PSY402 Theories of Learning Wednesday February 19, 2003

Stimulus Generalization Chapter 7

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.