conditioning, a term developed by Skinner (1938), can be defined as “when a
response occurs and is reinforced, the probability that it will occur again in
the presence of a similar stimuli is increased” (Bjork, 1997,
p. 149).
It has been observed that biological constraints exist in operant conditioning,
limiting the power that operant conditioning has on the control of learning and
behaviour. As a result, this has major implications for our understanding of
how behaviour is learned and leads to the question, is it possible to always
predict the learning of behaviour through reinforcement? According to the
instinctive drift phenomenon, this cannot always be predicted as behaviour
reinforcement can sometimes be overridden by instinct.

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During their use
of reinforcement techniques, two psychologist animal trainers observed “breakdowns
of conditioned operant behaviour” (Breland & Breland, 1961, p.
They noticed how after a behaviour was established through food reinforcement, over
time this behaviour was disrupted by some instinctive behaviour which the
species use to gather or prepare food. They referred to this phenomenon as “instinctive


The aim of Breland
and Breland’s (1961) study was to reinforce specific behaviours with several
animals. One of the instances involved a raccoon. Initially, the raccoon was
reinforced for simply picking up one coin and no problems were encountered.
Then a metal box was introduced but rather than dropping the coin in the box,
the raccoon would rub it against the inside of the container, pull it out and
hold on to the coin for several seconds. He would eventually let go of the coin,
dropping it in the box and receiving reinforcement. Finally, another coin was introduced,
and the raccoon was required to pick up both coins and place them in the metal
box for reinforcement. However, he had a lot of trouble letting go of the coins
and would spend minutes rubbing them together and dipping them in the
container. Despite not being reinforced for this behaviour, the rubbing became
worse as time went on. This is a demonstration of washing behaviour, carried
out by raccoons in nature when, for example, removing the exoskeleton of


Another instance
involved a chicken who would pull a rubber loop which released a capsule
containing a small toy. The capsule then rolls down a slide and comes to a rest
near the end of the slide. The chicken pecks on the capsule, knocking it off
the slide to receive automatic food reinforcement. The loop pulling presented
no problem. However, after successfully pecking a few capsules off the slide,
20% of all the chickens began to grab the capsule and drag it back into the
cage, where they would pound it up and down on the floor. These chickens were exhibiting
instinctive behaviour related to the breaking open of seed pods or the killing
of insects and grubs.


Lastly, a pig
was required to pick up coins and carry them to a piggy bank for food
reinforcement. Pigs naturally have ravenous appetites and so, as expected, the
pig would initially pick up a dollar eagerly, carry it to the bank, quickly run
back for another dollar and so on, receiving reinforcement. Surprisingly, over
a period of weeks this behaviour became slower and the pig began to repeatedly
drop the coin on the way to the piggy bank, root it, drop it again, pick it up,
toss it in the air and so on. This behaviour persisted even when the pig was
hungry and was observed in different pigs. This rooting and shaking response is
related to natural behaviours built into this species to get food.


Breland and
Breland (1961) reported numerous other examples of instinctive drift, observing
situations where “the animal simply does not do what he has been conditioned to
do” (Breland & Breland, 1961).




In conclusion, the
instinctive drift phenomenon is a biological constraint of operant
conditioning, highlighting innate behaviours that simply cannot be eliminated
by reinforcement. Indeed, as a result some researchers have suggested that the
concept of reinforcement is inadequate and should be renounced (Timberlake
& Bloomington, 1983). Nevertheless, some of the animals in
Breland and Breland’s (1961) study were successfully conditioned (for example,
only 20% of chickens displayed instinctive drift) and the use of token
economies has consistently been found to be effective in real-life situations (Blackerby,
Ultimately, although it is a concept that should not be completely overlooked,
the biological constraints found suggest that we should be cautious when using
operant conditioning to explain behaviour.