What is stimulus

1
What is stimulus?

• Not simple.
• We seem to respond more than one stimulus.
• E.g., Tone
• Original CS (50 hz)
• After conditioning - 40, 45, 50, 55, 60
• Stimulus generalization

2
To restrict the range..

• Use stimulus discrimination training
• E.g., Tone
• CS 50hz
• CS- 60hz
• Animals will not respond to 60hz

3
What does it all mean?

• We dont form single association between a
  stimulus and a response.
• Conditioning is much more complex than that.

4
And, it gets worse...

• When you use more than one CS.
• Compound stimulus
• What would be the effect of presenting more than
  one CS?
• Would every CS equally become an effective
  signal?
• Yes and no.

5
Overshadowing Kamin (1969)

• Acquisition Phase
• CS (light) Loud Noise (80db) - UCS
• CS (light) Not-so-loud Noise (50db) - UCS
• Test
• Light
• Loud Noise (80db)
• Not-so-loud Noise (50db)

6
Which elicited response?

• Light - CR
• Loud Noise - much less
• Not-so-loud Noise - much much much less
• But, all these were paired with UCS.
• Why didnt they become equally effective?
• Kamin - Salient CS prevents others from forming
  association.

7
Blocking

• Phase I
• CS1 - UCS
• Phase II
• CS1 CS2 - UCS
• Phase III
• CS1 - CR
• CS2 - No CR

8
Configural cue

• We dont always form separate association with
  individual elements.
• We sometimes form association with the stimulus
  as a whole.
• AB - UCS and CD - UCS
• If we formed separate association with each
  element, then..

9

• AD - CR
• BC - CR
• But, if association is based on stimulus as a
  whole
• AD - no CR
• BC - no CR
• So, conditioning is more complicated than you
  might think.

10
What is response?

• Pavlov
• CR is the same as UCR
• Stimulus substitution - CS is substituting UCS
• That is not the case.

11
Siegel et al

• Used morphine as UCS.
• Acquisition
• CS - UCS (morphine) - UCR (analgesia)
• Test
• CS - ????
• Stimulus substitution - analgesia
• But, they found - hypoanalgesia

12
But, CR is not always the opposite of UCR.

• Siegel et al
• Acquisition
• CS - UCS (mega insulin) - UCR (convulsion)
• Test
• CS - CR (convulsion)

13
Why?

• Some activates opponent process
• Two phase responses
• Phase I - analgesia
• Phase II - increase sensitivity to compensate
• Sometimes CS forms association with Phase II
  response.
• Wagner - SOP sometime opponent process theory

14

• Basis of drug addiction.
• We become more and more resistant as CS activate
  more and more opponent responses.
• E.g.,
• CS (taste) - UCS (alcohol) - UCR (depressed nerve
  activities)
• CS (taste) - CR (increased nerve activities)
• Need to drink more and more to feel the alcohol

15
So

• We know stimulus is more complicated than it
  seems.
• We know response is more complicated than it
  seems.
• And, when a CS is paired with a UCS, the CS
  starts to elicit a response.
• But, why?
• Two theories

16
Pavlov

• It is based on the law of contiguity.
• An association is formed when two elements are
  presented together in a contiguous fashion.
  (Brown, 1882)
• Obviously CS-UCS pair satisfies this condition.

17
But,

• A contiguous presentation of CS and UCS does not
  always produce association.
• Rescorla
• CS - UCS
• CS - UCS UCS
• CS - UCS CS
• As CS and UCS are presented between trials, the
  situation becomes less predictable.

18
Found

• Conditioning is more effective when the situation
  is more predictable.
• Contiguity alone is not enough to produce
  association.
• Pavlov was wrong.

19
Wagner and Rescorla Contingency theory

• Two assumptions
• An association is formed to the extent that a CS
  signals the occurrence or non-occurrence of a UCS
  (contingency).
• An association is formed to the extent that the
  occurrence or non-occurrence of a UCS is
  surprising (surprisingness).

20
Math Formula

• ?V ? (? - V)
• ? Maximum associative strength a given UCS can
  support
• V Current strength
• ? Rate of learning
• ?V Change in associative strength after a trial.

21
How does it work?

• ? 100, ? .20
• Acquisition curve

22
When you stop presenting UCS

• ? 0, ? .20
• Extinction curve

23
Supportive evidence

• Blocking
• ? 100, ? .60
• Why does CS2 fail to form association?
• What would be the solution?

24
Evidence against

• latent inhibition
• Presentation of CS alone prior to experiment
  makes it more difficult to produce conditioning.
• Why?
• ? 0, ? .20

25
Application

• Prevention of craving.
• Difficult to quit using drug because anything
  that related activates craving response.

26
So,

• Use classical conditioning to break that
  association.
• E.g., Smoking
• CS (anything that is related to smoking)
• CR (craving anticipating nicotine)

27
Treatment

• Present CS but not UCS
• Go though the motion of smoking.
• Light up a cigarette (CS)
• But, dont smoke, discard it (no UCS)
• After many repetition, craving will be
  extinguished.

28
Other applications

• Counter conditioning for fear response.
• Lowering immune reaction after transplant.
• Etc.