Conditioning-specific reflex modification of the rabbit (Oryctolagus cuniculus) nictitating membrane response is sensitive to context

Conditioning-specific reflex modification occurs when an unconditioned response is modified in theabsence of the conditioned stimulus as a result of pairings of the conditioned stimulus and an unconditioned stimulus. In two experiments, we assessed conditioning-specific reflex modification in either a novel context (Experiment 1) or a context different from, but equally familiar in relation to, the training context (Experiment 2). Conditioning-specific reflex modification did not demonstrate sensitivity to a novel context but did demonstrate sensitivity to a change in familiar context. The data cannot be explained by unconditioned stimulus preexposure, overtraining, or context insensitivity. The results suggest that conditioning-specific reflex modification models normal stress and may be used to evaluate theories of and treatments for posttraumatic stress disorder.     

The role of “nothing” in memory for event duration in pigeons

The research reported herein is designed to test a signal detection account of thechoose-short effect, which is the tendency of birds to report (after a long delay) that a short-duration sample was presented, regardless of whether a short or long sample initiated the trial. According to the detection account, the choose-short effect arises because birds learn to selectively search memory for evidence that the long sample appeared on a given trial. This idea is tested, in part, by replacing short-sample trials with nosample trials and showing that performance is unaffected by this manipulation for birds exhibiting a choose-short effect. In addition, when no samples and long samples were associated with the same choice alternative (and the short sample was associated with the other alternative), birds were flexible enough to learn to respond on the basis of the presence versus the absence of the short sample (and, as a result, a choose-long effect was observed).     

Reading‐retarded Icelandic Children: the discriminant validity of psychological tests

Discriminant validity of several psychological tests was investigated for a sample of reading‐retarded and normal Icelandic fifth grade children. Differentiation was greatest on verbal intelligence, accounting for 40% of the variation, and on various other verbal tests accounting for almost 40% of the remaining variation. Benton Visual Retention Test was the only visual‐spatial test that discriminated between the two groups. Apart from verbal intelligence the Expressive scale of the Luria‐Nebraska Neuropsychogical Battery discriminated most highly between the groups and was the only measure with incremental validity over the intelligence measures. Cluster analysis revealed two reading‐retarded subgroups. One was an undifferenti‐ated group characterized by lowered level of performance on all measures and heterogeneous individual profiles. The second cluster was very compact with specific delay on verbal measures, possibly indicating sequencing difficulties. The results indicate the need for an adequate intelligence measure in Iceland and the development of refined measures of specific verbal skills.

     

Errors in pigeons’ memory for number of events

In Experiment 1, pigeons were trained in a within-subjects design to discriminate sequences of light flashes (illumination of the feeder) that varied in number, but not in time (2f/4sec and 8f/4sec), and in time, but not in number (4f/2sec and 4f/8sec). Number samples required a response to one of two comparison dimensions (either color or line), whereas time samples required a response to the remaining comparison dimension. Delay testing revealed a significant choose-small bias following number samples and a significant choose-long bias following time samples. In Experiment 2, testing confirmed that in the absence of a sample, there was a bias to respond small to the number comparisons and long to the time comparisons. Additional tests indicated that the birds were discriminating time samples on the basis of the number of light flashes occurring during the last few seconds of the time samples, rather than on the basis of the total duration of the flash sequence. Consequently, the choose-long bias observed for time samples during delay testing was really a choose-small bias. In Experiment 3, the birds received baseline training with a 5-sec delay and were subsequently tested at shorter and longer delays. A choose-large bias occurred at delays shorter than the baseline training delay, whereas a choose-small bias was again observed at delays longer than the baseline delay. These findings provide additional empirical support for the conceptualizing of memory for number and time in terms of a common mechanism.     

