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Biomedical subjects

M L Spetch

Publications and source records attributed to M L Spetch.

13 recordsLinked to original sources
PubMed1999

Perception of coherent motion in random dot displays by pigeons and humans.

Pigeons and humans were required to discriminate coherent from random motion in dynamic random dot displays. Coherence and velocity thresholds were determined for both species, and both thresholds were found to be substantially higher for pigeons than for humans. The results are discussed with reference to differences in motion processing in mammals and birds. It is suggested that the inferior motion sensitivity of pigeons can be attributed to poorer spatiotemporal motion integration.

Adult↗
PubMed1996

Averaging temporal duration and spatial position.

Pigeons and humans performed on a task in which spatial position and elapsed time redundantly signaled the availability of reward. On each training trial, a landmark moved steadily across a monitor screen. After a fixed amount of time and movement, reward was available for a response. On occasional unrewarded tests, the landmark moved at 0.50, 0.75, 1.00, 1.50, or 2.00 times the training speed. In both pigeons and humans, the central tendency in the response distribution on tests differed across speeds, when measured in terms of both elapsed time and landmark position. Pigeons and humans seem to average a duration of time and a spatial position to find a single criterion time-place corresponding to the expected time-place of reward.

Animals↗
PubMed1996

Learning the configuration of a landmark array: I. Touch-screen studies with pigeons and humans.

Pigeons and humans searched on a touch-screen monitor for an unmarked goal located relative to an array of landmarks presented in varied screen locations. After training with the goal centered in various square arrays of 4 landmarks, humans, but not pigeons, transferred accurately to arrays with novel elements. Humans searched in the middle of expanded arrays, whereas pigeons preserved the distance and direction to a single landmark. When trained with the goal centered below 2 identical horizontally aligned landmarks, humans responded to horizontal expansions or contractions of the array by shifting their search vertically, preserving angles from landmarks to goal. Pigeons did not adjust their search vertically. Humans trained with a single landmark adjusted search distance when landmark size was changed. Both pigeons and humans use the configuration of a landmark array, but the underlying processes seem to differ.

Adult↗
PubMed1995

Overshadowing in landmark learning: touch-screen studies with pigeons and humans.

Overshadowing in landmark learning was studied in pigeons and undergraduates using a touch-screen spatial search task. Ss searched for an unmarked goal presented in varied locations on a computer screen. Graphic stimuli served as landmarks. The effect of the presence of other landmarks on the control acquired by a given landmark was assessed using a design in which each S was trained with 2 sets of landmarks. Both pigeons (Experiment 1) and humans (Experiments 2-4) showed evidence of learning more about a landmark that was the closest landmark of its set to the goal than about a landmark that was of equal distance to the goal but was not the closest landmark of its set. That is, control by a landmark was overshadowed when it occurred together with a landmark that was closer to the goal. Landmark effectiveness appears to depend not only on the absolute properties of a landmark but on relative factors. The relevance of basic principles of associative learning to spatial landmark learning is discussed.

Adolescent↗
PubMed1990

Choice with uncertain outcomes: conditioned reinforcement effects.

Pigeons responded on concurrent chains with equal initial- and terminal-link durations. In all conditions, the terminal links of one chain ended reliably in reinforcement; the terminal links on the alternative chain ended in either food or blackout. In Experiment 1, the terminal-link stimuli were correlated with (signaled) the outcome, and the durations of the initial and terminal links were varied across conditions. Preference did not vary systematically across conditions. In Experiment 2, terminal-link durations were varied under different stimulus conditions. The initial links were variable-interval 80-s schedules. Preference for the reliable alternative was generally higher in unsignaled than in signaled conditions. Preference increased with terminal-link durations only in the unsignaled conditions. There were no consistent differences between conditions with and without a common signal for reinforcement on the two chains. In the first series of conditions in Experiment 3, a single response was required in the initial links, and the stimulus conditions during 50-s terminal links were varied. Preference for the reliable outcome approached 1.0 in unsignaled conditions and was considerably lower (below .50 for 3 of 5 subjects) in signaled conditions. In a final series of signaled conditions with relatively long terminal links, preference varied with duration of the initial links. The results extend previous findings and are discussed in terms of the delay reduction signaled by terminal-link stimuli.

