Effect of sample presentation time on long-delay matching in the pigeon

The effect of sample stimulus presentation time on long-delay matching in highly practiced pigeons was investigated. The birds were found capable of above chance matching performance at a delay of 60 sec provided the sample stimulus was presented for 4 sec or longer. Matching accuracy increased as a negatively accelerated function of sample stimulus presentation time and decreased as a negatively accelerated function of time since the termination of the sample. The rate of forgetting was found to be independent of sample stimulus presentation time. The data were inconsistent with a temporal discrimination interpretation of the effect of presentation time on delayed matching. The data were interpreted as supporting a simple trace strength and decay model of pigeon delayed matching.     

Effects of a coactor's prediction on latencies to predict and indentify stimuli

On each of 300 trials E's confederate (C) verbalized which of two stimuli would occur; then S made a prediction. Following each presentation, S and C pulled a trigger to identify the stimulus. Two latencies were measured: the interval between C's and S's prediction (prediction time), and the interval between stimulus presentation and S's identification response (choice RT). Prediction times were significantly shorter when S's prediction agreed rather than disagreed with C's prediction, when S's preceding prediction was correct rather than incorrect, and when S was female rather than male. Choice RT was influenced by distributions of C's stimulus predictions and C's prediction outcomes in directions supporting an expectancy model.     

Prospective versus retrospective coding of samples of stimuli,responses, and reinforcers in delayed matching with pigeons

Pigeons' performance with samples of stimuli (red and green), number of responses (1 and 20), and reinforcers (food and no food) was assessed in a matching-to-sample preparation. Samples of red, 20 responses, and food were each associated with the red comparison stimulus; samples of green, 1 response, and no food were each associated with the green comparison stimulus. Interest focused on whether physically different samples associated with the same comparison stimulus each establish a unique memorial representation embodying the physical attributes of the sample (retrospective coding), or whether they activate a unitary memorial representation embodying an instruction for test responding (prospective coding). In the first experiment, accuracy of choice responding was independent of whether successive sample presentations within a trial involved the same physical sample or physically different but associatively identical samples. A second experiment revealed that, in contrast to other matching preparations, accuracy was not reduced when sample elements were compounded during presentation. It was concluded that physically different samples which are associated with the same comparison stimulus are coded prospectively in terms of an instruction for choice responding.     

Successive matching-to-sample in the pigeon: Variations on a theme by Konorski

In 1959, Konorski proposed a successive matching-to-sample paradigm with which to study short-term memory in animals. Although the technique has been little used, it affords several distinct advantages over more commonly employed matching-to-sample procedures. Konorski’s paradigm involves the successive presentation of a pair of discriminative stimuli with a brief interstimulus interval between them. Reinforcement is scheduled to occur only when the second stimulus of a pair matches the first; otherwise, nonreinforcement follows. An investigation of the pigeon’s food-reinforced keypecking behavior is reported using a variant of Konorski’s technique. Pigeons rapidly learned to differentiate matching and nonmatching stimulus pairs when brief (5-sec) color stimuli were separated by a 1-sec interstimulus interval. No such differentiation arose when control subjects were trained with reinforcement equiprobable on matching and nonmatching trials. No support was found for the notion that correct performance under this successive-matching procedure was due to overt mediating behaviors.     

Short-term proactive inhibition in the pigeon

Proactive inhibition in the pigeon was studied using a delayed-color-matching-to-sample task, with and without presentation of stimuli prior to the sample. Interference theory predicts that, relative to control performance, the disruptive effects of a prior stimulus should increase over a retention interval, while decay theory predicts that such disruptive effects should decrease over time. Results supported decay theory when performance was at a low level and interference theory when performance was at a high level. With performance at an intermediate level, parallel functions were obtained, an outcome supporting neither theory. It was concluded that the results supporting interference and decay theories were artifactually produced by floor and ceilling effects, respectively, and it was suggested that the results of earlier experiments using the present paradigm may well have been influenced by similar artifacts. Inserting a nondisruptive stimulus between a prior disruptive stimulus and the sample virtually eliminated the disruptive effects of the prior stimulus when tested immediately, but not when tested after 1 sec. The results of the present experiments and related findings can best be explained by either a modified decay theory (Grant, D. S. Proactive interference in pigeon short-term memory. Journal of Experimental Psychology: Animal Behavior Processes 1975, 104, 207–220) or a modified temporal discrimination theory.     

