Characteristics of serial order learning in common marmosets (Callithrix jacchus)

We investigated the characteristics of serial order learning in common marmosets (Callithrix jacchus). Five marmosets were trained in a sequential responding task in which they were required to touch four graphic patterns in a given order (A→B→C→D) to obtain a reward. All five marmosets learned the task with over 65% accuracy. Shuffling the positions of B, C, and D immediately after the marmoset had correctly identified and selected the first stimulus (A) either decreased accuracy or lengthened response latency for the second stimulus (B). These results suggest that the marmosets planned the response to the second stimulus before they touched the first stimulus. In addition, when we presented a pair of stimuli (AB, AC, AD, BC, BD, and CD pairs), the marmosets responded to the stimuli in the pair in the appropriate order, according to the learned order (A→B→C→D). The analyses of first and second response latencies clearly demonstrated both the first-item and missing-item effects in task performance. Our data provide direct evidence that marmosets can learn the relative order of the four stimuli in a sequential responding task. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

Testing for social learning and imitation in common marmosets, <Emphasis Type="Italic">Callithrix jacchus</Emphasis>, using an artificial fruit

We tested for social learning and imitation in common marmosets using an artificial foraging task and trained conspecific demonstrators. We trained a demonstrator marmoset to open an artificial fruit, providing a full demonstration of the task to be learned. Another marmoset provided a partial demonstration, controlling for stimulus enhancement effects, by eating food from the outside of the apparatus. We thus compared three observer groups, each consisting of four animals: those that received the full demonstration, those that received the partial demonstration, and a control group that saw no demonstration prior to testing. Although none of the observer marmosets succeeded in opening the artificial fruit during the test periods, there were clear effects of demonstration type. Those that saw the full demonstration manipulated the apparatus more overall, whereas those from the control group manipulated it the least of the three groups. Those from the full-demonstration group also contacted the particular parts of the artificial fruit that they had seen touched (localised stimulus enhancement) to a greater extent than the other two groups. There was also an interaction between the number of hand and mouth touches made to the artificial fruit for the full- and partial-demonstration groups. Whether or not these data represent evidence for imitation is discussed. We also propose that the clear differences between the groups suggest that social learning mechanisms provide real benefits to these animals in terms of developing novel food-processing skills analogous to the one presented here.     

阻碍效应范式中主题知识对类别学习的影响

三个实验采用阻碍效应研究范式探讨主题知识对类别学习的影响。实验1探讨定义特征维度为机械特征时,主题知识对类别学习的影响;实验2和实验3,通过考察定义特征维度为知识特征时,类别学习中阻碍效应的大小,继续探讨主题知识对类别学习的影响。实验结果发现：（1）当定义特征维度为机械特征时,主题知识的存在没有促进类别学习。这可能因为定义特征维度为机械特征,主题知识难以发现所致;（2）当定义特征维度为知识特征时,类别学习中的阻碍效应消失,证明主题知识的存在促进了类别学习。研究结果再次支持了类别学习不仅仅受到减少归类错误驱动的观点。     

Trial-and-error learning improves source memory among young and older adults

Trial-and-error learning, relative to errorless learning, has been shown to impair memory among older adults, despite evidence from young adults that errors may afford memorial benefits through richer encoding. However, previous studies on the effects of errorless versus trial-and-error learning in older adults has required production of errors based on perceptual cues. We hypothesized that producing errors conceptually associated with targets would boost memory for the encoding context in which information was studied, especially for older adults who do not spontaneously elaborate on targets at encoding. We report two studies examining the impact of generating errors during learning on source memory among young and older adults, with a process dissociation procedure employed in Study 1, and source memory assessed directly in Study 2. In both studies, participants were shown semantic category cues and generated an exemplar either with or without errors. In Study 1, for both age groups trial-and-error learning was associated with lower familiarity-based memory and higher recollection-based memory relative to errorless learning, and the latter effect was more marked for older than younger adults. Similarly, in Study 2, trial-and-error learning was associated with better source memory relative to errorless learning, particularly for the older adults. We argue that trial-and-error learning can enhance source memory and confer memorial benefits when making such errors facilitates semantic elaboration, especially for older adults who do not spontaneously engage in strategic encoding.     

