Memory for Objects and Positions: Delayed Non-matching-to-sample in Storing and Non-storing Tits

An operant delayed-non-matching-to-sample task using computer-presented images was used to test memory for position and object (shape and colour) cues in four species of tit (Parus), two food-storing species (P. palustris and P. ater) and two non-storing species (P. major and P. caeruleus). Both storers and non-storers performed successfully at retention intervals as long as 100 sec on all trial types, and there were no significant differences in performance between the two groups on any of the trial types. Performance by both groups was highest on trials in which both object and position cues were available and poorest on trials when object cues only were relevant. These data do not provide support for the hypothesis that food storers have a better memory for spatial cues than do non-storers.     

Spatial memory of four species of parus: Performance in an open-field analogue of a radial maze

The performance of four species of tit (marsh tit, Parus palustris; coal tit, P. ater; blue tit, P. caeruleus; and great tit, P. major) and one finch (greenfinch, Carduelis choris) was compared in an open field analogue of the radial maze. There were no differences between the tit species in either acquisition or asymptotic performance. The greenfinch showed less improvement with experience than the tits. When the retention interval between forced choice of four goal boxes and free choice of all eight was varied between 30 sec and 24 hr, performance declined with increasing interval. After 24 hr some individuals still performed above chance, and the food-storing tits combined (marsh and coal tit) were above chance, whilst the non-storers (blue and great tits) were not (this was primarily due to the poor performance of great tits). The results are discussed in relation to the hypothesis that food-storing tits have a specialized spatial memory.     

Preference for spatial cues in a non-storing songbird species

Male mammals typically outperform their conspecific females on spatial tasks. A sex difference in cues used to solve the task could underlie this performance difference as spatial ability is reliant on appropriate cue use. Although comparative studies of memory in food-storing and non-storing birds have examined species differences in cue preference, few studies have investigated differences in cue use within a species. In this study, we used a one-trial associative food-finding task to test for sex differences in cue use in the great tit, Parus major. Birds were trained to locate a food reward hidden in a well covered by a coloured cloth. To determine whether the colour of the cloth or the location of the well was learned during training, the birds were presented with three wells in the test phase: one in the original location, but covered by a cloth of a novel colour, a second in a new location covered with the original cloth and a third in a new location covered by a differently coloured cloth. Both sexes preferentially visited the well in the training location rather than either alternative. As great tits prefer colour cues over spatial cues in one-trial associative conditioning tasks, cue preference appears to be related to the task type rather than being species dependent.     

Memory for two stimulus-response items in pigeons

Six pigeons served in a discrete-trial experiment on short-term memory. Combinations of three key positions and two ordinal positions, yielding six possible sequences of stimulus-response pairs, were used as lists of items. A retention interval separated list presentation from the test phase in which two (for Group 1) or three (for Group 2) keys were illuminated with either red or green light. A reinforcer was delivered if a subject pecked the key of the first item on a red trial and the key of the second item on a green trial. When the retention interval was lengthened from one to five or nine seconds, a systematic loss of stimulus control resulted. Lengthening the interval between items from one to eight seconds had a much smaller effect for the birds in Group 1, whereas a systematic loss of stimulus control was found in red trials for the birds in Group 2. The functional relations between choice accuracy and delay provided an empirical basis for analysis of what relations among temporal events can become discriminative stimuli.     

Pigeons'' spatial memory: II. Acquisition of delayed matching of key location and transfer to new locations

Five hungry pigeons first received delayed matching of key location training. Trials began with a “ready” stimulus (brief operation of the grain feeder). Then one (randomly chosen) of a set of four keys from a three-by-three matrix was lit briefly as the sample. After a short delay (retention interval), the sample key was lit again along with one of the other eight keys. A peck at the key that had served as the sample produced grain reinforcement, whereas a peck to the other key produced only the intertrial interval. After delayed matching of key location was learned, the remaining five key locations were introduced as samples. Four of the five birds performed at considerably above-chance levels on the novel sample trials during the first as well as subsequent sessions. These results suggest that pigeons sometimes learn the single rule—“choose the location that matches the sample.” The relevance of these results to the issue of whether pigeons learn a generalized matching rule (i.e., a concept of “sameness”) is discussed.     

