Bob Kentridge 1995

<h1>Comparative Psychology: Lecture 8.</h1>

<h2>How general are learning processes?</h2>

Over the past seven lectures we have looked at the two main 
types of animal learning - classical and operant conditioning.  
After comparing these two types of learning I want to return to a 
more overtly comparative theme and look at the limits to these 
types of learning in different species.  I will then look at more 
complex learning tasks and ask how species differ in their 
performance across these tasks.  I then want to try and integrate 
these results, putting learning into a more general evolutionary 
framework and finally addressing the question of how we should 
view our learning abilities in this light.

<h2>Operant and Classical Conditioning.</h2>

Before looking at differences between the learning abilities of 
species it is as well to quickly consider the similarities and 
differences between operant and classical conditioning.  The most 
obvious difference between them is the nature of the response - 
in classical conditioning it must be a reflex whereas in 
instrumental learning it is a previously neutral piece of behaviour.  
In addition, in operant conditioning there is a contingency 
between response and reinforcement while in classical 
conditioning no such contingency applies - whether an animal 
makes a CR has no effect on the presentation of the US.  Are these 
differences artefacts of the different ways that learning has been 
studied in the laboratory?  Certainly when we considered the 
operant learning procedure in detail there appeared to be classical 
aspects to it - the animal almost certainly makes various 
associations to the US of food, probably including the whole 
setting of the experiment, the sound of the pellet dispenser and 
perhaps the discriminative stimulus.  In classical conditioning it is 
often possible to view the CR as an operant - salivation increases 
the palatability of food so one might view salivation as an operant 
and the toll of the bell as a discriminative stimulus.  Similarly, 
heart-rate reduction might decrease the unpleasant effect of 
shock and so be regarded as an operant.  This leads on to the 
question of whether the response in an overtly operant learning 
paradigm must be neutral - is it possible to operantly condition 
reflexes?  Experiments on operant conditioning of heart-rate 
elevation in rats indicate that it is.  Normally one would regard 
changes in heart-rate as being reflexive - we do not appear to 
have voluntary control over them.  We might, however, elevate 
our heart-rate indirectly by running or making other voluntary 
movements.  This confounding factor was eliminated in a classic 
experiment where rats were operantly conditioned with a 
contingency between a transient elevation of heart-rate and direct 
electrical brain-stimulation reward (which is about the most 
powerful reinforcer available) while paralysed with curare 
(another reason for using brain-stimulation, as it requires no 
active consumatory behaviour).  It is also possible to find examp-
les where a non-reflexive response appears to be classically 
conditioned.  Often the operant required from pigeons in operant 
conditioning experiments is a peck on a lighted key - during 
continuous reinforcement training each peck is reinforced with 
delivery of a seed of some grain.  Once the bird has been trained 
to eat the grain from its dispenser then if the key is lit ad grain is 
dispensed without any pecking contingency the pigeon will soon 
begin to peck at the key.  If the pecks were directed at the food 
then this would be a simple reflex.  If pecks aimed at the food 
hopper were elicited by the light then we might characterise the 
behaviour as straightforward classical conditioning, but pecks 
directed at the light do not seem reflexive yet they are sensitive 
to the contingency and predictability factors that determine the 
effectiveness of classical and not operant conditioning.  Rather 
than operant and pavolian conditioning being distinct categories of 
learning it begins to appear that all learning situations contain 
both operant and pavlovian qualities in different degrees.  A great 
deal of research has been carried out investigating how these 
facets interact.

<h2>Constraints on learning.</h2>

Both instrumental learning and classical conditioning have been 
presented up to now as quite general models of learning.  It 
should be possible to condition any neutral behaviour using any 
reinforcer and an operant contingency.  It should be possible to 
associate any neutral stimulus with a reflexive response in a 
classical conditioning procedure.  Although Skinner and Pavlov 
both believed that they were dealing with general theories of 
learning with the properties I have just described neither of the 
two previous statements is true. The most dramatic example of 
the lack of generality of learning is conditioned taste aversion 
(CTA).  This is an example of classical conditioning, the UR is the 
set of behaviours accompanying gastro-intestinal distress, induced 
by a gastric irritant as A US - injections of the simple salt lithium 
chloride (LiCl) are most often used.  The CS is some quality of a 
novel food.  If one pairs a novel tasting food with LiCl then part of 
the CR for a rat is a subsequent refusal to consume the novel 
tasting food.  In principle it should be just as easy to condition the 
rat to avoid novel foods on the basis of visual, or any other CS, 
characteristic, however, this is not the case.  Rats fail to learn CTA 
associations to foods with novel visual characteristics.  In contrast, 
birds can be conditioned to avoid drinking water coloured in novel 
ways, or even paired with distinctive noise (bright-noisy-water) 
but fail to learn CTA to novel flavours or odours.  The sensitivity 
of rats to associating odour cues with the outcomes of novel 
tasting foods is such that if a rats tastes a novel food in the 
presence of another rat which is made sick (but which has not 
eaten the novel food ) the first rat will subsequently avoid the 
novel food.  

