Delayed matching in the pigeon: Interference produced by the prior delayed matching trial

Pigeons’ delayed matching performance on Trial n was examined as a function of whether the correct and incorrect comparison stimuli from Trial n?1 were maintained in the same role on Trial n (positive transitions), were reversed in role on Trial n (negative transitions), or were absent on Trial n (neutral transitions). Relative to neutral transitions, positive transitions did not significantly facilitate performance. Negative transitions, however, produced significant proactive interference on Trial n, and the magnitude of proactive interference was greater when the Trial n retention interval was 1 sec than when it was 0 sec. As the intertriai interval increased from 2 to 10 sec, the amount of interference dissipated. The results suggest that a prior delayed matching trial can serve as a significant source of forgetting but not a significant source of facilitation on an immediately following delayed matching trial.     

Some relationships between outcome expectancies and sample stimuli in pigeons’ delayed matching

Two sets of experiments examined how differential outcomes affect conditional stimulus control by the samples in delayed matching-to-sample. Pigeons were initially trained on symbolic delayed matching with reinforcing outcomes that were either differential or nondiffereatial with respect to the samples. In one set of experiments, the outcome manipulation involved different (p = 1.0 vs. 0.2) versus the same (p = 0.6) probabilities of food; in the other, food and no-food outcomes were used. Following initial acquisition and mixed-delay tests, the matching procedure in each study was discontinued while the samples were nondifferentially reinforced with the same probability of food, or with food and no food, respectively. When later retested on delayed matching with those nondifferential outcomes, birds initially trained with different reinforcement probabilities matched at the same levels of accuracy as those trained with the same probability. By contrast, birds initially trained with food versus no-food outcomes showed lower levels of matching accuracy than their nondifferential controls. Subsequent transfer tests showed that matching performances by the differential birds in both studies had been originally cued in part by differential outcome expectancies. Apparently, the expectancies based upon different probabilities of food provided a source of conditional stimulus control that did not compete with the samples. By contrast, the expectation of food versus no food reduced (overshadowed) sample-stimulus control.     

Remembering as discrimination in delayed matching to sample: Discriminability and bias

Task difficulty in delayed matching-to-sample tasks (DMTS) is increased by increasing the length of a retention interval. When tasks become more difficult, choice behavior becomes more susceptible to bias produced by unequal reinforcer ratios. Delaying reinforcement from choice behavior also increases both task difficulty and the biasing effect of unequal reinforcer probability. Six pigeons completed nine DMTS conditions with retention intervals of 0, 2, 4, 6, and 8 sec, in which reinforcer delays of 0, 2, and 4 sec were combined with ratios of reinforcer probabilities of .5/.5, .2/.8, and .8/.2 for correct red and green responses. Discriminability (logd) decreased with both increasing retention interval duration and increasing reinforcer delay. Sensitivity to reinforcement, the tendency for ratios of choice responses to follow unequal reinforcer probabilities, also increased as a function of both increasing retention interval and increasing reinforcer delay. The result is consistent with the view that remembering in DMTS tasks is a discriminated operant in which increasing task difficulty increases sensitivity to reinforcement.     

Coding of hedonic and nonhedonic samples by pigeons in many-to-one delayed matching

In two experiments, pigeons were trained on many-to-one delayed matching in which samples of food and one hue were each associated with one shape comparison, and samples of no food and a different hue were each associated with a second shape comparison. When later tested with delays between sample and comparison stimuli, pigeons showed nonparallel delay functions, typically found with food and no-food samples (i.e., steeply declining food-sample delay functions, and relatively flat no-food-sample delay functions). Furthermore, the slopes of the hue-sample delay functions were similar to those on the food/no-food-sample trials. In Experiment 2, following many-toone delayed matching, when the hue samples were associated with new comparisons and then food and no-food samples replaced the hues, evidence was found for transfer of training indicative of the common coding of samples associated with the same comparison in original training. The transfer results suggest that the asymmetrical hue-sample functions resulted from the common coding of samples associated with the same comparison.     

The effect of sample and comparison ratio schedules on delayed matching to sample in the pigeon

In Experiment 1, three food-deprived pigeons received trials that began with red or green illumination of the center pecking key. Two or four pecks on this sample key turned it off and initiated a 0- to 10-sec delay. Following the delay, the two outer comparison keys were illuminated, one with red and one with green light. In one condition, a single peck on either of these keys turned the other key off and produced either grain reinforcement (if the comparison that was pecked matched the preceding sample) or the intertrial interval (if it did not match). In other conditions, 3 or 15 additional pecks were required to produce reinforcement or the intertrial interval. The frequency of pecking the matching comparison stimulus (matching accuracy) decreased as the delay increased, increased as the sample ratio was increased, and decreased as the comparison ratio was increased. The results of Experiment 2 suggested that higher comparison ratios adversely affect matching accuracy primarily by delaying reinforcement for choosing the correct comparison. The results of Experiment 3, in which delay of reinforcement for choosing the matching comparison was manipulated, confirmed that delayed reinforcement decreases matching accuracy.     

