A few observations.
For years I’ve been fascinated by synesthesia because since a kid I’ve experienced these effects. For example, as a mechanical tinkerer when I drop a spanner (wrench) onto concrete the sudden sound explodes as a bright light. As a result over the years I’ve adopted a number of precautions to limit these effects; wearing ear plugs, dark
glasses and so on. All of which I understand now are taken to limit/muffle intensity, and thus mitigate synesthestic effects.
The reference to ‘direct perception’ (p96 para 2) has a possible link to JJ Gibson. Does this imply no processing at this level?
And leading q#5: other examples of edgeless detectable brightness includes anything without microstructure as with holes, fog, mist, white-out, cloud. And for another sensory system like incense or its base, smoke, for olfaction. Now, if the word ‘discriminable’ is substituted for ‘detectable’ is there any difference in meaning? That is, are these words synonyms? I suspect not since discriminable is lower order (Eleanor Gibson this time)
[From Kent McClelland (2013.08.25.1710 EDT)]
In Rick’s study guide for Chapter 7, he discusses “deafferentation” experiments, which he says have been taken as evidence against the PCT model. Here’s how he describes these experiments in the study guide:
RM: One of the presumably strong pieces of evidence against the âcontrol of perceptionâ? view comes from studies of the behavior of organisms who have been surgically or naturally (due to disease) âdeafferentedâ? that is, who have lost or been deprived their lowest level (intensity) perceptions; who no longer have the ability to perceive the effort resulting from muscle tension. Many studies purport to show that deafferented organisms are nevertheless able to produce coherent behavior. It looks like the nervous systems of these organisms are able to command the muscles to produce intended forces even though the consequences of these forces cannot be perceived.
If the results of the deafferentiation studies show what they purport to show then it would be a significant blow to PCT. So I think itâs worth discussing these studies in the context of these chapters. If anyone has any knowledge about these studies it would be nice if we could start a discussion about this in class (on CSGNet).
KM: Having no expertise whatever in these matters, but still interested in any evidence that might be inconsistent with PCT, I took a quick (and admittedly superficial) look through some of the literature on deafferentation to see what kind of a challenge it might pose to the PCT model.
Here’s the citation and abstract of the article on deafferentation that gets first place in Google Scholar for the number of citations by other scholars, so, although it comes from 1982, I take it to be a foundational study in that line of research:
⢠J. C. ROTHWELL,
M. M. TRAUBB,
B. L. DAY,
 p; J. A. OBESO,
P. K. THOMAS,
and C. C. D. MARSDEN
MANUAL MOTOR PERFORMANCE IN A DEAFFERENTED MAN
Brain (1982) 105 (3): 515-542 doi:10.1093/brain/105.3.515
Summary
We have studied manual motor function in a man deafferented by a severe peripheral sensory neuropathy. Motor power was almost unaffected. Our patient could produce a very wide range of preprogrammed finger movements with remarkable accuracy, involving complex muscle synergies of the hand and forearm muscles. He could perform individual finger movements and outline figures in the air with his eyes closed. He had normal pre- and postmovement EEG potentials, and showed the normal bi/triphasic pattern of muscle activation in agonist and antagonist muscles during fast limb movements. He could also move his thumb accurately through three different distances at three different speeds, and could produce three different levels of force at his thumb pad when required. Although he could not judge the weights of objects placed in his hands without vision, he was able to match forces applied by the experimenter to the pad of each thumb if he was given a minimal
indication of thumb movement.
Despite his success with these laboratory tasks, his hands were relatively useless to him in daily life. He was unable to grasp a pen and write, to fasten his shirt buttons or to hold a cup in one hand. Part of his difficulty lay in the absence of any automatic reflex correction in his voluntary movements, and also to an inability to sustain constant levels of muscle contraction without visual feedback over periods of more than one or two seconds. He was also unable to maintain long sequences of simple motor programmes without vision.
