Context modulation of US signal value.

Context modulation of unconditioned stimulus (US) signal value was examined in two experiments. In Experiment 1, rats showed significantly more magazine entries after a single food pellet US in Context A (in which three additional pellets shortly followed) than in Context B (in which the delivery of three additional pellets was delayed). Experiment 2 replicated this effect and showed that any differences in contextual associative strength at the time the single food pellet was delivered did not importantly contribute to context modulation. Implications for theories of occasion setting and context modulation are considered.