A study of misbehavior: token reinforcement in the rat

The purpose of this research was to investigate the phenomenon of misbehavior described by Breland and Breland (1961). Rats were trained to obtain ball-bearings and drop them in a hole for food or water reinforcers. In confirmation of the Brelands' observation, many subjects were slow to deliver the balls, and frequently attempted to chew them before they were dropped. A series of four experiments, in which the same rats were used throughout, showed that delivery times tended to be longer with food than with water, and that these times increased when nylon balls were substituted. The effect of motivational level was investigated by varying both deprivation and amount of prefeeding; no effect on delivery time was detected, although other measures of performance were affected by motivational factors. Similar results were obtained in a final experiment that employed a new set of naive subjects. The studies demonstrated that misbehavior can be studied in an experimental situation, and the results supported an analysis in terms of competition between stimulus-reinforcer and response-reinforcer contingencies. The question of why such effects have not been reported in previous token reinforcer studies was unanswered.     

Resistance to extinction of conditioned odor perceptions: evaluative conditioning is not unique

A tasteless odor will smell sweeter after being sampled by mouth with sucrose and will smell sourer after being sampled with citric acid. This tasty-smell effect was found in experiments that compared odor-taste and color-taste pairings. Using odors and colors with minimal taste (Experiment 1), the authors found that repeated experience of odor-taste mixtures produced conditioned changes in odor qualities that were unaffected by intermixed color-taste trials (Experiment 2). An extinction procedure, consisting of postconditioning presentations of the odor in water, had no detectable effect on the changed perception of an odor (Experiments 3 and 4). In contrast, this procedure altered judgments about the expected taste of colored solutions. Evaluative conditioning (conditioned changes in liking) is claimed to be resistant to extinction. However, these results suggest that resistance to extinction in odors is related to the way they are encoded rather than to their hedonic properties.     

Self-starvation in the rat: running versus eating

Rats given the combination of unrestricted access to an activity wheel and restricted access to food can lose weight to the extent that they will die unless removed from these conditions. Although this has been known for forty years, why this happens has remained unclear. The phenomenon is paradoxical in that one might expect such rats to eat more as their weight decreases, but in fact they eat less than resting controls. This lecture first examines some of the factors than influence whether self-starvation will occur, such as age, time of food access, type of food and ambient temperature. It then compares competing explanations such as circadian adaptation, thermo-regulation and food aversion learning. As so often in psychology, it turns out that self-starvation results from a combination of many separate factors. The general implications of this research are examined, including whether it provides a useful animal model for human anorexia nervosa.     

Facial affect interpretation in boys with attention deficit/hyperactivity disorder.

Recent studies have produced mixed evidence of impairments in facial affect interpretation for children with attention deficit/hyperactivity disorder (ADHD). This study investigated the presence and nature of such impairments across different stimulus formats. Twenty-four boys with ADHD and 24 age-matched comparison boys completed a 72-trial task that included facial expressions of happiness, sadness, fear, anger, surprise, and disgust. Three versions of each expression were used: a static version, a dynamic version, and a dynamic version presented within a relevant situational context. Expressions were also presented in one of two portrayal modes (cartoon versus real-life). Results indicated significant impairments for boys with ADHD on two of the six emotions (fear and disgust), which were consistent across stimulus formats. Directions for further research to identify mediating factors in the expression of such impairments in children with ADHD are discussed.     

Learning about cues that prevent an outcome: Conditioned inhibition and differential inhibition in human predictive learning

Summation tests were used to assess whether participants in a human predictive judgement task learned that some cues (foods) prevented the occurrence of the outcome (migraine). In three experiments the preventative effect of a conditioned inhibitor, I, trained in the design, P+, PI-, I-, was stronger than that of a negative control cue, N, that had been presented alone with the same frequency and simply predicted no outcome. This control cue, N, also passed the summation test when compared to a novel control cue. Experiments 2 and 3 examined whether the latter negative control effect was attributable to differential inhibition. Manipulations designed to alter context learning and the magnitude of the negative contingency did not affect the properties of the negative control cue. Thus, these experiments did not support the possibility that a cue given simple negative training acquires differential inhibition. Regardless of the mechanism underlying the negative control effect, the consistent finding that the conditioned inhibition cue, I, reduced prediction of the outcome more than did the negative control cue, N, provides evidence for true conditioned inhibition whose acquisition requires co-occurrence of the preventative cue with a positive training cue.     

