Associative learning and latent inhibition in a conditioned suppression paradigm in humans

A paradigm based on conditioned suppression of ongoing motor activity, sens itive to latent inhibition (LI), was developed and tested in healthy volunt eers. Subjects were trained to move disks from one peg to another with a hi gh degree of regularity in the Tower of Toronto puzzle, a well-known cognit ive skill learning task. Once this was achieved, they were submitted to a P avlovian conditioning procedure. The conditioned stimulus (CS) was a pure t one and the unconditioned stimulus (US) a loud white noise. The resulting r esponse suppression was assessed by a transient increase in latency of the hand movements. In control subjects, there was non-contingent CS and US pre sentation. The results evidenced conditioning after a single CS-US pairing. Following five preexposures to the to-be-conditioned CS, however, conditio ning was abolished, seemingly expressing LI. Because a weak unconditioned r esponse to the tone was observed after its first two presentations, an addi tional experiment was performed with two preexposures to the to-be-conditio ned CS. With such procedure, conditioning was obtained, supporting the exis tence of LI in the preceding experiment. These results indicate that the pr esent paradigm may be useful for the study of LI in human subjects, having the advantage of being similar to the experimental conditions used in the m ajority of LI studies in experimental animals. (C) 2000 Elsevier Science B. V. All rights reserved.