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Biomedical subjects

S E Lea

Publications and source records attributed to S E Lea.

16 recordsLinked to original sources
PubMed1999

Inescapable shock-induced potentiation of morphine analgesia in rats: sites of action.

Inescapable shock (IS) enhances analgesia to systemic morphine (MOR) 24 hr later. IS activates serotonin neurons in the dorsal raphe nucleus (DRN), rendering them hyperexcitable. These studies tested whether IS potentiates the analgesic effect of MOR microinjected in the DRN, as predicted by this hypothesis. To test site specificity, the effect of previous IS was examined on MOR microinjected lateral to the DRN and into 2 other sites that support MOR analgesia, the nucleus raphe magnus (NRM) and spinal cord. Twenty-four hours after IS, potentiated analgesia was observed after 0.5 microg MOR microinjected into, but not lateral to, the DRN. Potentiated analgesia was also observed after NRM (1.0 microg) and spinal cord (3.0 microg) MOR microinjections. These data suggest that IS-induced excitability changes within the DRN synergize with opiates microinjected in other analgesia areas and that this potentiates the responses to opiates 24 hr after IS.

Analgesia↗
PubMed1997

Inescapable shock-induced potentiation of morphine analgesia.

Exposure to various stressors potentiates nociceptive and nonnociceptive responses to morphine. These phenomena have received little study despite their seeming generality and importance for understanding analgesia and opiate action. The present experiments characterize inescapable shock (IS)-induced potentiation of morphine analgesia. Rats were exposed to IS, equal escapable shocks (ESs), or restraint (control). Potentiation of analgesia (tail-flick [TF] test and hotplate test) was observed only in rats given IS 24 or 48 hr earlier, in agreement with previously reported learned-helplessness effects. Finally, no change in tail temperature or motor function was found that could be inaccurately interpreted as analgesia. The relevance of these findings to stressor-induced enhancement of morphine analgesia and potential substrates of IS effects are discussed.

Analgesics, Opioid↗
PubMed1996

Perception of emotion from dynamic point-light displays represented in dance.

It is well known that biological motion, as produced by point-light displays on a human body, gives a good representation of the represented body-eg its gender and the nature of the task which it is engaged in. The question is whether it is possible to judge the emotional state of a human body from motion information alone. An ability to make this kind of judgment may imply that people are able to perceive emotion from patterns of movement without having to compute the detailed shape first. Subjects were shown brief video clips of two trained dancers (one male, one female). The dancers were aiming to convey the following emotions: fear, anger, grief, joy, surprise, and disgust. The video clips portrayed fully lit scenes and point-light scenes, with thirteen small points of light attached to the body of each dancer. Half the stimuli were presented the right way up, while half were inverted. The subjects' task was to judge which emotion was being portrayed. Full-body clips gave good recognition of emotionality (88% correct), but the results for upright biological-motion displays were also significantly above chance (63% correct). Inversion of the display reduced biological-motion (but not full-body) performance to close to chance but still significantly above chance. A space-time analysis of the motion of the points of light was carried out, and was related to the discriminability of the different emotions. Biological-motion displays, which convey no information while static, are able to give a rich description of the subject matter, including the ability to judge emotional state. This ability is disrupted when the image is inverted.

Analysis of Variance↗
PubMed1994

Visual perception of intentional motion.

A series of experiments were performed to investigate how motion sequences provide information about the intentional structure of moving figures or actors. Observers had to detect simulations of biologically meaningful motion within a set of moving letters. In the first two experiments a factorial design was used, with type of instruction as a between-subject factor and six movement parameters (number of items, speed and directness of target and distractors, and 'relentlessness' of target movement) as within-subject factor; in the final two experiments, the visibility of the goal towards which the target moved and the use of a tracking movement to distinguish the target were varied. In such displays search time increases with increasing number of stimuli. It was found that (a) the more direct the motion, the more likely it was to be interpreted as intentional; (b) intentional motion was much easier to detect when the target moved faster than the distractors than when it moved more slowly; (c) recognition of intentionality was impaired but not abolished if the goal towards which the target was moving was invisible; and (d) participants did not report intentional movement when the target was distinguished by brightness rather than the manner in which it moved. We argue that the perception of intentionality is strongly related to observers' use of conceptual knowledge, which in turn is activated by particular combinations of features. This supports a process model, in which intentionality is seen as the result of a conceptual integration of objective visual features.

Animals↗
PubMed1993

Motion as a natural category for pigeons: Generalization and a feature-positive effect.

