Fixed Ratio (FR)
Reinforcement is delivered after a fixed number of responses. Pattern: High, steady rate with a post-reinforcement pause. Example: A factory worker is paid for every 10 widgets assembled (FR-10). Exam tip: FR schedules produce the highest rates of responding among ratio schedules when the ratio is not too large.
Variable Ratio (VR)
Reinforcement is delivered after a variable number of responses, averaging a specified number. Pattern: High, steady rate with no post-reinforcement pause. Example: A slot machine pays out after an average of 50 pulls (VR-50). Exam tip: VR schedules produce the highest overall response rates and are most resistant to extinction.
Fixed Interval (FI)
Reinforcement is delivered for the first response after a fixed amount of time has elapsed. Pattern: "Scallop" pattern with low responding after reinforcement, accelerating as the interval nears its end. Example: Checking the mail once a day when it is delivered at the same time (FI-24 hours). Exam tip: The scallop pattern is a classic exam question. Know how to identify it on a graph.
Variable Interval (VI)
Reinforcement is delivered for the first response after a variable amount of time has elapsed. Pattern: Moderate, steady rate of responding. Example: Checking email throughout the day when messages arrive unpredictably (VI-30 minutes). Exam tip: VI produces the most stable response rates of all four basic schedules.
Key Comparisons
Ratio schedules produce higher rates than interval schedules because every response counts toward reinforcement. Variable schedules produce steadier rates than fixed schedules because the exact requirement is unpredictable. VR produces the highest rates overall; VI produces the steadiest rates overall.