Spontaneous alternation and pattern of reinforcement

In Experiment I, rats were given one pair of trials per day in a T-maze; group RN were rewarded on the first trial only, NR were rewarded on the second trial only, while RR were rewarded on both trials. Alternation was approximately the same for all groups, and there was little decline in alternation over 28 days. There was, however, a difference in the choice behaviour on trials when rats failed to alternate, NR and RR, but not RN, choosing according to a position preference. These results are incompatible with several earlier theories of spontaneous alternation, and the hypothesis was put forward that alternation is initially part of an exploratory tendency, but that, when the maze becomes explored, the exploratory tendency dies down, and alternation only continues when rats have been reinforced (primarily or secondarily) for alternating. This hypothesis was tested in a second experiment, similar to the first but in which one group of rats was not rewarded on either trial; as predicted, this group showed significantly more decline in alternation than rewarded rats.     

Release from proactive interference by experimental amnesia: electroconvulsive shock improves radial-arm maze performance in rats

Rats were trained in an eight-arm radial maze and tested using a proactive interference (PI) procedure. Each test trial consisted of forced choices of four randomly selected arms followed, after a 2-h delay, by free choices among all eight arms. Normally, rats chose correctly during the free choices by entering and retrieving food from the four arms not yet visited during the test trial. Occasionally, an interference trial preceded the test trial by 1.5 or 3 h; interference trials consisted of forced choices of another four arms and an immediate test. The presence of an interference trial lowered test-trial performance (PI). Electroconvulsive shock (ECS) administered immediately after the interference trial had no effect; i.e., PI was still observed. When ECS was administered at the midpoint of the 3-h intertrial interval, performance increased to control (no ECS, no PI) levels. Such release from PI, however, was not obtained, and test-trial performance remained inaccurate when ECS was delivered immediately after the forced choices of the test trial (either 1.5 or 3 h after the interference trial).     

Repetition and alternation in rats

An experiment is reported in which rats were forced equally often to each arm of a T-maze, and, following each forced trial, were given a free trial. Group R were rewarded for repeating (i.e. choosing the side to which they had just been forced), group A for alternating. All rats began by alternating, but group R eventually learned to repeat. Various delays between free and forced trials were introduced, and the forgetting curve was found to be similar for the two groups. It is argued that these results show: (i) The decline in alternation with delay found in experiments on spontaneous and rewarded alternation is due to loss of information rather than a decline in the alternation tendency. (ii) The trace involved is sufficiently general to be regarded as a memory trace. The fact that rats can learn to repeat is inconsistent with the accounts of the memory trace suggested by the theories of Deutsch and Walker.     

Proactive interference in a two-tone pitch-comparison task without additional interfering tones

Two-tone pitch-comparison tasks typically comprise several successive pairs of successive tones separated by silent intervals. The serial occurrence of such pairs has been associated with degraded task performance, but the nature of this association is not fully understood. Human adult participants were presented with successive pairs of successive tones. The latter, to-be-compared tone of a pair could differ from the former, to-be-remembered tone of 1046.5 Hz by no more than ±15 Hz (25 cents). The direction of this difference was easier to identify when it was opposite to that of the preceding pair than when being the same. Merely responding accordingly (irrespectively of whether the response was correct or not) was found not to account for this finding. Our study demonstrates proactive interference in a two-tone pitch comparison task as the difficulty to remember when the first tone of the present pair occurred relative to the last tone of the immediately preceding pair.     

Retrieval plus scanning: Does it occur?

In the two experiments reported here, we tested the retrieval-plus-scan model of delayed probe recognition by adding a second probe 2 sec after subjects had responded to the first probe. According to this model, the list items should still be in consciousness from the first probe at the time of the second probe. Consequently, on tests in which the first probe had been tested immediately, we expected to find the same pattern of performance on both first and second probes. On tests in which the first probe came after a filled delay, we expected the first-probe data to show the effects of retrieval and proactive interference. These effects should not be present on the second probe. The results of the first-probe data in both experiments were consistent with the retrieval-plus-scan model. The second-probe data did not fit the model, however. In the first experiment, the second probe on what had been delayed first-probe trials still produced intercept differences, indicating the presence of retrieval. In the second experiment, the effects of proactive interference were still present on the second probe. It is suggested that these results not only invalidate the retrieval-plus-scan model for delayed probe recognition but that they, along with other results, cast doubt on a scanning operation in immediate probe recognition.     

