Electrodermal conditioning to potentially phobic stimuli: Effects of instructed extinction

It was hypothesized that electrodermal responses to potentially phobic stimuli “conditioned” through verbal threats about an aversive UCS should be equally resistant to instructed extinction as the responses obtained by actual CS-UCS pairings. Two groups of human subjects were exposed to pictures of either snakes and spiders (phobic CSs), or circles and triangles (neutral CSs) in a differential Pavlovian conditioning paradigm. Changes in skin conductance were recorded. Half of the subjects in each group were threatened with a shock-UCS while the other half were given shock-reinforced CS presentations. At the onset of extinction, all subjects in each of the four groups were informed that no more UCSs were to be delivered, and the shock electrodes were removed. All groups showed evidence of conditioning during acquisition. During extinction there was an immediate drop in responding in the two neutral groups, whereas the two phobic groups showed reliable evidence of resistance to extinction, with no differences between the threatened- and the CS-UCS-group. The observed resistance to extinction found in the phobic groups implies a similarity to the irrationality of real-life phobias. Furthermore, the data are in accordance with analysis of electrodermal fear-conditioning as a case of prepared learning.