms of how the nervous system functions to control these two systems. I would also take issue with the statement made by the discussant regarding the clinician performing treatment without understanding the mechanisms or the basics of the treatment. I look at the clinician essentially as an operator who has a tendency to "shoot first and ask questions later." And I think we can see the result of that kind of mentality in dentistry. I think some of the statements made earlier relating to orthodontia, for example Dr. Mason's statement, "Let the child go through puberty --let's see what happens," is an example. I would say it's extraordinarily important that the basic mechanisms are understood. I think it will affect and change treatment dramatically. Secondly, it's critical that the mentality of the clinician is such that he has a great respect for his non-understanding of basic mechanisms when he does treat, so that his treatment would be much more conservative and appropriate. I think we see the opposite. DR. STERN: I think your point is well taken. When I talk about empirical truths, remember that I put those "truths" in quotation marks. And some of them have turned out not to be so "truthful," as a function of further investigation. On the other hand, if the clinician waits until basic data are available, he'll be sitting in his office doing nothing at the present time. .ANE LIBRARY, STANFORD UNIVERSITY DR. STERN: We have to take a reasonable balance between the two positions. With respect to Dr. Bishop's comments, I was not saying that we should stay away from black boxes. My concern is that if we see that label on that black box often enough, we begin to think that we understand what that black box does, rather than accepting the fact that it's a description of a conceptual system, rather than a real system. Most black boxes deal with conceptual systems rather than neurophysiological systems to account for a given aspect of behavior. I don't want that to get lost; I am as devoted to the black box as you are. But every once in a while I have to stand back and say, "How much more do I know now that I've labels for the black box than I did before I labeled it?" Often times I have to say, "I really don't know any more than I did before, except I've given it a fancy label." DR. DWORKIN: First of all, we always know what the box does; the question we sometimes cannot answer is how it does it. It's no construct at all if we don't know what it does. But I'd like to address myself to this point of the usefulness of theory in practice. It's fairly obvious that if we wait around for a wiring diagram of the nervous system before we begin to do any treatment there are a lot of useful treatments we may have been able to apply, a lot of suffering that we may have been able to alleviate, which we wouldn't have. On the other hand, that doesn't mean we should try everything that's advertised in this month's trade magazine. That's a very serious problem. It's enormously difficult to identify that level of theory and analysis that's appropriate to the particular pathology and the particular treatment, and to try to understand and do experiments to elucidate the operations of those particular principles. We don't necessarily have to understand things at a neurophysiological level. We may not be able to understand things at this very complex information processing level. But maybe certain limited principles that we can identify and work with--that we can establish lawfulness among--will help us find appropriate modes of therapy. DR. GALE: I'm going to take the chairman's prerogative and say that closely agrees with my own feelings about the topic. I'd like to thank the presenters and discussants for their excellent presentations. SESSION II ORAL MOTOR BEHAVIORS AND ORAL DISORDERS OF ADULTS Chairperson: John D. Rugh Assistant Professor Division of Occlusion Department of Restorative Dentistry |