In five experiments using delay conditioning of magazine approach with rats, reinforcement rate was varied either by manipulating the mean interval between onset of the conditioned stimulus (CS) and unconditioned stimulus (US) or by manipulating the proportion of CS presentations that ended with the US (trial-based reinforcement rate). Both manipulations influenced the acquisition of responding. In each experiment, a specific comparison was made between two CSs that differed in their mean CS-US interval and in their trial-based reinforcement rate, such that the cumulative reinforcement rate-the cumulative duration of the CS between reinforcements-was the same for the two CSs. For example, a CS reinforced on 100% of trials with a mean CS-US interval of 60 s was compared with a CS reinforced on 33% of trials and a mean duration of 20 s. Across the five experiments, conditioning was virtually identical for the two CSs with matched cumulative reinforcement rate. This was true as long as the timing of the US was unpredictable, and thus response rates were uniform across the length of the CS. We conclude that the effects of CS-US interval and of trial-based reinforcement rate are reducible entirely to their common effect on cumulative reinforcement rate. We discuss the implications of this for rate-based, trial-based and real-time associative models of conditioning.

Schedule-induced drinking (SID) can occur when food-deprived rats are given access to water while receiving pellets on an intermittent reinforcement schedule. These conditions can increase water intake excessively. The possible role of adventitious reinforcement of postpellet drinking was assessed by testing whether response-reinforcer contiguity, the relative predictiveness of a response, and whether it is marked are important in the development of SID. Rats exposed to a short interpellet interval acquired SID most rapidly, with this acquired drinking response maintained when animals were transferred to a longer interpellet interval, thus indicating an easy-to-hard effect (Experiment 1). Further experiments demonstrated that a stimulus (a brief-flashing house light) occurring prior to pellet delivery could block the acquisition of SID (Experiment 2), while a lick-contingent tone, intended to increase the associability of this response, produced more rapid acquisition of SID (Experiment 3). Analysis of lick distributions revealed that licking became concentrated in the first half of an interpellet interval only after several sessions. Overall, the results indicated that similar factors affect the acquisition of both SID and instrumental conditioning with delayed reinforcement, as is consistent with a superstitious conditioning account of SID development.

In this article, schedule-induced drinking (SID) refers to increased drinking by hungry rats exposed to intermittent delivery of food pellets. Two major accounts of SID differ in their explanation of why such drinking tends be concentrated soon after pellet delivery. Temporal discrimination theories propose that drinking is a form of displacement activity that occurs when a pellet is least likely. Adventitious reinforcement theories propose that drinking is displaced to early in an interpellet interval (IPI) by magazine-directed behavior that occurs toward the end of an IPI. The main aim of this study was to examine the latter response-competition account by recording distributions of both licking and magazine entries as SID developed when pellets were delivered to different groups either on a fixed-time (FT 30 s) or on a variable-time schedule (VT 30 s), as in Experiment 1. Although VT 30-s schedules produced essentially flat distributions of magazine entries, licking still tended to be concentrated early in an IPI. Furthermore, there was no indication (Experiments 1 and 2) that magazine entry distributions developed ahead of licking distributions. Experiment 3 examined distributions of lever presses instead of licks: Initially high rates of lever pressing declined both with response-independent schedules (FT and VT) and when a minimal response-dependency was introduced (recycling conjunctive schedule), yet this response also tended to be most frequent soon after pellet delivery. Overall, the data were generally consistent with temporal conditioning theories.

Avoidance of a target flavor can be produced by providing rats with a highly nutritious solution of 20 % maltodextrin (20 %Malto) in some sessions and a 3 % maltodextrin (3 %Malto) solution containing the target flavor in intermixed sessions. Since 20 %Malto is both more nutritious and more palatable than 3 %Malto, flavor avoidance could arise because the flavor signals either a reduction in calories or reduced palatability, or both. Pilot testing established that rats strongly preferred 3 %Malto plus 0.1 % saccharin to both unflavored 3 %Malto and unflavored 20 %Malto. The two main experiments tested whether the palatability difference, which the pilot data had suggested was larger than the difference between 20 %Malto and 3 %Malto, could produce flavor avoidance. In both experiments, one group of rats were given 3 %Malto plus 0.1 % saccharin on some days, intermixed with other days on which this group was given 3 %Malto plus the target flavor, almond. Neither when trained and tested under conditions of food deprivation (Experiment 1) nor when trained and tested sated (Experiment 2) did palatability reduction produce almond avoidance. In contrast, calorie reduction produced almond avoidance under both conditions. These results suggest that flavor avoidance can be produced by intermixed training involving solutions that differ in nutritious value and palatability, but not when they differ only in palatability.Keywords Acquisition . Avoidance . Flavor . Palatability . Maltodextrin . Rats A dilute solution of the nonnutritious chemical saccharin is highly palatable to rats, as it is to humans. After rats have on several occasions drunk a saccharin solution to which has been added some relatively novel flavor, such as the almond used in the present experiments, they show increased preference for the flavor (e.g., Fanselow & Birk, 1982;Harris, Gorissen, Bailey, & Westbrook, 2000;Holman, 1975). Such results indicate that flavor preference learning can be based on flavor-flavor associations alone. Another method for producing an increase in preference for a flavor is to pair its ingestion with intragastric infusion of a nutrient, such as the hydrolyzed starch maltodextrin, also used in the present experiments (e.g., Sclafani, 1991;Sclafani & Nissenbaum, 1988;Yiin, Ackroff, & Sclafani, 2005). Since in these experiments the animals cannot taste the nutrient, flavor preference learning in this case must be based solely on associating the flavor with nutritional consequences-that is, on the acquisition of what are termed flavor-calorie or flavor-nutrient associations.The experiments reported here were prompted by the question of what is learned when rats develop avoidance of-rather than preference for-a flavor. Previously we had found that, when hungry rats had been given training that intermixed "good" and "bad" sessions, in subsequent twobottle choice tests they showed avoidance of the flavor that had been present on the bad sessions. The good sessions in those experiments were ones in which the rats were given...

Five experiments investigated how learning about the added feature in a feature-positive discrimination or feature-negative discrimination is related to the change in reinforcement rate that the feature signals. Rats were trained in a magazine-approach paradigm with 2 concurrent discriminations between A versus AX and B versus BY. In 2 experiments (1 and 3), X and Y signaled an increase of 0.3 in the probability of reinforcement, from 0.1 to 0.4 (A vs. AX), or from 0.6 to 0.9 (B vs. BY). After extended training, each session included probe test trials in which X and Y were presented alone (Experiment 1) or in compound with another excitatory conditional stimulus (CS), C (Experiment 3). There was no difference in response rate between the 2 types of test trial (X vs. Y; XC vs. YC), consistent with the fact that X and Y signaled the same absolute change in reinforcement. In Experiments 2 and 4, X and Y signaled a decrease of 0.3 in the probability of reinforcement, from 0.4 to 0.1 (A vs. AX) or from 0.9 to 0.6 (B vs. BY). Test trials in which X or Y was presented with C showed that X had greater inhibitory strength than Y, consistent with the fact that X signaled a larger relative change in reinforcement. This was confirmed in Experiment 5, in which X and Y had the same inhibitory strength on test after training in which they signaled the same relative change in reinforcement but different absolute changes (0.3 to 0.1 for A vs. AX; 0.9 to 0.3 for B vs. BY). The results show that excitatory conditioning is linearly related to the increase in reinforcement rate, whereas inhibitory learning is not linearly related to the decrease in reinforcement rate. Implications of this for theories of associative learning are discussed. (PsycINFO Database Record