Differential Reinforcement: Stimulus Control & Shaping Lesson 13

Modifying Behavior n Response variability l Engage in many different behaviors n Differential reinforcement l Some Bs reinforced, some not l Response selection n Stimulus control l Generalization & Discrimination n Shaping l Changes in response probability ~

Differential Reinforcement n Response differentiation l Differentiation of S D and S Δ n Contextual cues l S D : B  successful outcome l S Δ : B  unsuccessful outcome n Example: l switching lights for class ~

Differential Reinforcement n Example: Puzzle box l Contextual cues? l Possible responses? ~ SDsSDs B 1 : Flip left switch B 2 : Flip middle switch B 3 : Flip right switch

Differential Reinforcement: Continuous Variations in Behavior n On a single behavior l Variations in strength of extent n e.g., baking time for cookies l Not enough  doughy l Too much  burnt n S D s for good cookies? S  s for bad cookies? n Other examples? ~

Stimulus Control n Generalization l similar stimuli  similar response n Discrimination l after more experience l differential reinforcement l similar stimuli  different response n Stimulus generalization gradient l lower similarity  lower response ~

Stimulus Generalization n Present new stimulus l Similar to S D or CS l associative n Response occurs l even though not reinforced l or paired with US n Novel stimulus l presented only a few times ~

Stimulus Generalization Gradient Shades of Blue SDSD Strength of Response Hi Lo

Stimulus Discrimination n Distinguish between 2 similar stimuli l One never reinforced: S Δ n 2 classes of Discriminative stimuli lSDlSD l S Δ ~

S D vs S Δ n S D signals that B will be reinforced ~ S D (blue) : B (bar press)  S R (food)

Stimulus Similar to S D n Response occurs n S Δ signals that B will not be reinforced ~ S Δ (lighter blue) : B (bar press)  no S R (food)

SΔSΔ n After training (experience) n Signals that S R will NOT follow B S Δ (lighter blue) : no B (no bar press)

Before Additional Training: Generalization Number of Pecks Hi Lo Shades of Blue SDSD

Generalization  Discrimination Hi Lo Shades of Blue Number of Pecks SΔSΔ SΔSΔ Pecking not reinforced when S Δ present SDSD

Generalization  Discrimination Number of Pecks Hi Lo Shades of Blue Pecking not reinforced when S Δ present SΔSΔ SΔSΔ SDSD

Generalization  Discrimination Number of Pecks Hi Lo Shades of Blue Pecking not reinforced when S Δ present SΔSΔ SΔSΔ SDSD

Stimulus Discrimination Hi Lo Shades of Blue Number of Pecks Pecking during S Δ diminishes SΔSΔ SΔSΔ SDSD

Systematic Shaping n Bar pressing: natural behavior for rats? n Differential reinforcement of successive approximations l Reinforce Bs similar to part of desired B l Progressively shift to closer approximations l B – S R contingency ~

Shaping: Successive approximations

n RFT if orients toward ~

Shaping: Successive approximations