UCS-inflation and acquired fear responses in human conditioning

Four experiments concerning UCS-inflation in humans were conducted employing a differential conditioning paradigm. In Experiment 1 (n = 30) one neutral slide (CS+) was paired with a mild electric shock (UCS) and another neutral slide (CS−) was never paired with a shock. An inflation phase followed, during which unsignalled UCSs gradually increased in strength for the inflation group, while they were kept constant for the control group. During the post-inflation trials, only the inflation group showed relatively large skin conductance responses (SCRs) on CS+ trials and prolonged differential UCS expectancies. Experiment 2 (n = 20) was similar to the first experiment, with the exception that (i) the UCS was inflated in only one trial, (ii) slides depicting angry faces were used as CSs and (iii) subjective evaluations of the CSs were measured in addition to the SCRs. Neither at the physiological nor at the subjective level, conditioning effects emerged in the inflation group. In Experiment 3 (n = 42) and 4 (n = 33), erotic slides were used as CSs and a mild tone served as UCS. During the inflation stage, only the inflation group was told that the tone indicated, in fact, “blushing”. Experiment 4 sought to increase the aversiveness of the “blush” manipulation by having two observers seated inside the experimental room. Though the “blush” manipulation appeared to successfully inflate the UCS, neither study revealed strong data confirming the idea that human conditioned responding is susceptible to UCS-inflation. Thus, UCS-inflation in humans is, at best, a fragile phenomenon.