Similar effects occur in operant conditioning.  Maybe the most 
celebrated examples concern the problems of training animals for 
roles in TV commercials.  The classic case involved training a 
racoon to put a penny (a 1 cent coin) into a piggy bank.  The 
racoon could initially be trained easily using food reward but 
soon, instead of putting the penny straight into the piggy bank as 
trained it spent increasing amounts of time sniffing it, chewing it 
and directing other typical racoon food-related behaviours 
towards it.  The same sort of reinforcer specific behaviours have 
also been observed with aversive conditioning - animals have 
species typical response to threat and these can soon being to 
dominate the operant they have been trained to produce.

<h2>Adaptation of Learning as a General Process?</h2>

Examples like these are very hard for theories of learning which 
purport to have general applicability to deal with.  If we take a 
wider evolutionary viewpoint they become much easier to 
understand.  Learning is just one way for an individual to adapt to 
its environment.  Some aspects of the environment vary so slowly 
that natural selection will result in adaptations of a species 
(phylogenetic adaptation) allowing individuals to exploit or cope 
with these slowly varying qualities - developing a metabolism 
which can cope with particular diets or temperatures, for example.  
It is also possible to adapt to aspect of the environment which are 
a little more variable during an individual's development 
(epigenisis) - developing different amounts of body fat depending 
on diet and environment during the early stages of life is an 
example.  Once can even view aspects of sensori-motor 
coordination - coordinating visual signal and motor commands in 
grasping a fruit for example - as a form of adaptation which takes 
place on a very short time-scale.  Somewhere between 
sensorimotor coordination and epigenisis lies learning.  Once 
learning is seen in a general evolutionary framework it becomes 
clear that predictability of the types of learning tasks which will 
often be encountered may drive phylogenetic adaptation of 
learning preferences.  In the long term it may be a consistent 
feature of the environment-organism pair that taste receptor 
responses to the composition of food are good predictors of its 
nutritional outcome. But, on the same long time scale it is not 
possible to consistently pair particular tastes with particular 
outcomes.  An adaptation can, still, however, be made to 
preferentially learn about taste-nutrition relationships.

<h2>'Higher' learning.</h2>

As we near the end of the comparative psychology course it is 
natural to worry about the status of humankind (PC alert) in all 
this.  A naive person might assume that this has nothing to do 
with how people learn or what drives their behaviour.  Even if it 
is true that we are quite different from animals we cannot, of 
course, be sure of this without some evidence (unless we side with 
Descartes (who at least understood the importance of evidence) or, 
perhaps more fairly to Descartes, more conservative members
of 17th century society).  Let us consider species 
differences in some more complex learning tasks.  

<h2>Complex Learning Tasks.</h2>

I have mentioned some tasks which might be though to tax 
'higher' faculties than straightforward instrumental or classical 
conditioning already.  One is the problem of matching response 
allocation between two or more differently valued alternatives, 
another is sensitivity to changes in the value of a reinforcer - 
having expectations.  Other commonly used tasks include the 
ability to learn that the same task may change in its outcome 
while retaining the same general form - for example imagine a 
task in which an animal must respond on one of a with a pair of 
levers during hour long daily sessions, but the reinforced lever 
changes randomly between days - if an animal learns this 'meta' 
task then the speed with which it learns to respond to the correct 
lever each day will increase.

