Codes and coding processes in pigeon short-term memory

The delayed matching-to-sample (DMTS) task was used in three experiments to investigate how pigeons code information about sample stimuli. In all experiments, each trial consisted of a signaled presentation of a sample stimulus for a fixed duration followed, after some delay, by the presentation of three comparison stimuli. After incorrect first choices, the bird was allowed a second choice between the remaining two stimuli. It was found, in Experiment 1, that the probability of a second choice error declined with increasing sample duration. This result is consistent with a gradual short-term memory encoding process but not with a simple two-state all-or-none process. In the second experiment, it was found that the distribution of first-choice errors was affected by the particular sample occurring on a trial. This result is inconsistent with a two-stage discrete state memory/attention model based on the assumption that encoding of the sample and attention to the comparison stimuli are both independent all-or-none processes. The third experiment involved symbolic DMTS, in which the sample stimuli varied along a dimension different from that along which the comparison stimuli varied. With increasing delay between sample and comparison stimulus presentations, the pigeons were more likely to confuse test stimuli than to confuse sample stimuli. The results of these experiments lead to the conclusion that pigeon DMTS performance depends on a gradual encoding process in which a representation isomorphic with the test stimuli is generated and maintained.     

Time dependent effects of double cuing in directed forgetting

Previous research in directed forgetting in pigeons has focused on the effect of single forget cues (F-cues) interpolated within the retention interval in delayed matching-to-sample (DMTS). The present series of experiments focuses on the ability of a remember cue (R-cue) to cancel the effects of a previously presented forget cue both when the forget cue occurs within the retention interval and when the forget cue precedes sample presentation. In the first experiment, an R-cue decreased the effect of an F-cue within the same retention interval in successive DMTS if the R-cue immediately followed the F-cue, but not if the second cue was delayed until the end of the retention interval. In Experiment 2, the double-cue effect was extended to choice DMTS. In addition, when a novel stimulus replaced the R-cue in the double-cue probe trials, matching performance was not restored, indicating that through its conditioning history the R-cue had gained control over memory processes in a direction opposite to that of the F-cue. Experiment 3 presents evidence that presample R- and F-cues can also effectively gain control over matching performance. Matching to R-cued samples was superior to matching to F-cued samples. When F-cued samples were followed immediately by R-cues, matching performance was not restored to R-cue levels, suggesting differential encoding of the R-cued and F-cued samples.     

Short-term memory for haptic cues in monkeys (Macaca mulatta)

Short-term memory (STM) for haptic information was examined in a delayed matching-to-sample (DMTS) task. Three rhesus monkeys were tested in DMTS with all possible combinations of different-size spheres and cubes as the sample and comparison stimuli. The results showed that the decrease in percentage correct as a function of the retention intervals was relatively independent of the size and shape of the sample and comparison stimuli. In general, at each retention interval, percentage correct was higher when the (1) comparison stimuli differed in both size and shape than when the comparison stimuli differed in only size or shape, (2) size differences between the comparison stimuli increased, and (3) samples were spheres rather than cubes. This pattern of results suggests that dimensions of the haptic stimuli influenced discrimination but had little effect on the animals’ STM. In Experiment 2, the same three monkeys responded to the sample and comparison stimuli with the same hand or responded to the sample with one hand and the comparison stimuli with the opposite hand. The decrease in percentage correct across retention intervals was comparable for all possible hand combinations. These results suggest that the loss of information from STM is comparable when the sample and comparison stimuli are both felt with the same hand or with opposite hands.     

