Pigeons* key-peck rates under variable-ratio schedules are typically higher than under variable-interval schedules when between-schedule reinforcement rates are equated. Experiment 1 reproduced this between-schedule rate difference in a multiple variable-ratio, variable-interval schedule. However, when the short interresponse times typically reinforced under variable ratios were reqvured for variable-interval reinforcement, between-component rate differences diminished. Experiment 2 replicated Experiment 1 except that the long interresponse times reinforced under variable-interval schedules were,required for variable-ratio reinforcement. This . manipulation eliminated between-sehedule rate differences. In Experiment 3, one multiple-schedule component was at tandem variable-ratio, variable-interval schedule and the other was a tandem variable-interval, variable-ratio schedule. Unlike Experiments 1 and 2, each tandem had the same correlation between response rate and reinforcement rate. Therefore, only between-component differences in interresponse-time reinforcement could account for the higher rates maintained by the tandem terminating with the variable-ratio schedule. In a simulation, Shimp's (1969) interresponse-time response rule was used as an algorithm in a computer simulation to mimic the between-schedule rate difference. The results of the experiments and simulation show that interresponse-time reinforcement (a molecular factor), and not the feedback function between response rate and reinforcement rate (a molar factor), accounts for higher response rates under variable-ratio schedules and suggests that molecular accounts will prove more fruitful than molar accounts in explaining behavioral output. . Skinner (1938) proposed that response rate equivalent reinforcement rates, these schedules should serve as the dependent variable for differ in their reinforcing effectiveness. A secscaling the strength or vigor of schedule-main-ond interpretation remains possible: Responsetained behavior. The consistent interdepen-rate differences might reflect not differences dence he found between rates of responding in the strength of behavior that different and reinforcement spoke for the reasonable* schedules engender, but differences in the reness of this proposition. Nevertheless, the stat-inforcement contingencies characterizing difure'of this measure has been jeopardized in ferent schedules. recent years by the finding that different An exemplar of this problem can be seen schedules providing equal rates of reinforce-in a comparison of behavior maintained under ment produce consistently unequal response variable-interval (VI) and variable-ratio (VR) rates. According to Skinner, despite their schedules of reinforcement. These schedules differ in that the delivery of the reinforcerde-_1 ; '-r-pends on a response after elapsed time in the _,.. ,. . .. .. XT ,. ,-"-•"-VI and on number of responses in the VR.

No abstract

The experiments reported here were designed to determine the role of associative conditioning in reflex modification of the acoustic startle response, using gaps in background noise. The first experiment was done to characterize the efTectsof repeated testing for 9 days with 20-msec gaps in white noise as the preliminary stimulus (81) and a 120-dB, 40-msec 13-kHz tone as the eliciting stimulus (82). The second experiment was a test of associative conditioning. Three groups of rats were tested daily for 6 days under one of the following conditions: SI and 82 paired in a contingent manner, 82 only, or 81 only. All groups then received the contingent pairing of81 and 82 for an additional 9 days of testing. In the third experiment, aseparate group of rats was tested with either contingent or noncontingent presentation ofthe 81 and 82 for 6 days, and then, on the 7th day, both groups received the stimuli in a contingent fashion. Results indicate that the amount of inhibition increases with repeated, daily testing, and that it achieves asymptotic levels of inhibition after 5-6 daily sessions. The presentation of 81 and 82 together is a necessary, but not sufficient, condition for normal development of inhibition. Alternatively, the contingency that exists between the two stimuli is likely to be the determining factor necessary for development of the inhibition. These data imply that an associative learning process may be a rnajor factor in the gap-inhibition phenomenon.Reflex modification of the acoustic startle response (ASR) is the change in a stimulus-elicited response due to a perceptible antecedent change in the sensory environment (for a review, see Hoffman & Ison, 1980). A wide variety of sensory stimuli have been demonstrated to inhibit the ASR in the rat, including white noise and tone bursts (

Rats repeatedly acquired the performance of selecting only the four baited arms in an automated eight-arm radial maze, with the arms containing food pellets randomly assigned prior to each session. During each 14-trial (trial: obtain all four pellets) daily session, the number of errors (selecting nonbaited arms or repeating arm selections) showed a within-session decline, and choice accuracy for the first four arm selections showed a positive acceleration across trials for all rats. An index-ofcurvature statistic, calculated for total errors, was used to quantify both the within-and betweensession improvement of performance. Scopolamine (0.03 to 0.3 mg/kg, ip), but not methylscopolamine (0.3 mg/kg), reduced the accuracy of the first four selections of each trial and increased total withinsession errors for all rats. Session times also were increased by scopolamine. An examination of withinsession accuracy showed only slight signs of improvement at the higher dosages of scopolamine. The results indicate that behavior in transition states maintained by reinforcement contingencies in the radial maze is similar to that maintained by extended chained schedules, despite the fact that some of the stimuli controlling behavior in the maze are absent at the moment behavior is emitted.