Learning about water by hungry rats

In Experiments 1 and 2 hungry rats were trained in a straight alley with consistent food reward (FF), food and nonreward trials intermixed (FN), or food and water trials intermixed (FW). In Experiment 1 rats were tested with nonrewarded trials (extinction) and Groups FN and FW did not differ, both running faster then Group FF. In Experiment 2 rats were tested with consistent water reward, and Group FW ran faster then Group FN, which was superior to Group FF. In Experiment 3, one group of hungry rats was trained on a single alternating schedule of food and water in Phase 1 and was shifted to a single alternating schedule of food and nonreward in Phase 2 (Group FW); the second group (Group FN) received a single alternating schedule of food and nonreward in both phases. When Group FW was shifted to nonreward from water, performance to nonreward was temporarily disrupted. These results indicate that, contrary to previous conclusions, hungry rats can learn about water when drive is strong and food is received in the situation.     

Reversal learning as a function of changed reward location or changed drive

In two experiments, rats were trained with food in one location (e.g., black alley) and water in another location (white alley) under hunger or thirst. Subsequently, either the locations of the rewards were reversed, or the drive was changed (from hunger to thirst or thirst to hunger). Reversal of instrumental responses took considerably longer when drive was changed and rewards remained in the same locations than when reward locations were reversed. These results were interpreted as indicating that the animal's internal representations of the rewards received in each location transfer when drive is changed. These internal-reward representations interfere with reversal learning by eliciting the responses which were conditioned to them in Phase 1. Because the values of food and water reverse when drive is changed from hunger to thirst or vice versa, it was suggested that the reward representations surviving the drive shift are cognitive representations of the specific events received (food or water), independent of the value of the rewards under either hunger or thirst.     

Sequential effects on discrimination reversal

In Experiment 1 the sequence of trials to the positive (S+) and negative (S?) discriminanda was varied between groups during acquisition and reversal of a successive brightness discrimination. In Experiments 2 and 3, groups received different reward sequences in Phase 1 within S+. In general, groups given transitions from nonrewarded trials to rewarded trials (N-R transitions) in Phase 1 learned both the original discrimination and its reversal more slowly than groups given schedules devoid of N-R transitions. The results were discussed in relation to previously reported effects of partial reinforcement on acquisition and reversal of a discrimination and the role of sequential variables and internal, reward-produced cues in discrimination learning, reversal learning, and nonreversal shifts.     

Asymmetrical interactions between thirst and hunger in pavlovian-instrumental transfer

Pavlovian-instrumental transfer experiments have demonstrated that a stimulus paired with a sucrose solution under hunger will increase instrumental performance under thirst relative to a stimulus previously paired with food pellets. In Experiment 1 it was demonstrated that this difference is, in part, produced by suppression induced by the pellet stimulus, which, it was found, acted to reduce instrumental performance under thirst. In Experiment 2, the reverse shift was examined, comparing the effects of stimuli paired with either a saline solution or a sucrose solution under thirst on instrumental performance under hunger. Although the sucrose stimulus was found to elevate performance when hungry, the saline stimulus was found to be without effect. This asymmetry in the interaction between hunger and thirst is discussed in terms of the way motivational states control the interaction between sensory and affective components of the reinforcer.     

Control of instrumental behavior by deprivation stimuli

In Experiment 1, rats were given one trial per day in a straight alley under food deprivation on half of the trials and under water deprivation on the other half. Wet mash was available in the goal box under food deprivation for Group H and under water deprivation for Group T, the other deprivation being nonrewarded for each group. After 15--18 trials both groups ran significantly faster on their rewarded than on their nonrewarded deprivation days. A third group showed that random variation of alley color retarded formation of the discrimination. A fourth group was run in a conditional discrimination in which under food deprivation wet mash was available in a black alley, nonreward in a white alley, and vice versa under water deprivation. This group took 114 trials to begin running significantly faster in their rewarded than in their nonrewarded alley under each deprivation. In Experiment 2, it was shown that prior learning about deprivation cues "blocks" learning about alley color when alley color is subsequently presented in compound with the deprivation cue but that when both alley color and deprivation cues are relevant from the start of training, the rat learns about both cues. It is suggested that previous studies have underestimated the importance of deprivation cues by using conditional discrimination designs, choice measures rather than speeds, and parameters that are not optimal for discrimination learning.     

