474 Part VI Learning-Cognitive Theories
For humans, playing slot machines is an example of a variable-ratio schedule.
The machine is set to pay off at a certain rate, but the ratio must be flexible, that
is, variable, to prevent players from predicting payoffs.Fixed-Interval With the fixed-interval schedule, the organism is reinforced for
the first response following a designated period of time. For example, FI 5 indicates
that the organism is rewarded for its first response after every 5-minute interval.
Employees working for salary or wages approximate a fixed-interval schedule.
They are paid every week, every 2 weeks, or every month; but this pay schedule
is not strictly a fixed-interval schedule. Although pigeons typically show a spurt
in work toward the end of the time period, most human workers distribute their
efforts fairly evenly rather than loafing most of the time and then showing an end-
of-the-period spurt. This situation is due in part to such factors as watchful super-
visors, threats of dismissal, promises of promotion, or self-generated reinforcers.Variable-Interval A variable-interval schedule is one in which the organism is
reinforced after the lapse of random or varied periods of time. For example, VI 5
means that the organism is reinforced following random-length intervals that aver-
age 5 minutes. Such schedules result in more responses per interval than do fixed-
interval schedules. For humans, reinforcement results more often from one’s effort
rather than the passage of time. For this reason, ratio schedules are more common
than interval schedules, and the variable-interval schedule is probably the least
common of all.Because slot machines pay off on a variable-ratio schedule, some people become compulsive
gamblers. © Noel Hendrickson/Blend Images LLC