Incentive properties of sucrose and saccharin under different deprivation conditions

In Expt 1 it was found that hungry rats developed a 100% preference for 8% sucrose over water in a maze-choice situation, whereas thirsty rats developed no preference. When deprivation conditions for the two groups were reversed the pattern of preference relations also reversed. In a 2nd experiment nondeprived rats developed a preference for either 8% sucrose or 0.2% saccharin over water while thirsty Ss did not develop a preference for either of these over water. The results are discussed in terms of incentive theory.     

A comparison of factor scores under conditions of factor obliquity

Six different methods of computing factor scores were investigated in a simulation study. Population scores created from oblique factor patterns selected from the psychological literature served as the bases for the simulations, and the stability of the different methods was assessed through cross-validation in a subject-sampling model. Results from 5 evaluative criteria indicated that a simplified, unit-weighting procedure based on the factor score coefficients was generally superior to several unit-weighting procedures based on the pattern or structure coefficients. This simplified method of computing factor scores also compared favorably with an exact-weighting scheme based on the full factor score coefficient matrix. Results are discussed with regard to their potential impact on current practice, and several recommendations are offered.     

A comparison of neuronal reactions during classical and instrumental conditioning under similar conditions

During the elaboration of an instrumental reflex, it is not obligatory to use a conditioned stimulus, which signals the necessity to generate an instrumental reaction in order to receive reinforcement. However, the presence of a conditioned stimulus simplifies analysis of instrumental reaction, which in this case is the response to the conditioned stimulus. On the other hand, it is necessary to distinguish between instrumental and classical conditioning, since in both cases the response to a conditioned stimulus increases. We studied neuronal analogs of classical and instrumental conditioning in the identified neurons responsible for the defensive closure of the pneumostome in the Helix mollusk under the same conditions. During classical conditioning, a mollusk received punishment after a tactile stimulus. During instrumental conditioning, a mollusk received punishment when an identified neuron did not generate an action potential in response to a tactile stimulus. The appearance of a painful stimulus did not depend on the generation or failure of a spike in the related control neuron. Another tactile stimulus, which was never paired with an unconditioned stimulus, was used as a discriminated stimulus. We also compared the behavior of such identified neurons during pseudoconditioning. The experiments were carried out in a semi-intact preparation. We examined how responses to the tactile and painful stimuli changed during different forms of training. It was shown that the dynamics of neuronal responses to a conditioned tactile stimulus were much more complex during instrumental conditioning and consisted of several phases. Throughout a learning session, neural system consecutively acquired information as to which kind of learning was presented, whether a reaction of the neural system must be generated or inhibited and which instrumental reaction is correct. We have demonstrated that response to a painful stimulus during classical conditioning decreases after short-term initial increase. However, during instrumental learning, the neurons controlling instrumental action remained highly sensitive to the unconditioned stimulus. Meanwhile, foreign neurons decreased their responses to the unconditioned stimulus. We may tentatively conclude that classical and instrumental paradigms are fundamentally different at the cellular level.     

Successive, simultaneous, and anticipatory contrast in the consumption of saccharin solutions

Contrast effects were obtained in rats in the consumption of saccharin solutions in three different paradigms. Degree of negative contrast varied as a function of concentration disparity, but not equally in the three procedures. Successive negative contrast occurred following shifts from 0.15% to either 0.075% or 0.05% saccharin but did not occur following shifts to 0.10% or 0.125% saccharin. Some degree of simultaneous contrast was obtained with all four concentration disparities. Anticipatory contrast, where the intake of the first substance is suppressed by a more preferred second substance, occurred only in the case of the 0.05%-0.15% difference in concentrations. It was suggested that the several contrast paradigms engage somewhat different psychological processes differentially involving emotional, sensory, and associative mechanisms, but all lead to behavior based on relative value. A modification of Toates's (1981) incentive model of ingestive behavior was suggested to incorporate relativity effects based on both associative and nonassociative factors in the consumption of both nutritive and nonnutritive substances.     

