Page 39 - Zoo Animal Learning and Training

1.4 Operant Conditioning 11

VetBooks.ir and behaviour with a fixed ratio 5 (written as by the military in World War II to train
pigeons to guide missiles (Skinner 1960).
FR 5), then we would give him a piece of
sweet potato after every fifth response: the
number of required responses is fixed at 5. During this time, Skinner took a leave of
absence from the University of Minnesota
and moved his lab into a flour mill provided
by General Mills. Taking breaks from train­
1.4.3 Extinction
ing the soon to be missile guiding pigeons,
Extinction was discovered through another Skinner and his students noticed a wild flock
serendipitous event. During one of Skinner’s of pigeons hanging around the mill. One day
experiments on satiation, a rat was pressing in 1943, Skinner and his students decided to
the lever when the pellet dispenser jammed. teach a pigeon to bowl (Skinner 1958). To
Skinner was not in his lab at the time and thus achieve this behaviour the pigeon needed to
couldn’t simply fill the dispenser. However, first swipe a ball with its beck. The group got
when he returned he found an interesting prepared to reinforce the first swipe, but
curve. Skinner states in his book, ‘The change nothing happened. In the hopes of speeding
was more orderly than the extinction of a sali­ up the process they decided to reinforce sim­
vary reflex in Pavlov’s setting and I was terri­ ply looking at the ball, then a behaviour
bly excited. It was a Friday afternoon and ‘which more closely approximated the final
there was no one in the laboratory whom I form’ (Skinner 1958, p. 94). Although Skinner
could tell. All that weekend I crossed streets had used shaping before, this was the first
with particular care and avoided all unneces­ time he had hand‐shaped an animal to per­
sary risks to protect my discovery from loss form a behaviour (Peterson 2004). It wouldn’t
through my death’ (Skinner 1979, p. 95). be until 1951 when an article by LOOK
Extinction is defined as withholding magazine was published that showed Skinner
reinforcement from a previously reinforced training a Dalmatian to jump, that the pro­
response. As a training process, during cedure of shaping was disseminated to the
extinction, there is a zero probability of rein­ general public.
forcement for the response you were previ­ Today the term shaping is widely known
ously reinforcing. As a behavioural process, to anyone that has tried to train their dog or
extinction is a decline in the rate of respond­ has taken an introductory psychology
ing caused by withdrawal of reinforcement. course. Shaping is training closer and closer
The interesting curve that Skinner found approximations to the target behaviour. For
was probably an extinction burst. When the example, a rough shaping plan for getting a
extinction procedure has started, a sharp dog into a crate on its own using shaping
increase in responding occurs, followed by a may look like this:
slow decline in responding as the trials con­ Start with the dog 2 ft (60 cm) from the
tinue. An example that you have probably wit­ crate. Decrease the distance between the dog
nessed is when you wait for an elevator. If you and the crate. When the dog is close enough,
press the button and the doors don’t open, you have the dog touch the crate with its paw.
press it again. You are then frustrated so you After the dog is touching the crate you might
press it 10 times in a row (extinction burst). If ask the dog for one paw in the crate and then
the doors still don’t open, you might press it increase the distance into the crate until the
one or two times more before taking the stairs. entire dog is in the crate. Finally you would
work on closing the crate door whilst the dog
is inside.
1.4.4 Shaping
Shaping allows animal trainers to set out a
The story of Skinner’s discovery of shaping is plan that will bring the target behaviour to
quite interesting so I thought I would include fruition. However, more importantly, shap­
it in this chapter. Skinner was commissioned ing is an essential process in teaching because