Two experiments were designed to study with rats the effects of a preshock stimulus (Experiment I) and a prefood stimulus (Experiment II) on lever pressing maintained by a multiple fixed-ratio 100 fixed-interval 90 s schedule of food reinforcement. The purpose was to determine if the effects of these stimuli, identified as Pavlovian Css, were related to where within each component\u27s schedule they occurred; early in a ratio interval, or late in a ratio or interval.
Experiment I indicated that when the CS was presented early in a ratio or interval, or late in an interval, nearly equivalent suppression occurred for contingent and noncontingent control subjects. When the CS was presented late in a ratio, suppression was greatest for the contingent subjects. One subject, who received the CS-US pair on-the-baseline, showed suppression during the CS, and depressed responding in the absence of the CS, at both points within each component schedule. These effects were accompanied by post-CS suppression and by a sharp increase in FR PRPs and work times.
Experiment II showed a generally small effect of the CS on responding at both points within each component schedule; this was seen for contingent and noncontingent control subjects alike. In contrast, on-the-baseline training produced an increase in initial FR and FI responding during, and in the absence of, the CS that was accompanied by a decrease in FR and FI PRPs. In contrast, responding late in a ratio or interval was minimally affected.
The present Experiment I provides the basis for rejecting earlier accounts of negative conditioned suppression of FR and FI maintained responding. In addition, Experiment I yielded new evidence regarding a) off- vs on-the-baseline conditioning procedures, and c) residual baseline effects.
The present Experiment II provides evidence relevant to positive conditioned suppression of FR and FI maintained responding. In addition to yielding new information regarding this phenomenon, these data, together with a portion of those from Experiment I, question the traditional assumption that conditioned suppression (or acceleration) results from the contingent relation between a CS and a US