Effects of locus of a brief stimulus in a second-order schedule with pigeons

On the completion by pigeons of four equal fixed intervals on one key, a light on a second key signaled that one peck on that key would be followed by food. In condition A, a brief stimulus of a further color was produced on the first key by the pecks that ended the first three (but not the fourth) fixed intervals. In condition B, no brief stimuli occurred at the end of the first three fixed intervals (tandem schedule). In condition C, the unpaired brief stimulus was presented on the second key after the pecks on the first key that ended the first three fixed intervals. An ABACA reversal design was used. Postreinforcement pauses were longer in condition B (tandem) than in condition A, an effect similar to that reported in similar conventional one-key second-order schedules. Postreinforcement pauses in condition C, with the brief stimulus on the second key, were also longer than in condition A, with the brief stimulus on the first key, although similar pauses were observed after the brief stimuli in both conditions. The locus of the brief stimulus appears to affect the control it exerts over behavior in a second-order schedule.     

Effects of stimulus dimension and of trial and intertrial illumination on acquisition of a match/mismatch task by pigeons

Birds were trained on a higher order conditional discrimination task, one that required birds to match samples and comparisons on some trials and to mismatch on other trials. Which task component was in effect was indicated by the level of chamber illumination (houselight-on and houselight-off instructions). Acquisition of the components of a color (red and green) match/mismatch task in the first half of the experiment was not differentially affected by the level of illumination associated with each task component, by houselight changes per se, or by the level of illumination during the intertriai interval (ITI). However, when shapes (plus and circle) were used to train the task in the second half of the experiment, performance on the houselight-cued task component exceeded performance on the dark-cued task component, and ITI illumination facilitated performance on both task components. These results suggest that attention to shape stimuli, but not to colors, may vary systematically as a function of chamber illumination level.     

Common coding by pigeons in a many-to-one delayed matching task as evidenced by facilitation and interference effects

Pigeons were first trained on many-to-one delayed matching in which pairs of hue and line-orientation samples were associated with individual comparison stimuli. They were then trained to match two of the original samples (either hues or line orientations) to new comparisons, after which 2-sec delays were inserted between the samples and comparisons. In testing, the remaining samples were presented as interpolated stimuli during the delays. When the interpolated stimulus had been associated with the same comparison as the sample in many-to-one matehing, performance was significantly more accurate than when it had been associated with a different comparison. This finding adds to the evidence that samples sharing common comparison associations are commonly coded.     

Effects of discrimination training on stimulus generalization in pigeons: Role of resistance to extinction and response-produced stimuli

In Experiment 1, two groups (n = 10) of pigeons received 17 sessions of TD (true discrimination) or ND (nondifferential) training with line angles. Seventeen sessions of SS (single stimulus) training with a wavelength preceded this training and two followed it. Subsequent wavelength generalization testing in extinction revealed a sharper TD than ND gradient. This slope difference was evident from the very first test stimulus presentation and remained stable throughout testing. As a consequence of substantial overtraining, there was no reduction of response strength and no sharpening of generalization during testing for either group. In Experiment 2, two groups (n = 16) of pigeons received 10 sessions of TD or PD (pseudodiscrimination) training with line angles, followed by four sessions of SS training with a single wavelength. During this training and in subsequent wavelength generalization testing in extinction, brief blackouts separated stimulus presentations. Again, the TD group yielded the sharper gradient. Although responding weakened and the gradients sharpened during the test, these effects were comparable in the two groups. Furthermore, gradients based on the percentage of trials with at least one response showed the same TD-PD slope difference. This finding indicates that differential control over responding by response-produced feedback is inadequate to account for the TD-PD difference in generalization slope. Both experiments indicate that a purported difference in resistance to extinction is also an inadequate explanation.     

