Non-spatial delayed alternation by the pigeon

Pigeons were trained on a non-spatial delayed alternation task in which the color not pecked on the previous trial was correct. When varying delays were interposed between trials, alternation accuracy decreased as a function of delay, but remained greater than chance with a 45-sec delay. Successful alternation on the longer delays was accomplished without behavioral mediation of the delay intervals. Also, during initial testing when a position cue was available in addition to the color cue after incorrect trials, alternation accuracy was greater after a preceding incorrect trial than after a correct trial. When the position cue was removed, no differences occurred as a function of the outcome of the preceding trial.     

Color alternation learning in the pigeon under fixed-ratio schedules of reinforcement

Pigeons were trained on a non-spatial delayed alternation task in which the correct stimulus was that color not responded to on the preceding trial. Subjects required to emit either 15 or 30 pecks to the correct stimulus within a trial learned the task, those required to emit only one or five pecks did not. Also, alternation was learned more easily after an incorrect than after a correct trial. Later experiments showed that a minimum fixed-ratio value was required for successful color alternation to occur, even though no fixed-ratio requirement was necessary when a position cue was available. The mechanism of the fixed-ratio effects derived from the pigeons' tendency to repeat their response in the presence of the color reinforced on the last trial. Whereas subjects trained on larger fixed-ratios corrected this error tendency within a trial, subjects trained on smaller fixed ratios did not.     

Delayed alternation in honeybees (Apis mellifera)

Previous experiments with honeybees (Apis mellifera) failed to show learned control of performance by short-ten memory. In this study, honeybees were trained with an improved technique to choose 1 of 2 colors that was either the same as a recently rewarded sample (perseveration) or different (alteration). Because any increase in associative strength stemming from the sample experience would tend to promote perseveration and contravene alternation, the equal difficulty of the 2 tasks suggests that the role played by the sample was primarily discriminative. The animals remembered on each trial the immediately preceding experience with reward and learned to use that information appropriately. These new results extend the list of what may well be fundamental similarities in the learning of vertebrates and honeybees.     

Delayed alternation in the rat: Effect of contextual stimuli on proactive interference

The effect of contextual stimuli on proactive interference in the rat was investigated in three experiments. The task was a modified delayed alternation procedure in which the rat was initially forced to one side of a T maze (the interfering forcing) followed by a forcing to the opposite side (the target forcing). A free choice run followed the target forcing in which a turn in either direction could be made. In order to obtain reinforcement on the free choice run, the rat was required to turn in the direction opposite that of the target forcing (i.e., in the same direction as the interfering forcing). Manipulation of the context prevailing during the interfering forcing, target forcing, and free choice runs revealed that free choice accuracy was (a) greater when the interfering and target forcings were conducted in different contexts than when they were conducted in the same context and (b) influenced only slightly, if at all, by whether the free choice context coincided with that prevailing during the interfering forcing or with that prevailing during the target forcing.     

Delayed signal detection, differential reinforcement, and short-term memory in the pigeon.

In two discrete-trial delayed-detection experiments, six pigeons were trained on dependent concurrent variable-interval schedules. Pecking a red side key was reinforced when the brighter of two white lights (S1) had been presented on the center key, and pecking a green side key was reinforced when the duller of two white lights (S2) had been presented on the center key. Incorrect responses were red side-key pecks following S2 presentations and green side-key pecks following S1 presentations; these resulted in three-second blackouts. In Experiment 1, the time between presentation of S1 or S2 on the center key and the onset of the red and green side keys was varied nonsystematically from 0.06 seconds to 19.69 seconds across experimental conditions. Stimulus discriminability decreased as the stimulus-choice delay increased. A rectangular-hyperbolic function better described this decrease in discriminability over time than did a negative-exponential function. In Experiment 2, at each of three stimulus-choice delays (0.06, 3.85, and 10.36 seconds), relative reinforcer frequency for correct responses to the red and green side keys was varied by changing the values of the dependent concurrent variable-interval schedules. The sensitivity of choice to relative reinforcer frequency was independent of the decrease in stimulus discriminability with increasing stimulus-choice delay.     

Delayed matching in the pigeon: Effect on performance of sample-specific observing responses and differential delay behavior

Pigeons were trained on a delayed matching-to-sample task with a 0-sec delay and then transferred to a 1-sec delay (Experiment 1) or were trained with mixed 0-sec/1-sec delays and then transferred to longer mixed delays up to 28 sec (Experiment 2). Four groups were distinguished by the nature of the observing response required to each sample color (red and blue). For Group NN pecks were allowed to neither color. For Group PcPc pecks were required to both colors. For Group PcN pecks were required to red but were not allowed to blue. For Group PcPt pecks were required at the center key in the presence of red, but at a key located directly above the center key in the presence of blue. The results of both experiments indicated significant effects of both Pecking vs Not Pecking, and Sample-Specific vs Sample-Independent Responding. At the longer delays individual differences in sample-specific delay behavior were a better predictor of performance than the behavior required in the presence of the sample.     

