Game Development Reference
The psychologist B.F. Skinner created reinforcement schedules in the
1930s and '40s while exploring the idea of operant conditioning . Whereas
classical conditioning is about manipulating a creature's involuntary re-
sponses (as in Pavlov's famous dog bell experiment), operant conditioning
is about manipulating apparently voluntary behavior using rewards and
punishments. When you give a treat to a dog after it performs a trick,
you're using operant conditioning to make it perform that trick again.
To explore operant conditioning, Skinner invented the so-called
“Skinner box.” A Skinner box is a small enclosure in which rats or pigeons
can be placed. The box might contain levers, hamster wheels, sensors,
lights, loudspeakers, food dispensers, or electrical shockers, depending on
the experiment. These devices are linked together by an unseen mecha-
nism that creates a relationship between them.
For example, in one configuration, the dispenser would give out a
pellet of food each time the lever was pushed. In another, it would give
food every 10 th push. In another, it would randomly produce pellets 10% of
the time each time it was pushed. Each of these configurations is a differ-
ent reinforcement schedule.
Skinner wanted to see what different reinforcement schedules would
do to the rat's behavior. How would the rat respond if it got food every time
it pushed the lever? What if it got a pellet randomly, or on a timer, or after
it ran a certain distance on the wheel? Skinner found that the animal's
behavior would change depending on when the rewards appeared—but
not always in obvious ways. Even slight changes in the reinforcement
schedules could cause drastic differences in behavior.
Such reinforcement schedules aren't just for Skinner boxes. Games
are full of them. When you defeat an orc to get a gold piece, you're playing a
reinforcement schedule created by a game designer. Just as with Skinner's
rats, the details of that reinforcement schedule will affect how motivated
you are to keep playing. For game designers, these schedules are tools we
can use to motivate players.
There are an infinite variety of possible schedules, but the two most
important ones are fixed ratio and variable ratio .
A fixed ratio reinforcement schedule gives rewards at a fixed ratio to ac-
tions taken. For example, in a Skinner box, a rat might get a food pellet
every time it pushes the lever. In a game, a player might get a gold piece
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