PSY 402 Theories of Learning Wednesday February 19

PSY 402 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. l l ¡ Reward or punishment is the UCS. The stimulus signaling reward or punishment is the CS. The CR motivates operant behavior. l 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. l l ¡ 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. l Steep gradients mean narrow response (stimuli must be very similar).

Kinds of Gradients ¡ Excitatory conditioning (S+) – a CSUCS response to a stimulus is learned. l ¡ 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. l Inhibitory gradient – the S- is varied and the CR is measured.

Shapes of Gradients ¡ Most sensory stimuli produce similar gradients. l l ¡ Pigeons pecking at colored lights. Tones paired with shocks. Words paired with pretzels or candy: l l 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. l ¡ 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. l l 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. ¡