The bisection of a brightness interval by pigeons

Pigeons were trained on a discrete trials, successive discrimination procedure, in which the stimuli were two luminance values on the center key. Behavior was maintained by 25% reinforcement of correct responses on two side-keys. During occasional test trials the luminance of the center key was maintained at one of a number of values, intermediate to those of the two training stimuli, and a function relating the relative frequency of responses on the two side keys to stimulus intensity was obtained. The intersection of this function with the 50% line provided an estimate of the bisection point. Since no bisection point occurred below the geometric mean of the interval, the results were not consistent with a logarithmic scale of brightness but fitted the general mean theorem with an exponent of 0.24. With continued testing, the performance of individual subjects oscillated in an irregular manner about the mean bisection point. The relative stability of the test behavior and the absence of context effects indicated that the method was suitable as a general procedure for measuring stimulus distances.     

Successive discrimination training with equated reinforcement frequencies: failure to obtain behavioral contrast

In two experiments, pigeons were trained on two-component multiple schedules in which responding in one component (S₁) was always maintained by a variable-interval schedule. In Experiment I, low response rates were reinforced in the second (S₂) component for six master subjects. This schedule was adjusted to equate reinforcement frequencies in the two components. These subjects were compared to yoked partners, for which reinforcement in the S₂ component was made available on a variable-interval schedule whose value was determined by the master subjects. A similar procedure was used in Experiment II, where the S₂ schedule for master subjects made reinforcers contingent on the absence of responding. No evidence was found in either experiment for a behavioral contrast effect in the S₁ component attributable to response reduction in the S₂ component. A reliable contrast effect was obtained from a group of pigeons given extinction conditions in the S₂ component, which was compared to a group maintained throughout on a multiple variable-interval schedule. The results suggest that previous indications of behavioral contrast in similar situations were probably caused by uneven reinforcement distributions or reflect uncontrolled fluctuations in response rates.     

Behavioral contrast without response-rate reduction

Behavioral contrast was obtained in two experiments, which both employed a standard free-operant successive discrimination (a multiple variable-interval extinction schedule), without the occurrence of reductions of response rate in the extinction component. In Experiment I, one group of four pigeons was trained on a multiple schedule in which one stimulus was associated with a variable-interval schedule and the second stimulus with response-independent reinforcement on a free variable-interval schedule. Though by the end of this training three pigeons were responding very little to the second stimulus, when this stimulus was associated with extinction all subjects showed a contrast effect. In Experiment II, eight pigeons were trained extensively to respond to a single stimulus on a variable-interval schedule, before a second stimulus associated with extinction was introduced. This second stimulus was dissimilar to the initial stimulus and five pigeons never responded in its presence. Nevertheless, all pigeons showed a contrast effect and there was no evidence that the effect was smaller in errorless subjects or smaller than in a subsequent discrimination where all subjects made many errors. Both experiments indicated that response reduction in one component of a multiple schedule is not a necessary condition for the occurrence of contrast.     

Implicit and explicit tests of odor memory reveal different outcomes following interference

Experiencing two odors as a mixture can later increase their perceived similarity when presented separately. Such an increase in similarity can be used as an implicit measure of how well participants remember the mixture. Three experiments tested the resistance to interference of this effect by first giving participants exposure to two 2-odor mixtures and then presenting each odor from one mixture (interfered pair) separately many times. After the latter interference phase, participants rated the similarity of the two odors in each pair. The experiments varied in terms of the number of initial exposures to the mixtures, the number of odor presentations in the interference phase, and the control conditions employed. No difference in similarity ratings for the interfered and non-interfered pair was found in any experiment. In contrast to the lack of interference with this implicit measure, an explicit measure of memory based on participants’ ratings of odor frequency revealed that they could recall to some degree that the interfered odors had been presented alone in the second phase. These results suggest that implicit memory for odor mixtures is highly resistant to interference and is consistent with a configural encoding account of this effect.