The effects of calcium channel antagonists on short- and long-term retention in mice using spontaneous alternation behavior

The effect of calcium channel antagonists (CCA's) on working and reference memory in mice was studied using spontaneous alternation (SA) behavior in a T maze. Mice were given either one or four forced trials to either the right or the left arm on the training session (T1) followed by a free choice test (T2) at varying intervals after the initial trial. Untreated animals given one forced trial exhibited significantly greater levels of SA than chance at all delay intervals out to 20 min but not at 30, 60, or 180 min. Animals given four forced trials showed significant levels of SA 24 h after exposure but not at 72 h. Additional groups of mice were treated with amlodipine, nimodipine, diltiazem, and verapamil 1 h before T1. Mice given one forced trial were tested 30, 60, or 180 min after T1 while mice given four forced trials were tested 72 h after T1. Results showed that all of the CCA's except verapamil produced significant SA at the 30-min interval and nimodipine and diltiazem also significantly increased SA at the 60-min-delay interval. No significant effects were observed at the 180-min test. In the four trial groups, all of the CCA's with the exception of verapamil produced significant levels of SA at the 72-h interval. These results indicate that representative CCA's from both the dihydropyridine and the benzothiazapine classes can facilitate both short- and long-interval SA, thereby providing further confirmation that CCA's can enhance memory processing in young animals.     

Remembering change: The critical role of recursive remindings in proactive effects of memory

In three experiments, we examined the role of the detection and recollection of change in proactive effects of memory in a classic A–B, A–D paradigm. Participants studied two lists of word pairs that included pairs repeated across lists (A–B, A–B), pairs with the same cue but a changed response (A–B, A–D) in the second list, and control pairs (A–B, C–D). The results revealed that performance on A–B, A–D pairs reflected a mixture of facilitation and interference effects. Proactive facilitation occurred when changes in responses were detected and recollected, whereas proactive interference occurred when change was not detected or when it was not recollected. We describe detecting change as involving recursive remindings that result in memory for the List 1 response being embedded in the representation of memory for the List 2 response. These embedded representations preserve the temporal order of the responses. Our findings highlight the importance of detection and recollection of change for proactive effects of memory.     

Proactive interference in sentence recall: Topic-similarity effects and individual differences

The effect of topic similarity on proactive interference in sentence recall was investigated in two experiments using the Brown-Peterson paradigm. In Experiment 1, successive sentences about the same topic and related topics were both associated with substantial and progressive amounts of proactive interference; however, a significant trials × condition interaction indicated that the effect was stronger in the related-topics condition. Moreover, significant negative correlations were found between individual differences in susceptibility to proactive interference and academic achievement test scores. In Experiment 2, relatively weak effects leveling off on the second trial were obtained with sentences about unrelated topics. With some assumptions about the spread of activation during retrieval, the results were attributed to response-set interference. The practical implications of these data were also considered, and it was suggested that proactive interference might be a common cause of learning problems.     

Fetal Alcohol-Exposed Rats Exhibit Differential Response to Cholinergic Drugs on a Delay-Dependent Memory Task

Fetal alcohol exposure in human and rodents produces a number of cognitive deficits including impairments in learning and memory. Recent evidence in our laboratory has shown that fetal alcohol-exposed (FAE) rats respond differently to systemic administration of cholinergic drugs when tested for vigilance and locomotor activity. The present study examined the effects of muscarinic and nicotinic agonists and antagonists on memory performance in a delayed alternation task. Subjects were male offspring of Sprague-Dawley rats fed a 35% ethanol-derived caloric diet, pair-fed with sucrose, or chow-fed with lab chow during the last 2 weeks of gestation. Rats (3 months old) were food-deprived prior to training in the T-maze. Rats were first trained in the alternation task at no delay for five sessions. Rats were then trained at longer delays (20, 60, 180 s) until all groups showed similar performance for two consecutive sessions. Each animal was then tested following systemic injections of the cholinergic antagonists scopolamine and mecamylamine (60-s delay) and the cholinergic agonists pilocarpine and nicotine (180-s delay). Rats received saline injections on alternate days of testing. The results revealed that FAE rats exhibited no impairments in alternation performance at the no delay and 20-s delay, but showed impairments on both the 60- and 180-s delays during the initial sessions. However, with additional training, FAE rats showed performance similar to that of control groups at these delays. Following both pilocarpine and nicotine injections, control groups, but not the FAE group, showed significant memory enhancement in the alternation task. Following scopolamine injections, the FAE rats showed a significant impairment, while control groups showed a nonsignificant decrease in performance. All three groups showed impairments in the alternation task following administration of mecamylamine compared to saline treatment. These findings suggest that alterations in the cholinergic system in FAE rats may underlie some of the cognitive deficits observed with prenatal alcohol exposure.     

Assessing the age-related effects of proactive interference on working memory tasks using the Rasch model

Inhibition-reduction theory (L. Hasher & R. Zacks, 1988) hypothesizes that the age-related decline in working memory (WM) span is a result of a decrease in the ability to inhibit irrelevant information in WM. Using the Rasch psychometric model, this study found that later trials on 2 WM span tasks were more difficult for older adults than for younger adults, consistent with inhibition-reduction theory's hypothesis that older adults are more susceptible to the effects of proactive interference (PI). Furthermore, after accounting for differential susceptibility to the effects of PI, age-related variance in WM span was reduced by about half. These results suggest that differential susceptibility to PI may account for a substantial portion, although not all, of the age-related decline in WM span.     

