Editing Classical conditioning (section)

==Phenomena observed==

===Acquisition===
During acquisition, the CS and US are paired as described above. The extent of conditioning may be tracked by test trials. In these test trials, the CS is presented alone and the CR is measured. A single CS-US pairing may suffice to yield a CR on a test, but usually a number of pairings are necessary and there is a gradual increase in the conditioned response to the CS. This repeated number of trials increase the strength and/or frequency of the CR gradually. The speed of conditioning depends on a number of factors, such as the nature and strength of both the CS and the US, previous experience and the animal's [[motivation]]al state.<ref name="Shettleworth_2010"/><ref name="Bouton_2016"/> The process slows down as it nears completion.<ref name="Schacter_2009">{{cite book |last=Schacter |first=Daniel L|name-list-style=vanc |title=Psychology |year=2009 |publisher=Catherine Woods |isbn=978-1-4292-3719-2 |page=[https://archive.org/details/psychology0000scha/page/267 267] |url=https://archive.org/details/psychology0000scha/page/267}}</ref>

===Extinction===
If the CS is presented without the US, and this process is repeated often enough, the CS will eventually stop eliciting a CR. At this point the CR is said to be "extinguished."<ref name="Shettleworth_2010"/><ref>{{cite journal |vauthors=Chan CK, Harris JA |title=Extinction of Pavlovian conditioning: The influence of trial number and reinforcement history |journal=Behavioural Processes |volume=141 |issue=Pt 1 |pages=19–25 |date=August 2017 |pmid=28473250 |doi=10.1016/j.beproc.2017.04.017 |series=SQAB 2016: Persistence and Relapse |s2cid=3483001 |url=http://psyarxiv.com/5v4wt/ |access-date=2021-05-25 |archive-date=2021-06-27 |archive-url=https://web.archive.org/web/20210627125622/https://psyarxiv.com/5v4wt/ |url-status=live }}</ref>

[[File:Classical conditioning - extinction.svg]]

===External inhibition===
[[External inhibition]] may be observed if a strong or unfamiliar stimulus is presented just before, or at the same time as, the CS. This causes a reduction in the conditioned response to the CS.

===Recovery from extinction===
Several procedures lead to the recovery of a CR that had been first conditioned and then extinguished. This illustrates that the extinction procedure does not eliminate the effect of conditioning.<ref name="Bouton_2016"/> These procedures are the following:
* Reacquisition: If the CS is again paired with the US, a CR is again acquired, but this second acquisition usually happens much faster than the first one.
* [[Spontaneous recovery]]: Spontaneous recovery is defined as the reappearance of a previously extinguished conditioned response after a rest period. That is, if the CS is tested at a later time (for example an hour or a day) after extinction it will again elicit a CR. This renewed CR is usually much weaker than the CR observed prior to extinction.
* [[Disinhibition#Associative learning concept|Disinhibition]]: If the CS is tested just after extinction and an intense but associatively neutral stimulus has occurred, there may be a temporary recovery of the conditioned response to the CS.
* Reinstatement: If the US used in conditioning is presented to a subject in the same place where conditioning and extinction occurred, but without the CS being present, the CS often elicits a response when it is tested later.
* Renewal: Renewal is a reemergence of a conditioned response following extinction when an animal is returned to the environment (or similar environment) in which the conditioned response was acquired.

===Stimulus generalization===
''Stimulus generalization'' is said to occur if, after a particular CS has come to elicit a CR, a similar test stimulus is found to elicit the same CR. Usually the more similar the test stimulus is to the CS the stronger the CR will be to the test stimulus.<ref name="Shettleworth_2010"/> Conversely, the more the test stimulus differs from the CS, the weaker the CR will be, or the more it will differ from that previously observed.

===Stimulus discrimination===
One observes ''stimulus discrimination'' when one stimulus ("CS1") elicits one CR and another stimulus ("CS2") elicits either another CR or no CR at all. This can be brought about by, for example, pairing CS1 with an effective US and presenting CS2 with no US.<ref name="Shettleworth_2010"/>

===Latent inhibition===
{{main|Latent inhibition}}
Latent inhibition refers to the observation that it takes longer for a familiar stimulus to become a CS than it does for a novel stimulus to become a CS, when the stimulus is paired with an effective US.<ref name="Shettleworth_2010"/>

===Conditioned suppression===
This is one of the most common ways to measure the strength of learning in classical conditioning. A typical example of this procedure is as follows: a rat first learns to press a lever through [[operant conditioning]]. Then, in a series of trials, the rat is exposed to a CS, a light or a noise, followed by the US, a mild electric shock. An association between the CS and US develops, and the rat slows or stops its lever pressing when the CS comes on. The rate of pressing during the CS measures the strength of classical conditioning; that is, the slower the rat presses, the stronger the association of the CS and the US. (Slow pressing indicates a "fear" conditioned response, and it is an example of a conditioned emotional response; see section below.)

===Conditioned inhibition===
Typically, three phases of conditioning are used.

====Phase 1====
A CS (CS+) is paired with a US until [[Asymptote|asymptotic]] CR levels are reached.

====Phase 2====
CS+/US trials are continued, but these are interspersed with trials on which the CS+ is paired with a second CS, (the CS-) but not with the US (i.e. CS+/CS- trials). Typically, organisms show CRs on CS+/US trials, but stop responding on CS+/CS− trials.

====Phase 3====
* ''Summation test for conditioned inhibition:'' The CS- from phase 2 is presented together with a new CS+ that was conditioned as in phase 1. Conditioned inhibition is found if the response is less to the CS+/CS- pair than it is to the CS+ alone.
* ''Retardation test for conditioned inhibition:'' The CS- from phase 2 is paired with the US. If conditioned inhibition has occurred, the rate of acquisition to the previous CS− should be less than the rate of acquisition that would be found without the phase 2 treatment.

===Blocking===
{{main|Blocking effect}}
This form of classical conditioning involves two phases.

====Phase 1====
A CS (CS1) is paired with a US.

====Phase 2====
A compound CS (CS1+CS2) is paired with a US.

====Test====
A separate test for each CS (CS1 and CS2) is performed. The blocking effect is observed in a lack of conditional response to CS2, suggesting that the first phase of training blocked the acquisition of the second CS.
[[File:Classical conditioning - blocking.svg]]