Problems For Studies Of Human Eyeblink Classical Conditioning

In all forms of classical conditioning, the responses are considered primarily reflexive in nature. For example, the UR is an innate, automatic, "reflexive" reaction to the puff of air that is delivered to the eye. With repeated pairing of a CS and a US a learned, conditioned response develops. This response is also thought to be reflexive and, as such, should not require cognitive involvement. Nevertheless, although an eyeblink response can be involuntary, clearly the eyeblink response can also be brought under voluntary control. If individuals become aware of the fact that the CS predicts the US, they are in a position to voluntarily blink their eyes to avoid the airpuff (i.e., blink on purpose). This circumstance has caused concern among experimentalists because it has been argued, at least since the 1940s, that the processes and characteristics of responses that are voluntary are very different from those that are involuntary or reflexive. That is, classical conditioning measures involuntary, automatic responses, not purposeful behavior. Therefore, some means of identifying voluntary responses needed to be developed so that they could either be discarded as contaminants or analyzed separately.

Two criteria emerged for identifying voluntary responses. The first was based on the slope of the response. Voluntary responses were believed to be more rapid and thus to have a characteristically steeper slope than a true CR. The second was based on response latency. Voluntary responses were believed to have a short onset latency (which also involved a steep slope), and eye closure was maintained until the onset of the US. Despite these improvements, there is no consensus about the most appropriate methods for detecting voluntary responses. In fact, the only large-scale study to test the validity of these two criteria (slope and latency) found that neither was fully satisfactory for discriminating voluntary responses from conditioned responses.

By the 1960s, studies of human eyeblink classical conditioning began to wane. This gradual decrease in human eyeblink classical conditioning research was likely due to a combination of at least two factors. First, researchers were never completely successful in identifying and dealing with the issue of voluntary vs conditioned responding. Second, researchers never reached a consensus on what the "standard" conditions should be for conditioning studies. Various laboratories used different CS and US intensities, different ISIs and ITIs, and different criterion for determining if responses were CRs. Consequently, there were persistent problems with obtaining reproducible results between different laboratories, which essentially prevented progress in exploring interesting variables.

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