Artificial grammar learning in pigeons

In two experiments, we developed a new methodology for studying complex stimulus control by spatial sequences of letters generated by artificial grammars. An artificial grammar is a system of rules that defines which letter sequences or strings are “grammatical.” In Experiment 1, pigeons learned to respond differently to strings conforming to a grammar versus strings that were nongrammatical distortions. Several different criteria all suggested that performance was controlled both by some short chunks of strings shared between reinforced training strings and novel transfer strings and by more complex sequential regularities. In Experiment 2, pigeons quickly and accurately learned to respond differently to strings conforming to one or the other of two different artificial grammars. As in Experiment 1, performance was controlled both by some short chunks and by more complex sequential regularities. The results are interpreted in terms of family resemblance and pose new goals for theories of complex stimulus control.     

Differential effects of omitting comparison stimuli on symbolic and identity matching to sample: Evidence for altered instructional processes in pigeon short-term memory

Two experiments were performed to determine the effects of omitting the comparison stimuli in a matching-to-sample task. In Experiment 1, birds were trained initially on both symbolic and identity matching to sample. Comparison stimuli were then omitted following the presentation of a particular sample stimulus, and this decreased the number of sample (observing) responses. The reintroduction of the comparison stimuli on subsequent probe trials revealed that the accuracy of symbolic matching was reduced to chance levels, while identity matching accuracy was significantly below chance. In Experiment 2, a similar procedure was employed; however, observing responses to the comparison-omitted samples were maintained by direct reinforcement (fixed ratio 20). Matching accuracy during probe trials was again at chance levels for symbolic matching but, contrary to Experiment 1, was significantly above chance for identity matching. The differential effects of omitting comparison stimuli on symbolic and identity matching trials in these two experiments were interpreted within a framework which assumes that instructional processes are altered by comparison-omission procedures.     

Contextual cues and the retrieval of competing memories of goal events

In Experiment 1, four groups of rats were initially trained on a discrimination which established a stimulus as a signal for reinforcement. That signal was then presented during subsequent partial reinforcement training in a way that could potentially interfere with retrieval of the memory of nonreinforcement (S^N) on the preceding trial either because (1) thestorage and retrieval contexts for S^N were different (retrieval failure hypothesis), or (2) the memory of reinforcement produced by the signal acted as a competing memory (competing memory hypothesis). Experiment 1 supported the competing memory hypothesis. In Experiment 2, we investigated the effect of stimulus change on the capacity of the context to retrieve a competing memory of a temporally remote reinforcement event with which the context was strongly associated. Retrieval of a competing memory was impaired by differences between the storage and retrieval contexts in a manner analogous to the effect of context on retrieval of a reinforcement event memory from an immediately preceding trial.     

Trial and intertrial durations in appetitive conditioning in rats

The effects of trial (T) and intertrial (I) durations were examined in two Pavlovian conditioning experiments with rats, in which a noise conditioned stimulus (CS) was paired with food delivery. In Experiment 1,T was either 10 or 20 sec, andI ranged from 15 to 960 sec, in separate groups of rats. The acquisition rate and final level of conditioned responding showed ratio invariance: They were better predicted by theI/T ratio than byI orT alone. In Experiment 2, theI/T ratio was 6.0 in all the groups, andT was 20, 40, 80, or 160 sec. Ratio invariance was not observed: Despite the commonI/T ratio, the rate of acquisition, final level of conditioned responding, and the ability of the CS to block conditioning of another stimulus differed among the groups. At the same time, the temporal distribution of conditioned responding withinT was similar in all the groups throughout conditioning and extinction and showed superpositioning when normalized acrossT. Many but not all aspects of the data were consistent with scalar timing theory.     

Sign and goal tracking during delay and trace autoshaping in pigeons

In two experiments, pigeons were exposed to an autoshaping procedure in which a keylight was followed by food under delay or trace conditions, while measures were taken of keypecking and time spent near the key. In Experiment 1, the birds in the trace group spent less time near the key than did the delay birds. Moreover, the trace birds exhibited a pattern of withdrawal from the key during the trial. In Experiment 2, visual observations of the birds’ location and latencies to eat both indicated that the trace birds’ withdrawal from the conditioned stimulus was accompanied by goal tracking. The difference in performance between the delay and trace conditions was taken as evidence that a trace stimulus may exert control over behavior as an occasion setter.     