Effects of sucrose concentrations on single alternation runway responding in rats

Rats received runway training under alternating reward and nonreward in which rewarded (R) trials provided 32 or 4% sucrose concentration from a drinking tube and nonrewarded (N) trials provided a dry tube or, for half of the rats in the 32% condition, plain water. Both 32 and 4% concentrations yielded faster running on R trials than on N trials; but this effect was reliable only for the 32% condition. Compared to 4% sucrose, 32% sucrose yielded reliably slower running on N trials and unreliably faster running on R trials.     

Perceptual learning in flavor-aversion learning: Alternating and blocked exposure to a compound of flavors and to an element of that compound

Rats received different schedules of pre-exposure to a compound flavor (AX) and to one element of that compound (X). In Group ALT, exposure consisted of alternating trials with AX and X; Group BLK received a block with all AX trials before a separate block with all X trials (or vice versa). Discrimination between AX and X was assessed then by establishing an aversion to X and measuring the generalization of this aversion to AX. In Experiments 1A and 1B, generalization was less in Group ALT than in Group BLK. In Experiment 2, this latter result was confirmed and furthermore only Group ALT, and not Group BLK, showed less generalization than a group that received exposure to X alone. These results are discussed in terms of their implications for theories of perceptual learning.     

Stimulus control of responding in the early trials of differential conditioning

In Experiment 1 two groups of rats were given 12 differential conditioning trials, seven to the rewarded alley (S+) and five to the nonrewarded alley (S?), prior to being extinguished in both alleys. Group S?S+ received S+ trials, following S? trials in acquisition, while Group S+S? did not receive S+ trials following S? trials in acquisition. In extinction S+ and S? trials were presented according to a quasi-random sequence for both groups. Running on the last 3 trials of acquisition was found to be faster following S+ than following S? trials. Group S?S+ showed greater resistance to extinction and less discriminative responding in extinction than Group S+S?. These results suggest that responding in differential conditioning is controlled not merely by S+ and S? but by the memories of reward (S^R) and of nonreward (S^N) as well. When the joint effects of both classes of cues were considered, e.g., S^R+S+, responding in the early trials of differential conditioning was shown to be highly orderly. Experiment 2 was highly similar to Experiment 1 except that Groups S?S+ and S+S? were equated along dimensions not equated in Experiment 1. The results obtained in Experiment 2 were highly similar to those obtained in Experiment 1.     

Repetition and alternation in rats

An experiment is reported in which rats were forced equally often to each arm of a T-maze, and, following each forced trial, were given a free trial. Group R were rewarded for repeating (i.e. choosing the side to which they had just been forced), group A for alternating. All rats began by alternating, but group R eventually learned to repeat. Various delays between free and forced trials were introduced, and the forgetting curve was found to be similar for the two groups. It is argued that these results show: (i) The decline in alternation with delay found in experiments on spontaneous and rewarded alternation is due to loss of information rather than a decline in the alternation tendency. (ii) The trace involved is sufficiently general to be regarded as a memory trace. The fact that rats can learn to repeat is inconsistent with the accounts of the memory trace suggested by the theories of Deutsch and Walker.     

Spontaneous alternation and pattern of reinforcement

In Experiment I, rats were given one pair of trials per day in a T-maze; group RN were rewarded on the first trial only, NR were rewarded on the second trial only, while RR were rewarded on both trials. Alternation was approximately the same for all groups, and there was little decline in alternation over 28 days. There was, however, a difference in the choice behaviour on trials when rats failed to alternate, NR and RR, but not RN, choosing according to a position preference. These results are incompatible with several earlier theories of spontaneous alternation, and the hypothesis was put forward that alternation is initially part of an exploratory tendency, but that, when the maze becomes explored, the exploratory tendency dies down, and alternation only continues when rats have been reinforced (primarily or secondarily) for alternating. This hypothesis was tested in a second experiment, similar to the first but in which one group of rats was not rewarded on either trial; as predicted, this group showed significantly more decline in alternation than rewarded rats.     

Alternating exposure to two compound flavors creates inhibitory associations between their unique features

Rats were exposed to two compound solutions, saline-lemon and sucrose-lemon. In Group ALT, trials with one solution alternated with trials with the other. Group BLK received all trials with one solution before any trials with the other. Previous retardation tests had implied that only alternating exposure would establish sucrose as an inhibitor of saline. To provide a complementary summation test for this inhibition, in Experiment 1, all the animals received pairings of peppermint and saline and were tested for consumption of peppermint-sucrose under sodium depletion. Consumption was increased by sodium depletion only in Group BLK. In Experiment 2, a retardation test was used to show that presentation of saline-lemon before sucrose-lemon on each exposure day would establish sucrose as an inhibitor of saline. Neither exposure to sucrose-lemon before saline-lemon nor alternating exposure to sucrose and saline alone had the same effect. These results provide support for an associative theory of perceptual learning that suggests that exposure to complex stimuli aids later discrimination partially as a result of establishing inhibitory associations between their unique elements.     

