The nature of the response in simon discriminations by pigeons

Spence (1952) postulated that under some conditions, responding in simple discriminations is controlled by compounds or patterns consisting of the nominal discriminative cue, plus its spatial position. Stimulus control by such compounds was said to develop when no single cue or element was systematically reinforced more than any other. This analysis has been applied to good effect in understanding some peculiar accuracy results obtained from pigeons performing Simon discrimination tasks. This article describes how Spence's cue-position analysis provides a better account of pigeons' performance in this task than do nominal cue-only and configurational views of the functional discriminative stimuli. Adding a value transfer assumption improves the ability of the cue-position hypothesis to account for the accuracy data.     

Determinants of value transfer and contrast in simultaneous discriminations by pigeons

In a simultaneous discrimination involving a positive (S+) and a negative (S₋) stimulus, positive value appears to transfer from the S+ to the S₋. However, negative value does not appear to transfer from the S₋ to the S+. Instead, when sufficient experience with the contingencies associated with responding to the S₋ is provided, it appears that the presence of the S₋ enhances the value of the S+ (i.e., a contrast effect is found). The purpose of the present experiments was to further examine the influence of the S+ on the S₋ in a simultaneous discrimination (between subjects in Experiment 1 and within subjects in Experiment 2). In both experiments, we found that under typical training conditions, given little direct experience with the value of the S₋, value transfers from the S+ to the S₋. If sufficient experience with the value of the S₋ is provided, however, contrast between the S+ and the S₋ can be demonstrated. Thus, in a simultaneous discrimination, value transfer from the S+ to the S₋ depends on the animal’s having responded relatively little to the S₋.     

Effects of component training and subsequent sequencing of stimuli on shuttlebox avoidance responding of rats

The serial presentation of two different CSs, with each stimulus having an 8-sec duration (S1₈/S2₈), consistently has resulted in most of the shuttlebox avoidance responses being recorded to the S2 component. Experiment 1 attempted to attenuate this serial CS, delayed-response effect by conditioning the separate components of a serial CS prior to ordering them sequentially. Ten component-training trials were administered, with subjects receiving CS-US pairing to S1 only, S2 only, or to both S1 and S2 presented on separate trials. Two CS durations (8 or 16 sec) during this phase also were compared. Subjects were then given 100 avoidance test trials using the standard serial procedure. The 10 best avoidance responders in each group were selected for analysis. Shorter avoidance latencies were obtained only for subjects receiving component conditioning to S1. CS duration was not a factor in establishing the shorter latencies. Component conditioning to S2 resulted in increasing the total avoidances. Experiment 2 increased the number of component-training trials and the generality of the findings by using a different strain of rats and by extending the testing phase of the study so that all subjects could be included in the analysis. Comparable results were obtained. The theoretical implications of these data were discussed.     

Common coding in pigeons: Partial versus total reversals of one-to-many conditional discriminations

Common coding in pigeons was examined using a delayed conditional discrimination in which each sample stimulus was associated with two different comparison stimuli (one-to-many mapping). In Experiment 1, pigeons matched circle and dot samples to red and green hues and vertical and horizontal line orientations. In Experiment 2, the samples were red and green and the comparisons were vertical and horizontal spatial positions (up vs. down and left vs. right). Following acquisition to high levels of accuracy in each experiment, the associations between the samples and either both sets or only one set of comparisons were reversed. Pigeons learned the total reversals faster than the partial reversals. These results suggest that when different comparisons are associated with a common sample, they may become functionally equivalent.     

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.     

Simultaneous processing of visual and spatial stimuli in pigeons

Pigeons were trained to symbolically match comparison stimuli to either visual sample stimuli presented on a center key or to spatial sample stimuli presented on side keys. Tests were carried out in which visual and spatial cues were simultaneously presented in compound and short-term memory was probed for either visual or spatial information. Symmetrical interference with the matching of visual and spatial components of compounds was found when the visual and spatial cues were presented on separate keys. However, when visual and spatial cues were superimposed on the same side key, no interference was observed relative to element control tests. Discussion of these findings focuses on accounts in terms of limited processing capacity, coding decrement, and receptor orientation mechanisms.     