Delayed matching to sample: Reinforcement has opposite effects on resistance to change in two related procedures

The effects of reinforcement on delayed matching to sample (DMTS) have been studied in two within-subjects procedures. In one, reinforcer magnitudes or probabilities vary from trial to trial and are signaled within trials (designated signaled DMTS trials). In the other, reinforcer probabilities are consistent for a series of trials produced by responding on variable-interval (VI) schedules within multiple-schedule components (designated multiple VI DMTS). In both procedures, forgetting functions in rich trials or components are higher than and roughly parallel to those in lean trials or components. However, during disruption, accuracy has been found to decrease more in rich than in lean signaled DMTS trials and, conversely, to decrease more in lean than in rich multiple VI DMTS components. In the present study, we compared these procedures in two groups of pigeons. In baseline, forgetting functions in rich trials or components were higher than and roughly parallel to those in lean trials or components, and were similar between the procedures. During disruption by prefeeding or extinction, accuracy decreased more in rich signaled DMTS trials, whereas accuracy decreased more in lean multiple VI DMTS components. These results replicate earlier studies and are predicted by a model of DMTS from Nevin, Davison, Odum, and Shahan (2007).     

Retrospective and prospective short-term memory in delayed response tasks in rats

Separate groups of rats were trained and tested on asymmetrically and symmetrically reinforced successive delayed matching-to-sample (DMTS) or delayed discrimination (DD) tasks in Experiment 1. Each rat received training and testing on symmetrically reinforced DMTS and DD tasks in Experiment 2. The only difference between each task was that the rats had to respond correctly to a light or tone test stimulus, S₂, if it matched a light or tone sample stimulus, S₁, in DMTS, but could respond to either S₂ if S₁ had been a particular stimulus in DD. Only correct leverpresses were reinforced in the asymmetrically reinforced version of each task. Both correct presses and correct omissions were reinforced in the symmetrically reinforced version of each task. Response biases to leverpress during tests for delayed responding to S₁ were reduced in both symmetrically reinforced tasks, but only in the DD task did such contingencies produce consistently poorer performance in responding to either S, in Experiment 1. Declines in accuracy of performance that occurred in both experiments were greater to the visual than to the auditory S₁ only in the DMTS tasks with increased intervals between S₁ and S₂. A third experiment, in which rats had to respond to S₂ if it matched S₁ (DMTS) or if S₂ mismatched S, (DMmTS), was carried out. Modality of S₁ similarly affected accuracy of delayed responding in each task, as in the first two experiments. Methodological and theoretical implications of these results are discussed in terms of Honig and Thompson’s (1982) dual-process theory of working memory.     

Retrograde amnesia for extinction: Similarities with amnesia for original acquisition memories

Two experiments were conducted using rats to determine whether extinction is susceptible to a traditional amnestic agent (i.e., hypothermia) and to examine whether amnesia for extinction follows the same characteristics as those that occur with original memories. In Experiment 1, rats received hypothermia immediately, 60 min, or 120 min after extinction. When tested, the subjects cooled shortly after extinction showed little memory of the extinction training. This amnesia for extinction disappeared with longer postextinction delays, demonstrating a temporal gradient. Experiment 2 replicated the basic finding and demonstrated that an amnestic-extinguished memory could be recovered by reexposing the subjects to the amnestic agent and that the recovered extinction memory did not persist. These findings provide more evidence that extinction is a form of new learning and are consistent with retrograde amnesia research for original memories showing a temporal gradient and alleviation of retrograde amnesia by reexposure to the amnestic agent.     

Do Phonological and Executive Processes in English Learners at Risk for Reading Disabilities in Grade 1 Predict Performance in Grade 2?

This study determined the degree to which the phonological and executive components of memory reflect language‐specific capacities in reading achievement. We tested whether the memory processes in a sample of English‐language learners that played a major role in predicting second‐language acquisition and risk for reading disability (RD) in Grade 1 (Swanson, Sáez, Gerber, & Leafstedt, 2004) also predicted reading performance in Grade 2. The present results showed that Spanish short‐term memory (STM) performance in Grade 1 predicted basic Spanish‐reading skills and Spanish comprehension in Grade 2, whereas Grade 1 English STM performance predicted English vocabulary and English comprehension in Grade 2. More importantly, children at risk for RD in Grade 1 differed from the counterparts in Grade 2 on both English and Spanish measures of reading, whereas their memory deficits were isolated to Spanish STM and working memory (WM). The relationship between language‐specific processes in memory and reading are discussed.     