Response patterning in goldfish: single alternation in a Pavlovian aversive paradigm

Single alternation behavior was studied in a Pavlovian aversive shuttle-response situation using goldfish. Independent groups of fish were given either a fixed interval between alternating reinforced (R) and nonreinforced (N) trials or were given differential temporal information between trials. Although all groups exhibited higher response probabilities on reinforced than on nonreinforced trials, goldfish receiving a short interval (10 s) following R trials and a long interval (60 s) following N trials (R10N60) demonstrated significantly superior alternation performance compared with subjects receiving a fixed intertrial interval (R35N35) or a long interval following R trials and a short interval following N trials (R60N10). The alternation performance exhibited by the R10N60 group was shown to be equivalent to that of subjects receiving standard color discrimination training. However, the alternation performance in group R35N35 showed a great deal of within-subject variability and raises questions concerning the elusive nature of alternation using Pavlovian conditioning procedures.     

Recovery of Lost Transfer Effects

Tracking tasks known to facilitate or interfere with one another were investigated under various sequences of alternation. Double and treble alternating sequences of 2 tasks were used. 6 groups of 12 Ss practiced for 20 10-sec. trials, with 50-sec. intertrial intervals. Trend analyses were employed in comparing the results of the double and treble alternating sequences with the single alternating sequence and postshift trials of the previous study (Laszlo & Pritchard, 1969). The results showed that facilitation or interference lost with single alternation was recovered with double or treble alternating sequences. Rate and degree of recovery appeared to depend upon the degree of transfer between tasks and strategies employed by S. These results were discussed in terms of motor program consolidation.     

Analysis of the perceptual learning effect in flavour aversion learning: Evidence for stimulus differentiation

Rats received exposure to two compound flavours, AX and BX, where A and B were sucrose and saline and X was acid. For group intermixed (I), exposure consisted of alternating trials with AX and BX; group blocked (B) received a block of AX trials and a separate block of BX trials. Experiment 1 showed that generalization to BX after conditioning with AX was less profound in group I than in group B. Separate examination of the elements of the compound showed that the source of this difference lay in the strength acquired by the X element. X acquired less strength in group I than in group B (Experiments 1 and 2), whereas for the A element (Experiments 3 and 4) the reverse pattern was obtained. These results support the proposal that the perceptual learning effect (restricted generalization from AX to BX in group I) depends on a process that enhances the effectiveness of unique stimulus elements (A and B) and reduces that of common elements (such as X).     

Detecting a nonevent: Delayed presence-versus-absence discrimination in pigeons

Eight pigeons were trained on a delayed presence-versus-absence discrimination paradigm in which a sample stimulus was presented on some trials but not on others. If a sample was presented, then a response to one choice key produced food. If no sample was presented, a response to the other choice key produced food. The basic finding was that performance remained constant and well above 50% correct on no-sample trials as the retention interval increased, whereas performance dropped precipitously (to below 50% correct) on sample trials. In the second phase of the experiment, all of the trials were no-sample trials, and reinforcers were delivered probabilistically for one group of pigeons and according to time-based schedules for the other group. The exact reinforcement probabilities used in Phase 2 were those calculated to be in effect on no-sample trials in Phase 1 (according to a discrete-state model of performance). Subjects did not show exclusive preference for the richer alternative on no-sample trials in the first phase, but those in the probabilistic group developed near-exclusive preference for the richer alternative during the second phase. These data are inconsistent with the predictions of the discrete-state model, but are easily accommodated by an account based on signal detection theory, which also can be applied effectively to discrimination of event duration and the “subjective shortening” effect.     

Trace fear conditioning is reduced in the aging rat

Auditory trace fear conditioning is a hippocampus-dependent learning task that requires animals to associate an auditory conditioned stimulus (CS) and a fear-producing shock-unconditioned stimulus (US) that are separated by an empty 20-s trace interval. Previous studies have shown that aging impairs learning performance on hippocampus-dependent tasks. This study measured heart rate (HR) and freezing fear responses to determine if aging impairs hippocampus-dependent auditory trace fear conditioning in freely moving rats. Aging and Young rats received one long-trace fear conditioning session (10 trials). Each trial consisted of a tone-CS (5 s) and a shock-US separated by an empty 20-s trace interval. The next day rats received CS-alone retention trials. Young rats showed significantly larger HR and freezing responses on the initial CS-alone retention trials compared to the Aging rats. A control group of aging rats received fear conditioning trials with a short 1-s trace interval separating the CS and US. The Aging Short-Trace Group showed HR and freezing responses on the initial CS alone retention trials that were similar to the Young Long-Trace Group, but greater than the Aging Long-Trace Group. A second aging control group received unpaired CSs and USs, and showed no HR or freezing responses on CS-alone retention trials. These data show that HR and freezing are effective measures for detecting aging-related deficits in trace fear conditioning.     

