Sensory Preconditioning

Sensory preconditioning is a phenomenon in classical conditioning in which two neutral stimuli are first paired together with each other, before either one has been paired with an unconditioned stimulus, and this initial pairing is later found to allow both stimuli to elicit a conditioned response even though only one of them was ever directly paired with the unconditioned stimulus. The psychologist W. J. Brogden identified and first documented the phenomenon in 1939 in research conducted at Johns Hopkins University, published in the Journal of Experimental Psychology. In the standard procedure, two neutral stimuli, such as a light and a tone, are repeatedly presented together during an initial stage in which neither produces any particular response; in a second stage, one of the two stimuli is then paired with an unconditioned stimulus, such as a taste that produces salivation, and comes to elicit the conditioned response on its own. The other stimulus, which was never itself paired with the unconditioned stimulus, is then also found to elicit the same conditioned response when tested separately, a result understood to occur through an associative chain linking the two originally neutral stimuli together, rather than through any direct stimulus-response learning, since no response existed to be learned during the first stage when both stimuli were still neutral.