Skinnerian “Schedules of Reinforcement”    [bottom of page 12 of handout]
(Ferster and Skinner, 1957)

Continuous Reinforcement (=CRF; =FR1)
      A reward is given after every response.

Fixed Ratio (FR)
      A reward is given after every n responses (e.g. 10)

Variable Ratio (VR)
      A reward is given after every n responses (e.g. 10) on average, but the exact number of responses is unpredictable.

Fixed Interval (FI)
      A reward is available for just one response, but only after a fixed time (e.g. one minute) has elapsed since the last reward.

Variable Interval (VI)
     A reward is available for just one response, but only after an unpredictable amount of time has elapsed (n minutes on average) since the last reward.