Effects of carbon monoxide on fixed-consecutive-number performance in rats.

Four rats were trained under a fixed-consecutive-number (FCN) schedule to make sequences of 20 or more consecutive responses on one lever followed by a single response on a second lever. When performance was stable, they were exposed to 200, 400, and 600 parts-per-million (PPM) carbon monoxide (CO) for either 30 or 60 min before and during a 45-min session. Decreases in response rate at CO levels as low as 200 ppm were due to both decreased local response rate and extended pauses. A lowered percentage of reinforcement, due to decreases in response sequence length, was also found at CO levels as low as 200 ppm. This decreased sequence length may reflect effects of CO on response rate, or a disruption of discriminative aspects of FCN schedule performance.

Conditioned suppression under positive, negative, and no contingency between conditioned and unconditioned stimuli.

Using a conditioned suppression procedure, the effects of three contingent relationships between conditioned (CS) and unconditioned (US) stimuli were investigated. A traditional positive (if CS-then US) contingency suppressed response rate during the CS relative to responding during stimulus-free minutes of the session. A negative (if CS-then no US) contingency resulted in suppressed responding during CS-off minutes, and rate increases during the CS. A no-contingency control procedure, during which CS and US were randomly related, almost totally suppressed responding throughout the session and showed no differential effects of the CS on response rate. An analysis of changes in response rate during the minute after US-offset revealed acceleration under the no-contingency condition and, to a somewhat lesser degree, under the negative contingency. Both conditioned suppression and non-suppression are analyzed in terms of the temporal relationship between CS and US.