Working memory interference control deficit in children referred by teachers for ADHD symptoms.

It has been hypothesised that children with Attention Deficit/Hyperactivity Disorder (ADHD) present memory problems, including working memory deficits. This research is aimed at finding clearer evidence of a working memory deficit in these children. In the first study 22 children that had been referred by teachers as having ADHD symptoms were compared with a control group. Their performance on a listening span test, drawn up by De Beni, Palladino, Pazzaglia, and Cornoldi (1998), was investigated. In this task the subjects were asked to select the names of animals in word strings and to remember the last word in each string. In a second study, 34 children with ADHD symptoms and 50 control children were presented with a visuospatial working memory task mirroring the verbal task used in Study 1. In both studies, the children with ADHD symptoms had difficulty in remembering the last item in the string and had a higher number of intrusions when memorising items that were not in the final position. The results were interpreted that children with ADHD symptoms have working memory problems because they are not capable of suppressing information that initially has to be processed, and subsequently excluded from memory. This particular difficulty can be interpreted as an inhibitory processing deficit. The implications of the results in understanding learning difficulties in children with ADHD are discussed.     

Strength of hand preference and dual task performance by common marmosets

Study of avian and piscine species has shown that animals with stronger lateralization of the brain are able to perform two tasks presented simultaneously better than can animals with weaker lateralization. We investigated whether this might apply also to primates by testing common marmosets to see whether there is a relationship between the strength of hand preference, as an indicator of strength of brain lateralization, and the ability to carry out two tasks simultaneously. A model predator was introduced into the testing room while the marmoset was foraging. Marmosets with stronger hand preferences detected the ‘predator’ after shorter latency than those with weaker hand preferences. Furthermore, the marmosets with stronger hand preferences produced more mobbing (tsik) vocalizations when they reacted to the predators than did those with weaker hand preferences. There was no such association between hand preference and either latency to respond to the predator or mobbing reaction when the marmosets were not foraging at the time the predator was introduced. Hence, strength of lateralization is associated with the ability to perform foraging and predator detection simultaneously. These results are discussed with reference to the evolution of brain lateralization.     

Perception of the stereokinetic illusion by the common marmoset (<Emphasis Type="Italic">Callithrix jacchus</Emphasis>)

Stereokinetic illusions have never been investigated in non-human primates, nor in other mammalian species. These illusions consist in the perception of a 3D solid object when certain 2D stimuli are rotated slowly in the plane perpendicular to the line of sight. The ability to perceive the stereokinetic illusion was investigated in the common marmoset (Callithrix jacchus). Four adult marmosets were trained to discriminate between a solid cylinder and a solid cone for food reward. Once learning criterion was reached, the marmosets were tested in sets of eight probe trials in which the two solid objects used at training were replaced by two rotating 2D stimuli. Only one of these stimuli produced, at least to the human observer, the stereokinetic illusion corresponding to the solid object previously reinforced. At test, the general behaviour and the total time spent by the marmosets observing each stimulus were recorded. The subjects stayed longer near the stimulus producing the stereokinetic illusion corresponding to the solid object reinforced at training than they did near the illusion corresponding to the previously non-rewarded stimulus. Hence, the common marmosets behaved as if they could perceive stereokinetic illusions.     

The effects of intradimensional and extradimensional shifts on visual discrimination learning in humans and non-human primates

Human subjects and non-human primates (the common marmoset) were trained on a series of reversals of both a simple (stimuli varying along one dimension) and compound (stimuli varying along two different dimensions) visual discrimination, using computer-generated stimuli. They were then shifted to a third series of reversals using completely novel compound stimuli. Those humans and marmosets for which the previously relevant dimension remained relevant, following the shift (shapes to shapes or lines to lines; intradimensional shift) made fewer errors than those for which the previously irrelevant dimension became relevant (shapes to lines or lines to shapes; extradimensional shift). These findings suggest that both humans and marmosets can learn to attend to the specific attributes or dimensions of a stimulus and use this information in visual discrimination learning.     