Attentional enhancement in matching-to-sample: Facilitation in matching acquisition by sample-discrimination training

In three experiments, we examined how matching-to-sample by pigeons is affected by discrimination versus nondifferential training between the matching stimuli. In Experiment 1A, pigeons responding differentially to the sample stimuli off-baseline acquired accurate matching performances more rapidly than did pigeons responding nondifferentially to those same stimuli. In Experiment 1B, tests involving reversal of the off-baseline requirements demonstrated that the birds were primarily controlled in their matching choices by the sample stimuli. The results of Experiment 2 showed that off-baseline nondifferential training did not retard acquisition relative to comparable training between stimuli unrelated to the matching task. Together, these results suggest that discrimination training can facilitate matching acquisition by enhancing attention to the sample stimuli.     

Representation strength in pigeon short-term memory: Effect of delay training

An attempt was madeto manipulate the strength of internal stimulus representations by exposing pigeons to brief delays between sample offset and comparison onset in a delayed conditional discrimination. In Experiment 1, pigeons were first trained on delayed conditional discrimination with either short (0.5-sec) delays or no delays. When delays were increased by 2.0 sec, birds trained with a delay performed at a higher level than did birds trained with no delays. In Experiment 2, subjects were first trained on a delayed simple discrimination. Following a circle stimulus, responses to a white key were reinforced; however, following a dot stimulus, responses to the white key were not reinforced. The pigeons were then trained on a delayed conditional discrimination involving hue samples and line-orientation comparisons with differential outcomes. Choice of vertical following red yielded food; choice of horizontal following green yielded no food. Mixed delays were then introduced to birds in Group Delay, whereas birds in the control group received overtraining. When tested on a delayed simple discrimination with hue stimuli (red and green initial stimuli followed by white response stimulus), pigeons in Group Delay tended to perform at a higher level than did birds in the control group (i.e., although the birds in both groups responded more following red than following green, birds in Group Delay did this to a greater extent than did birds in the control group). Thus, experience with delays appears to strengthen stimulus representations established during training.     

Conditioning history and inhibitory instrumental stimulus control: Independent-groups and within-subjects measures

The effects of excitatory conditioning history on establishing inhibitory stimulus control have been investigated in classical conditioning, but not in the free-operant paradigm. The present experiments address this question within the context of discriminated free-operant avoidance in which rats’ barpressing postponed shock. When a stimulus with only a history of signaling safety was combined, on a summation test, with a stimulus that maintained avoidance, avoidance rate was reduced, on average, by 60%. In comparison, after a stimulus acquired an excitatory free-operant avoidance history, nonreinforcement alone was not adequate to make it a predictable and effective inhibitor of avoidance on a summation test. These results, consistent with the classical conditioning literature, were produced by both between-group (Experiment 1) and within-subject (Experiment 2) comparisons. These findings are discussed in terms of (1) Konorski’s distinction between “primary” and “secondary” inhibitory stimuli, (2) the Rescorla-Wagner model, (3) the potential contribution of the “reinstatement of fear” to the outcome of summation tests, and (4) their implications for assaying the effectiveness of behavior-modification treatments of phobias.     

Matching-to-sample in pigeons: In the absence of sample memory,sample frequency is a better predictor of comparison choice than the probability of reinforcement for comparison choice

In matching-to-sample, comparison choice should be controlled by the identity of the sample and, when the sample is not available, by the overall probability of reinforcement associated with each of the comparisons. In the present research, pigeons were trained to match a frequent sample (appearing on 80% of the trials) to one comparison (C _fr) and an infrequent sample (appearing on 20% of the trials) to the other (C _inf), with the number of reinforcements associated with each sample equated. In Experiment 1, the task was identity matching; in Experiments 2 and 3, it was symbolic matching. We asked whether, when control of comparison choice by the sample was reduced (by inserting a delay between the sample and the comparisons), pigeons would choose comparisons on the basis of (1) the number of reinforcements per comparison (and thus show no comparison bias), (2) the comparison associated with the more frequent sample during training (and show a preference forC _fr), or (3) the probability of reinforcement given a correct response (and show a preference forC _inf), or (4) inhibition produced by nonreinforced choice of the more frequently correct comparison (and show a preference forC _inf). Pigeons showed a significant tendency to chooseC _fr. In Experiment 3, we showed that this bias did not result from the effects of intertrial facilitation or interference. Thus, it appears that when control of comparison choice by the sample is reduced, pigeons’ choice is controlled not merely by the probability of reinforcement but also by overall sample frequency.     

