Blocking of Pavlovian conditioning in humans

Despite the many demonstrations of blocking in animals, there is still little evidence of blocking with human subjects, which is problematic for general teaming and behavior theory. The purpose of this research was to examine blocking with human subjects using a design and behavioral procedure (conditioned suppression) similar to those commonly used in animal research. First, subjects learned an operant task. Later, they were instructed to suppress responding when a visual US was presented. Two Pavlovlian acquisition phases and a test phase occurred while the subjects were performing the operant task. In the first Pavlovian phase, CS A predicted the US for the experimental group, but was uncorrelated with the US for the control group. In the second Pavlovian phase, a compound CS AX predicted the US for both groups. At test, CS X was presented to all subjects and suppression ratios were assessed. Experimental subjects suppressed responding in the presence of CS X less than did control subjects, thereby demonstrating a blocking effect. This research, in demonstrating blocking in humans, adds to the known similarities in animal and human behavior. (C) 1997 Academic Press.