Delayed temporal discrimination in pigeons: A comparison of two procedures

A within-subjects comparison was made of pigeons' performance on two temporal discrimination procedures that were signaled by differently colored keylight samples. During stimulus trials, a peck on the key displaying a slanted line was reinforced following short keylight samples, and a peck on the key displaying a horizontal line was reinforced following long keylight samples, regardless of the location of the stimuli on those two choice keys. During position trials, a peck on the left key was reinforced following short keylight samples and a peck on the right key was reinforced following long keylight samples, regardless of which line stimulus appeared on the correct key. Thus, on stimulus trials, the correct choice key could not be discriminated prior to the presentation of the test stimuli, whereas on position trials, the correct choice key could be discriminated during the presentation of the sample stimulus. During Phase 1, with a 0-s delay between sample and choice stimuli, discrimination learning was faster on position trials than on stimulus trials for all 4 birds. During Phase 2, 0-, 0.5-, and 1.0-s delays produced differential loss of stimulus control under the two tasks for 2 birds. Response patterns during the delay intervals provided some evidence for differential mediation of the two delayed discriminations. These between-task differences suggest that the same processes may not mediate performance in each.     

Evidence for inhibitory associations between the unique elements of two compound flavours

In each of two experiments, rats were pre-exposed to two flavoured solutions, saline-lemon and sucrose-lemon. For group ALT, trials with one solution alternated with trials with the other. Group BLK received all trials with one solution in a block, before any trials with the other. An associative theory suggests that the alternating, but not the blocked, schedule would establish an inhibitory association between sucrose and saline. To provide a retardation test of this inhibition, some animals in each group were then given a single pairing of saline and sucrose, experienced sodium depletion, and were finally tested for their consumption of sucrose. Sodium depletion increased consumption of sucrose more in group BLK than in group ALT. In groups given no saline-sucrose pairing, sodium depletion had only a small effect on sucrose consumption, which was the same in both groups. After multiple pairings of saline and sucrose, sodium depletion had an equally large effect on sucrose consumption in both ALT and BLK groups. These results imply that alternating pre-exposure to two compound solutions does establish an inhibitory association between their unique elements, and thus provide support for an associative theory of perceptual learning.     

Results of the healthy body healthy spirit trial.

Healthy Body Healthy Spirit was a multicomponent intervention to increase fruit and vegetable (F & V) consumption and physical activity (PA) delivered through Black churches. Sixteen churches were randomly assigned to 3 intervention conditions. At baseline, 1,056 individuals were recruited across the 16 churches, of which 906 (86%) were assessed at 1-year follow-up. Group 1 received standard educational materials, Group 2 received culturally targeted self-help nutrition and PA materials, and Group 3 received the same intervention as did Group 2 as well as 4 telephone counseling calls based on motivational interviewing (MI) delivered over the course of 1 year. At 1-year follow-up, Groups 2 and 3 showed significant changes in both F & V intake and PA. Changes were somewhat larger for F & V. For F & V, but not PA, there was a clear additive effect for the MI intervention.     

Golden hamsters on the eight-arm maze in light and darkness: The role of dead reckoning

This paper examines whether golden hamsters can rely on dead reckoning (getting positional information from updated signals generated during locomotion) on an eight-arm maze. Two groups of hamsters were tested: Group L under ordinary room light, Group D in darkness. To enhance the role of dead reckoning, each subject could climb from its own home cage onto the central platform of the maze. In a first experimental phase (15 trials), the L subjects learned to master the maze through developing a locomotor rule (arm chaining) after three to four trials. The D subjects developed arm chaining less readily and fluctuated more in their performance than did the L subjects. In a second experimental phase (15 trials), four arms were blocked at the beginning of each trial. In both experimental groups the performance decreased, yet remained well above chance level. Success and arm chaining were positively correlated in Phase 1 and negatively correlated with success in Phase 2. We assume that in Phase 2 the L subjects switched to the predominant use of visual cues, and the D subjects to dead reckoning.