Use of a single-code/default strategy by pigeons to acquire duration sample discriminations

Past evidence that pigeons may adopt a single-code/default strategy to solve duration sample discriminations may be attributable to the similarity between the intertrial interval (ITI) and the retention interval. The present experiments tested whether pigeons would adopt a single-code/default strategy when possible ITI-retention-interval ambiguity was eliminated and sample salience was increased. Previous studies of duration sample discriminations that have purported to show evidence for the use of a single-code/default coding strategy have used durations of 0, 2, and 10 sec (Zentall, Klein, & Singer, 2004). However, the results of Experiment 1 suggest that the use of a 0-sec sample may produce an artifact resulting in inadvertent present/absent sample matching. In Experiment 2, when pigeons were trained with three nonzero duration samples (2, 8, and 32 sec), clear evidence for the use of a single-code/default strategy was found.     

Association of conditioned stimuli during serial conditioning by pigeons

CS2-CS1-US autoshaping was given to hungry pigeons and evidence of CS2-CS1 association was sought. Pigeons pecked that key of a two-key compound CS2 located where the upcoming CS1 key light was to occur. Such CS2-CS1 association was: (1) quickly acquired, (2) quite durable, and (3) stronger with simultaneous than with successive discrimination tasks.     

The acquisition of trace supraordinate stimulus control in pigeons

Match-to-sample and oddity-from-sample problems with four colors were acquired by two pigeons under the supraordinate control of a line tilt superimposed on samples, Since the supraordinate stimulus terminated before the comparison stimuli were presented, accurate matching and oddity performance indicated trace stimulus control as well, The temporal extent of trace control was assessed in one subject by presenting probes—trials without a line tilt on the sample—in which the basis of correct responding was the supraordinate stimulus presented on the previous trial, Trace supraordinate control did not extend between trials, Subsequently, the delay between the termination of the supraordinate stimulus and the presentation of the comparison stimuli was gradually increased within a trial, Both subjects were able to perform matching and oddity over longer delays, and eventually on probe trials, although accuracy decreased, Results were discussed in terms of instructional stimulus control and memory.     

Factors influencing the acquisition of tactual random figure discriminations by rhesus monkeys

Rhesus monkeys learned to perform two-object random figure discrimination problems by touch. This performance was compared to the visual acquisition of the same problems (reported earlier). In both modalities, choice latencies were shorter to the correct than to the incorrect figure. As compared to visual, however, tactual learning required significantly more trials to criterion, was independent of stimulus figure complexity, and was characterized by significantly shorter choice latencies. Rotation of the figures 180 deg after criterion performance was achieved, yielded partial recognition of the figures visually, but no recognition tactually. These results are explained by different observational or cue-utilization strategies. The majority of the figure is inspected visually, but only the same small section of the perimeter is used tactually. Thus, restricted use of the available cues characterizes tactual performance and is responsible for generating differences in various measures of learning between vision and touch in the monkey.     

Preference effects on acquisition and retention of concurrent discriminations by rhesus monkeys

Ten rhesus monkeys were trained on five tasks, each of which consisted of eight concurrently presented object discrimination problems. Sequences of presentation were devised to allow one, two, or three new tasks to intervene between acquisition and retention tests or to provide a 30-day period of no testing. Equivalent and proficient performances were obtained in all retention tests, and no relationship was observed between retention and the initial preference characteristics of various objects. Object pReferences did produce significant influences upon acquisition, but these effects were not as pronounced in early tasks as in later ones. An additional retention test provided support for the contention that monkeys do not necessarily process information about specific object pair discriminations. Rather, they appeared to retain a list of previously rewarded objects even when object pairings were different from those provided during acquisition. Concurrent discriminations involving many distinct objects were resistant to interference and independent of preference characteristics over long retention periods.     

On the acquisition and measurement of stimulus control in pigeons

Two experiments were performed to investigate the relationship between excitatory stimulus control (number of responses to a training stimulus) and dimensional stimulus control (generalization gradient slope). In experiment 1, after being trained to peck a green key, pigeons received either 20, 40, or 80 brief (.5, 2, 4, or 8 sec) presentations of a 45-deg line followed by reinforcement (12 groups) or 20, 40, or 80 reinforcements for pecking a continuously presented 45-deg line (3 groups). Number of reinforcements determined the slope (percent of total responses to 45 deg) of a subsequent line-angle generalization gradient, but number of responses to the 45-deg line in the test was controlled by total experience with 45 deg as measured by either total exposure time or total responses to 45 deg in training. In a second experiment, it was shown that increasing the number of days of pretraining to green decreased the slope of the gradient (in subjects given 2-sec presentations), but had no effect on number of responses to 45 deg in the test. Furthermore, continuous presentation yielded flatter gradients but more responding to the 45-deg line in the test than did 2-sec presentations. It was concluded that the measures of dimensional stimulus control and excitatory stimulus control reflect different processes because they vary differentially (sometimes in different directions) in response to the same independent variable manipulations.     