(A pdf of the full text of the study is available at this URL: http://e.guigon.free.fr/rsc/article/RothwellEtAl82.pdf )
KM: The first paragraph of this summary seems like a clear refutation of the PCT model. As Rick told us, the authors report that the deafferented man they studied was able to produce many types of coherent movement. But notice the kicker in paragraph two. “[H]is hands were relatively useless to him in daily life” outside the laboratory. And even in the first paragraph, the authors note that “he could not judge the weights of objects placed in his hands without vision …”
My PCT interpretation of this study is that the laboratory tasks assigned to him involved perceptions at the configuration level or above, and that the control-system-units in his brain for accomplishing these tasks get their incoming signals from more than one mode of perceptual feedback, probably visual feedback and proprioceptive feedback about the positions of limbs and digits, as well as his deafferented muscle-effort intensity receptors. Even with one of the modes of feedback gone, he could still control the perceptions involved in the laboratory tasks reasonably well, because feedback from the other perceptual modes could “pinch hit” for the lost information. The authors’ emphasis on the importance of visual feedback seems consistent with this PCT interpretation. The fact of his “inability to sustain constant levels of muscle contraction without visual feedback over periods of more than one or two seconds” also makes it clear that without the
intensity-level feedback from muscles his effort-control systems just weren’t working properly.
I looked at the abstracts of a few of the other highly-cited studies on the topic, but didn’t find anything that seemed to provide any stronger evidence against the PCT model than this study, and my conclusion from this quick survey is that deafferentation studies are not all that big a deal (and in fact might provide some evidence that supports the PCT model). Of course, I’m no expert and I’m biased …
Kent
On Aug 25, 2013, at 2:53 PM, Richard Marken wrote:
[From Rick Marken (2013.08.25.1150)]
Rupert Young (2013.08.24.1230)–
Thanks for this Rupert. My summary of this chapter will be a bit late
this time I’m afraid; have to grade papers;-)
But I’ll try to comment quickly on your post:
This chapter is fairly understandable, and uncontroversial, as it extends
concepts previously encountered and puts the basic unit of control in the
context of the boundary between the environment and the organism,
characterising perceptions as one-dimensional signals of the intensity
(quantity) of environmental characteristics present, of a particular domain.
Though I can’t say I followed the gamma reference signal section and I don’t
have a feel for the biological plausibility of what was presented, such as
figure 7.3.
RM: I agree, the gamma reference stuff is tough for me too. The best
way to try to get it would probably be to build a model that
corresponds to figure 7.3 and see how it works. I don’t have time for
that right now but if someone could do that it would be a nice
contribution to the course!!
The analysis is important as it provides a simple mathematical model of the
role of feedback in determining compensating actions of the system, rather
than specific actions being computed in order to generate specific
behaviour.
I do have doubts though whether we can actually consciously perceive
perceptions at this level, or whether what we perceive, when tensing muscles
for example, are higher level sensations say. How do we tell? We don’t
experience the intensity perceptions in the operation of iris movements; why
not?
I think we can perceive what Bill called intensity perceptions. Your
answer to the first leading questoin suggests that you can, indeed,
perceive them. I think we can’t experience the iris intensity signals
because the are just too small. But that’s a good question. But I
think we don’t have to tense muscles to experience intensity; the
subjective experience of intensity can be had by trying to pay
attention only to the “how much” of any perception and ignoring
everything else about it – like whether it’s a color, a sounds, a
tension, etc. It’s kind of an exercise in introspection.
Leading questions:
- Yes, I can feel something when I tense muscles. The feeling is the same for
different muscles, but I can’t say whether the feeling corresponds to amount
of effort; how can you? Is pain also a first-order signal?
The pure feeling of magnitude when you tense a muscle is the intensity
perception. Experiencing that perception as “effort” is, I believe, a
higher level perception. The magnitide of pain is an intensity
perception; the fact that it’s pain rather than some other kind of
perception is, I would say, a sensation level perception.
- Yes, the level of the perceptions is high, in terms of amount of perception.
Great, then you are experiencing intensity (pay no attention to all
those other higher level aspects ofthe perception).
- Quiet, dim and bland.
No. No.
I don’t understand these answers.
4.Yes, if you can hear a sound then it must have a pitch.
I think the point here is that w/o loudness there can be no pitch.So
in order for a sound to have a detectable loudness it is not necessary
that it have a detectable pitch.
No, I can view the centre of a piece of paper where there is brightness but
no edges.
Right!
Best
Rick
Regards,
Rupert
–
Richard S. Marken PhD
rsmarken@gmail.com
www.mindreadings.com