Download Principles of Appetitive Conditioning

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PRINCIPLES OF APPETITIVE
CONDITIONING
Chapter 6
Early Contributors
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
Thorndike’s Contribution


Emphasized Laws of Behavior
 Demonstrated trial by trial learning
 S-R learning
Skinner’s contribution

Emphasized Contingency
 A specified relationship between behavior and
reinforcement in a given situation
 The environment “sets” the contingencies S(R->O)
A “Faux” Distinction
3

Instrumental conditioning


A conditioning procedure in which the environment
constrains the opportunity for reward (discrete trial)
Operant conditioning

When a specific response produces reinforcement, and
the frequency of the response determines the amount
of reinforcement obtained (continuous responding,
schedules of reinforcement)
Thorndikes’ Law of Effect
4
S-R associations are stamped
in by reward (satisfiers)
Stimulus
Response
Thorndike: “What is learned?”
5
Habit Learning
S
Reinforcement
“stamps in” this
connection
R
Is that it?
6
Instrumental Association
S
R
?
?
Pavlovian Association
O
“O” matters
7


The Importance of Past Experience
Depression/Negative Contrast


The effect in which a shift from high to low reward
magnitude produces a lower level of response than if the
reward magnitude had always been low.
Elation/Positive Contrast

The effect in which a shift from low to high reward
magnitude produces a greater level of responding than if
the reward magnitude had always been high.
Negative and Positive Contrast
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Logic of Devaluation Experiment
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Max
Responding
R-O or Goal Directed: Controlled by the
current value of the reinforced, and so it
should be reduced to zero after devaluation.
S-R or Habit: Responding that is not
controlled by the current value of the
reward, and so it is insensitive to reinforcer
devaluation.
Min
Normal Devalued
R-O Association (aka the instrumental
association)
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Phase 1
Devaluation
Push LeftPellet
Pellet+LiCl
Number of Pushes
Push RightSucrose Sucrose+LiCl
Test
Right?
Left?
Right Pushes
Left Pushes
Devalued
Pellet
Devalued
Sucrose
Summary of Devaluation
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


Neutered male rats lower but do not eliminate their
responding previously associated with access to a
“ripe” female rat.
Rats satiated for reward#1 preferentially lower
responding to get reward#1 more than reward#2.
Goal devaluation effects tend to shrink with
continued training and goal-directed responding is
replaced by habit learning.
S-O Association (aka Pavlovian
Association)
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Stage 1
Stage 2
Test
RightPellet
TonePellet
Tone: Left? Right?
LeftSucrose
LightSucrose
Light: Left? Right?
Number of
Presses
Left
Right
Tone
Light
Skinner’s Contributions
13


Automatic
Easy measurements that
can be compared across
species
Three Terms Define the Contingency
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
Three term contingency



Discriminative stimulus (S+ or S-)
Operant (R)
Consequence (O)
Operant Strengthened
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S+
R
O
Bite
Light-On
Skinner Box
Groom
Lick
Reinforcer
Rear
Push Lever
Techniques and Concepts
16

Shaping: Successive approximations
 Require
closer and closer appoximations to the target
behaviour

Secondary Reinforcers:
 Stimuli

accompanying reinforcer delivery
Marking:
 Feedback
that a response had occurred
Shaping
17

Shaping (or successive approximation procedure)

Select a highly occurring operant behavior, then slowly
changing the contingency until the desired behavior is
learned
Training a Rat to Bar Press
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



Step 1: reinforce for eating out of the food
dispenser
Step 2: reinforce for moving away from the food
dispenser
Step 3: reinforce for moving in direction of bar
Step 4: reinforce for pressing bar
Appetive Reinforcers
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
Primary reinforcer


An activity whose reinforcing properties are innate
Secondary reinforcer

An event that has developed its reinforcing properties
through its association with primary reinforcers
Primary Reward Magnitude
20

The Acquisition of an Instrumental or Operant
Response


The greater the magnitude of the reward, the faster the
task is learned
The differences in performance may reflect
motivational differences
Magnitude
21
Primary Reward and Degraded
Contingency
22
= bar press
Perfect
contingency
Strong
Responding
Degraded
contingency
Weak
Responding
= food
Strength of Secondary Reinforcers
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
Several variables affect the strength of secondary
reinforcers



The magnitude of the primary reinforcer
The greater the number of primary-secondary pairings,
the stronger the reinforcing power of the secondary
reinforcer
The time elapsing between the presentation of the
secondary reinforcer and the primary reinforcer
affects the strength of the secondary reinforcer
Primary-Secondary Pairings
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Schedules of Reinforcement
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
Schedules of reinforcement

A contingency that specifies how often or when we must
act to receive reinforcement
Schedules of Reinforcement
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
Fixed Ratio



Reinforcement is given after
a given number of
responses
Short pauses
Variable Ratio

After a varying number of
responses
Schedules of Reinforcement
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
Fixed Interval



First response after a given
interval is rewarded
FI Scallop
Variable Interval


Like FI but varies with a
given average
Scallop disappears
Fixed Interval Schedule
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
Fixed interval schedule


Reinforcement is available only after a specified period
of time and the first response emitted after the interval
has elapsed is reinforced
Scallop effect


Experience - the ability to withhold the response until
close to the end of the interval increases with
experience
The pause is longer with longer FI schedules
Variable Interval Schedules
29

Variable interval schedule





An average interval of time between available
reinforcers, but the interval varies from one
reinforcement to the next contingency
Characterized by steady rates of responding
The longer the interval, the lower the response rate
Scallop effect does not occur on VI schedules
Encourages S-R habit learning
Some Other Schedules
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


