Sensory preconditioning

Sensory preconditioning pairing of two neutral stimuli prior to one of them being used as the conditioned stimulus in a standard classical conditioning procedure, leading to the other stimulus acquiring the power to evoke the conditioned response. If this account is correct, it should be possible to trigger classical conditioning using paired neutral stimuli that themselves evoke no dramatic responses. Evidence that this can occur comes from a phenomenon called sensory preconditioning, first demonstrated by Brogden (1939) and confirmed many times since. In Brogden’s experiment, the animals in the critical experimental condition received a first stage of training consisting of paired presentations of two neutral stimuli, a light and a buzzer. If our theory is correct, an association should be formed between the central representations of these stimuli. The problem is to find a way to reveal this association. Brogden’s solution was to give a second stage of training in which one of the original stimuli (say the light) was given orthodox conditioning, being paired with a US until it came to evoke a CR (in this procedure, a response of flexing the leg). A final test showed that the buzzer was also able to evoke the leg flexion response, even though the buzzer had never previously been paired with the US. This result is what might be expected on the basis of the stimulus–stimulus association theory. The light evokes the CR by virtue of its direct association with the US, whereas the buzzer is able to do so ‘by proxy’ because its association with the light allows it to activate the representation of that stimulus.