Abstract-concept learning in Black-billed magpies (<Emphasis Type="Italic">Pica hudsonia</Emphasis>)

Abstract relational concepts depend upon relationships between stimuli (e.g., same vs. different) and transcend features of the training stimuli. Recent evidence shows that learning abstract concepts is shared across a variety species including birds. Our recent work with a highly-skilled food-storing bird, Clark’s nutcracker, revealed superior same/different abstract-concept learning compared to rhesus monkeys, capuchin monkeys, and pigeons. Here we test a more social, but less reliant on food-storing, corvid species, the Black-billed magpie (Pica hudsonia). We used the same procedures and training exemplars (eight pairs of the same rule, and 56 pairs of the different rule) as were used to test the other species. Magpies (n = 10) showed a level of abstract-concept learning that was equivalent to nutcrackers and greater than the primates and pigeons tested with these same exemplars. These findings suggest that superior initial abstract-concept learning abilities may be shared across corvids generally, rather than confined to those strongly reliant on spatial memory.     

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

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

Retroactive interference in rats: Independent effects of time and similarity of the intervening event with respect to acquisition

Events occurring during the retention intervals for a 5-min delayed alternation task were used to investigate the factors that influence retroactive interference. Appetitive reinforcement in an E-maze was employed to train rats on the delayed alternation task consisting of a forced-choice (target event) trial followed by a free-choice (test) trial. Occasional probe trials added a potentially interfering event either at the beginning, middle, or end of the retention period. These events also varied in similarity to the target events, ranging from low similarity to the converse of the target event. Interference increased both with the interval between the target and intervening events and with the similarity between the converse of the target event and the intervening event; however, there was no tendency, significant or otherwise, towards an interaction between stimulus similarity and the interval between the target and intervening events. Control groups demonstrated that the interference was of an associative nature and that the interval between the intervening event and the test trial was little consequence. These results are discussed in terms of two separate types of interference: similarity interference which depends on stimulus similarity of the intervening event to the converse of the target event but not on the temporal location of the intervening event, and processing interference which depends on the temporal location of the intervening event but not on its similarity to the converse of the target event.     

Theoretical and methodological considerations for the study of imagery in animals

Transformation of a moving stimulus is an operational definition of imagery that is useful in animal research. This definition was developed from structural, functional, and interactive theories of imagery in humans. The historical roots of the definition are traced to behavioristic methodologies within cognitive psychology. An imagery procedure for animals was developed that tests this definition with extrapolated movement. Pigeons were reinforced for discriminating between a rectangle that rotated at constant velocity from a rectangle whose final location violated constant velocity. Imagery trials included a short-term memory component in which the task of the pigeon was to discriminate between extrapolated trajectories of rotation while the rectangle was absent. The evidence supports similarities between human and animal representations of movement. A visible transformation employed as a sample stimulus and followed by a retention interval provides a powerful procedure for measuring the interaction between perception and memory. An advantage of this paradigm is that it could be employed to investigate imagery at the neural level or to obtain comparative behavioral data from different species.     

Development of object permanence in food-storing magpies (Pica pica)

The development of object permanence was investigated in black-billed magpies (Pica pica), a food-storing passerine bird. The authors tested the hypothesis that food-storing development should be correlated with object-permanence development and that specific stages of object permanence should be achieved before magpies become independent. As predicted, Piagetian Stages 4 and 5 were reached before independence was achieved, and the ability to represent a fully hidden object (Piagetian Stage 4) emerged by the age when magpies begin to retrieve food. Contrary to psittacine birds and humans, but as in dogs and cats, no "A-not-B error" occurred. Although magpies also mastered 5 of 6 invisible displacement tasks, evidence of Piagetian Stage 6 competence was ambiguous.     

Place learning in the Morris water task: making the memory stick

Although the Morris water task has been used in hundreds of studies of place learning, there have been no systematic studies of retention of the place memory. We report that retention, as measured by selective search behavior on a probe trial, is excellent when the retention interval is short (5-10 min). However, performance rapidly deteriorates, so that by approximately 4 h the search is no longer selective. Additional experiments revealed that selective search at longer retention intervals was improved by inserting gaps between blocks of training trials, but this effect was a non-monotonic function of the interval separating trial blocks. Our experiments also revealed that the location of the first block of trials (Room A or Room B) was irrelevant to long-term retention. A memory modulation theoretical framework may provide a useful way to understand these findings.     