Three groups of pigeons were trained with a modified discriminative autoshaping procedure to discriminate video images of other pigeons on the basis of movement. Birds of all groups were shown the same video images of other pigeons, which were either moving or still. The group to whom food was presented only after moving images learned the discrimination very quickly. A second group, to whom food was given only after still images, and a pseudocategory group, to whom food was presented after arbitrarily chosen stimuli, showed no evidence of discrimination during acquisition training. Extinction conditions led to clear differences in peck rates to moving and still images in the second group but not in the pseudocategory group. The result is related to the feature-positive effect. Generalization tests showed that the discrimination performance was based on visual features of the stimuli but was invariant against changes of size, perspective, brightness, and color. Furthermore, discrimination was maintained when novel images of pigeons under different viewing angles and seven other types of motion categories were presented. It is argued that the discrimination is based not on a common motion feature but on motion concepts or high-order generalization across motion categories.

Journal Article↗
PubMed1990

Category discrimination by pigeons using five polymorphous features.

Eight pigeons were trained to discriminate between sets of color photographs of natural scenes. The scenes differed along five two-valued dimensions (site, weather, camera distance, camera orientation, and camera height), and all combinations of the feature values were used. One value of each dimension was designated as positive, and slides containing three or more positive feature values were members of the positive stimulus set. Thus, each feature had an equal, low, correlation with reinforcement, and all features had zero correlations with each other. Seven of the 8 pigeons learned this discrimination, and their responding came under the control of all five features. Within the positive and negative stimulus sets, response rates were higher to stimuli that contained more positive feature values. Once discrimination had been achieved, reversal training was given using a subset of the slides. In this subset, only a single feature was correlated with reinforcement. All pigeons learned this reversal successfully and generalized it to additional photographs with the same feature content. After reversal, the original reinforcement contingencies were reinstated, and training was continued using all the slides except those that had been used in reversal. Reversal generalized to these slides to some extent. Analysis of the response rates to individual slides showed that, compared with prereversal training, only the feature that had been subjected to reversal contingencies showed a reversed correlation with response rate. The remaining features showed the same correlation with response rate as they had before reversal training. Thus, reversal on some members of a category following category discrimination training led to generalization to stimuli within the category that were not involved in the reversal, but not to features that were not reversed. It is therefore inappropriate to refer to the pigeons as learning a concept.

Journal Article↗
PubMed1989

Children's choice: Sensitivity to changes in reinforcer density.

Two experiments were carried out in which children's sensitivity to changes in reinforcer density (number of reinforcers per session) was measured in a choice paradigm. In Experiment 1, 24 girls (ages 6, 9, and 12 years) performed on concurrent-chain schedules of reinforcement. The initial links were variable-interval 10-s schedules. One terminal link always gave three tokens after 30 s, but the parameters associated with the other were varied. Independent manipulations of reinforcer size (two tokens or four tokens) and prereinforcement delay (25 s or 65 s) led to equal changes in the relative density of tokens that could be earned on the schedules. Subjects at all ages were sensitive to changes in reinforcer density brought about by changes in reinforcer size, whereas only 3 12-year-olds showed sensitivity to the changes brought about by manipulation of prereinforcer delay. In Experiment 2, titration procedures were used to test the extent of this insensitivity to delay in 32 6- and 12-year-old children. In these procedures, a repeated choice of the large reinforcer increased the delay to its delivery, and a repeated choice of the small reinforcer reduced the delay to the delivery of the large reinforcer. Whereas 6-year-old boys and girls tended to maintain a strong preference for the large reinforcer, so increasing the delay to its delivery, 12-year-olds tended to distribute their responses to both alternatives, thus producing a stable level of delay to the large reinforcer. The results from the two experiments support the idea of two stages in the development of adaptive intertemporal choice.

Journal Article↗
PubMed1989

The development of adaptive choice in a self-control paradigm.

Sixteen girls (ages 4, 6, 9, and 12) performed on concurrent-chain schedules of reinforcement. The initial links were variable-interval 10-s schedules, and the terminal links offered a long delay (20, 30, 40, or 50 s) followed by two tokens or a short delay (10 s) followed by one token. Tokens were used to buy toys and sweets. The effect of increasing the delay to the large reward differed significantly across age groups. Whereas 6- and 9-year-olds maintained a strong preference for the larger, more delayed reward under all delay conditions, half of the 4-year-olds and all the 12-year-olds showed increasing preference for the small reward as the delay to the large reward increased. The results suggest a two-stage account of the development of self-control. In the first stage, behavior is increasingly controlled by reward size, as children learn how to wait for delayed rewards, and in the second phase behavior is increasingly controlled by reward rate, as children learn when it is in fact profitable to wait.

Journal Article↗
PubMed1989

Algorithmic shaping and misbehavior in the acquisition of token deposit by rats.