Interactions between view changes and shape changes in picture-picture matching

Four experiments are reported in which pictures of different morphs of novel, complex, 3-D objects, similar to objects which we must identify in the real world, were presented. We investigated how changes of viewpoint influence our ability to discriminate between morphs. View changes had a powerful effect on performance in picture-picture matching tasks when similarly shaped morphs had to be discriminated. Shape changes were detected faster and more accurately when morphs were depicted from the same rather than different views. In contrast, view change had no effect when dissimilarly shaped morphs had to be discriminated. This interaction between the effects of view change and shape change was found both for simultaneous stimulus presentation and for sequential presentation with interstimulus intervals up to 3600 ms. The interaction was found after repeated presentations of the stimuli before the matching task and after practice at the matching task as well as after no such pre-exposure to the stimuli or to the task. The results demonstrate the difficulty in activating abstract, view-insensitive representations to help to achieve object constancy, even when matching over long interstimulus intervals or after stimuli have already been seen many times.     

Male versus female Siamese fighting fish as reinforcing stimuli for conspecific males in single- and two-choice operant situations

Two experiments attempted to determine the reinforcing effectiveness of visual exposure to a female versus a male stimulus in male Siamese fighting fish (Betta splendens). This was accomplished by making male or female presentation contingent upon an operant ring swimming response in single- (Experiment 1) and two-choice (Experiment 2) continuous reinforcement operant situations for 1 hr per day. It was found that visual exposure to a female stimulus was behaviorally reinforcing in a way comparable to that typically found in intermale studies. If given a choice, male test subjects were observed to demonstrate a consistent preference for the female as opposed to the male stimulus. The results are discussed in terms of stimulus discrimination and approach-avoidance conflict as differentially elicited by male and female target stimuli.     

Age related changes in the effectiveness of name and visual codes in recognition memory

In the first of three studies college, third grade, and kindergarten Ss were able to determine that two stimuli presented 700 msec apart were the same more quickly if they were visually identical than if they shared the same name. If 3000 msec elapsed between stimulus presentations third grade and college Ss responded at the same rate in making both types of matches, whereas kindergarten Ss appeared to continue to respond more quickly in making visual matches. Study II was an unsuccessful attempt to replicate the kindergarten finding. A warning signal, presented 500 msec prior to the second stimulus, reduced RTs at both interstimulus intervals, but no significant differences in making visual and name matches occurred. In Study III first-graders, responding either with or without a warning signal, were found to respond like the older Ss in Study I. The warning signal again reduced RT at both intervals. The results suggest that Ss across a wide age range are able to use the visual properties of a stimulus for only a very brief period as the basis for making matching judgments.     

Development of a single-code/default coding strategy in pigeons

We tested the hypothesis that pigeons could use a cognitively efficient coding strategy by training them on a conditional discrimination (delayed symbolic matching) in which one alternative was correct following the presentation of one sample (one-to-one), whereas the other alternative was correct following the presentation of any one of four other samples (many-to-one). When retention intervals of different durations were inserted between the offset of the sample and the onset of the choice stimuli, divergent retention functions were found. With increasing retention interval, matching accuracy on trials involving any of the many-to-one samples was increasingly better than matching accuracy on trials involving the one-to-one sample. Furthermore, following this test, pigeons treated a novel sample as if it had been one of the many-to-one samples. The data suggest that rather than learning each of the five sample-comparison associations independently, the pigeons developed a cognitively efficient single-code/default coding strategy.     

Effect of stimulus pulse duration and interstimulus interval on cross-modal matching of auditory and lingual vibrotactile stimuli

Cross-modal matching functions for eight intensity levels of a 1000-Hz auditory stimulus and a 250-Hz lingual vibrotactile stimulus were obtained for two groups of subjects. Group 1 adjusted the vibrotactile stimulus to match the auditory stimulus, and Group 2 adjusted the auditory stimulus to match the vibrotactile stimulus. Stimulus-pulse durations and interstimulus intervals were varied over six experimental conditions for both groups. The variations in stimulus-pulse durations and interstimulus intervals had no appreciable effect on mean matching-function exponents for the two groups. A possible regression effect consistent with data from other psychophysical scaling studies was noted for matching functions of the two stimuli.     

A model for the time-order error in contrast discrimination

Trials in a temporal two-interval forced-choice discrimination experiment consist of two sequential intervals presenting stimuli that differ from one another as to magnitude along some continuum. The observer must report in which interval the stimulus had a larger magnitude. The standard difference model from signal detection theory analyses poses that order of presentation should not affect the results of the comparison, something known as the balance condition (J.-C. Falmagne, 1985, in Elements of Psychophysical Theory). But empirical data prove otherwise and consistently reveal what Fechner (1860/1966, in Elements of Psychophysics) called time-order errors, whereby the magnitude of the stimulus presented in one of the intervals is systematically underestimated relative to the other. Here we discuss sensory factors (temporary desensitization) and procedural glitches (short interstimulus or intertrial intervals and response bias) that might explain the time-order error, and we derive a formal model indicating how these factors make observed performance vary with presentation order despite a single underlying mechanism. Experimental results are also presented illustrating the conventional failure of the balance condition and testing the hypothesis that time-order errors result from contamination by the factors included in the model.     