Bidirectional associations

Associations are usually assumed to have only a predictive directionality, from Event 1 (E1) to Event 2 (E2). However, this unidirectionality, if it really exists, could be specific to the use of conditioned responses as the index of learning (i.e., conditioned responses are ordinarily elicited only when a conditioned stimulus [CS] predicts an unconditioned stimulus [US]). The present research used neutral stimuli, devoid of CS-US directionality, in order to test whether the underlying associative mechanism was unidirectional in nature. We used colors and figures as E1s and E2s. In Experiment 1, human subjects saw the events in the E1→E2 direction during training. In theconsistent group, the same E1 was always followed by the same E2; in theinconsistent group, E1s and E2s were paired randomly. In a subsequent test phase, we presented an E2 and subjects had to judge whether a particular E1 was associated with it. The judgments of the consistent group were higher than those of the inconsistent group, thereby suggesting that the association that the consistent subjects had learned was bidirectional. Experiments 2 and 3 confirmed the results of Experiment 1 while controlling for some alternative interpretations based on the representation-mediated formation of associations.     

Memory codes for temporal and nontemporal samples in many-to-one matching by pigeons

Pigeons were trained to match temporal (2 and 8 sec of keylight) and color (red and green) samples to vertical and horizontal comparison stimuli. In Experiment 1, samples that were associated with the same correct comparison stimulus displayed similar retention functions; and there was no significant choose-short effect following temporal samples. This finding was replicated in Phase 1 of Experiment 2 for birds maintained on the many-to-one mapping, and it was also obtained in birds that had been switched to a one-to-one mapping by changing the comparison stimuli following color samples. However, in Phase 2 of Experiment 2, when the one-to-one mapping was produced by changing the comparison stimuli following temporal samples, a significant choose-short effect was observed. In Experiment 3, intratrial interference tests gave evidence of temporal summation effects when either temporal presamples or color presamples preceded temporal targets. This occurred even though these interference tests followed delay tests that failed to reveal significant choose-short effects. The absence of significant choose-short effects in Experiment 1 and in Phase 1 of Experiment 2 indicates that temporal samples are not retrospectively and analogically coded when temporal and nontemporal samples are mapped onto the same set of comparisons The interference test results suggest that the temporal summation effect arises from nonmemorial properties of the timing system and is independent of the memory code being used     

Mini managers: Children strategically divide cognitive labor among collaborators,but with a self-serving bias

Strategic collaboration according to the law of comparative advantage involves dividing tasks based on the relative capabilities of group members. Three experiments (N = 405, primarily White and Asian, 45% female, collected 2016–2019 in Canada) examined how this strategy develops in children when dividing cognitive labor. Children divided questions about numbers between two partners. By 7 years, children allocated difficult questions to the skilled partner (Experiment 1, d = 1.42; Experiment 2, d = 0.87). However, younger children demonstrated a self-serving bias, choosing the easiest questions for themselves. Only when engaging in a third-party collaborative task did 5-year-olds assign harder questions to the more skilled individual (Experiment 3, d = 0.55). These findings demonstrate early understanding of strategic collaboration subject to a self-serving bias.     

