Transcript Document

Psychology 2250
Last Class
Characteristics of Habituation and Sensitization
-time course
-stimulus-specificity
-effects of strong extraneous stimuli (dishabituation)
Habituation and Sensitization in Aplysia
Opponent Process Theory
Pavlovian Conditioning
Excitatory Conditioning
Some Examples of Excitatory
Classical Conditioning
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Fear Conditioning
Eyeblink conditioning
Sign Tracking (Autoshaping)
Taste Aversion Learning
Fear Conditioning
Little Albert
With rats, the aversive stimulus (US) is typically a brief
shock delivered to the feet through a metal grid floor
The CS may be a light or tone
Tone
Shock
The CR in this case is typically freezing
Fear Conditioning
Although the typical response of rats is to become
motionless, we don’t always measure freezing directly.
We often measure conditioned fear by observing how
the CS disrupts the animal’s ongoing behavior
A popular technique is the Conditioned Emotional
Response (CER) procedure
Also called Conditioned Suppression
Conditioned Emotional Response (CER)
First train rats to barpress for food until they reach stable
baseline of responding
Then give Pavlovian pairings of T
shock
The shock will normally stop the rats from making the
BP response
After a few T shock pairings, look at suppression
of BP when the T comes on.
Our measure of conditioning to the T is a suppression ratio
suppression ratio = B/A+B;
A = # BP before tone comes on (pre-CS)
B = # BP during tone
A+B = total BP
If Tone is 5 sec, then measure BP for 5 sec before tone
comes on and for 5 sec while the tone is presented.
If the T CS is not effective, then the rat will make as many
barpresses during the tone as during the pre-CS interval
before the tone comes on.
For ex., B/A+B = 20/20+20 = 20/40 = 0.5
suppression ratio = 0.5 (indicates no conditioning)
Rat is equally likely to make response in the presence or
absence of the CS.
If the CS is effective, the suppression ratio will be
closer to 0.
For ex., B/A+B = 10/ 30+10 = 10/40 = .25
(i.e., 10 responses during the T, but 30 pre-CS responses)
A value closer to 0 means more suppression
(i.e., better/stronger CS)
Eyeblink Conditioning
The procedure for classical conditioning of the eye-blink response.
Sign Tracking or Autoshaping
Much of the work on autoshaping has been done
using pigeons as subjects
Keylight
food
Keylight = light comes on behind a translucent disk
called a key
After a few pairings of this keylight with food, the
pigeons peck at the disk
Food is given whether the pigeons peck at the key or not
Sign Tracking or Autoshaping
Taste-Aversion Learning
Subjects consume a novel-flavored food or drink.
Then subjects are given a treatment (e.g., drug, radiation,
motion) which makes them sick.
Then when the flavor is presented again, animals don’t
consume as much as on the original trial
We can’t measure sickness directly (as with salivation) but
we infer the association has taken place when the animal
stops drinking.
Taste-Aversion Learning
CS = taste
US = drug, radiation
Saccharin
LiCl
Special features of conditioned taste aversions (CTA)
-one trial learning
-long-delay learning
Excitatory Pavlovian Conditioning Procedures
The course of classical conditioning is determined by the
timing of the CS and the US
Each presentation of the CS and US represents a single
Conditioning trial
The time from the end of one conditioning trial to the start
of the next trial is called the intertrial interval or ITI
The time from the start of the CS to the start of the US is
the interstimulus interval or ISI or CS-US interval
ISI < ITI
Excitatory Pavlovian Conditioning Procedures
Time
On
Short-delayed
conditioning
Trace
conditioning
Long-delayed
conditioning
CS
US
CS
US
CS
US
Off
CS
Simultaneous
conditioning
Backward
conditioning
US
CS
US
Effects of the CS-US interval
on the strength of the CR
CS-US Interval
Measuring Conditioned Responses
To compare the effectiveness of different conditioning
procedures, we use a test trial – present the CS without
the US
Behavior during the CS can be quantified in several ways:
magnitude
probability
latency
Control Procedures
To determine whether changes in behavior are due to
Conditioning procedures, must have a comparison group
(Control Group)
Pseudoconditioning – increased responding not due to a
CS-US association (i.e., presentations of the US alone)
Random Control procedure – present CS and US at
random during the experiment
Explicitly unpaired control – CS and US are presented far
apart to prevent their association
Basic Stages in a Conditioning Experiment
Acquisition
The time during which the subject acquires the association,
as evidenced by the development of the CR
i.e., autoshaping in pigeons— see increase in # pecks at the
keylight)
Extinction
Occurs when a CS is given without a US.
The CR strength declines during extinction trials.
(covered in Ch. 9)
Phases of classical conditioning: Classical conditioning proceeds through
several phases, depending on the time of presentation of the two stimuli.
If the conditioned stimulus regularly precedes the unconditioned stimulus,
acquisition occurs. If the conditioned stimulus is presented by itself, extinction
occurs. A pause after extinction yields a brief spontaneous recovery.
Extinction does not abolish the CS-US association
Spontaneous recovery
Give a rest period after the extinction phase and the CR
will recover
A likely explanation is renewed attention
acquisition— increases attention to the CS
extinction— decreases attention to the CS
S.R. — renewed attention to the CS
Disinhibition
If you present a novel stimulus along with the CS during
extinction, see recovery of the CR.
For ex., pair L
shock in rats,
see freezing in anticipation of shock.
Freezing decreases during extinction
(animals start to move around again).
Present T with the L during extinction and the freezing
reappears.
Similar to dishabituation
CR renewal
If extinction occurs in a different environment than
acquisition, putting the animal back in the original
environment evokes the CR again.
For ex., Room A: T
food pairings
(acquisition— dog salivates to T)
Room B: T
no food
(extinction— dog stops salivating to T)
Put dog back in Room A again
Dog will now salivate to T again.
Reinstatement
Exposure to the US alone can reinstate conditioned
responding
T
shock pairings; see CR to T
Give T alone; CR decreases
Give shock alone
Present T and see CR
These 4 procedures
.
show that extinction does not
abolish the CS-US association
The CR is merely inhibited
Inhibitory Pavlovian Conditioning
Stimuli can become conditioned to signal the absence
of a US in addition to signaling the presence of a US—
such learning is called Inhibitory Conditioning
CS+ = excitatory CS = CS
CS- = inhibitory CS = CS
US
no US
Conditioned inhibition teaches an animal to inhibit,
or hold back, a CR.
An important prerequisite for conditioning a stimulus to
signal the absence of some US is that the US be periodically
presented in that context or situation
For ex., put rat in a box
T
- (i.e., no US)
This means nothing to the rat
But if the rat is normally given food in that box,
then T could become a conditioned inhibitor.
Inhibitory Conditioning only occurs if there is an
excitatory context
For the absence of a US to be a significant event,
the US must periodically occur in this situation
Procedures for Inhibitory Conditioning
Conditional (standard)
CS+ (CS
US)
CS+/CS- (CS/CS
no US)
— the CS- gradually becomes a signal for the
absence of the US
— only get the US when the CS+ occurs. When the
CS+ occurs in combination with the CS-, no US is
given
What is the excitatory context in this example?
Explicitly unpaired/Negative contingency
Explicit CS+ training is not necessary for inhibitory
conditioning
Negative CS-US contingency (correlation)
p(US/CS-) < p(US/no CS)
If a US is presented in the experimental chamber
but it is not signaled by explicit cues (i.e., no CS+), get some
conditioning to the experimental chamber cues
Box; normally get food US
T- ; T becomes a CI
p(food/T)< p(food/no T)