Rats exhibit asymmetrical retention functions for hedonic and nonhedonic samples in many-to-one symbolic delayed matching to sample

Rats were initially trained in a symbolic delayed matching-to-sample task either to discriminate hedonic samples that consisted of food or no food or to discriminate tone samples that differed in frequency and location. The retention functions for both the hedonic and tone samples were asymmetric, with forgetting of the food sample or the high-frequency tone occurring more rapidly than forgetting of the no-food sample or the low-frequency tone. Next, many-to-one (MTO) training was given in which tone samples were added for the rats initially trained with hedonic samples, and hedonic samples were added for the rats initially trained with tone samples. For both groups, a food sample and a tone sample (tone-F) were associated with responding to one lever (e.g., stationary), and a no-food sample and a different tone sample (tone-NF) were associated with responding to the alternative lever (e.g., moving). During retention testing, we found equivalent forgetting for the food and no-food samples, but forgetting of the tone-F sample occurred more rapidly than forgetting of the tone-NF sample. This is the first MTO study to suggest that rats, like pigeons, may use hedonic samples as the basis for the common coding of nonhedonic samples in MTO delayed matching.     

Overall and local contrast in multiple schedules: Effects of stimulus similarity and discrimination performance

An experiment with pigeons related overall and local behavioral contrast to similarity between stimuli signaling multiple-schedule components. Similarity was defined both physically and by discrimination performance. Initial and final baseline conditions used two equal random-interval schedules. During two intervening test periods, the schedule accompanying one component was changed to extinction. In the first test, components alternated strictly; in the second test, random component sequences were used. Signaling wavelength stimuli were separated by 1.5, 2, or 14 nm. Overall positive contrast occurred reliably, but its amount depended neither on wavelength difference nor on discrimination performance. Local positive contrast was less frequently observed when signaling stimuli were physically dissimilar; however, the effect was most closely related to actual discrimination performance. The relationship between discrimination and local contrast was nonmonotonic, indicating maximum local contrast at intermediate discriminations.     

Role of perceptual and conceptual similarity in category matching at age two years

Perceptual and categorical similarity were varied independently in a concept-matching task administered to 26-month-old children (N = 25). 44 test sets were assembled. Each set included a 3-dimensional standard and an array of 4 pictures, one of which was a member of the same basic or superordinate category as the standard. On each trial, placing the standard on the matching picture resulted in activation of 1 of 12 mechanical displays. The test sets varied in the perceptual and categorical resemblance of the standard to the match and to the nonmatches, as determined by adults' ratings. Perceptual similarity proved to be the primary determinant of difficulty level. When perceptual resemblance of the standard and the match were equated, superordinate and basic matches were equally difficult. When perceptual resemblance was minimal, most children were unable to recognize matches at either the basic or superordinate level.     

Prospective representation: The effects of varied mapping of sample stimuli to comparison stimuli and differential trial outcomes on pigeons’ working memory

The mapping of sample stimuli onto comparison stimuli and the nature of trial outcomes were factorially manipulated in a delayed matching-to-sample procedure. In the many-to-one condition (MTO), responding to a particular comparison was correct following several sample stimuli, whereas in the one-to-many condition (OTM), responding to several comparison stimuli was correct following a particular sample. Probabilities of reinforcement for correct responding to comparison stimuli were either differential (DO) or nondifferential (NDO). Four groups of pigeons were trained under four combinations of mapping and outcome conditions, MTO-DO, MTO-NDO, OTM-DO, and OTM-NDO. Testing at delay intervals of 1, 2, 4, and 8 sec revealed significant effects due to both the mapping variable and the differential outcomes variable. It was argued that the poorer performance obtained in the OTM condition was due to the differential prospective coding requirements placed on reference and working memory by this mapping. In the OTM conditions, a greater number of response codes had to be retrieved from reference memory and multiple response codes may have overburdened working memory, which has a limited capacity.     

Delayed matching in pigeons with food and no-food samples: Further examination of backward associations

When pigeons are trained on a delayed conditional discrimination with presence versus absence samples and tested with delays, a bias to choose the comparison associated with the absence sample is observed with increasing delay. Additionally, when the samples consist of food versus no food, this trial-type performance difference is reversed on short-delay trials: a bias to choose the comparison associated with the presence sample develops with delay testing. This reversal in comparison bias at short delays has been attributed to a preference produced by backward associations between the hedonic samples and the nonhedonic choice stimuli. In the present experiment, we tested an alternative hypothesis, that the short-delay comparison bias is produced by proactive interference—in particular, from reinforcement obtained on the previous trial—by including a group trained with reinforcement on only half of the trials with a correct response. According to the proactive interference account, this group should have shown a smaller short-delay comparison bias than would the typical 100% reinforcement group. Instead, consistent with a backward-association interpretation, the magnitude of the short-delay comparison bias shown by the 50% group was significantly greater than that shown by the 100% group.     

