Inhibitory Pavlovian Conditioning

Stimuli can become conditioned to signal the absence of a US— such learning is called Inhibitory Conditioning

CS+ = excitatory CS = CS USCS- = inhibitory CS = CS no US

Inhibitory Conditioning only occurs if there is an excitatory context

Procedures for Inhibitory Conditioning

• On some trials:

CS+ US

On other trials:

CS+/CS- no US

• Whether the CS+ is followed by the US is conditional on the presence of the CS-.

Conditional (standard)

Explicitly unpaired/Negative contingency p(US/CS-) < p(US/no CS)

• On some trials:

US alone

On other trials:

CS- alone

• The CS- occurs on different trials than the US, which is not signalled by a specific CS+.

Differential procedure

• On some trials:

CS+ US

On other trials:

CS- no US

• The CS- occurs on different trials than the CS+ and US.

• The background cues provide the excitatory context

Backward conditioning

US CS

If the US comes on before the CS, then the CS actually signals the absence of the US (because the US has already happened).

Trace or Long-Delay conditioning

CS US

The CS comes on but there is a long interval before the US is delivered. The CS essentially signals a period whenthe US is absent

Measuring Conditioned Inhibition

Once an animal learns that a stimulus signals the absence of the US, what does it do with this information?

What is the behavior?

With excitatory conditioning, the CS comes to elicit certain behaviors (i.e., salivation, eyeblink, keypecking)

The identification of a conditioned inhibitory response canbe more difficult

• Directed Behavior Test

• Summation Test

• Retardation of Acquisition Test

Measuring Conditioned Inhibition

Directed Behavior Test

• Sometimes inhibition can be measured directly by just presenting the CS-

• but only if conditioned behavior varies above and below a baseline level (e.g., heart rate, blood pressure, temperature).

• If CS+/US resulted in increase in behavior, inhibition would be evident if the behavior decreased on presentation of CS-.

• Subjects can also approach a CS+ and avoid a CS-

If the CR is not bidirectional,

Summation (or Compound Stimulus) Test

present the CS- in combination with a newCS+ that signals the US

conditioned inhibition is indicated if the CR to CS+ is less when CS- is present than when CS+ is presented alone.

Summation Test (Cole, Barnet, & Miller, 1997)

Training: On some trials: Light ShockOn other trials: Light + Noise No ShockOn yet other trials: Clicker Shock

The time it took the rats to complete 5 seconds of drinking was measured in the presence of:

Test:

►the light (conditioned excitor)

►the clicker (conditioned excitor)

►the light + noise (conditioned inhibitor)

►the clicker + noise (conditioned inhibitor)

Clicker Clicker & Noise

Clicker & Buzzer

Results:

Light & Noise

Light

Text p.85

Light = conditioned excitorClicker = conditioned excitor

Noise = conditioned inhibitor

The important test was Clicker alone vs Clicker + Noise

The rats feared the clicker alone (the rats took longer to drink), but the presence of the noise (which had signalled no shock when paired with the light and had never been paired with the clicker) reduced the fear elicited by the clicker.

The excitatory effect of the clicker (expect shock; fear) and the inhibitory effect of the noise (do not expect shock; reduced fear) summate, and produce a reduced conditioned fear response.

Retardation-of-Acquisition Test

If the CS- is a conditioned inhibitor for a particular US, it should:

Be harder than a neutral stimulus to turn into a conditioned excitor (i.e., a CS+)

That is, learning that the stimulus now predicts the US should be retarded relative to controls that did not have the CS previously conditioned as an inhibitor.

Example of Retardation of Acquisition Test

On a test:

All groups get

Conditioned Inhibition Group

On some trials: Light Shock

On other trials: Light + Noise No Shock

Control Group

Light

Noise Shock

Shock

Conditioned Inhibition Group should take longer to acquire a CR than the Control Group.

Compare strength of conditioning for conditioned inhibition and control groups

CIGroup

ControlGroup

MeanTime

Noise was previouslytrained as a CI in theCI group

Noise previouslyreceived no training inthe Control group

Lick Suppression Test

Comparison of CE and CI

Excitation is quicker and easier to get than inhibitory conditioning

-US is a more salient event than no-US

Extinction is different with CS+ versus CS--can’t simply give CS by itself

What can reduce/extinguish a CI?

-presentation of the US

-even if given randomly; not necessary to have CS-US pairings

-change from a negative contingency to a ‘0’ contingency (i.e., no predictive relationship)