Problem solving in great apes (Pan paniscus, Pan troglodytes, Gorilla gorilla, and Pongo abelii): the effect of visual feedback

What kind of information animals use when solving problems is a controversial topic. Previous research suggests that, in some situations, great apes prefer to use causally relevant cues over arbitrary ones. To further examine to what extent great apes are able to use information about causal relations, we presented three different puzzle box problems to the four nonhuman great ape species. Of primary interest here was a comparison between one group of apes that received visual access to the functional mechanisms of the puzzle boxes and one group that did not. Apes' performance in the first two, less complex puzzle boxes revealed that they are able to solve such problems by means of trial-and-error learning, requiring no information about the causal structure of the problem. However, visual inspection of the functional mechanisms of the puzzle boxes reduced the amount of time needed to solve the problems. In the case of the most complex problem, which required the use of a crank, visual feedback about what happened when the handle of the crank was turned was necessary for the apes to solve the task. Once the solution was acquired, however, visual feedback was no longer required. We conclude that visual feedback about the consequences of their actions helps great apes to solve complex problems. As the crank task matches the basic requirements of vertical string pulling in birds, the present results are discussed in light of recent findings with corvids.     

Classification errors and response times over multiple distributed sessions as a function of category structure

Learning difficulty orderings for categorical stimuli have long provided an empirical foundation for concept learning and categorization research. The conventional approach seeks to determine learning difficulty orderings in terms of mean classification accuracy. However, it is relatively rare that the stability of such orderings is tested over a period of extended learning. Further, research rarely explores dependent variables beyond classification accuracy that may also indicate relative learning difficulty, such as classification response times (RTs). Using a family of category structures defined over three binary dimensions and four positive examples that is well-known for its robust learning difficulty ordering, we report the results of two experiments that test the stability of the ordering (in terms of both errors and RTs) over multiple category learning sessions. The experimental stimuli consisted of instantiations of each of the six category structures in the family. These take the form of categories consisting of four “flasks” that vary along the binary features of size (large or small), shape (circular or triangular), and color (black or white). Experiment 1 shows that when participants are randomly presented instances of all six types, the difficulty ordering remains stable across all three sessions. This stability is present in terms of mean accuracy (errors) as well as mean RTs. In Experiment 2, participants were repeatedly exposed to category instances of a single type. In terms of errors, the ordering is revealed in the first session and disappears in later sessions. The opposite trend is observed for classification RTs: The ordering is not present in the first session but is revealed in later sessions. This suggests that even when individuals reach a relative degree of expertise in terms of reduced errors, the original degree of difficulty continues to influence processing. We interpret these results in the context of the concept learning and perceptual expertise literatures.     

Modulation of physical understanding by common marmosets (<Emphasis Type="Italic">Callithrix jacchus</Emphasis>)

The understanding of physical causality in common marmosets was tested using support problems in which a pair of sheets was presented to determine whether subjects would choose the sheet that had a food item on it (i.e., the sheet was supporting the food item). In two experiments, the conditions were manipulated in terms of the length of the sheet, the distance between the sheet and the food item, the presence of a gap separating the two sheets, and the size of the food item. In Experiment 1, the marmosets had difficulty rejecting an irretrievable food item when it was located closer to them than a retrievable item. Although their performance was strongly affected by the size of the irretrievable food item, they quickly learned to reject that alternative. In contrast, no improvement was found when one sheet was divided into two pieces such that the food item could not be retrieved when its near side was pulled. A similar response tendency was observed in Experiment 2, in which the effects of the large food item were examined in three different conditions. Thus, common marmosets were influenced by the perceptual features of the food in solving the support problems, as are other non-human primates. In addition, they consistently failed to appreciate the presence of a gap and, therefore, failed to reject the distracter alternative. However, all animals rapidly learned that the size of the food item was an irrelevant variable, and some showed an elementary conceptual understanding of support. These findings suggest that marmosets’ physical understanding may improve with experience.     