Delayed matching in the capuchin monkey with brief sample durations

Two capuchin monkeys were trained in a delayed matching-to-sample task in which the duration that the sample was available for viewing was very brief, 0.075 to 0.45 sec. The matching performance of one animal was above chance with delay (retention) intervals as long as 4 min; the other S showed significant matching with a 2-min retention interval. The performance of both Ss was independent of sample exposure duration, indicating that their capacity to match successfully at long retention intervals is not dependent on repeated viewing of the sample stimulus. The marked practice effect shown by one S with prolonged training at 2-min delay suggests the capacity of “learning how to remember.” A constant high performance level on 2-sec delay control trials indicates that the observed practice effect was not the result of enhanced attending to the sample stimulus.     

Memory for sequences of stimuli and responses

Two experiments sought to determine if pigeons could discriminate and remember recent sequences of stimuli and responses. A variant of Konorski's short-term memory procedure involving successive presentation of sample and test stimuli was used. The samples were stimulus-response pairs of the form, (S-R)₁–(S-R)₂. Differential test responding disclosed memory of the two-item samples, with birds showing earlier and greater control by the second item than the first (Experiment 1). When the retention interval separating the second item of the sample sequence from the test stimulus was lenghtened from .5 to 2.0 or 4.0 sec, a systematic loss of stimulus control resulted; however, when varied over the same temporal range, the interval between the two items of the sample sequence had a much smaller effect, or none at all (Experiment 2). These results support an account of response-sequence differentiation that stresses short-term memory of organized behavior patterns.     

线索提示对表征动量的影响

研究结合线索提示和表征动量范式,实验1、2均采用2有无线索(有线索,无线索)×4诱导期间时距(1250ms,1750ms,2250ms,2750ms)混合实验设计,探讨线索呈现的加工阶段和时距对表征动量的影响。实验1恒定保持间隔时距,在不同时距的诱导期间呈现线索,发现线索主效应不显著,但表征动量呈减小趋势;时距主效应不显著。实验2变化诱导时距,在恒定的保持间隔呈现线索,发生向后偏移现象,线索主效应显著;时距主效应不显著。研究结果表明,随着注意的增加,表征动量效应减小;注意时距不显著影响表征动量,而注意阶段显著影响表征动量。研究结果为表征动量的双加工理论提供了实证支持。     

Visual–spatial attention aids the maintenance of object representations in visual working memory

Theories have proposed that the maintenance of object representations in visual working memory is aided by a spatial rehearsal mechanism. In this study, we used two different approaches to test the hypothesis that overt and covert visual–spatial attention mechanisms contribute to the maintenance of object representations in visual working memory. First, we tracked observers’ eye movements while they remembered a variable number of objects during change-detection tasks. We observed that during the blank retention interval, participants spontaneously shifted gaze to the locations that the objects had occupied in the memory array. Next, we hypothesized that if attention mechanisms contribute to the maintenance of object representations, then drawing attention away from the object locations during the retention interval should impair object memory during these change-detection tasks. Supporting this prediction, we found that attending to the fixation point in anticipation of a brief probe stimulus during the retention interval reduced change-detection accuracy, even on the trials in which no probe occurred. These findings support models of working memory in which visual–spatial selection mechanisms contribute to the maintenance of object representations.     

Reference frame and effects of orientation on finding the tops of rotated objects.

Effects of stimulus orientation across trial blocks and the spatial reference frame were investigated with a task in which Ss, with their head upright or tilted, judged a dot to be near the top or the bottom of rotated line drawings of objects. Objects used in this task were also named. Response times from the first block of trials increased linearly for objects rotated from 0 degrees to 120 degrees from the upright. Across blocks, orientation effects diminished for naming but remained the same for top-bottom discriminations. Practice with top-bottom discriminations diminished orientation effects when the same objects were subsequently named. The spatial reference frame for top-bottom discriminations was midway between retinal and environmental coordinates. Specifying the location of object features is of greater importance for top-bottom discriminations than for naming and underlies orientation effects in these tasks.     