Strength vs. temporal-order information in delayed-matching-to-sample performance by monkeys

The usual procedure in delayed-matching-to-sample (DMTS) experiments is that the most recently presented sample stimulus is correct on choice tests. The present paper reports two experments in which the first of two samples was always correct. Theories based on trace strength, such as the Roberts and Grant trace strength competition model, predict that such a procedure will yield below chance performance, because on the average the more recently presented stimulus will have the greater trace strength. In contrast, D’Amato and others have proposed that DMTS performance is mediated by a temporal discrimination process and, since either stimulus may act as S+ in a discrimination problem, monkeys should be capable of learning to choose either the secondor the first of two sample stimuli. Performance did not exceed chance in either experiment. The generality of these results is tentatively explored.     

Effects of signaled retention intervals on pigeon short-term memory

In three delayed matching-to-sample experiments, pigeons were given distinctive stimuli that were either correlated or uncorrelated with the scheduled retention intervals. Experiment 1 employed a single-key, go/no-go matching procedure with colors as the sample and test stimuli; lines of differing orientations signaled short or long delays for one group, whereas the lines and the delays were uncorrelated for the other group. The function relating discriminative test performance to delay length was steeper in the correlated group than in the uncorrelated group. In addition, the line orientation stimuli controlled differential rates of sample responding in the correlated group, but not in the uncorrelated group. In Experiment 2, subjects extensively trained with correlated line orientations were exposed to reversed cues on probe trials. Miscuing decreased discriminative test responding at the short delay, but enhanced it at the long delay. As in the correlated group of the first experiment, rates of sample keypecking were higher in the presence of the “short” time tag than in the presence of the ”long” time tag. Experiment 3 used a three-key choice-matching procedure and a within-subjects design, and equated reinforcement rate at the short and long delays. When auditory stimuli were correlated with delay length, the function relating choice accuracy to delay was steeper than when the stimuli and the delays were uncorrelated. The consistent effects of signaled retention intervals on memory performance may be understood in terms of differential attention to the sample stimuli.     

Temporal integration in second-order conditioning and sensory preconditioning

Lick suppression experiments with rats revealed that the magnitude of both second-order conditioning (Experiment 1) and sensory preconditioning (Experiment 2) was superior when that conditioning was based on backward (US→CS) relative to forward (CS→US) first-order pairings of a CS and US. The superiority of backward relative to forward first-order conditioning on suppression to the higher order cues can be understood by assuming that the magnitude of higher order conditioning was determined by a memory representation of the higher order cues that provided information about the expected temporal location of the US. The results suggest that temporal information such as order between paired CSs and USs was encoded, preserved, and integrated with memory for the higher order stimuli. The relevance of these findings to memory integration in Pavlovian learning, the temporal coding hypothesis (Barnet, Arnold, & Miller, 1991; Matzel, Held, & Miller, 1988), backward excitatory conditioning, and the associative structure that underlies second-order Pavlovian fear conditioning are discussed.     

Additive summation by stimulus compounding irrespective of behavioral contrast during discrimination training: An investigation with positive reinforcement and avoidance schedules