Differential inhibition and stimulus generalization cannot account for value transfer in simultaneous discrimination learning by pigeons: Reply to Aitken

Aitken (1999) argues that, in a simultaneous discrimination, reports of the transfer of value from the positive to the negative stimulus can be more readily explained in terms of an artifact produced by the procedure in which differential inhibition accrues to the negative test stimuli during training, together with stimulus generalization (similarity between the positive and negative stimuli). We argue that (1) there is little evidence for differential inhibition, and it often occurs in the wrong direction; (2) value transfer can be demonstrated when differential value is established to the positive stimuli afterdiscrimination training, when differential inhibition is not likely to be a factor; and (3) on both logical and empirical grounds, stimulus similarity does not provide an adequate account of the transfer of value from the positive to the negative stimulus (i.e., the strongest evidence for value transfer occurs when there is least stimulus similarity). We propose that value transfer occurs whenever there is relatively little experience with the negative stimuli. However, when there is extended experience with the negative stimuli, contrast will be found.     

The “disinhibition” of extinguished operant behavior in pigeons: Trial-tempo shifts and novel stimulus effects

After conditioning and extinction of keypecking with 25-see intertrial intervals between key illuminations, an immediate change to 5-sec intertrial intervals reinstated pecking during trials. Brief illuminations of the chamber during intertrial intervals also temporarily restored extinguished keypecking. The same manipulations of trial tempo and chamber illumination usually weakened well established, still reinforced keypecking. No recovery of extinguished behavior occurred when the intertrial interval was shifted upward from 5 sec to 25 sec. These and other behavioral findings were examined in relation to (a) Pavlov’s and Skinner’s research and views on “disinhibition” and “external inhibition” and to (b) analogous phenomena in physiological studies of habituation and dishabituation. The reliable evidence of disinhibition obtained in the present experiments suggests the involvement of an inhibitory process in extinction.     

坚持最低纲领与最高纲领的统一

党的纲领是党的一面旗帜，是一个政党的政治主张的集中体现。中国共产党人必须坚持最低纲领与最高纲领的统一，以“三个代表”为指导，为实现现阶段的基本纲领而奋斗。     

Effects of sample duration,retention interval,and passage of time in the test on pigeons’ matching-to-sample performance

Four pigeons served as subjects in an experiment using the go/no-go delayed matching-to-sample paradigm. The go/no-go method was used because it permits the experimenter to track the time course of discriminative performance throughout the test period, unlike the conventional choice matching procedure. It was found that discriminative test performance increased with longer sample durations; performance decreased with longer retention intervals and also as time passed in the test period. The rate of forgetting was virtually the same when either the retention interval was lengthened or time elapsed in the test. These findings support a modified trace theory, which proposes that the sample stimulus trace decays at a constant rate from the point of sample offset, and that the decaying memory trace is repeatedly compared with the prevailing test stimulus as time passes in the test period.     

Memory for a stimulus versus anticipation of a response: Contrasting effects of proactive interference in two delayed comparison tasks

Pigeons were trained to perform two delayed comparison tasks that differed only in the temporal placement of the retention interval relative to the sample and comparison stimuli. In one task (conditional delayed response—CDR), the subject could determine the correct response prior to the retention interval. In the second task (delayed conditional response—DCR), the subject was required to compare stimuli presented before and after the retention interval. Although overt mediational responding was not observed in the CDR condition, retention was, nevertheless, greater than in the DCR condition. Furthermore, this difference was amplified at short intertrial intervals. Finally, retention in the DCR, but not the CDR, condition was disrupted by proactive interference (PI) from previous sample stimuli. The results suggest that memory is less closely tied to the sample stimulus when the stimuli necessary to determine the correct response are presented prior to the retention interval (CDR and other delayed response tasks) than when the subject must compare stimuli across the retention interval (DCR, or delayed matching-to-sample, tasks). This difference may lead directly, or indirectly through an interaction with PI, to task differences in retention.     

Limits of dynamic object perception in pigeons: Dynamic stimulus presentation does not enhance perception and discrimination of complex shape

A go/no-go procedure was used to train pigeons to discriminate pictures of human faces differing only in shape, with either static images or movies of human faces dynamically rotating in depth. On the basis of experimental findings in humans and some earlier studies on three-dimensional object perception in pigeons, we expected dynamic stimulus presentation to support the pigeon’s perception of the complex morphology of a human face. However, the performance of the subjects presented with movies was either worse than (AVI format movies) or did not differ from (uncompressed dynamic presentation) that of the subjects trained with a single or with multiple static images of the faces. Furthermore, generalization tests to other presentation conditions and to novel static views revealed no promoting effect of dynamic training. Except for the subjects trained on multiple static views, performance dropped to chance level with views outside the training range. These results are in contrast to some prior reports from the literature, since they suggest that pigeons, unlike humans, have difficulty using the additional structural information provided by the dynamic presentation and integrating the multiple views into a three-dimensional object.