Does attention affect visual feature integration?

Two questions are investigated in this work: first, whether the integration of color and shape information is affected by attending to the stimulus location, and second, whether attending to a stimulus location enhances the perceptual representation of the stimulus or merely affects decision processes. In three experiments, subjects were briefly presented with colored letters. On most trials, subjects were precued to the stimulus location (valid cue); on some trials, a nonstimulus location was cued (invalid cue). Subjects were less likely to incorrectly combine colors and letter shapes following a valid cue. The attentional facilitation afforded by the cue was not limited to feature integration but also affected the registration of features. However, when the amount of feature information was strictly controlled, attention still affected feature integration. The results indicate that orienting attention to the location of the cue affects the quality of the perceptual representation for features and their integration.     

Parallel working memory for spatial location and food-related object cues in foraging pigeons: binocular and lateralized monocular performance

During foraging, animals can increase their success by both remembering feeding sites and remembering food-related object cues. Because earlier studies have tested either the site or object memory in isolation, the aim of the present study was to evaluate how efficiently birds can utilize both memories simultaneously. Furthermore, the idea was tested that lateralization might be the principle of brain organization that allows for efficient parallel processing. Pigeons learned to search for food in a complex maze with 16 baited sites. To obtain the maximum reward they had to perform two tasks in parallel, a spatial working memory task and an object-specific working memory task. Birds performed well on this dual task but, compared with spatial working memory alone, they were impaired during the first choices of a trial (Experiment 1). When the left and the right brain hemispheres were tested separately by means of monocular occlusion (Experiment 2), object discrimination was better when birds used their right eye/left hemisphere. This was most pronounced during the first choices of a trial. On the spatial component of the task, performance on binocular trials was better than on monocular trials, but monocularly both hemispheres performed at the same level. Results show that on this dual task, discrimination of food-related object cues predominantly involved the left brain hemisphere whereas both hemispheres contributed equally to spatial performance.     

Delayed temporal discrimination in pigeons: A comparison of two procedures

A within-subjects comparison was made of pigeons' performance on two temporal discrimination procedures that were signaled by differently colored keylight samples. During stimulus trials, a peck on the key displaying a slanted line was reinforced following short keylight samples, and a peck on the key displaying a horizontal line was reinforced following long keylight samples, regardless of the location of the stimuli on those two choice keys. During position trials, a peck on the left key was reinforced following short keylight samples and a peck on the right key was reinforced following long keylight samples, regardless of which line stimulus appeared on the correct key. Thus, on stimulus trials, the correct choice key could not be discriminated prior to the presentation of the test stimuli, whereas on position trials, the correct choice key could be discriminated during the presentation of the sample stimulus. During Phase 1, with a 0-s delay between sample and choice stimuli, discrimination learning was faster on position trials than on stimulus trials for all 4 birds. During Phase 2, 0-, 0.5-, and 1.0-s delays produced differential loss of stimulus control under the two tasks for 2 birds. Response patterns during the delay intervals provided some evidence for differential mediation of the two delayed discriminations. These between-task differences suggest that the same processes may not mediate performance in each.     

Long-term memory of color stimuli in the jungle crow (Corvus macrorhynchos)

Wild-caught jungle crows (n = 20) were trained to discriminate between color stimuli in a two-alternative discrimination task. Next, crows were tested for long-term memory after 1-, 2-, 3-, 6-, and 10-month retention intervals. This preliminary study showed that jungle crows learn the task and reach a discrimination criterion (80% or more correct choices in two consecutive sessions of ten trials) in a few trials, and some even in a single session. Most, if not all, crows successfully remembered the constantly reinforced visual stimulus during training after all retention intervals. These results suggest that jungle crows have a high retention capacity for learned information, at least after a 10-month retention interval and make no or very few errors. This study is the first to show long-term memory capacity of color stimuli in corvids following a brief training that memory rather than rehearsal was apparent. Memory of visual color information is vital for exploitation of biological resources in crows. We suspect that jungle crows could remember the learned color discrimination task even after a much longer retention interval.