Effects of pretraining on acquisition of novel configural discriminations in human predictive learning

In two experiments, participants acquired one of two target configural discriminations (a biconditional or negative patterning discrimination) in a predictive learning task. In Experiment 1, participants were pretrained with either a configural or an elemental discrimination; in Experiment 2, they were pretrained with a configural discrimination, an elemental discrimination, or a control discrimination that was not expected to bias them toward elemental or configural processing. In both experiments, acquisition of the target configural discriminations was faster after configural pretraining than after elemental pretraining. In addition, the negative patterning discrimination was acquired faster than the biconditional discrimination. Finally, the results of Experiment 2 were more consistent with the notion that elemental pretraining hindered acquisition of the target discriminations than with the notion that configural pretraining enhanced their acquisition. Implications of these findings are discussed.     

Tests of the conditioned reinforcement value of sequential stimuli in pigeons

Egger and Miller (1962) hypothesized that the conditioned reinforcing value of stimuli depends on their information value. Egger and Miller and others have tested this hypothesis by comparing the conditioned reinforcing value of S1 and S2 following S1-S2-reward training. However, none of these experiments have controlled for differential generalization of conditioned reinforcement value from training to comparison tests. That is, the S1 cue pattern during the conditioned reinforcement tests has been very similar to the S1 cue pattern of training, while the training and test S2 cue patterns have been quite dissimilar. In Experiment 1, pigeons in a procedure unconfounded by differential generalization produced S2 reliably more frequently than S1, and pigeons in a confounded procedure produced S1 somewhat more frequently than S2. A significant groups × stimuli interaction was attributed to differential stimulus generalization from training to test for S1 and S2 in the confounded condition. In Experiment 2, pigeons in an unconfounded procedure again produced S2 reliably more frequently under a different testing procedure. The results are interpreted as demonstrating that, following S1-S2-food training trials, S2 is the more effective conditioned reinforcer in unconfounded conditions. A reconceptualization of the information hypothesis is shown to be consistent with these results.     

Control of pigeons’ keypecking by the left-right arrangement of stimuli

Control of pigeons’ keypecking by conditionalities in the spatial arrangement of two element stimuli (designated A and B) was investigated. In Experiment 1, reinforcement for keypecking was made conditional upon the left-right location of A and B: Reinforcement was available when A was on the left and B was on the right (AB), but not on BA, AA, or BB trials. The pigeons successfully discriminated the rewarded AB configuration, but only after a stage in which a particular element in a particular location (e.g., A on left) primarily controlled pecking. Experiments 2 and 3 systematically replicated these findings and included controls to discount discrimination of the AB compound on the basis of the temporal order (e.g., A followed by B) rather than the spatial configuration of the elements. During a generalization test in Experiment 4, the elements were presented singly either in the left (AX, BX) or right (XA, XB) positions. As would be expected had the animals learned “A on the left, B on the right is rewarded,” responding on AX trials exceeded that on XA trials, and responding on XB trials exceeded that on BX trials.     

The role of test stimuli in matching to compound samples by pigeons

Two pigeons matched to sample in a three-key operant conditioning chamber. In Experiment I, two different kinds of samples were presented on the center key.Element samples were members of one of two sample sets — colors (a red or blue disk) or lines (a vertical or horizontal orientation of a set of white lines). These samples were followed by their respective sample sets on the side keys as comparison stimuli.Compound samples consisted of a set of lines superimposed on a colored disk. Following these samples, either sample set could appear as comparison stimuli. Matching to compound samples was less accurate than matching to element samples. One interpretation is that sharing of attention among elements of a compound sample weakened stimulus control by each element. A different interpretation is that an element sample controlled matching better because it was physically identical to a comparison stimulus whereas a compound sample was not. Experiments II–IV evaluated this “generalization decrement” alternative by testing element- vs. compound sample control with both element and compound comparison stimuli. Irrelevant elements were added to form compound comparison stimuli, some of which were physically identical to a preceding compound sample, but never identical to an element sample. In all experiments, the addition of irrelevant elements of comparison stimuli reduced sample control. However, the generalization decrement hypothesis failed to predict how differences in performance maintained by element and compound samples were affected by different tests of sample control. Matching accuracy appeared to be independently determined by the number of elements in a sample and whether irrelevant elements were present during tests of sample control.     