Animals↗
PubMed1990

Suboptimal choice in a percentage-reinforcement procedure: effects of signal condition and terminal-link length.

Pigeons' choice between reliable (100%) and unreliable (50%) reinforcement was studied using a concurrent-chains procedure. Initial links were fixed-ratio 1 schedules, and terminal links were equal fixed-time schedules. The duration of the terminal links was varied across conditions. The terminal link on the reliable side always ended in food; the terminal link on the unreliable side ended with food 50% of the time and otherwise with blackout. Different stimuli present during the 50% terminal links signaled food or blackout outcomes under signaled conditions but were uncorrelated with outcomes under unsignaled conditions. In signaled conditions, most pigeons displayed a nearly exclusive preference for the 100% alternative when terminal links were short (5 or 10 s), but with terminal links of 30 s or longer, preference for the 100% alternative was sharply reduced (often to below .5). In unsignaled conditions, most pigeons showed extreme preference for the 100% alternative with either short (5 s) or longer (30 s) terminal links. Thus, pigeons' choice between reliable and unreliable reinforcement is influenced by both the signal conditions on the unreliable alternative and the duration of the terminal-link delay. With a long delay and signaled outcomes, many pigeons display a suboptimal tendency to choose the unreliable side.

Animals↗
PubMed1987

Choice between reliable and unreliable outcomes: mixed percentage-reinforcement in concurrent chains.

Pigeons' choices between alternatives that provided different percentages of reinforcement in mixed schedules were studied using the concurrent-chains procedure. In Experiment 1, the alternatives were terminal-link schedules that were equal in delay and magnitude of reinforcement, but that provided different percentages of reinforcement, with one schedule providing, reinforcement twice as reliably as the other. All pigeons preferred the more reliable schedule, and their level of preference was not systematically affected by variation in the absolute percentage values, or in the magnitude of reinforcement. In Experiment 2, preference for a schedule providing 100% reinforcement over one providing 33% reinforcement increased systematically with increases in the duration of the terminal links. In contrast, preference decreased systematically with increases in the duration of the initial links. Experiment 3 examined choice with equal percentages of reinforcement but unequal delays to reinforcement. Preference for the shorter delay to reinforcement was not systematically affected by variation in the absolute percentage of reinforcement. The overall pattern of results supported predictions based on an extension of the delay-reduction hypothesis to choice procedures involving mixed schedules of percentage reinforcement.

Animals↗
PubMed1986

Caloric regulation in the rat: control by two factors.

These experiments demonstrate that rats can immediately adjust their meal size in response to variations in the caloric density of a novel diet. However, this immediate caloric sensitivity only seems to appear when rats have been adapted to small, calorically insufficient meals. Rats in Experiment 1 were given timed access to unlimited quantities of an oil/water diet during baseline, and they showed no indication of compensating for changes in the caloric density of the oil/water diet during a test meal. Instead, they consumed about the same amount they had consumed during the preceding baseline meal, suggesting that a learned habit of consuming a certain volume of food controlled their meal size. In contrast, rats that were accustomed to receiving only a very small quantity of food for one of their daily meals during baseline immediately responded to the caloric density of an oil/water test diet by consuming a larger meal if the diet was dilute than if it was calorically more concentrated (Experiments 2 and 3). This immediate sensitivity to caloric density occurred whether or not the rats were exposed to the oil/water diet during baseline, suggesting that rats have some way of directly "metering" the caloric density of new foods. Thus, rats' caloric intake during a meal appears to be controlled by two factors: under certain conditions, control is by caloric learning, under other conditions control is by a caloric metering mechanism.