The similarity in the discrimination training leading to behavioral contrast and that preceding tests producing response enhancement to combined discriminative stimuli suggested that the two phenomena might be related. This was investigated by determining if contrast indiscrimination training was necessary for this outcome of stimulus compounding. Responding to tone, light, and to the simultaneous absence of tone and light (T + L) was maintained during baseline training by food reinforcement in Experiment I and by shock avoidance in Experiment II. During subsequent discrimination training, responding was reduced in T + L by programming nonreinforcement in Experiment I and safety or response-punishment in Experiment II. In the first experiment, one rat exhibited positive behavioral contrast, i.e., tone and light rates increased while his T + L rate decreased. In Experiment II, rats punished in T + L showed contrast in tone and light, this being the first demonstration of punishment contrast on an avoidance baseline with rats. The discrimination acquisition data are discussed in the light of current explanations of contrast by Gamzu and Schwartz (1973) and Terrace (1972). During stimulus compounding tests, all subjects in both experiments emitted more responses to tone-plus-light than to tone or light (additive summation). An analysis of the terminal training baselines suggests that the factors producing these test results seem unrelated to whether or not contrast occurred during discrimination training. It was concluded that the stimulus compounding test reveals the operation of the terminal baseline response associations and reinforcement associations conditioned on these multicomponent free-operant schedules of reinforcement.

     

Connecting the Dots Between Past and Future: Constraints in Episodic Future Thinking in Early Childhood

Preschoolers have limited capacity to use past experiences to prepare for the future. Two experiments sought to further understand these limitations. Experiment 1 (N = 42) showed that 3- to 4-year olds’ difficulty performing anticipated future actions was constrained by their memory for relevant past actions, especially those including temporal information. Experiment 2 (N = 94) sought to determine whether preschoolers fail to see that past experiences can inform future-oriented actions. When the connection between the past and future was experimentally heightened, future thinking accuracy improved, but only if preschoolers remembered past experiences. The results indicate that past recall is a prerequisite for future thinking but failure to bridge past and future further accounts for observed limitations in future thinking in early childhood.     

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     

Delayed matching-to-successive-samples in pigeons: Short-term memory for item and order information

Short-term memory for order information in pigeons was explored by using a delayed matching-to-successive-samples task (DMTSS). Experiment 1 indicated that pigeons can accurately report the order of two successively presented samples. Experiments 2, 3 and 4 specifically addressed the representation of order information in short-term memory. Experiment 2 showed that when the duration of the first sample (S1) was very long, or when the duration of the second sample (S2) was very short, order errors increased relative to baseline (S1 and S2 of equal duration), suggesting that memory strength plays an important role in the discrimination of order. The possibility that strength information is necessary for accurate DMTSS performance was tested in Experiments 3 and 4. Pigeons continued to match accurately when memory strength and order were uncorrelated.     

Cognitive and Linguistic Precursors to Early Literacy Achievement in Children With Specific Language Impairment

This study investigated the role of cognitive and language skills as predictors of early literacy skills in children with Specific Language Impairment. A range of cognitive and linguistic skills were assessed in a sample of 137 eight-year-old children with SLI at the beginning of the school year, and 6 months later on word decoding and reading comprehension. The cognitive and linguistic measures revealed four factors that were called language, speech, short-term memory, and phonological awareness. Structural equation modeling showed word decoding to be predicted by speech, short-term memory, and phonological awareness, whereas reading comprehension was predicted by word decoding skills and short-term memory. It can be concluded that in children with SLI variations in early word decoding are mostly determined by speech abilities and short-term memory, and to a lesser extent by phonological awareness. Moreover, reading comprehension turns out to be highly dependent on word decoding and short-term memory.     

Sample and comparison location as factors in matching acquisition,transfer, and acquired equivalence

Pigeons learned symbolic matching with samples appearing equally often on left and right keys. For a location-relevant group, the reinforced comparison choice for each sample reversed across sample locations; for a location-irrelevant group, the reinforced choices were the same. Consistent with the hypothesis that samples at different locations are functionally different for pigeons, Experiment 1 showed that matching acquisition was comparable in these two groups. Nevertheless, the location-irrelevant group eventually ignored sample location, given that their performances subsequently transferred to a novel (center-key) sample location. This transfer was not simply due to sample familiarity at different training locations; rather, it required that left- and right-key samples occasion the same reinforced choices in training. Acquired equivalence between those samples was then assessed in Experiment 2. The location-irrelevant group showed the predicted equivalence effects, but the location-relevant group did not—in fact, its results were the opposite of those predicted by equivalence. Their results indicate that the functional comparison stimuli are also defined in terms of their locations.     