Response time distributions in multidimensional perceptual categorization

Three speeded categorization experiments were conducted using separable dimension stimuli. The form of the category boundary was manipulated across experiments, and the distance from category exemplars to the category boundary was manipulated within each experiment. Observers completed several sessions in each experiment, yielding 300–400 repetitions of each stimulus. The large sample sizes permitted accurate estimates of the response time (RT) distributions and RT hazard functions. Analyses of these data indicated: (1) RT was faster for stimuli farther from the category boundary, and this stochastic dominance held at the level of the RT distributions; (2) RT was invariant for all stimuli the same distance from the category boundary; (3) when task difficulty was high, errors were slower than correct responses, whereas this difference disappeared when difficulty was low; (4) small, consistent response biases appeared to have a large effect on the relation between correct and error RT; (5) the shape of the RT hazard function was qualitatively affected by distance to the category boundary. These data establish a rich set of empirical constraints for testing developing models of categorization RT.     

Conditional discrimination in mentally retarded subjects: programming acquisition and learning set.

In Experiment 1, 3 subjects with retardation were exposed to two visual-visual arbitrary matching-to-sample problems each day. One conditional discrimination was presented under trial-and-error conditions, and the other was presented under a component training procedure. The latter began by establishing the comparison discrimination and its rapid reversal. The successive discrimination between the sample stimuli was established through differential naming. Then, sample naming was maintained in conditional discrimination sessions in which the same sample was presented in blocks of consecutive trials. Block size was decreased across sessions until sample presentation was randomized as in trial-and-error training (but with naming maintained). Two subjects initially learned only with component training. The performance of the 3rd subject was inconsistent across conditional discriminations. One of the successful subjects ultimately learned rapidly and consistently with trial-and-error procedures. Experiment 2 sought to demonstrate learning set in the other 2 subjects. Elements of the component training procedure were withdrawn over successive conditional discriminations. Ultimately, 1 subject nearly always learned under trial-and-error conditions, and the other learned under trial-and-error conditions combined with differential sample naming.     

New strings for old: The role of similarity processing in an incidental learning task

This paper reports three experiments that examine the role of similarity processing in McGeorge and Burton's (1990) incidental learning task. In the experiments subjects performed a distractor task involving four-digit number strings, all of which conformed to a simple hidden rule. They were then given a forced-choice memory test in which they were presented with pairs of strings and were led to believe that one string of each pair had appeared in the prior learning phase. Although this was not the case, one string of each pair did conform to the hidden rule. Experiment 1 showed that, as in the McGeorge and Burton study, subjects were significantly more likely to select test strings that conformed to the hidden rule. However, additional analyses suggested that rather than having implicitly abstracted the rule, subjects may have been selecting strings that were in some way similar to those seen during the learning phase. Experiments 2 and 3 were designed to try to separate out effects due to similarity from those due to implicit rule abstraction. It was found that the results were more consistent with a similarity-based model than implicit rule abstraction per se.     

An associative account of the development of word learning

Word learning is a notoriously difficult induction problem because meaning is underdetermined by positive examples. How do children solve this problem? Some have argued that word learning is achieved by means of inference: young word learners rely on a number of assumptions that reduce the overall hypothesis space by favoring some meanings over others. However, these approaches have difficulty explaining how words are learned from conversations or text, without pointing or explicit instruction. In this research, we propose an associative mechanism that can account for such learning. In a series of experiments, 4-year-olds and adults were presented with sets of words that included a single nonsense word (e.g. dax). Some lists were taxonomic (i.,e., all items were members of a given category), some were associative (i.e., all items were associates of a given category, but not members), and some were mixed. Participants were asked to indicate whether the nonsense word was an animal or an artifact. Adults exhibited evidence of learning when lists consisted of either associatively or taxonomically related items. In contrast, children exhibited evidence of word learning only when lists consisted of associatively related items. These results present challenges to several extant models of word learning, and a new model based on the distinction between syntagmatic and paradigmatic associations is proposed.     

