Hockenbury Discovering Psychology 5th txtbk

Operant Conditioning211Cumulative number of responses1000750500250Variable-ratioFixed-ratio00 10 20 30 40ReinforcerFixed-intervalTime, in minutesVariable-interval50 60 70 80Figure 5.6 Schedules of Reinforcementand Response Patterns Different patternsof responding are produced by the fourbasic schedules of reinforcement. The predictablenature of a fixed-ratio schedule(the blue line at far left) produces a highrate of responding, with a pause after thereinforcer is delivered. The unpredictablenature of variable-ratio schedules (red) alsoproduces high, steady rates of responding,but with hardly any pausing between reinforcers.Fixed-interval schedules (purple)produce a scallop-shaped pattern of res -ponding. The unpredictable nature ofvariable-interval schedules (orange) producesa moderate but steady rate of responding.(Based on Skinner, 1961.)in any activity that requires a precise number of responses in order to obtain reinforcement.Piecework—work for which you are paid for producing a specificnumber of items, such as being paid $1 for every 100 envelopes you stuff—is anexample of an FR-100 schedule.With a variable-ratio (VR) schedule, reinforcement occurs after an averagenumber of responses, which varies from trial to trial. A rat on a variable-ratio-20schedule (abbreviated VR-20) might have to press the bar 25 times on the first trialbefore being reinforced and only 15 times on the second trial before reinforcement.Although the number of responses required on any specific trial is unpredictable,over repeated trials the ratio of responses to reinforcers works out to the predeterminedaverage.Variable-ratio schedules of reinforcement produce high, steady rates of respondingwith hardly any pausing between trials or after reinforcement. Gambling is theclassic example of a variable-ratio schedule in real life. Each spin of the roulettewheel, toss of the dice, or purchase of a lottery ticket could be the big one, and themore often you gamble, the more opportunities you have to win (and lose, as casinoowners are well aware).On a fixed-interval (FI) schedule, a reinforcer is delivered for the first responseemitted after the preset time interval has elapsed. A rat on a two-minute fixedintervalschedule (abbreviated FI-2 minutes) would receive no food pellets for anybar presses made during the first two minutes. But the first bar press after the twominuteinterval had elapsed would be reinforced.Fixed-interval schedules typically produce a scallop-shaped pattern of respondingin which the number of responses tends to increase as the time for the next reinforcerdraws near. For example, if your instructor gives you a test every four weeks,your studying behavior would probably follow the same scallop-shaped pattern ofresponding as the rat’s bar-pressing behavior. As the end of the four-week intervaldraws near, studying behavior increases. After the test, studying behavior drops offuntil the end of the next four-week interval approaches.On a variable-interval (VI) schedule, reinforcement occurs for the firstresponse emitted after an average amount of time has elapsed, but the interval variesfrom trial to trial. Hence, a rat on a VI-30 seconds schedule might be reinforced forthe first bar press after only 10 seconds have elapsed on the first trial, for the firstbar press after 50 seconds have elapsed on the second trial, and for the first bar pressafter 30 seconds have elapsed on the third trial. This works out to an average of onereinforcer every 30 seconds.Generally, the unpredictable nature of variable-interval schedules tends to producemoderate but steady rates of responding, especially when the average intervalvariable-ratio (VR) scheduleA reinforcement schedule in which a reinforceris delivered after an average numberof responses, which varies unpredictablyfrom trial to trial.fixed-interval (FI) scheduleA reinforcement schedule in which a reinforceris delivered for the first response thatoccurs after a preset time interval haselapsed.variable-interval (VI) scheduleA reinforcement schedule in which a reinforceris delivered for the first response thatoccurs after an average time interval, whichvaries unpredictably from trial to trial.