In two experiments, rats were trained to deposit ball bearings down a hole in the floor, using an algorithmic version of shaping. The experimenter coded responses expected to be precursors of the target response, ball bearing deposit; a computer program reinforced these responses, or not, according to an algorithm that mimicked the processes thought to occur in conventional shaping. In the first experiment, 8 of 10 rats were successfully shaped; in the second, 5 of 5 were successfully shaped, and the median number of sessions required was the same as for a control group trained using conventional shaping. In both experiments, "misbehavior," that is, excessive handling and chewing of the ball bearings, was observed, and when the algorithmic shaping procedure was used, misbehavior could be shown to occur in spite of reduced reinforcement for the responses involved.

Journal Article↗
PubMed1980

Coding processes in normal and learning-disabled children: evidence for modality-specific pathways to the cognitive system.

In Experiment 1, normal 10-yr.-olds and 10-yr.-olds diagnosed as learning disabled (LD) were presented with items in visual and auditory modalities for free and cued recall. The LD children had deficits in auditory and/or visual memory. Recall by LD children was worse than for nonimpaired peers only on tasks in the impaired modality, and on cued recall the deficit was confined to recall given a semantic category cue: Recall given perceptual cues was unimpaired. In Experiment 2, presentation-time tasks were used to create a bias toward either perceptual or semantic encoding. The semantic-encoding task removed the modality-specific deficit between LD children and controls. We conclude that deficits in semantically cued recall for children with only one impaired modality had their origins at presentation time. The most parsimonious explanation of these results involves separate pathways linking the auditory and visual modalities to the semantic system.

Child↗
PubMed1977

The matching law in and within groups of rats.

In each of the two experiments, a group of five rats lived in a complex maze containing four small single-lever operant chambers. In two of these chambers, food was available on variable-interval schedules of reinforcement. In Experiment I, nine combinations of variable intervals were used, and the aggregate lever-pressing rates (by the five rats together) were studied. The log ratio of the rates in the two chambers was linearly related to the log ratio of the reinforcement rates in them; this is an instance of Herrnstein's matching law, as generalized by Baum. Summing over the two food chambers, food consumption decreased, and response output increased, as the time required to earn each pellet increased. In Experiment II, the behavior of individual rats was observed by time-sampling on selected days, while different variable-interval schedules were arranged in the two chambers where food was available. Individual lever-pressing rates for the rats were obtained, and their median bore the same "matching" relationship to the reinforcement rates as the group aggregate in Experiment I. There were differences between the rats in their distribution of time and responses between the two food chambers; these differences were correlated with differences in the proportions of reinforcements the rats obtained from each chamber.

Journal Article↗
PubMed1977

Demand for food on fixed-ratio schedules as a function of the quality of concurrently available reinforcement.

Six rats lever pressed for food on concurrent fixed-ratio schedules, in a two-compartment chamber. In one compartment, mixed diet pellets were delivered on fixed-ratio schedules of 1, 6, 11, and 16; in the other, either no food was delivered, or sucrose or mixed diet pellets were delivered on fixed-ratio 8. The number of pellets obtained in the first compartment declined as a function of fixed-ratio size in that compartment in all three conditions, but the decline was greatest overall with mixed diet pellets concurrently available in the other compartment, and least with no food concurrently available. The result is discussed in terms of economic demand theory, and is consistent with the prediction that elasticity of demand for a commodity (defined in operant terms as the ratio of the proportionate change in number of reinforcements per session to the proportionate change in fixed-ratio size) is greater the more substitutable for that commodity are any concurrently available commodities.

Journal Article↗
PubMed1976

Titration of schedule parameters by pigeons.

Pigeons were tested in a computer-controlled two-key chamber. A standard (nonchanging) schedule of reinforcement was in force on one key, and an adjusting schedule on the other. The schedules were available concurrently after each reinforcement, but after the first peck on either key (the choice peck), the schedule on the other key was made inoperative. The parameter of the adjusting schedule was decreased when the standard schedule was chosen and increased when the adjusting schedule was chosen. The standard schedule was changed only between sessions. Fixed intervals and fixed ratios were used as standard schedules, and intervals and ratios were used as adjusting schedules. When standard and adjusting schedules were of the same type, median parameters on the adjusting key equalled those of the standard schedules, at four values of each standard schedule. For four of five birds, and for the group median, similar curves could be plotted through the indifference points obtained from a standard ratio with an adjusting interval, and from a standard interval with an adjusting ratio. These points showed consistent individual differences, but they could be predicted by assuming that the median time from the choice peck to reinforcement should be the same on both keys. This is equivalent to treating the schedule as a concurrent chain and assuming that Herrnstein's quantitative law of effect applies.

Journal Article↗