DRL, Differential reinforcement for low rates of
responding
DRH, Differential reinforcement for high rates of
responding
DR0, Different reinforcement of anything but the
target behavior
Compound Schedules
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
Compound schedule

A complex contingency where two or more schedules of
reinforcement are combined
Schedule this….
32

Concurrent schedules permit the subject to alternate
between different schedules; or to repeatedly
choose between working on different schedules
A
B
$5VI-30
today
$50
VI-60
wait
Matching Law
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
B1/(B1+B2) = R1/(R1+R2)
B
stands for numbers of a certain behavior
 R stands for numbers of a reinforcers earned
Sniffy the Rat
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Schedule
Behavior B1/(B1+B2)
R1/(R1+R2)
VI-30 vs VI-10
25%
25%
VI-10 vs VI-30
75%
75%
VI-10 vs VI-50
83.3%
83.3%
VI-50 vs VI-10
16.7%
16.7%
VI-30 vs VI-30
50%
50%
VI-10 vs VI-10
50%
50%
“1” vs “2”
Typical Result
35
Deviations From Matching
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
Bias represents a preference for responding on one
response more than the other that has nothing to do
with the schedules programmed
 one
pigeon key requires more force to close its contact
than the other, so that the pigeon has to peck harder
 one food hopper delivers food more quickly than
another
Sensitivity
37


Overmatching -- the relative rate of responding is
more extreme than predicted by matching. The
subject appears to be “too sensitive" to the
schedule differences.
Undermatching -- the relative rate of responding
on a key is less extreme than predicted by matching.
The subject appears to by “insensitive" to the
schedule differences.
Overmatching
Poor Self-Control
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A
B
small
Direct Choice
(Concurrent Schedule)
LARGE
Self-Control and Overmatching
40

Concurrent Choice
 Human
and nonhumans often chose a immediate small
reward over a larger delayed reward (delayed
rewards are “discounted”)
Another Example of Impulsivity
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“Free” reinforcers given every 20s
Lever press advances delivery of the first
pellet, and deletes the second pellet
20s
40s
60s
So, if you press at 2 seconds, you get a pellet immediately,
but you get no other pellets until the 60 second pellet is
available.
Delay of Reinforcement
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
Delayed reinforcers are
steeply discounted
Loss of self-control and
impulsivity
100
90
Reinforcer Potency

80
70
small
immediate
60
50
large
delayed
40
30
20
10
0
-9
-6
Delay
-3
0
A
B
43
A
B
small
Concurrent Chain
(Pre-committment)
LARGE
Behavioral Methods for Self Control
44
 Pre-commitment
Self-Exclusion
Contracts
 Distraction
 Modeling
 Shaping
Waiting
Reduce delay for small
Increase delay for
large
The Discontinuance of Reinforcement
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
Extinction


The elimination or suppression of a response caused by
the discontinuation of reinforcement or the removal of
the unconditioned stimulus
When reinforcement is first discontinued, the rate of
responding remains high

Under some conditions, it even increases
Extinction Paradox
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

Stronger Learning ≠ Slower Extinction
Partial Reinforcement Extinction Effect or PREE
Importance of Consistency of Reward
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

Extinction is slower following partial rather than
continuous reinforcement
Partial reinforcement extinction effect (PREE): the
greater resistance to extinction of an instrumental or
operant response following intermittent rather than
continuous reinforcement during acquisition

One of the most reliable phenomena in psychology
Acquisition with Differing Percentages
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100%
Speed
80/50/30%
Day
Extinction with Differing Percentages
Speed
49
80%
100%
Day
50%
30%
Explanations
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


Mowrer-Bitterman Discrimination Hypothesis
Amsel’s Frustration Theory (Emotional)
Capaldi’s Sequential Theory (Cognitive)
Theios Experiment (not just
discrimination)
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PHASE 1
G1
PHASE 2
EXT
100%
0%
G2
100%
100%
0%
G3
50%
100%
0%
G4
50%
-
0%
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PHASE 1
Speed
G1
G1, G2
100%
PHASE 2
EXT
100%
0%
G2
100%
100%
0%
G3
50%
100%
0%
G4
50%
-
0%
G3, G4
50%
Extinction Trials
Amsel’s Frustration Theory
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Amsel’s Frustration Theory
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100% Reinforcement
Group
Amsel’s Frustration Theory
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50% Reinforcement Group
Amsel (Percentage Reinforcement)
Speed
56
100%
Extinction Trials
50%
Amsel’s Frustration Theory
57
EXT
GROUP 1
T F 100%
T-
BETWEEN
SUBJECT
PREE
GROUP 2
WITHIN
SUBJECT
TRIALS
1,3,6….
TRIALS
2,4,5….
N F
50%
TF
100%
N-
T-
Reversed
PREE
NF
50%
N-
Influence of Reward Magnitude
58


The influence of reward magnitude on resistance is
dependent upon the amount of acquisition training.
With extended acquisition, a small consistent
reward may produce more resistance to extinction
than a large reward (absence more frustrating).
Reward Magnitude and Percentage
59
Sequential Theory
60

Sequential theory
 If
reward follows nonreward, the animal will associate
the memory of the nonrewarded experience with the
operant or instrumental response
 During extinction, the only memory present after the
first nonrewarded experience is that of the
nonrewarded experience
61


Animals receiving continuous reward do not
experience nonrewarded responses and so they do
not associate nonrewarded responses with later
reward
Thus, the memory of receiving a reward after
persistence in the face of nonreward becomes a cue
for continued responding
 # of N-R transitions
 N length
 Variability of N-length
62

What is the significance of PRE?

It encourages organisms to persist even though every
behavior is not reinforced
 In
the natural environment, not every attempt to attain a
desired goal is successful
 PRE is adaptive because it motivates animals not to give up
too easily