PSY402 Theories of Learning Wednesday November 12, 2003 Chapter 7 – Stimulus Control

The Role of Environmental Stimuli In operant conditioning, the stimulus becomes associated with the reinforcer or punishment. Reward or punishment is the UCS. The stimulus signaling reward or punishment is the CS. The CR motivates operant behavior. Responding can be used as a measure of the strength of a CR.

Definitions of Terms Stimulus control -- Environmental stimuli signal the opportunity for reward or punishment. Generalization – responding in the same way to similar stimuli. Discrimination – responding to some stimuli but not to others.

Generalization Gradient Degrees of generalization occur. In some situations, the same response occurs to similar stimuli. In other situations, the amount of response varies with the similarity. Generalization gradient – a graph showing how the strength of response changes with similarity. Steep gradients mean narrow response (stimuli must be very similar).

Kinds of Gradients Excitatory conditioning (S+) – a CS-UCS response to a stimulus is learned. Excitatory gradient – the S+ is varied and the CR is measured. Inhibitory conditioning (S-) – a CS signals absence of the UCS and thus inhibits the CR. Inhibitory gradient – the S- is varied and the CR is measured.

Shapes of Gradients Most sensory stimuli produce similar gradients. Pigeons pecking at colored lights. Tones paired with shocks. Words paired with pretzels or candy: Synonyms and homonyms produce salivation. Semantic similarity works best.

Flat Gradients A flat gradient means all stimuli are being responded to as if they were the same. Responding with a gradient to a tone occurred only when the tone signaled reward during training.

Generalization of Inhibition Inhibition example: fear of dating. A good experience leads to less fear of dating a different person. Inhibition gradients are similar to excitatory gradients – the more the stimulus varies, the less inhibition.

Explanation Lashley-Wade theory – people and animals generalize because they are unable to discriminate. Can’t tell the difference between stimuli A contrast is needed during training to enable discrimination. Discrimination training leads to steeper generalization gradients. Perceptual experience matters.

Discrimination Learning Important to recognize when reinforcement is not available so that responding can be withheld. Discriminative stimulus: SD – reinforcement is available (S+) SD – reinforcement is unavailable (S-) Conditioned stimuli always produce a response. Discriminative stimuli signal the opportunity to respond.

Two-Choice Discrimination Tasks The discriminative stimuli are on the same dimension: Red vs green light. Need not be presented simultaneously. Two-choice discrimination includes one SD and one SD . Other tasks can use multiple multiple SD or multiple SD.

Three Phases Subjects begin by responding equally to both stimuli – prediscrimination phase. Discrimination phase -- with training, response to SD increases and response to SD declines. Shift back to non-differential reinforcement to show that behavior was caused by reinforcement.

Conditional Discrimination Availability of reinforcement depends on the condition of a stimulus. The stimulus does not always signal the same thing. More difficult to learn. Nissen’s chimpanzees: Large, small squares, white or black. SD = large white, small black.

Behavioral Contrast Behavioral contrast – the increased responding to the differential stimulus, decreased response to SD Contrast also occurs with changes in the duration of reinforcement. VI-10 to VI-3 Local contrast – emotional Sustained contrast – related to the differential reinforcement.

Anticipatory Contrast Williams – sustained contrast occurs due to anticipation of a future reinforcement contingency. Not due to recall of past contingency. VI-3, VI-6, VI-3 Compare the first and third VI-3 behavior. VI-6 affected the first VI-3 more than the last VI-3 -- a prospective effect.

Occasion Setting A conditioned stimulus (CS) can create the conditions for operant responding to a second conditioned stimulus (CS). Occasion setting – ability of one stimulus to enhance the response to another stimulus. The facilitating stimulus does not produce a CR by itself.

SD as an Occasion Setter A Pavlovian occasion-setter can increase operant responding. Example: A meal elicits CR craving for cigarette. Requesting a cigarette after a meal – an operant behavior caused by CR. Conditional occasion-setting: Second stimulus modifies meaning of first discriminative stimulus.

Conclusions An occasion-setter can increase operant responding. A discriminative stimulus (SD) can increase response to a CR (Pavlovian conditioning). This implies interchangeability of Pavlovian occasion-setters and discriminative stimuli.

Central Motivational States Conditioned stimuli influence operant behavior through their effect on motivational states: Appetitive Aversive Emotional responses influence operant behavior.