Value transfer in concurrent-schedule discriminations by pigeons

When pigeons are trained on a discrete-trial simultaneous discrimination, some of the value associated with the positive stimulus appears to transfer to the negative stimulus (Zentall & Sherburne, 1994). Pigeons preferred a negative stimulus that had been discriminated from an always-positive stimulus (S+) over a negative stimulus that had been discriminated from a sometimes-positive stimulus (S±). A very different finding (suggestive of transitivity of preference or contrast) was reported by Belke (1992). On concurrent probe tests of stimuli associated with equal variable interval (VI) schedules but originally trained in alternative concurrent pairs (one with a richer schedule, the other with a poorer schedule—VI 20 sec vs. VI 40 sec and VI 40 sec vs. VI 80 sec), the stimulus originally paired with the poorer schedule was preferred. But Belke’s results may have been obtained because the pigeons had been trained to peck the VI 40 sec paired with the poorer schedule and they had been trained not to peck the VI 40 sec paired with the richer schedule. In the present experiment, we avoided this bias by training pigeons on two concurrent schedules in which the tested stimuli both had been associated with the poorer schedule of the pair [A(VI 20 sec) vs. B(VI 80 sec) and C(VI 40 sec) vs. D(VI 80 sec)]. Evidence for value transfer was demonstrated when on probe trials pigeons preferred B over D.     

Directed forgetting in monkeys

Based on several recent demonstrations of a directed forgetting effect in pigeons, three experiments were carried out in an attempt to demonstrate directed forgetting in three squirrel monkeys. During initial training with a delayed matching-to-sample procedure, retention tests were always given for sample stimuli followed by remember cues (R-cues) and were always omitted for sample stimuli followed by forget cues (F-cues). Retention of F-cued items was tested on probe trials after initial training. The first two experiments examined the effects of R- and F-cues on memory for slide-projected pictures, with different pictures used on each trial of a session. In Experiment 1, a complex design was used in which one or two sample pictures were presented on each trial; when two pictures were presented, both could be R-cued or F-cued, or one could be R-cued and the other F-cued. A simpler design was used in Experiment 2, with only single pictures presented as sample stimuli and half the trials within a session R-cued and the other half F-cued. In both of these experiments, no differential retention of R- and F-cued stimuli was found, even at a retention interval as long as 16 sec. In Experiment 3, a series of studies was performed to test for directed forgetting when only two sample stimuli were used repeatedly throughout training and testing. With two pictures as sample stimuli, clear evidence of directed forgetting was found in Experiment 3b. It is suggested that the directed forgetting effect may arise only when a small set of sample stimuli is used.     

Summation and overexpectation with qualitatively different outcomes

In five experiments, a Pavlovian appetitive conditioning preparation was used with rats to explore the interaction of associations with different, but equivalently valued, outcomes. Experiment 1 demonstrated summation in magazine responding when two stimuli previously associated with different outcomes were combined. Experiments 2A and 2B found that pairing that stimulus compound with one of the outcomes led to a decrease in performance (overexpectation) for both of the stimulus elements. Experiments 3A and 3B confirmed that result but demonstrated the continued presence of the original stimulus-outcome associations. The results are consonant with a view in which replacing one outcome with another leads to an associative structure containing both stimulus-outcome associations and an outcome-independent depressive process.     

Preweanling and adult rats treat conditioned light-tone combinations differently

Ontogenetic differences in processing light-tone compounds were discovered in preweanling (17-day-old) and adult (60–80-day-old) rats. Suppression of general activity was used as an index of the magnitude of conditioned fear following a single training session in which a CS+ was paired with mild footshock. In Experiment 1, rats were trained on discriminations in which the CS? consisted of a light and the CS+ was either a tone alone (simple discrimination) or a light-tone compound (simultaneous feature-positive discrimination). Adults and preweanlings given each type of discrimination were then tested for fear of the CS? and a target stimulus (tone alone or light-tone compound). Adults in all groups displayed greater fear of the target than of the CS?. Preweanlings, however, discriminated the CS? from the target only when the target was the same as the original CS+. Experiment 2 revealed that age-related differences in conventional stimulus generalization is not a likely explanation for the pattern of results found in Experiment 1. Experiment 3 revealed age-related differences in expressed fear of a serial feature-positive discrimination; adults, but not preweanlings, showed greater fear of the compound than of the CS?. Alternative interpretations of the results from these experiments are discussed, and the general conclusion is that adults appear more inclined to process elements of a compound stimulus selectively, whereas preweanlings seem more likely to process the compound unselectively, with roughly equivalent processing of each element.