[from Jeff Vancouver 970627.15:30 EST]
I submit, for your approval, I recent study published in _Current
Directions in Psychological Science_ (1996) titled "On the neural
computation of utility" p. 37-43 by Shizgal & Conover. Current directions
publishes, mostly solicited, cutting-edge stuff meant for the general
psychological community so the articles are short and readable.
Anyway, these guys (Peter & Kent) stick electrodes into rats and watch
what they do to get pulses from the electrodes. They call the pulses
brain stimulation reward (BSR). Let me quote some key statements
(partially because I am interested in how they will be interpreted).
"We assume our rats to be rational consumers insofar as they will prefer
under nonsatiating conditions, an alternative that provides more of a
given appetitive goal object (e.g., food) over an alternative that
provides less." (p. 37).
This is utility, which accounts for the title.
BTW, nonsatiating conditions means there is still error in the control
system. If you do not believe me read on (please read on even if you do
believe me).
They note "a second unusual property of BSR is the absence of satiation"
p. 38.
Now they did some experiments on these rats (sorry, no computer models).
For example, they gave them a choice of pressing a bar for electric pulses
and a bar for getting sucrose directly injected into their mouths. They
found:
"The presents of the sucrose led the rat to forgo moderate-strength
trains (34 and 38 pulses) of brain stimulation for which it would have
worked had the sucrose been unavailable. THis would not have occurred
had the rats used a categorical rule, selecting the brain stimulation
whenever its value was above a certain threshold. Such categorical
choice does not require a common evaluation of the two rewards. In
contrast, the results obtained imply that on a given trial, the rat
selected the alternative that registered a larger value in a commen
system of measurement." p 39.
In other word, in the brain, the signalling system is all using the same
metric. I think this is what you all refer to a scalar.
Anyway, after doing things with rats that cannot be done with humans,
like cutting off feedback signals, the researchers conclude:
"Each foodstuff is a chemically complex package of resources germane to
the operation of different regulatory systems, such as those controlling
energy, mineral, and fluid balance. If the animal is to maximize return
on its foraging efforts, it must weight the components of each food by
past experiment and by the state of the relevant physiological variables
and then combine the weighted values so as to obtain an overall
assessment of the utility of each complex foodstuff." p. 41.
I do not think the researchers are suggesting these calculations are
going on on some conscious level.
and
"The results in Figs... suggest that the utility calculation took
physiological state into account in the case of the tastant but not in
the case of the brain stimulation." p. 42.
They go on to speculate that the BSR is reproducing a response in the
brain further down the processing chain then the comparator (though they
do not use that exact word).
Bottom line. What these researchers do is to show how a relatively
simple model (the rat) can control several perceptions simultaneously.
They clearly demonstrate it is control and that it is perceptions that
are being controlled, but that given limited degrees of freedom, behavior
is affected. A highly recommended read.
later
Jeff
···
_________________________________________________________________________
Jeffrey B. Vancouver
Assistant Professor Phone: (212)998-7816
Department of Psychology Fax: (212)995-4018
New York University e-mail: jeffv@xp.psych.nyu.edu
6 Washington Pl., Rm 572
New York, NY 10003