Classical Conditioning

Classical Conditioning in Humans

Emotions such as fear can be readily classically conditioned in both humans and lower animals. A common classical conditioning procedure with humans involves pairing a neutral CS such as a mild tone with an aversive UCS (e.g., moderately [Page 276]intense electric shock). The CR is usually measured by changes in autonomic responses such as heart rate and skin conductance following the CS. A conditioned emotional response can be established sometimes with only one pairing of the CS with the UCS. If the CS is subsequently presented a number of times without the UCS, the CR will gradually decline and completely vanish, a phenomenon known as extinction. However, in the absence of any extinction procedure, a CR may remain over time, even if the person realizes that the response no longer seems rational.

In order to ensure that the autonomic changes are truly conditioned to the CS, rather than general sensitization to all stimuli, it is common to randomly intermix presentation of two different CSs. Of the two CSs, only one, the CS+, is paired with the UCS, whereas the control CS, the CS−, is explicitly not paired with the UCS. Alternatively, the control CS can be randomly associated with the UCS in a separate control group. Evidence of successful conditioning is indicated by greater responding to the CS+ than the control CS.

Many individual differences in aversive conditioning have been reported, some of which are associated with the forms of psychopathology (mental illness). For example, a number of studies have found that psychopaths show impaired classical conditioning with aversive UCSs. This is particularly true for psychopaths with callousness and emotional detachment rather than simply antisocial behavior. Yu Gao and colleagues found that poor autonomic fear conditioning at age 3 was associated with criminal behavior at age 23. All in all, these results are consistent with the hypothesis that low fear of socializing punishments is associated with psychopathy. Classical conditioning is also thought to be the basis of many phobias, in which some originally neutral object (a dog, for instance, the CS) is paired with intense fear and pain (being bitten, the UCS), leading to fear of dogs (the CR). Ease of acquiring conditioned fear responses also may be related to anxiety disorders.

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