A reinforcement schedule is a rule that
specifies the timing and frequency of reinforcers. In his early experiments on operant conditioning, Skinner rewarded animals
with food every time they made the desired response—a schedule known as continuous reinforcement. Skinner soon tried
rewarding only some instances of the desired response and not others—a schedule known as partial reinforcement. To his
surprise, he found that animals showed entirely different behavior patterns.
Skinner and other psychologists found
that partial reinforcement schedules are often more effective at strengthening behavior than continuous reinforcement schedules,
for two reasons. First, they usually produce more responding, at a faster rate. Second, a behavior learned through a partial
reinforcement schedule has greater resistance to extinction—if the rewards for the behavior are discontinued, the behavior
will persist for a longer period of time before stopping. One reason extinction is slower after partial reinforcement is that
the learner has become accustomed to making responses without receiving a reinforcer each time. There are four main types
of partial reinforcement schedules: fixed-ratio, variable-ratio, fixed-interval, and variable-interval. Each produces a distinctly
different pattern of behavior.
On a fixed-ratio schedule, individuals
receive a reinforcer each time they make a fixed number of responses. For example, a factory worker may earn a certain amount
of money for every 100 items assembled. This type of schedule usually produces a stop-and-go pattern of responding: The individual
works steadily until receiving one reinforcer, then takes a break, then works steadily until receiving another reinforcer,
and so on.
On a variable-ratio schedule, individuals
must also make a number of responses before receiving a reinforcer, but the number is variable and unpredictable. Slot machines,
roulette wheels, and other forms of gambling are examples of variable-ratio schedules. Behaviors reinforced on these schedules
tend to occur at a rapid, steady rate, with few pauses. Thus, many people will drop coins into a slot machine over and over
again on the chance of winning the jackpot, which serves as the reinforcer.
On a fixed-interval schedule, individuals
receive reinforcement for their response only after a fixed amount of time elapses. For example, in a laboratory experiment
with a fixed-interval one-minute schedule, at least one minute must elapse between the deliveries of the reinforcer. Any responses
that occur before one minute has passed have no effect. On these schedules, animals usually do not respond at the beginning
of the interval, but they respond faster and faster as the time for reinforcement approaches. Fixed-interval schedules rarely
occur outside the laboratory, but one close approximation is the clock-watching behavior of students during a class. Students
watch the clock only occasionally at the start of a class period, but they watch more and more as the end of the period gets
Variable-interval schedules also require
the passage of time before providing reinforcement, but the amount of time is variable and unpredictable. Behavior on these
schedules tends to be steady, but slower than on ratio schedules. For example, a person trying to call someone whose phone
line is busy may redial every few minutes until the call gets through.