As we have seen it is possible to classically condition nearly 
anything.  Similarly, all vertebrates seem sensitive to well chosen 
operant contingencies (it is not use trying to condition a rat using 
coloured discriminative stimuli as they are colour blind).  It had 
been believed, however, that species differences between 
vertebrates could be detected in these complex tasks.  A number 
of investigators have, however, found effective probability 
(matching), reward-shift and reversal learning it fish, amphibia 
and reptiles provided the stimuli, reinforcers and task setting are 
tailored to suit the species under investigations.  Provided the 
task is set up so it is akin to one the species may need to learn in 
its environment then it seems that all vertebrates can learn these 
more complex tasks.  Of course, it is reasonable to argue that these 
tasks are trivial for humans and that all of our learning is 
mediated by reflective thought - by intentional explicit problem 
solving.  If this were true what prediction might we make about 
human learning capabilities?

<h2>Human learning, thought and language.</h2>

It is clear that, souls apart (for the seventeenth century 
conservatives amongst us), what distinguishes humans from 
animals is language.  This is not a course on language or cognitive 
psychology, and I leave it up to those courses to teach you about 
the nature of language.  Although there have been many long 
complex studies aimed at discerning language-learning abilities in 
non-humans the evidence for this is weak.  Language is not the 
same as communication or about the association of arbitrary 
symbols with things and events in the real world - rats can learn 
to use tools we choose to give them to fulfil these functions quite 
easily.  Language is about learning to use relationships between 
symbols to denote specific consequences.  In our language we use 
complex structures in which the relationships between pairs of 
words in a sentence separated by many intervening phrases can 
nevertheless determine the meaning of a sentence.  The rules 
which implicitly govern the interpretation of structures like this 
are quite different from the 'if-then' contingencies governing 
operant conditioning or even the  more complex animal learning 
tasks I described earlier.  Does this make animal learning theory 
irrelevant to the understanding of human behaviour?  It might if 
we thought all of our actions out carefully, but we don't.  (t might 
if we had the ability to use language from birth, but we don't.  
Given this, however, we still need to discover whether the 
principles of animal learning apply to those aspects of human 
behaviour which are not linguistically mediated.

<h2>Human conditioning.</h2>

Little Albert is often cited as an early example of classical 
conditioning in humans.  In fact the iron bar was struck as Albert 
moved to touch the rat so it may, in fact be an example of o-
operant punishment with the rat as a discriminative stimulus.  
There have, however, been numerous better controlled studies of 
classical conditioning in humans.  In particular it has been shown 
that, given similar species specific constraints to those I discussed 
earlier, that  new-born humans classically condition well.  A 
number of techniques used to treat people with phobias are 
closely based on classical conditioning principles - the fact that 
these procedures are effective in modifying patients' behaviour 
indicates that these phobias may themselves have been the result 
of earlier fortuitous classical conditioning.

Babies have been are very good at instrumental learning.  It is, 
perhaps, less easy to show operant than classical conditioning in 
adults.  This is not because adults are insensitive to contingencies 
of reinforcement of do not learn about them but because they 
often find it easy to identify them explicitly and, for out purposes, 
if they can articulate the contingency they might not be doing the 
same type of learning that animals do.  In a well devised 
experiment, however it is easy to demonstrate covert conditioning 
in adults.  A typical apocryphal example is the class that was quiet 
and well behaved when their lecturer stood on the left side of the 
theatre but noisy when he stood to the right.  Gradually they 
shaped his behaviour by moving the position at which they 
switched their behaviour gradually towards the door until their 
lectures were delivered from the corridor outside.  In a quite non-
apocryphal experiment subjects were successfully conditioned to 
blink their eyes on an FR 8 schedule while they actually believed 
they were working on a key pressing task - there was no 
contingency between key-pressing an reward and their key-
pressing rate did not increase during the experimental period 
while their eye-blink rate did, yet they had no idea that their 
eye-blinks were determining the delivery of reinforcement.  It is 
possible to demonstrate all the features of animals responses to 
different schedules of reinforcement provided suitable 
precautions are taken to avoid verbal mediation of tasks - humans 
produce FI scallops provided they cannot, or have no reason to, 
count the interval in their heads.  Operant principles have been 
and still are used to treat behavioural disorders and have been 
used in various educational schemes.  It is not, however, these 
overt application of conditioning which are so important, it is 
more that in the course of our lives we are subject to so many 
contingencies and correlations we are not consciously aware of 
which we are quite capable of learning without ever knowing.  We 
may think that our behaviour is determined quite differently 
from that of animals, but, from introspection, who are we to 
know?