How to be proactive about interference: lessons from animal memory

Processes of proactive interference were explored using the pigeon as a model system of memory. This study shows that proactive interference extends back in time at least 16 trials (and as many minutes), revealing a continuum of interference and providing a framework for studying memory. Pigeons were tested in a delayed same/different task containing trial-unique pictures. On interference trials, sample pictures from previous trials reappeared as test pictures on different trials. Proactive-interference functions showed greatest interference from the most recent trial and with the longer of two delays (10 s vs. 1 s). These interference functions are accounted for by a time-estimation model based on signal detection theory. The model predicts that accuracy at test is determined solely by the ratio of the elapsed time since the offset of the current-trial sample to the elapsed time since the offset of the interfering sample. Implications for comparing memory of different species and different types of memory (e.g., familiarity vs. recollection) are discussed.     

A revised spatial serial learning and memory procedure using Corsi's Block-tapping apparatus

The purpose of this study was to use Corsi's Block Tapping Test as a spatial analog of Benton's Serial Digit Learning Test, using the cognitive neuroscience approach utilized in the California Verbal Learning Test. 60 normal participants, ages 19-52 years, were included and administered an 8-block sequence for 9 trials or until they recalled the entire sequence for 3 consecutive errorless trials. The score was the number of blocks tapped in the correct serial order. An interference trial was administered. Following a 10-min. delay, free recall of the original sequence, cued recall, and recognition measures were obtained. Retroactive interference was significant, but no proactive interference emerged. Scores showed a strong primacy effect. Most participants who learned the sequence to the criterion of three successive errorless trials recalled the sequence after the 10-min. delay. Scores on the cued recall and recognition trials tended to support their validity as less demanding retrieval tasks. The use of this spatial learning and memory procedure allows finer discriminations among nonverbal memory deficits and may facilitate direct comparisons with scores on verbal memory tasks such as Serial Digit Learning and the California Verbal Learning Test.     

Proactive effects of memory in young and older adults: The role of change recollection

Age-related deficits in episodic memory are sometimes attributed to older adults being more susceptible to proactive interference. These deficits have been explained by impaired abilities to inhibit competing information and to recollect target information. In the present article, I propose that a change recollection deficit also contributes to age differences in proactive interference. Change recollection occurs when individuals can remember how information changed across episodes, and this counteracts proactive interference by preserving the temporal order of information. Three experiments were conducted to determine whether older adults are less likely to counteract proactive interference by recollecting change. Paired-associate learning paradigms with two lists of word pairs included pairs that repeated across lists, pairs that only appeared in List 2 (control items), and pairs with cues that repeated and responses that changed across lists. Young and older adults’ abilities to detect changed pairs in List 2 and to later recollect those changes at test were measured, along with cued recall of the List 2 responses and confidence in recall performance. Change recollection produced proactive facilitation in the recall of changed pairs, whereas the failure to recollect change resulted in proactive interference. Confidence judgments were sensitive to these effects. The critical finding was that older adults recollected change less than did young adults, and this partially explained older adults’ greater susceptibility to proactive interference. These findings have theoretical implications, showing that a change recollection deficit contributes to age-related deficits in episodic memory.     

Rats’ memory for time and relational responding in the duration-comparison procedure

Rats were trained in a duration-comparison task to press one lever if the comparison duration (c) was 1.2-s shorter than a standard duration (s), and another lever if c was 1.2-s longer than s. The interval between s and c duration was 1 s. The 10 duration pairs used during training controlled for the absolute duration of c and the total duration of an s-c pair. The total duration of an s-c pair was not predictive of the correct response. In Experiment 1, during equal-duration pair test trials, rats increasingly responded long (i.e., c > s) as the s-c delay was lengthened. In Experiment 2, long responding increased as the s-c delay was lengthened, even when the illumination condition during the s-c delay differed from that during the intertrial interval (ITI). In Experiment 3, transfer to novel duration pairs was assessed. Overall accuracy for the novel duration pairs was significantly above chance, but transfer performance was also affected by the absolute value of the novel c durations. This is the first study to demonstrate that rats can acquire relational duration discriminations. As in previous studies with pigeons the evidence was consistent with subjective-shortening of the standard duration and there was also evidence of a reliance on a mixture of absolute and relational strategies in responding.     