Activity of common marmosets (Callithrix jacchus) in limited spaces: hand movement characteristics

The increasing popularity of marmoset monkeys (Callithrix jacchus) in anatomical, behavioral, and electrophysiological studies has called for a detailed analysis of their natural behavior within limited spaces. In the present study, the authors analyzed hand movements during horizontal and vertical progressions in a cylinder. The trajectory of each hand covered the entire cylinder floor during horizontal progressions and the entire cylinder wall during vertical progressions. Different marmosets have different patterns of hand movement. The average maximum angle of hand movements for all marmosets during horizontal and vertical progressions oscillates, although the average over time is constant and similar for both hands, whereas head movements during horizontal progressions become smaller with successive progressions. Another observed difference between rats and monkeys was in the size of head and hand movements at the beginning of each experimental session. During the 1st horizontal progression, all marmosets moved their heads to a greater extent than their hands. This sequential head and hand movement is referred as bistable behavior. The bistable pattern of motor behavior, which was also observed in successive progressions, may be derived from an inherent fear of predators or exploratory interest of a novel environment.     

Normal aging and the dissociable prototype learning systems

Dissociable prototype learning systems have been demonstrated behaviorally and with neuroimaging in younger adults as well as with patient populations. In A/not-A (AN) prototype learning, participants are shown members of category A during training, and during test are asked to decide whether novel items are in category A or are not in category A. Research suggests that AN learning is mediated by a perceptual learning system. In A/B (AB) prototype learning, participants are shown members of category A and B during training, and during test are asked to decide whether novel items are in category A or category B. In contrast to AN, research suggests that AB learning is mediated by a declarative memory system. The current study examined the effects of normal aging on AN and AB prototype learning. We observed an age-related deficit in AB learning, but an age-related advantage in AN learning. Computational modeling supports one possible interpretation based on narrower selective attentional focus in older adults in the AB task and broader selective attention in the AN task. Neuropsychological testing in older participants suggested that executive functioning and attentional control were associated with better performance in both tasks. However, nonverbal memory was associated with better AN performance, while visual attention was associated with worse AB performance. The results support an interactive memory systems approach and suggest that age-related declines in one memory system can lead to deficits in some tasks, but to enhanced performance in others.     

类别学习的阻碍效应与双机制理论

通过对类别学习中的阻碍效应进行系统研究,尝试性的提出了类别学习的双机制理论。三个实验分别考察：当样例特征随机呈现时;定义特征固定呈现在样例首位时;以及刺激材料为知觉图形材料时,类别学习中的阻碍效应。三个实验的研究结果都发现：在类别学习中存在一定程度的阻碍效应,支持类别学习同时存在联结学习机制和认知学习机制的双机制观点。     

类别成员跨维度特征关系对类别学习的影响

探讨类别成员具有多维度相同特征与多维度匹配特征条件下对人们类别学习的影响。被试来自华南师范大学一年级本科生,要求他们学习不同特征结构的类别材料,然后进行测试,以学习阶段的单元数与错误率、测试阶段的反应时与错误率为指标。共包括3个实验,实验1探讨了类别成员具有双维度相同特征、双维度匹配特征与非匹配特征条件下进行类别学习的成绩。实验2探讨类别成员在空间位置分离的两个维度上具有相同特征对类别学习的影响。实验3进一步探讨类别间成员具有双维度相同特征对类别学习的影响。结果表明：（1）类别成员具有双维度相同特征时,人们在归类学习中会将这两个维度看成是一个维度,从而促进类别学习;（2）类别成员具有双维度匹配特征,或者在两个不相邻维度具有相同特征时,对于类别学习没有起到这种特定的促进作用;（3）如果类别间成员具有双维度相同特征,则对类别学习产生消极影响。研究结果表明,在类别学习过程中,特征相似性状况对维度的确立也会产生影响。