[Martin Taylor 2004.11.01.09.14]
[From Rick Marken (2004.10.31.1210)]
Martin Taylor (2004.10.31.12.04)
Rick Marken (2004.10.31.0820)--
Well, you just go ahead and settle back in your armchair. I think
I'll
take Bill's advice and do the experiment myself if I can't find
something similar in the literature.
That isn't really what I'm doing, literally or metaphorically. Quite
the contrary, actually. I'm trying to keep, if not my head, at least
my nostrils above water in the swamp of work.
I hope you didn't think I was implying that you're lazy, Martin. I know
you're not.
Well, it did look that way. Thanks for the clarification. I know what
you mean about armchair scientists, and I agree with it.
I was just
hoping to see if we could come up with an empirical test of an aspect
of the PCT model right here on CSGNet, rather than just always
_talking_ about the model. Perhaps you could give a go at describing
an appropriate experiment to test you ideas about bidirectionality.
I started to try to do that last night, but, being Halloween, the
goblins soon found a way to cause mischief.
The mischief was actually embedded in the prior discussion. It is the
question: "what is the question?"
My original foray into this was to ask whether there was a way within
strict HPCT to account for a phenomenon that had not been clearly
described in PCT-compatible language by Bruce Gregory. I tried to put
it in PCT language, which I can paraphrase by saying that people
often experience the (imagined) perception of a label when confronted
by a visual scene, or experience an (imagined) visual scene when
presented with a label. In some manner, the output of a function that
generates the perception of either can facilitate the perception of
the other when the data for the other are not presented to the
senses. My (and I think Bruce's) question was whether there was a
connection path within strict HPCT that allows for such a
bidirectional facilitation.
Bill P. offered a kind of story that I don't fully understand, which
involves a higher-level control system whose input is derived from
both the picture category-level perceiver and the label
category-level perceiver, and for which there is error if either
input (but not both) is null. The output of that higher-level system
invokes in some way the imagination loop for the missing
category-level system, thereby creating the joint perception. I hope
I've correctly abstracted the essence of what Bill was saying, though
I can't say I quite understand how it works.
So, if Bill's presentation is fleshed out into a workable model,
that's the answer to the original question. An experiment would have
to probe the workings of that model, by comparing something with the
simulation predictions of the model.
But the experiment you suggested answered a different (and
worthwhile) question, which was to determine whether the picture
perception and the label perception could be said to be at different
levels, given that each independently would be evoked by sensory
data, assuming that HPCT provided a correct model.
When I started to try to devise an experiment (which I was basing on
the long tradition of "priming" studies and of Stroop tests), I was
looking at yet another question. My question assumed the correctness
of the original statement about the bidirectional experiences, and
posed Bill's "strict HPCT" model against a model that, while possibly
hierarchic, did not invoke control at all, but allowed for cross
connections in which each perceptual function's output formed part of
the other's input. I was then going to try to work out an experiment
that did not use brain imaging (too expensive, I think, for anyone on
CSGnet), by using priming and Stroop to affect the timing of when a
subject would accept that a picture had formed after a label was
presented, or that a correct label had been perceived after a picture
was presented.
The priming would be the prior presentation of, say "airplane" before
showing a picture of a river or of an airplane, and asking the
subject to press a button when a label for the picture had come to
mind, and in the other sense showing a picture of an airplane before
showing the word "airplane" or "river" and asking the subject to
press when an appropriate picture had come to mind.
Stroop would be a similar kind of study, except that the "airplane"
word would be presented along with the picture of an airplane or a
river, instead of beforehand.
In both priming and Stroop situations, a "neutral" pattern of "XXXXX"
or a random dot pattern would serve as a baseline condition.
The experiment might give results, but then I asked myself what those
results would tell, in respect of the two models. What would the
models predict the effects of the priming or Stroop presentation to
be? And I didn't know, for either model. For the cross-connected
perceptual functions model, one might be able to make some
qualitative predictions, but I don't know about Bill's model. Would
the qualitative predictions be any different?
At that point, I decided to go to bed, so I could awake on All
Saints' Day, and trusting that the saints who post on CSGnet might be
able to help.
Martin