Adaptation, Psychological↗
PubMed1986

Does effort play a role in the effect of response requirements on delayed matching to sample?

The possible role of "effort" in the accuracy of pigeons' performance on a delayed matching-to-sample procedure was investigated by examining the effects of response requirements that accompanied a trial-initiating stimulus and that accompanied a sample stimulus. In the first experiment, the effect of varying the size of a fixed-ratio requirement for responses during an initiating stimulus was compared to that of varying a similar requirement for responses during the sample stimulus. Accuracy increased reliably with increases in the ratio scheduled during the sample stimulus, but was not significantly affected by increases in the ratio scheduled on the key during the initiating stimulus. In another phase of Experiment 1, sample duration was held constant while the ratio requirement was varied during the initiating stimulus. Again, accuracy of matching to sample was not significantly affected by the size of the ratio scheduled during the initiating stimulus. Experiment 2 provided a systematic replication of these results in another group of pigeons and included a more detailed analysis of responding. These results support the view that increases in sample-response requirement facilitate accuracy of delayed matching by increasing the durations of exposure to the sample stimuli, and do not support a role of effort in the sample-response effect. In Experiment 3, the facilitative effect of responses on the sample but not of those on the initiating stimulus was replicated using a simultaneous matching-to-sample procedure. This finding provides further evidence against an interpretation of response-requirement effects that appeals to effort; the finding also suggests that sample exposure might affect initial discrimination of the sample rather than remembering the sample.

Animals↗
PubMed1984

Caloric regulation in the rat: evidence for a calibration mechanism.

Rats were given access to small quantities of a 50% oil/water mixture on each of 7 baseline days. On the eighth day, a 30 min compensation test was conducted during which control rats had access to the 50% oil/water mixture and experimental rats had access to either a more concentrated or a more dilute oil/water mixture. Experimental rats given the more concentrated mixture consumed significantly less than controls, while rats given the dilute mixture consumed significantly more than controls. These results suggested that rats can immediately adjust their food intake in response to changes in the caloric density of their diets. In a second experiment, immediate adjustment for caloric change was inhibited by giving rats a supplementary meal directly after access to the 50% oil/water mixture during the baseline phase. These results were discussed in terms of a hypothetical "calibration" mechanism which allows rats to estimate the density of novel caloric concentrations on the basis of a standard concentration.

Animals↗
PubMed1984

The effect of d-amphetamine on short-term memory for time in pigeons.

The effect of d-amphetamine on pigeons' perception and short-term memory of time was investigated within a delayed symbolic matching to sample paradigm in which pigeons were rewarded for choosing one color after a 1-sec sample and another color after a 5-sec sample. On trials with no delay between sample offset and onset of the choice phase, d-amphetamine produced a bias toward choosing the color that was correct after long samples, suggesting that the birds overestimated the sample durations under amphetamine. With a 20-sec retention delay, d-amphetamine lowered choice accuracy to chance level, suggesting that it impaired the bird's short-term memory for sample durations. It was postulated that an amphetamine-induced increase in the rate of perceptual processing could mediate the effects of amphetamine on both time perception and memory.

Animals↗
PubMed1983

Variety in the flavor of food enhances eating in the rat: a controlled demonstration.

The effect of variety in the flavor of food on rats' consumption of a meal was examined in two experiments in which the confounding factors of diet composition and palatability could be ruled out. Experiment 1 showed that rats ate more of a four-course meal when each course was flavored differently than when each course was flavored the same; furthermore, this "variety effect" did not appear to depend upon the rats' prior experience with the flavors. Experiment 2 replicated and extended these findings by showing that the enhancement of eating by variety did not depend critically upon the rat's level of food motivation. The results were discussed in terms of their implications for the etiology and control of obesity, as well as for theories of satiety. It was suggested that the "variety effect" may represent an adaptive mechanism in the control of feeding.

Animals↗