Ohman, A., Ericksson, G. and Lofberg, I. (1975a) Phobias and preparedness: phobic versus neutral pictures as conditioned stimuli for human autonomic responses. Journal of Abnormal Psychology, 84, 41-5.

Two sets of Ss (64 in all) exposure of pictures of 'phobic' (snakes) or neutral (faces or houses) stimuli as CS signal for shock US.

Galvanic Skin Response (GSR) measured on the left hand, shocks given to the right hand (50ms at level “definitely uncomfortable but not painful” at the end of the 8 sec CS)
- 8 sec CS 1-4 secs= 'CS', 4-8 secs = 'pre-UCS', 8-12 secs = 'post-UCS'

in 10 conditioning trials groups were equal in conditioned GSRs, but in extinction phobic but not neutral stimuli retained CS and 'post UCS' responses.

Instructions that no more shocks would be given AND disconnecting the right hand electrodes, did not change CS anticipatory response, put post-UCS responses dropped.. Both instructed and non-instructed groups with neutral stimuli extinguished rapidly.

For phobic stimuli, the Post UCS responding was reduced in the instructed group, but anticipatory responses at the beginning of the 8-sec phobic CS did not diminish over time for the instructed group but remained higher than for control stimuli.

The non-instructed group went down over the 30 extinction trials (5 blocks of 6) to a similar level to that of the instructed group at the beginning of extinction.

Both the instructed and non-instructed groups with phobic stimuli showed lasting conditioning effects, but the groups with neutral stimuli extinguished rapidly