From newshub.ccs.yorku.ca!ists!torn.onet.on.ca!utgpu!news-server.csri.toronto.edu!psych.toronto.edu!michael Tue Jun  9 10:07:12 EDT 1992
Article 6099 of comp.ai.philosophy:
Newsgroups: comp.ai.philosophy
Path: newshub.ccs.yorku.ca!ists!torn.onet.on.ca!utgpu!news-server.csri.toronto.edu!psych.toronto.edu!michael
>From: michael@psych.toronto.edu (Michael Gemar)
Subject: Re: Homunculus and the witch's brew
Organization: Department of Psychology, University of Toronto
References: <l2iea9INN44p@exodus.Eng.Sun.COM> <1992May31.212826.1778@news.media.mit.edu> <1992Jun1.020633.15541@Princeton.EDU>
Message-ID: <BpDor5.J5B@psych.toronto.edu>
Keywords: computation, transduction, homunculus, sensorimotor physiology
Date: Fri, 5 Jun 1992 15:09:03 GMT

In article <1992Jun1.020633.15541@Princeton.EDU> harnad@phoenix.Princeton.EDU (Stevan Harnad) writes:

[in response to Minsky's claim that transducers involve many-to-one mapping]

>Marvin, I'm not an engineer, so if I've picked a technical term that is
>at odds with my intended meaning, I'd be happy to susbstitute the
>correct one for it (what is the correct one?). I had no idea that a
>many-to-one mapping was criterial for a transducer. I would have wanted
>a term that leaves room for 1:1 analog transformations and through-put
>too, as the dictionary definitions below do. Physiologists, I believe,
>often refer to the sensory surfaces as transducers, yet many of those
>simply transduce (traduce?) input in analog form. (But I have to add,
>as a point of logic, that even if transduction refers only to a
>many-to-one conversion, that does not necessarily make it homuncular.)
>-- SH
>
>Collins:
>trans+duc+er (traenz`dju:s) n. any device, such as a microphone or
>electric motor, that converts one form of energy into another.
>[C20: from Latin transducere to lead across, from
>trans-+ducere to lead] 
>
>Websters:
>transducer
>L [italic transducere] to lead across, fr. [italic trans-] + [italic 
>ducere] to lead -- more at [mini TOW]
>a device that is actuated by power from one system and supplies 
>power in any other form to a second system (as a telephone receiver 
>that is actuated by electric power and supplies acoustic power to the 
>surrounding air)

These are the kinds of definitions that I would use as well, and they seem
completely at odds with your claim that much of the *brain* involves
transduction.  As I understand the term, transduction involves the conversion
of energy from one form into another.  In the case of humans, *all* conversion
of forms of energy occurs at the extreme periphery of the nervous system.
Cells in the retina transform visible light into electrochemical pulses.
Cells in the auditory perceptual mechanisms transform mechanical energy into
electrochemical pulses.  Cells in the skin transform heat energy into    
electrochemical pulses.  Once past the peripheral sensors, *the same form
of energy is used by the nervous system*.  There simply is no transduction
going on beyond the periphery that *I* can see.  *All* the energy used by
the brain is of the same form.

So, unless I have missed some alternative explication of "transducer" that
you are using, I fail to see how it can be claimed that transduction goes
on within the brain itself.  In other words, it seems to me that a
"brain-in-a-vat" does not have any "implicit" tranduction going on, and that
a virtual environment that stimulated the neurons directly (rather than through
sensory transduction) is an instance of tranduction-less experience.  Therefore,
transducers are not the solution to the symbol grounding problem. 

- michael
 
  