Effects of associatively significant posttrial stimuli on learning and memory

Pigeons were trained on a delayed conditional discrimination in which the choice between two simultaneously presented stimuli depended on how the trial started. Choice of one of the stimuli was reinforced if the trial had been initiated by presentation of a food sample and choice of the other was reinforced if no sample had been presented. Subsequently, test trials were administered on which an associatively significant stimulus was presented during the retention interval. This manipulation was intended to modulate the short-term retention of information about the food sample. It was found that performance on food sample test trials was enhanced by presentation of an excitor for food, disrupted by presentation of an inhibitor for food and unaffected by presentation of an associatively neutral stimulus. The impact of these posttrial stimuli was also assessed on the ability of the food sample to serve as a reinforcer. This was done by recording the development of responding to a keylight that signalled the food sample on these test trials. Compared to the associatively neutral stimulus, both the excitor and the inhibitor interfered with the development of keypecking. These results are discussed with regard to the issue of how posttrial events modulate associative learning.     

Choice As A Function Of Reinforcement Ratios In Delayed Matching-to-sample

Pigeons were studied in two experiments using a delayed matching-to-sample task. In Experiment 1, 4 subjects were exposed to a task in which the proportion of reinforcement associated with matching and nonmatching, and the overall proportion of reinforcement associated with selecting each choice, regardless of the sample stimulus, were varied. Choice was sensitive to both proportions. A least squares regression analysis showed that Wixted's (1989) proportions of reinforcement model closely fit the data from Experiment 1; however, the model failed to make accurate qualitative predictions for some test conditions. In Experiment 2, 4 subjects were exposed to a delayed matching-to-sample task in which the retention intervals and the reduction in delay to reinforcement signaled by the onset of the sample stimulus were independently varied. When the retention interval was short and when the delay-reduction value of the sample stimulus was high, the sample exerted greater control over choice; the control by the overall proportion of reinforcements for selecting each choice stimulus was correspondingly low. Conversely, when the retention interval was long and the delay-reduction value of the sample stimulus was low, the sample exerted relatively less control over choice; control by the overall proportion of reinforcements obtained for selecting each choice stimulus was correspondingly high. A signal detection analysis found that sensitivity to reinforcement varied directly with retention interval. Data were also consistent with misallocation models. No evidence was found to suggest that pigeons ignore the rate at which selecting individual choice stimuli is reinforced, as has been reported in studies with human subjects.     

Pigeons' spatial memory: III. Effect of distractors on delayed matching of key location.

The effect of distractors on pigeons' delayed matching of key location was investigated. Baseline trials began with a "ready" stimulus (brief operation of the grain feeder). Then one (randomly chosen) key from a three-by-three matrix was lit briefly as the sample. After a short delay (retention interval) the sample key was lit again along with one of the other eight keys. A peck at the key that had served as the sample (correct comparison) produced grain reinforcement, whereas a peck to the other key (incorrect comparison) produced only the intertrial interval. In Experiment 1, a houselight distractor, presented during either the sample, retention interval, or choice phases of the trial, had little if any effect on accuracy of matching key location. In Experiment 2, one of three types of spatial stimuli was interpolated during the retention interval, or the interval was blank as during baseline trials. The three stimuli were: the sample (correct comparison) location for that trial, the incorrect comparison location for that trial, or one of the seven unused locations for that trial. Relative to blank trials, accuracy improved slightly on sample-interpolated trials, decreased slightly on unused location-interpolated trials, and decreased considerably on incorrect comparison-interpolated trials. In Experiment 3, retention intervals were blank or had one of six types of interpolation: the sample, the incorrect comparison, two presentations of the sample, two presentations of the incorrect comparison, the sample followed by the incorrect comparison, or the incorrect comparison followed by the sample.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pigeons may not remember the stimuli that reinforced their recent behavior

In two experiments the conditioned reinforcing and delayed discriminative stimulus functions of stimuli that signal delays to reinforcement were studied. Pigeons' pecks to a center key produced delayed-matching-to-sample trials according to a variable-interval 60-s (or 30-s in 1 pigeon) schedule (Experiment 1) or a multiple variable-interval 20-s variable-interval 120-s schedule (Experiment 2). The trials consisted of a 2-s illumination of one of two sample key colors followed by delays ranging across phases from 0.1 to 27.0 s followed in turn by the presentation of matching and nonmatching comparison stimuli on the side keys. Pecks to the key color that matched the sample were reinforced with 4-s access to grain. Under some conditions of Experiment 1, pecks to nonmatching comparison stimuli produced a 4-s blackout and the start of the next interval. Under other conditions of Experiment 1 and each condition of Experiment 2, pecks to nonmatching stimuli had no effect and trials ended only when pigeons pecked the other, matching stimulus and received food. The functions relating pretrial response rates to delays differed markedly from those relating matching-to-sample accuracy to delays. Specifically, response rates remained relatively high until the longest delays (15.0 to 27.0 s) were arranged, at which point they fell to low levels. Matching accuracy was high at short delays, but fell to chance at delays between 3.0 and 9.0 s. In Experiment 2, both matching accuracy and response rates remained high over a wider range of delays in the variable-interval 120-s component relative to the variable-interval 20-s component. The difference in matching accuracy between the components was not due to an increased tendency in the variable-interval 20-s component toward proactive interference following short intervals. Thus, under these experimental conditions the conditioned reinforcing and the delayed discriminative functions of the sample stimulus depended on the same variables (delay and variable-interval value), but were nevertheless dissociated.     

