Transcript Chap7b
PSY 402 Theories of Learning Chapter 7 – Behavior & Its Consequences Instrumental & Operant Learning Stimulus Control Skinner discovered that stimuli (cues) provide information about the opportunity for reinforcement (reward). The stimulus sets the occasion for the behavior. Fading – gradually transferring stimulus control from a simple stimulus to a more complex one. Operant behavior is controlled by both stimuli and reinforcers. Discriminative Stimuli Discriminative stimuli act as “occasion setters” (see Chap 5) in classical conditioning. The stimulus that signals the opportunity for responding and gaining a reward is SD. The stimulus that signals the absence of opportunity is SD. 7.6 Simple demonstration of stimulus control SD Light signals that reward is available. SD Types of Reinforcers Primary reinforcer – stimuli or events that reinforce because of their intrinsic properties: Food, water, sex Secondary reinforcer – stimuli or events that reinforce because of their association with a primary reinforcer: Money, praise, grades, sounds (clicks) Called conditioned reinforcers. Behavior Chains Secondary (conditioned) reinforcers reward intermediate steps in a chain of behavior leading to a primary reinforcer. Secondary reinforcers can also be discriminative stimuli that set the occasion for more responding. Classical conditioning is a glue that enables chains of behavior leading to a goal. 7.7 A behavior chain: Each response produces a stimulus Schedules of Reinforcement Behavior is recorded continuously on a drum recorder. A cumulative graph shows the rate of responding over time. The steepness of the line indicates how quickly the rat is responding Hash marks indicate when reward was given. CRF (Continuous reinforcement) – the rat is rewarded every time it does the behavior. 7.8 Cumulative recorder (Part 1) Drum recorder 7.8 Cumulative Record: Results (Part 2) Ratio Schedules Fixed Ratio (FR) – there is a ratio between responding and reward. The rate is rewarded for every xth behavior. FR-15 means the rat gets one reward for every 15 behaviors (e.g., bar presses). Variable Ratio (VR) – the number of responses needed varies, but averages out to a particular ratio. VR-15 – the ratio varies but averages to 1:15. Interval Schedules Fixed Interval (FI) – rewards are given for the first response after a given amount of time has passed. FI-15 means one reward is given after 15 minutes, but only if the rat does the behavior. Variable Interval (VI) – rewards are given after varying amounts of time that average to a particular interval. VI-15 means one reward after average of 15 min. 7.9 Cumulative records showing typical responding on different schedules of reinforcement Pause after each reward Response is inconsistent Best Worst Effects of Schedule on Behavior FR leads to steady responding but post reinforcement pauses occur after each reward. VR leads to a high rate of responding with no pauses – never know when reward will occur. FI leads to behavior right before the end of each interval, with goofing off in between. Scallops in the cumulative record VI leads to the lowest rate of responding. Compound Schedules Multiple schedules – two or more schedules alternate, each signaled by a different SD. Chained schedules – completion of one leads to the beginning of a new schedule (with SD). Mixed schedules – schedules alternate but no stimulus signals which type is being used. Tandem schedules – liked chained but no SD. Differential High/Low Responding – specifies the behavior and the deadline (interval). Choice Concurrent schedules – two different types of behavior are offered, each with its own schedule of reinforcement. Behavior on concurrent schedules follows Herrnstein’s Matching Law. The proportion of behavior allocated to a choice is the same as the proportion of reward offered. B1 / (B1 + B2) = R1 / (R1 + R2) or B1 / B2 = R1 / R2 7.10 Matching on concurrent VI VI schedules (Part 1) 7.10 Matching on concurrent VI VI schedules (Part 2) 7.11 Matching in humans The Law Works for Reward Size The amount of responding is proportionate to the relative reward sizes. If V1 and V2 are different reward sizes, then B1 / B2 = V1 / V2 The Matching Law says nothing about what people or rats are thinking. Melioration – a strategy of shifting between two choices until the rewards are equal. A Law for One Choice If the total amount of behavior (B1 + B2) is K, then the rate of responding to a single choice (B1) is: B1 = K x R1 / (R1 + Ro) Ro is the reinforcement rate for some other choice (the reward for doing something else). This is called the Quantitative Law of Effect because it predicts the amount of responding. 7.12 Response rates of six pigeons, each one tested with several different VI schedules Implications of the Law According to the Law, a particular behavior can be weakened by providing rewards for other behaviors in the environment. Drug abuse is more likely for people who have little other reward in their lives. Problems can be prevented by making sure there are reinforcers for pro-social behaviors. More positive environments can be built. Impulsiveness Delayed gratification – the willingness to set aside an immediate reward in favor of a longterm, larger reward. People find this difficult to do. Self-control = delaying gratification. Impulsive behavior is more likely when small rewards are imminent (immediate, salient). 7.13 Self-control increases as the time between a choice and reward increases 7.14 The present value of a delayed reward depends on how far you are from the reward in time Small reward is worth more than large reward at this time. Hot and Cold Thoughts Imagining the desirable qualities of an immediate reward undermines self control. Distraction by thinking about something unrelated supports self control. Drug abusers have difficult with self-control. Impulsivity may be domain-specific (depend on the kind of reward involved). Although mentalistic, “self-control” is defined in terms of specific behaviors and choices. Behavioral Economics Not all reinforcers are alike – substitutability is a continuum (varies). Demand curve – does consumption vary with price? Elastic commodities do, inelastic ones (necessities) do not. Reinforcers can be substitutes, independents, or complements, depending on their demand curves. 7.15 These curves describe the demand for a commodity as a function of its price 7.16 Demand for two commodities as one of them increases in price Theories of Reinforcement Drive Reduction – Hull Reinforcement occurs when the consequence of behavior reduces a drive (hunger, thirst). Not everything reinforcing reduces a drive, and some reinforcers increase drives (stimulation). Premack’s Principle – behaviors can be reinforcers (not just stimuli such as food). The chance to do a preferred behavior is a reward Problems with Premack’s Principle Prior preferences are important to the theory, but how can they be determined in advance? Restricting a behavior creates a void where the person must do something – this may account for the observed increase, not reward. Access to even a less-preferred but restricted behavior can be reinforcing. The reinforcer need not be preferred behavior. Behavioral Regulation Theory Response deprivation theory – every behavior has a natural level (the amount someone wants to do if there are no restrictions). A behavior will be rewarding if restricted below the natural level. Also called behavioral regulation theory. Blisspoint The blisspoint is the amount of each of two behaviors someone would do if unrestricted. Minimum distance model – someone will do enough of each of two behaviors to get as close as possible to the blisspoint. When two behaviors are contingent, the blisspoint is the perpendicular distance from the line for a reinforcement schedule. 7.17 Reinforcing effect as a function of the rat's preference for each reinforcer 7.18 The minimum distance model 7.19 Number of responses to reach “bliss point” depends on the reinforcement schedule Selection by Consequences Reinforcers select behaviors by weeding out the ones that are less efficient in obtaining rewards. Skinner called this “selection by consequences.” A process similar to evolution encourages some behaviors and leads to extinction of others, shaped by consequences of actions.