Discrete-trial alternation in the rat

The acquisition and maintenance by rats of single alternation, double alternation, and four other repeating patterns of reinforced and non-reinforced trials was studied in a discrete-trial lever-pressing situation. The rats learned all these patterns in a small number of experimental sessions. Single alternation was learned more rapidly than the more complex patterns. Rate of learning single and double alternation decreased moderately as inter-trial interval increased. Abrupt changes in the scheduling of trials, either by doubling the inter-trial interval or by shifting from fixed to variable trial spacing, temporarily disrupted the patterned performance. Two hypotheses concerned with the means by which the rats could have learned to conform to the pattern were examined: (1) “timing” of the interval between successive reinforcements; and (2) control of responding on a trial by the outcome of preceding trials, depending on the consistency with which these outcomes were associated with reinforced or non-reinforced trials in the pattern and on how many trials back these outcomes occurred. The second hypothesis accounted for the relative frequency of errors on trials at various locations in the sequences, and predicted most of the changes in error frequency observed in experiments in which “inter-trial stimuli” were added to the sequences.     

Three-configuration matching-to-sample in the pigeon

Pigeons were trained on a zero-delay matching-to-sample procedure during which only three of the four possible stimulus configurations were presented. Subsequently, all birds were exposed to all four configurations as a transfer test. A high degree of negative transfer from the three training configurations was obtained in Experiment 1. The results of Experiment 2 indicated that three-configuration training produced differential position-preference effects. During the transfer test, responding after one sample stimulus was apparently based on position, while responding after the other sample was based on color.     

Food satiation in the pigeon

The experiment was designed to find the shape of food satiation curves of the pigeon as a function of hours of deprivation or percentage of free-feeding weight, and to study the fluctuation in free-feeding weight as a function of deprivation and satiation. At a systematically and progressively increased number of hours'' deprivation, eight birds were allowed to satiate on grain presented contingent upon the emission of a pecking response. In the second part of the experiment, in which two birds were used, a similar procedure was followed except that the independent variable was percentage of free-feeding weight. These were the conclusions.1. Approximately 64% of the satiation curves were classified as straight with an abrupt stop. The next highest percentage of curves was 18% for curves classified as straight with a curvilinear stop. No “classic” satiation curves, curvilinear with curvilinear stop, were found.2. The pigeons responded at fairly constant rate during the early part of each satiation session, or they did not respond at all. The critical weight, above which they did not respond, was 85% of free feeding.     

Titrating-delay matching-to-sample in the pigeon

The titrating-delay matching-to-sample (TDMTS) procedure offers researchers an additional behavioral task thought to capture some important features of remembering. In this procedure, the delay between sample offset and comparison onset adjusts as a function of the subject's performance. Specifically, correct matches increase the delay and incorrect matches decrease the delay, and steady-state titrated delays serve as the primary dependent measure. The present series of experiments investigated the effects of several procedural variables on performance in TDMTS procedures in an effort to elucidate better its features to allow for more precision in future use. Experiment 1 reports results from a parametric analysis of fixed-ratio response requirements on the sample key that indicated improved remembering in the form of higher daily titrated delay values as the requirement was increased. Experiment 2 investigated the extent to which the initial delay value in each session affected session-wide delay values. Results indicated that regardless of value of the initial delay, the subjects' performances adjusted the delay values in the direction of the known baseline delay-value levels. Experiment 3 manipulated the step size by which delay values were adjusted and the results indicated that larger step sizes increased both session-to-session variability and within-session range of titrated delay values, although the average values remained approximately the same. These results suggest that the TDMTS task serves as a promising procedure to study what many refer to as memory.     

Visual dominance in the pigeon

In Experiment 1, three pigeons were trained to obtain grain by depressing one foot treadle in the presence of a 746-Hertz tone stimulus and by depressing a second foot treadle in the presence of a red light stimulus. Intertrial stimuli included white light and the absence of tone. The latencies to respond on auditory element trials were as fast, or faster, than on visual element trials, but pigeons always responded on the visual treadle when presented with a compound stimulus composed of the auditory and visual elements. In Experiment 2, pigeons were trained on the auditory-visual discrimination task using as trial stimuli increases in the intensity of auditory or visual intertrial stimuli. Again, pigeons showed visual dominance on subsequent compound stimulus test trials. In Experiment 3, on compound test trials, the onset of the visual stimulus was delayed relative to the onset of the auditory stimulus. Visual treadle responses generally occurred with delay intervals of less than 500 milliseconds, and auditory treadle responses generally occurred with delay intervals of greater than 500 milliseconds. The results are discussed in terms of Posner, Nissen, and Klein's (1976) theory of visual dominance in humans.     

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.