Stimulus discrimination and generalization are key concepts in learning theory. They explain how organisms respond to specific stimuli and apply learned behaviors to similar situations. These processes shape how we interact with our environment and adapt to new experiences.

Understanding stimulus control helps us grasp how behaviors are influenced by environmental cues. This knowledge is crucial for effective learning and behavior modification, impacting fields like education, animal training, and therapy.

Stimulus Control and Discrimination

Understanding Stimulus Control

• Stimulus control occurs when a behavior is more likely to occur in the presence of a specific stimulus than in its absence
• A behavior under stimulus control is said to be "under the control of" or "controlled by" the stimulus
• Stimulus control is established through discrimination training where reinforcement is provided in the presence of the stimulus but not in its absence
• Examples of stimulus control include a dog sitting when commanded to "sit" (verbal stimulus controls sitting behavior) and a rat pressing a lever only when a light is on (light stimulus controls lever pressing behavior)

Stimulus Discrimination and Discriminative Stimuli

• Stimulus discrimination is the process by which an organism learns to respond differently to different stimuli
• A discriminative stimulus (SD) is a stimulus in the presence of which a particular behavior is reinforced
• In the presence of the SD, the behavior is more likely to occur and be reinforced compared to when the SD is absent
• Examples of stimulus discrimination include a pigeon pecking a key only when it is illuminated with a specific color (color is the SD) and a student raising their hand to answer a question only when the teacher asks a question (teacher's question is the SD)

Behavioral Contrast

• Behavioral contrast refers to a change in the rate of a response in one stimulus situation as a result of a change in the rate of reinforcement in another stimulus situation
• Positive behavioral contrast occurs when the rate of a response increases in one situation because the rate of reinforcement has decreased in another situation
• Negative behavioral contrast occurs when the rate of a response decreases in one situation because the rate of reinforcement has increased in another situation
• An example of behavioral contrast is when a pigeon's rate of key pecking in the presence of a green light increases after the rate of reinforcement in the presence of a red light is reduced (positive behavioral contrast)

Stimulus Generalization

Understanding Stimulus Generalization

• Stimulus generalization occurs when an organism responds to stimuli that are similar to the original discriminative stimulus
• Generalization allows an organism to respond appropriately to novel stimuli based on their similarity to previously encountered stimuli
• The extent to which an organism responds to similar stimuli is called the generalization gradient
• An example of stimulus generalization is a dog that has been trained to sit on command generalizing this behavior to similar verbal commands like "sit down" or "sit up"

Generalization Gradient and Peak Shift

• The generalization gradient represents the strength of a response to stimuli that are increasingly different from the original discriminative stimulus
• The peak of the generalization gradient typically occurs at the original discriminative stimulus and decreases as the stimuli become more dissimilar
• Peak shift is a phenomenon where the peak of the generalization gradient shifts away from the original discriminative stimulus in the direction opposite to the stimulus that was not reinforced during discrimination training
• An example of peak shift is when a pigeon is trained to peck a key in the presence of a 550 nm wavelength light (SD) and not in the presence of a 570 nm wavelength light (S-delta), the peak of the generalization gradient may shift to a shorter wavelength (e.g., 530 nm) that is farther away from the S-delta

Stimulus Interaction Effects

Overshadowing and Blocking

• Overshadowing occurs when the presence of a more salient stimulus during conditioning reduces the conditioning to a less salient stimulus
• In overshadowing, the more salient stimulus "overshadows" the less salient stimulus, making it less effective in controlling the conditioned response
• Blocking is a phenomenon where prior conditioning to one stimulus can prevent or reduce conditioning to a second stimulus when the two stimuli are presented together
• An example of overshadowing is when a tone and a light are presented together during conditioning, and the tone is more salient, leading to weaker conditioning to the light
• An example of blocking is when an animal is first conditioned to respond to a light, and then a tone is presented together with the light, the animal may not develop a strong conditioned response to the tone due to the previous conditioning to the light

Sensory Preconditioning

• Sensory preconditioning is a phenomenon where an association between two stimuli can be formed even without direct reinforcement
• In sensory preconditioning, two neutral stimuli are presented together repeatedly, and then one of the stimuli is paired with a reinforcer or an unconditioned stimulus
• As a result, the other stimulus (which was never directly paired with the reinforcer) can also elicit the conditioned response
• An example of sensory preconditioning is when a tone and a light are repeatedly presented together (without reinforcement), and then the light is paired with food, the tone may also elicit a conditioned response (e.g., salivation) even though it was never directly paired with food