The basis of feeling-of-knowing judgments in patients with schizophrenia

We examined the basis of feeling-of-knowing judgments (FOK) in patients with schizophrenia. Such patients typically have impaired memory and awareness, but not metamemory-accuracy deficits. The magnitude of FOKs are lower for patients with schizophrenia than for healthy participants, but judgments equally predict memory performance. In healthy participants, FOK is based on accessible information, including retrieval of partial-target (e.g., retrieving the first letter) and contextual information (e.g., related facts). In Experiment 1, we examined if accessible information predicts FOKs for episodic memory in patients with schizophrenia. Patients and healthy controls learned names paired with drawings of imaginary animals. The results showed that patients’ FOK increased with the retrieval of partial-target and contextual information. In Experiment 2, using semantic-memory general-information questions, accessible partial-target information predicted FOKs in patients with schizophrenia. The accessibility model of FOK applies to patients with schizophrenia, and it is important to determine what occurs in other memory-impaired populations.     

Sequential processes in the generalization and transfer of stimulus control

Prior research indicated that a training sequence consisting of a negative stimulus followed by a positive stimulus constitutes the minimal condition for the production of postdiscrimination phenomena typically observed after training with random sequences of the discriminanda. The present experiments, employing multiple schedules with pigeon subjects, confirmed the earlier findings but indicated that they are restricted to procedures in which the reinforcing stimulus may acquire a discriminative function that competes with the control exerted by the nominal discriminanda. The sequences in which the discriminanda were presented did not differentially affect subsequent measures of generalization and transfer if the discriminative function of reinforcement were degraded either by introducing some reinforcers during the negative stimulus (Experiment 1) or by omitting some reinforcers during the positive stimulus (Experiment 2). It was concluded that the sequence in which the discriminanda are presented during discrimination training does not contribute fundamentally to the processes responsible for discrimination formation with random training sequences.     

Interference and auditory short-term memory in the bottlenosed dolphin

Interference in auditory short-term memory in the bottlenosed dolphin,Tursiops truncatus (Montagu), was studied using a delayed matching-to-sample task. At each trial, one of two sample sounds, chosen randomly, was projected underwater for 4 sec and then, after a variable delay interval, both sounds were presented. A response to the sound matching the initial sample was reinforced. Correct matching was significantly reduced following short intervals between trials in combination with long delays after the sample (proactive interference), or when a near continuous irrelevant sound was inserted into the delay interval (retroactive interference). There was rapid habituation to interference if the irrelevant sound was short in duration relative to the delay interval. For both proactive and retroactive interference, the errors were predominantly responses to the sample sound appropriate to the prior trial rather than to the current trial, indicating that memory for the relative recency of events (temporal memory) was degraded by interference. When interference was deleted or minimized, temporal memory remained nearly perfect over 30-sec delay intervals, the longest tested. The importance of distinguishing between temporal memory and nontemporal, or event, memory in different forms of the delayed matching task was emphasized.     

Conditioned inhibitory effects of discriminated Pavlovian training with food in rats depend on interactions of search modes, related repertoires, and response measures

Like other accounts of conditioned inhibition, behavior systems predicts (and Experiment 1 shows) that during summation and retardation tests, presentation of a negative conditioned stimulus (a CS−) created by discriminative Pavlovian food conditioning will interfere with a focal search response, such as nosing in the feeder. Unlike most other views, behavior systems predicts (and Experiment 2 shows) that the same CS− can potentiate a general search response, like attending to a moving artificial prey stimulus. Contacting the prey stimulus in extinction increased over baseline when a CS- but not a CS Novel preceded it. Experiment 3 showed this effect was not due to unconditioned qualities of the CS−. It appears that the effects of a discriminative CS-depend on the interaction of the training contingency with search modes related to the unconditioned stimulus (US), their perceptual-motor repertoires and environmental support, and the choice of response measure.