Differential
Reinforcement:
Stimulus Control
& Shaping
Lesson 13
Modifying Behavior
Response variability
 Engage in many different behaviors
 Differential reinforcement
 Some Bs reinforced, some not
 Response selection
 Stimulus control
 Generalization & Discrimination
 Shaping
 Changes in response probability ~

Differential Reinforcement
Response differentiation
D
Δ
 Differentiation of S and S
 Contextual cues
D
 S : B  successful outcome
Δ
 S : B  unsuccessful outcome
 Example:
 switching lights for class ~

Differential Reinforcement
B1: Flip left switch
SDs
B2: Flip middle switch
B3: Flip right switch

Example: Puzzle box
 Contextual cues?
 Possible responses? ~
Differential Reinforcement:
Continuous Variations in Behavior
On a single behavior
 Variations in strength of extent
 e.g., baking time for cookies
 Not enough  doughy
 Too much  burnt
 SDs for good cookies?
D
 S s for bad cookies?
 Other examples? ~

Stimulus Control
Generalization
 similar stimuli  similar response
 Discrimination
 after more experience
 differential reinforcement
 similar stimuli  different response
 Stimulus generalization gradient
 lower similarity  lower response ~

Stimulus Generalization
Present new stimulus
D or CS
 Similar to S
 associative
 Response occurs
 even though not reinforced
 or paired with US
 Novel stimulus
 presented only a few times ~

Stimulus Generalization Gradient
Hi
SD
Strength
of Response
Lo
Shades of Blue
Stimulus Discrimination
Distinguish between 2 similar stimuli
Δ
 One never reinforced: S
 2 classes of Discriminative stimuli
D
 S
Δ
 S
~

SD vs SΔ

SD signals that B will be reinforced ~
SD(blue) : B (bar press)  SR(food)
Stimulus Similar to SD

Response occurs
SΔ (lighter blue)

:
B (bar press)  no SR(food)
SΔ signals that B will not be reinforced ~
SΔ
After training (experience)
 Signals that SR will NOT follow B

SΔ (lighter blue) :
no B (no bar press)
Before Additional Training:
Generalization
Hi
SD
Number
of Pecks
Lo
Shades of Blue
Generalization  Discrimination
Pecking not reinforced when SΔ present
Hi
SD
SΔ
SΔ
Number
of Pecks
Lo
Shades of Blue
Generalization  Discrimination
Pecking not reinforced when SΔ present
Hi
SD
Number
of Pecks
SΔ
SΔ
Lo
Shades of Blue
Generalization  Discrimination
Pecking not reinforced when SΔ present
Hi
SD
Number
of Pecks
SΔ
SΔ
Lo
Shades of Blue
Stimulus Discrimination
Pecking during SΔ diminishes
Hi
SD
Number
of Pecks
SΔ
SΔ
Lo
Shades of Blue
Systematic Shaping
Bar pressing: natural behavior for
rats?
 Differential reinforcement of
successive approximations
 Reinforce Bs similar to part of
desired B
 Progressively shift to closer
approximations
R
 B – S contingency ~

Shaping: Successive approximations
Shaping: Successive approximations

RFT if orients toward ~
Shaping: Successive approximations
Shaping: Successive approximations
Shaping: Successive approximations
Shaping: Successive approximations