Inflation of comparator stimuli following CS training

Water-deprived rats served in seven conditioned lick suppression experiments designed to assess the effects on responding to a target CS of a series of unsignaled USs given in the training context following completion of CS training. Such treatment has been hypothesized to increase (inflate) the associative strength of the background cues from training (putatively, the CS’s comparator stimuli), thereby reducing responding to excitatory CSs and increasing the inhibitory potential of inhibitory CSs. Although posttraining extinction (deflation) of the CS’s comparator stimuli usually decreases inhibitory potential and increases excitatory potential of the target CS, posttraining inflation of the comparator stimuli had no effect on either excitatory responding to the target CS or summation test performance indicative of conditioned inhibition. This outcome was consistently obtained across a number of training, inflation, and test conditions selected to maximize sensitivity to any possible effects of comparator inflation. Implications of these null results for the comparator hypothesis of conditionedresponse generationare discussed.     

Reinstatement of postresponse stimuli prior to reward in delayed-reward discrimination learning by pigeons

Delayed-reward learning in pigeons was examined using a simultaneous red-green visual discrimination task in which the conditions during the delay interval were varied between groups. The nondifferential group received training in which the stimulus present during the 1-min delay was the same following a peck on the correct and incorrect colors. The other three groups received 1-min delay training in which different stimuli occurred in the delay interval following correct and incorrect choices. The differential group received continuous, differential stimuli during the delay. The reinstatement group received the differential stimuli in the 10 sec immediately following the choice and during the last 10 sec of the delay. The reversedcue group was treated in the same way, except that the 10-sec delay stimulus immediately following an incorrect response was also presented for 10 sec prior to reward on correct choices, and the stimulus following a correct response also occurred 10 sec before nonreward on incorrect choices. Nondifferential birds failed to learn the discrimination, while differential and reinstatement birds learned it readily. The reversed-cue birds learned to choose the incorrect stimulus. Differential and reinstatement birds showed no decrement in performance when the delay was increased to 2 min. These findings suggest that similarity of prereward and postresponse delay stimuli controls choice responding in long-delay learning, a finding compatible with both memorial and conditioned reinforcement interpretations.     

Effect of prior nonreward on subsequent incentive growth during brief acquisition

Four experiments compared runway extinction or hurdle-jumping from nonreward performance following brief (10 trials) continuous or partial reinforcement acquisition. Some of the partial groups received all nonrewarded trials prior to any rewards. The major findings were that (l) rats receiving all nonrewarded experiences prior to rewarded ones were more persistent during extinction than continuously rewarded subjects; (2) rats receiving nonrewarded placements prior to rewarded ones in one compartment of a two-compartment box, failed to learn a hurdle-jumping response to escape nonreward, whereas rats not receiving the initial nonrewards did learn the escape response; (3) increasing the number of rewarded placements following initial nonrewarded ones offset the effect noted in (2). The results, which are discussed in the context of a frustration analysis of the small-trials partial reinforcement effect, suggest that incentive growth over rewarded trials is retarded when the rewards have been preceded by nonrewards. The similarity of these results to those investigating the phenomenon of latent inhibition is apparent, and possible mechanisms responsible for the present results are suggested in current theoretical accounts of latent inhibition.     

Interocular transfer in pigeons of color discrimination but not motor response training

Adult pigeons with one eye covered were trained to peck a response key using grain as a reinforcer. In subsequent tests, with the trained eye covered and the control eye open, the birds failed to peck the key. The subjects were then divided into two groups for a second experiment. The first group was trained on a single-key, peck/no-peck color discrimination task with the original control eye covered. When tested for interocular transfer of discrimination performance, these birds failed to respond at all. They were then trained to peck a blank response key with the training eye covered and the control eye open. Control-eye tests after this motor response training resulted in excellent transfer of color discrimination performance. The second group of subjects was trained to peck a blank key with first one eye covered and then the other, before monocular discrimination training was begun. These birds showed excellent transfer of discrimination performance during control-eye tests. These results show that, at least in the operant paradigm, motor response training does not transfer interocularly and this lack of transfer may interfere with transfer of discrimination performance.