Instrumental Conditioning I

Transcription

1 Instrumental Conditioning I Basic Procedures and Processes Instrumental or Operant Conditioning? These terms both refer to learned changes in behavior that occur as a result of the consequences of the behavior. Instrumental refers to the fact that the behavior is instrumental in bringing about a given consequence. Operant refers to the fact that the behavior operates on the environment, that is, has an effect there. Which term you prefer to use will probably depend on whether you use a discrete-trialsor free-operant methodology. Discrete-Trials Procedures Organized as a series of learning trials Start of each trial is under control of the experimenter, not the animal. Usually focus on group averages and statistical analysis. Dependent variables: latency, speed, number of errors, etc. as functions of trials and conditions. Examples Thorndike s puzzle-box experiments Maze learning Researchers using these procedures prefer the term instrumental conditioning. Straight Alley Start Box Goal Box 1

2 Free-Operant Procedures Monitored behavior is free to occur at any time; under the control of the animal Dependent variable usually the frequency or probability of response as functions of time and conditions Focus is on the individual subject averaging over subjects and inferential statistics discouraged. Technology pioneered by B. F. Skinner Researchers using these procedures prefer the term operant conditioning. Rat in the operant chamber above is free to press the lever at any time. Operant Chamber (Rat Version) Pigeon Chamber in Sound- Isolation Box Computer used to arrange contingencies and collect data 2

3 Cumulative Recorder Clock drive moves paper under pen at constant rate. Pen moves across by a small amount with each response. Slope of line indicates rate of responding. Reading the Cumulative Record The pen moves up a notch with each response. Consequently, the position of the pen at any moment indicates the total or cumulative number of responses produced up to that moment. The pen resets to bottom when it reaches the top of the graph, so that it stays on the paper. The paper moves under the pen at a constant rate. Tick-marks indicate reinforcer deliveries. The slope of the line at any point indicates the rate of responding. Zero rate generates a horizontal line. Some Definitions Operant Some well-specified behavioral act, such as pressing a lever. Reinforcer A consequence of a behavior that serves to strengthen the behavior. Stronger behavior is behavior that occurs more frequently, with higher probability, with shorter latency. Reinforcement The procedure of making a reinforcer consequent on the occurrence of an operant. 3

4 Basic Processes Acquisition Extinction Spontaneous recovery from extinction Generalization and Discrimination Acquisition Each leverpress delivers a pellet of food to the hungry rat. From Skinner (1938) After a few presses and pellet-deliveries, responding accelerates to a high rate. Extinction Pellets were no longer delivered following leverpresses. The rate of responding declined toward zero. 4

5 Spontaneous Recovery Note jump in rate at start of session Spontaneous recovery is observed at the start of each new extinction session after a period of rest. Generalization/Discrimination Generalization Gradient S+ A pigeon received grain for pecking a key while a vertical line (S+) was projected on the key. Extinction was in effect when S+ was absent. Tests were conducted in extinction while lines of various angle were projected on the key. The Discriminative Stimulus A stimulus in the presence of which a response is reinforced. A stimulus that sets the occasion for a response. Sometimes symbolized as S D or as S + Behavior analysts refer to the three-term contingency in which reinforcement of a response is contingent upon the presence of S D Explains why behavior reinforced in one context does not become stronger in all contexts. Equivalent to Thorndike s situation. 5