Flooding therapy: Effectiveness,stimulus characteristics,and the value of brief in vivo exposure

Three analogue experiments examined flooding therapy. Experiment 1 showed that flooding was more effective than standardized desensitization in reducing snake phobia. Experiment 2 examined three different modes of presenting the feared stimuli in flooding: taped auditory presentation, pictorial presentation, and a combination of these two. An additional combination group were given a brief in vivo exposure to the feared object immediately after each of three treatment sessions. Both a behavioral test and subjective estimates of fear showed advantages for the combined group that had the in vivo exposure, although it appeared that auditory instructions to imagine interaction with the snake was the best method for presenting the feared stimuli. Experiment 3 compared the auditory imagined method with and without ‘aversive’ or ‘implosive’ scenes, and with either an immediate or a delayed in vivo exposure. The only procedure to produce marked effects was the one that omitted ‘aversive’ scenes and provided immediate post-treatment in vivo exposure.     

Local and Global Sources of Control in Pigeon Delayed Matching-to-sample Performance

The present study employed a behavioural detection approach to investigate the combined effects of sample duration and sample presentation frequency on delayed matching accuracy of pigeons. Experiment 1 showed that when both samples were exposed at each of the two possible durations within a two-alternative, delayed matching session, discriminability was higher to the longer duration sample than to the short-duration sample, as found when sample duration is varied between sessions. Experiment 2's asymmetrical procedure increased bias toward the more frequent of the two samples but had no influence on discriminability. Initial discriminability was higher to samples exposed for longer durations, irrespective of stimulus presentation frequency. The results suggest qualitatively different effects of the two sources of stimulus control under consideration: Sample duration (a local or within-trial manipulation) exerted its effect on discrimination of the stimuli, whereas sample presentation frequence (a global factor) exerted its major effect on response bias. An interpretation of the data in terms of Blough's (1996) analysis of errors in matching tasks suggests that the amount of behaviour under control of the sample stimulus markedly changed with different sample durations. The analysis also showed that the biasing manipulation exerted most of its effect on the portion of behaviour outside of control by the critical stimulus. We argue that theoretical accounts of delayed matching performance need to consider both local and global factors as determinants of matching accuracy.     

Manipulation of CS-US conditional probability and of the US-US trace interval on conditioning to the CS and to a background stimulus in a CER situation

Two experiments examined the relationship between conditioning to the CS and background using a novel CER paradigm, in which a long background stimulus played the role of more conventional contextual cues. Experiment 1 manipulated the probability of US occurrence given the CS (p(US/CS)). Conditioning to the background was not a monotonically decreasing function of p(US/CS) at all shock intensities, and conditioning to the CS was remarkably insensitive to the value of p(US/CS) when assessed off the baseline. Experiment 2 manipulated the trace interval between the CS and US. Although conditioning to the CS decreased as the trace interval increased, conditioning to the background was dependent upon whether it served as the interstimulus interval (ISI; interval between the CS and US) or intertrial interval (ITI; interval between CS-US pairs) stimulus. Conditioning to the ISI background decreased as the trace interval increased, but conditioning to the ITI background at first increased, but then decreased as the trace interval was further increased. These results are discussed with respect to the adequacy of contemporary models of conditioning.     

Comparisons of learning procedures: Effects of constant and random presentations

The retention interval hypothesis (Izawa 1972) was formulated on the basis of retention interval distributions given in random order to account for inconsistent performance differences between anticipation and study-test procedures, which have been regarded as a puzzle for nearly two decades. Under the anticipation procedure a presentation of the stimulus term of a paired-associate (a test event) is immediately followed by a presentation of both stimulus and response terms of the pair (a study event), whereas under the study-test procedure, study and test events are given on separate cycles. The retention interval hypothesis was specifically tested in a situation without any random distributions of the retention intervals i.e., under a constant item presentation order from cycle to cycle, in addition to random presentation orders, in a paired-associate learning experiment, using 80 college students. As predicted by the theory, significantly superior performances were obtained for the study-test method vis-à-vis the anticipation method also under a constant item presentation order. The constant presentation-order- arrangements significantly outperformed the random ones. Directions for further theoretical elaborations are suggested.