Biasing the pacemaker in the behavioral theory of timing

In the behavioral theory of timing, pacemaker rate is determined by overall rate of reinforcement. A two-alternative free-operant psychophysical procedure was employed to investigate whether pacemaker period was also sensitive to the differential rate of reinforcement. Responding on a left key during the first 25 s and on a right key during the second 25 s of a 50-s trial was reinforced at variable intervals, and variable-interval schedule values during the two halves of the trials were varied systematically. Responding on the right key during the first 25 s and on the left key during the second 25 s was not reinforced. Estimates of pacemaker period were derived from fits of a function predicted by the behavioral theory of timing to right-key response proportions in consecutive 5-s bins of the 50-s trial. Estimates of pacemaker period were shortest when the differential reinforcer rate most strongly favored right-key responses, and were longest when the differential reinforcer rate most strongly favored left-key responses. The results were consistent with the conclusion that pacemaker rate is influenced by relative reinforcer rate.     

Proactive control of proactive interference using the method of loci

Proactive interferencebuilds up with exposure to multiple lists of similar items with a resulting reduction in recall. This study examined the effectiveness of using a proactive strategy of the method of loci to reduce proactive interference in a list recall paradigm of categorically similar words. While all participants reported using some form of strategy to recall list words, this study demonstrated that young adults were able to proactively use the method of loci after 25 min of instruction to reduce proactive interference as compared with other personal spontaneous strategies. The implications of this study are that top-down proactive strategies such as the method of loci can significantly reduce proactive interference, and that the use of image and sequence or location are especially useful in this regard.     

Buildup and release from proactive interference in a rhesus monkey

The potential of the buildup and release from proactive interference (PI) technique in the study of animal categorization was demonstrated with a rhesus monkey. A serial probe recognition task was used with a list of 4 consecutive slide pictures (upper screen) followed by a single probe picture (lower screen). The monkey moved a lever to indicate whether or not the probe was contained in the list. PI built over 40 consecutive trials tested with either flowers or primate faces. PI was released on category change and then built during 40 trials with the second category. The first 2 serial positions showed somewhat greater PI buildup and release, supporting conclusions from human studies that the effects occur primarily in secondary memory. A second experiment provided 2 replications of the main effect and showed through color border changes and elimination of color differences that color was not a critical feature.     

Sequential congruency effects: disentangling priming and conflict adaptation

Responding to the color of a word is slower and less accurate if the word refers to a different color (incongruent condition) than if it refers to the same color (congruent condition). This phenomenon, known as the Stroop effect, is modulated by sequential effects: it is bigger when the current trial is preceded by a congruent condition than by an incongruent one in the previous trial. Whether this phenomenon is due to priming mechanisms or to cognitive control is still debated. To disentangle the contribution of priming with respect to conflict adaptation mechanisms in determining sequential effects, two experiments were designed here with a four-alternative forced choice (4-AFC) Stroop task: in the first one only trials with complete alternations of features were used, while in the second experiment all possible types of repetitions were presented. Both response times (RTs) and errors were evaluated. Conflict adaptation effects on RTs were limited to congruent trials and were exclusively due to priming: they disappeared in the priming-free experiment and, in the second experiment, they occurred in sequences with feature repetitions but not in complete alternation sequences. Error results, instead, support the presence of conflict adaptation effects in incongruent trials. In priming-free sequences (Experiment 1 and complete alternation sequences of Experiment 2) with incongruent previous trials there was no error Stroop effect, while this effect was significant with congruent previous trials. These results indicate that cognitive control may modulate performance above and beyond priming effects.     

Sequential search processes in long-term memory

In an experiment employing the symbol-element recognition task (Mohs, Wescourt, & Atkinson, 1975), subjects first learned six lists consisting of four words (elements) each. Each list was associated with a unique consonant (symbol). Subsequently, on each of a series of test trials, subjects were presented with one, two, or four symbol-element pairs. A positive response was required if all test words were correctly paired with their associated consonants and a negative response if any one test word was incorrectly paired with a consonant. Of primary concern was the way reaction time (RT) varied with number of pairs presented, the type of response required, and, on negative trials, the position of the mismatched pair in the test display. RT increased with the number of pairs presented on a trial and the increase was greater for positive than for negative trials. For negative pair trials, RT increased with the distance of the mismatched pair from the top of the test display. On negative trials in which the top pair in the test display was the mismatched pair, RT increased with the total number of pairs presented on the trial. A serial, probabilistic order of processing model is proposed to account for these results, and applications of the model to other paradigms are discussed.     

Local proactive interference in delayed matching to sample: the role of reinforcement

Discriminability in delayed matching to sample was lower when the samples on consecutive trials differed compared with when samples on consecutive trials were the same. This local proactive interference occurred when correct choices on the previous trial were reinforced but not when correct choices on the previous trial were not reinforced. When the choice on the previous trial was incorrect, discriminability was higher on different consecutive trials than on same trials. These effects were amplified by varying the ratio of reinforcers for correct choices, as predicted by a model that attributes local proactive interference to an interaction between control by the sample on the current trial and the influence of reinforcers for correct choices on previous trials.