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Miller, N.E. (1948) Studies of fear as an aquirable drive. Journal of Experimental Psychology, 38, 89-101.
25 rats were tested in a one-way shuttle box. One compartment was white, the other black, and there was a door between them.
1. Rats were first allowed to explore the box with the door open. Result: there was no preference for one compartment over the other.
2. There were then 10 conditioning trials in which they were placed in the white compartment and shocks were delivered which they could escape by running through the open door. Result: all animals ran to the black compartment.
3. Next there were 5 trials in which Ss were placed in the white compartment without shock with the door open. Result: all animals ran to the black compartment.
4. Now there were 16 trials in which Ss were left in the white compartment (with no further shocks). The door was closed but could be opened if a wheel above it was turned slightly. Result: 13 of the 25 rats opened the door by accident during the first few trials and from then on became quicker at opening the door by turning the wheel.
5. Finally there were 10 more trials in which the 13 animals which had learned to turn the wheel were put in the white compartment with the door closed. The wheel no longer opened the door, but pushing a bar projecting into the white compartment next to the door would open it. Result: 12/13 Ss stopped turning the wheel and learned to push the bar to open the door. (The other rat turned the wheel 530 rotations).
Rats learn to perform new instrumental responses in order to reduce fear.