Effects of anorectic drugs on food intake under progressive-ratio and free-access conditions in rats

The effects of two anorectic drugs, dexfenfluramine and phentermine, on food intake under different food-access conditions were examined. Experiment 1 compared the effects of these drugs on food intake under a progressive-ratio (PR) schedule and free-access conditions. Dexfenfluramine decreased food intake under both conditions, but the doses required to decrease intake under free-access conditions were higher than those required to reduce intake under the PR condition. Intermediate doses of phentermine sometimes increased breaking points, and higher doses decreased them. Phentermine decreased food intake at the same doses under both access conditions. Thus the potency of dexfenfluramine, but not phentermine, to decrease food-maintained behavior depended upon the food-access condition. Experiment 2 used a novel mixed progressive-ratio schedule of food delivery to study the duration of drug effects. Sessions consisted of five components separated by 3-hr timeouts. The ratio requirement reset at the beginning of each component and a new breaking point was obtained. Both dexfenfluramine and phentermine dose-dependently decreased breaking points early in the session. In some rats, compensatory increases in breaking point were observed. That is, breaking points later in the session increased over control levels, resulting in no change in the total number of food pellets earned for the session compared to control. The present findings suggest that the effects of some anorectic drugs depend upon the access conditions for food; increasing the effort to obtain food may enhance their ability to decrease food-maintained behavior.     

Concurrent phencyclidine and saccharin access: presentation of an alternative reinforcer reduces drug intake.

Six monkeys self-administered orally delivered phencyclidine ("angel dust") and saccharin under concurrent fixed-ratio 16 schedules during daily three-hour sessions. Liquid deliveries were contingent upon lip-contact responses on solenoid-operated drinking spouts. Three saccharin concentrations (0.003%, 0.03% and 0.3%, wt/vol) were tested in a nonsystematic order. For each saccharin concentration, the following series of phencyclidine concentrations (mg/ml) was presented: 0.25, 0.5, 1, 0.25 (retest), 0.125, 0.0625, 0.0312, 0.25 (retest) and 0 (water with stimuli signaling phencyclidine). As the saccharin concentration increased, the number of drug deliveries decreased, and the peaks of the concentration-response functions were shifted to the right. The lowest saccharin concentration (0.003%, wt/vol) maintained responding in excess of phencyclidine levels in only one monkey. The two higher saccharin concentrations maintained behavior far in excess of phencyclidine, but saccharin deliveries decreased in some monkeys as phencyclidine concentration and intake (mg/kg) increased. The time course and patterns of phencyclidine-reinforced responding were also altered when saccharin was concurrently available. The results are discussed in terms of strategies to reduce drug-reinforced behavior, preference between different reinforcers, and measures of reinforcing efficacy.     

Some effects of thiamine deficiency and reduced caloric intake on “behaviour under stress” and on learning

The main purpose of the investigation was to determine the effects of thiamine deficiency in rats on behaviour under stress and on learning. Since thiamine deficiency reduces food intake, it was necessary to have two control groups. The first received adequate thiamine, but a food intake reduced to that of the vitamin-deficient animals; the second received adequate thiamine and an unrestricted food intake. It was thus possible to study the effects both of thiamine deficiency and of reduced caloric intake on the behaviour variables measured.

The experimental group was maintained on a thiamine-deficient diet throughout the entire experimental period. Because of the effects of thiamine deficiency on caloric intake, food-hunger was never used as a form of motivation. Behaviour in four different situations was studied: in Hall's open-field test, in two discrimination situations both involving exposure to insoluble and soluble problems, and in a water maze.

Contrary to the findings of several previous studies, there were no significant effects of thiamine deficiency on behaviour prior to the onset of polyneuritis with its debilitating effects on motor co-ordination. There was also no evidence of impairment in any of the behaviour studied which could be attributed to restrictions in caloric intake. This was the case even though the restrictions continued for a period of somewhat more than twelve months. Although these restrictions did not lead to impairment they were associated with certain changes in performance. Animals whose feeding was restricted were more active and, during the soluble phase of one discrimination situation, showed more vicarious trial and error and learned more readily than animals fed ad libitum on the same diet. It is suggested that these differences may be interpreted in terms of the effects of what previous investigators have referred to as “irrelevant drives”.     

Anticipation of future food: suppression and facilitation of saccharin intake depending on the delay and type of future food

A series of studies examined the (Sprague-Dawley) rat's tendency to suppress intake of .15% saccharin when it was followed by a second food after 4-, 16-, or 32-min delays. The second foods examined were 32% sucrose, 64% sucrose, lab chow, a Nutrasweet solution, skim milk, and chocolate milk. Saccharin intake was influenced by both the delay and the specific food available. Subsequent analysis showed that saccharin intake before the 4-min delay was an inverse function of the caloric value of the second food. However, saccharin intake before the 16-min delay was better predicted as an inverse function of the hedonic value of the second food. The results suggest that the caloric and hedonic values of a food may influence food selection across different time courses, and that the effective time horizon for the sequential comparison of foods depends on the specific foods that are compared.