Individual differences in working memory capacity and learning: Evidence from the serial reaction time task

High and low working memory (WM) capacity individuals performed the serial reaction time task under both incidental and intentional learning conditions to determine the role of WM capacity in the learning of sequential information. WM capacity differences emerged in conditions of intentional but not incidental learning, indicating that individual differences in WM capacity occur in tasks requiring some form of control, with little difference appearing on tasks that required relatively automatic processing. Furthermore, an index of learning was significantly related to a measure of general fluid intelligence under intentional conditions only. Thus, the degree of learning was significantly related to higher order cognition, but only when intentional processing was emphasized.     

A catalog of Boolean concepts

Boolean concepts are concepts whose membership is determined by a Boolean function, such as that expressed by a formula of propositional logic. Certain Boolean concepts have been much studied in the psychological literature, in particular with regard to their ease of learning. But research attention has been somewhat uneven, with a great deal of attention paid to certain concepts and little to others, in part because of the unavailability of a comprehensive catalog. This paper gives a complete classification of Boolean concepts up to congruence (isomorphism of logical form). Tables give complete details of all concepts determined by up to four Boolean variables. For each concept type, the tables give a canonic logical expression, an approximately minimal logical expression, the Boolean complexity (length of the minimal expression), the number of distinct Boolean concepts of that type, and a pictorial depiction of the concept as a set of vertices in Boolean D-space. Some psychological properties of Boolean concepts are also discussed.     

Categorical invariance and structural complexity in human concept learning

An alternative account of human concept learning based on an invariance measure of the categorical stimulus is proposed. The categorical invariance model (CIM) characterizes the degree of structural complexity of a Boolean category as a function of its inherent degree of invariance and its cardinality or size. To do this we introduce a mathematical framework based on the notion of a Boolean differential operator on Boolean categories that generates the degrees of invariance (i.e., logical manifold) of the category in respect to its dimensions. Using this framework, we propose that the structural complexity of a Boolean category is indirectly proportional to its degree of categorical invariance and directly proportional to its cardinality or size. Consequently, complexity and invariance notions are formally unified to account for concept learning difficulty. Beyond developing the above unifying mathematical framework, the CIM is significant in that: (1) it precisely predicts the key learning difficulty ordering of the SHJ [Shepard, R. N., Hovland, C. L., & Jenkins, H. M. (1961). Learning and memorization of classifications. Psychological Monographs: General and Applied, 75(13), 1-42] Boolean category types consisting of three binary dimensions and four positive examples; (2) it is, in general, a good quantitative predictor of the degree of learning difficulty of a large class of categories (in particular, the 41 category types studied by Feldman [Feldman, J. (2000). Minimization of Boolean complexity in human concept learning. Nature, 407, 630-633]); (3) it is, in general, a good quantitative predictor of parity effects for this large class of categories; (4) it does all of the above without free parameters; and (5) it is cognitively plausible (e.g., cognitively tractable).     

On the nature of nonverbal working memory fractionation: a case of selective spatial short-term memory deficit in a child

Several lines of research on adult subjects demonstrate a visual/spatial fractionation of nonverbal working memory (WM), while behavioral studies on normal children support the idea of a static/dynamic distinction. In the present paper, we report a child (Z.M.) who failed on nonverbal WM tasks. To verify the nature of his defect, we carried out two experiments: in Experiment 1, Z.M. failed on spatial WM tasks but not on visual WM tasks and was not affected by the static/dynamic format of stimulus presentation; in Experiment 2, this visual/spatial dissociation was extended to the imagery domain. These results are best accounted for within the visual/spatial fractionation of WM and confirmed the role of WM in mental imagery. Clinical and rehabilitative implications of the present findings are also discussed.     

On the Nature of Nonverbal Working Memory Fractionation: A Case of Selective Spatial Short-Term Memory Deficit in a Child

Several lines of research on adult subjects demonstrate a visual/spatial fractionation of nonverbal working memory (WM), while behavioral studies on normal children support the idea of a static/dynamic distinction. In the present paper, we report a child (Z.M.) who failed on nonverbal WM tasks. To verify the nature of his defect, we carried out two experiments: in Experiment 1, Z.M. failed on spatial WM tasks but not on visual WM tasks and was not affected by the static/dynamic format of stimulus presentation; in Experiment 2, this visual/spatial dissociation was extended to the imagery domain. These results are best accounted for within the visual/spatial fractionation of WM and confirmed the role of WM in mental imagery. Clinical and rehabilitative implications of the present findings are also discussed.     

The most efficient sequence of study depends on the type of test

Across three experiments featuring naturalistic concepts (psychology concepts) and naïve learners, we extend previous research showing an effect of the sequence of study on learning outcomes, by demonstrating that the sequence of examples during study changes the representation the learner creates of the study materials. We compared participants' performance in test tasks requiring different representations and evaluated which sequence yields better learning in which type of tests. We found that interleaved study, in which examples from different concepts are mixed, leads to the creation of relatively interrelated concepts that are represented by contrast to each other and based on discriminating properties. Conversely, blocked study, in which several examples of the same concept are presented together, leads to the creation of relatively isolated concepts that are represented in terms of their central and characteristic properties. These results argue for the integrated investigation of the benefits of different sequences of study as depending on the characteristics of the study and testing situation.     

Typicality effects in logically defined categories

Subjects learned to categorize geometric designs by some rule combining two features, x and y. When xy stimuli (stimuli with both features) are always positive, the rule (concept) is inclusive disjunctive; when xy stimuli are always negative, the rule is exclusive disjunctive. In three other experimental conditions, the probability of xy stimuli being positive during acquisition was .25, .50, and .75. In a variety of postacquisition tests, xy stimuli were chosen as prototypical despite their less than consistent occurrence in the positive category. Stimuli with one relevant feature (x or y), although consistently assigned to the positive category, were often evaluated as poorer examples of the concept. These results are interpreted in terms of a schema model in which information acquired during learning is organized according to probability density functions over feature dimensions. This theory appears to be general enough to accommodate the evidence from laboratory studies of both logical and natural concepts.     

Using TD learning to simulate working memory performance in a model of the prefrontal cortex and basal ganglia

Delayed-response tasks (DRTs) have been used to assess working memory (WM) processes in human and nonhuman animals. Experiments have shown that the basal ganglia (BG) and dorsolateral prefrontal cortex (DLPFC) subserve DRT performance. Here, we report the results of simulation studies of a systems-level model of DRT performance. The model was trained using the temporal difference (TD) algorithm and uses an actor-critic architecture. The matrisomes of the BG represent the actor and the striosomes represent the critic. Unlike existing models, we hypothesize that the BG subserve the selection of both motor- and cognitive-related information in these tasks. We also assume that the learning of both processes is based on reward presentation. A novel feature of the model is the incorporation of delay-active neurons in the matrisomes, in addition to DLPFC. Another novel feature of the model is the subdivision of the matrisomal neurons into segregated winner-take-all (WTA) networks consisting of delay- versus transiently-active units.Our simulation model proposes a new neural mechanism to account for the occurrence of perseverative responses in WM tasks in striatal-, as well as in prefrontal damaged subjects. Simulation results also show that the model both accounts for the phenomenon of time shifting of dopamine phasic signals and the effects of partial reinforcement and reward magnitude on WM performance at both behavioral and neural levels. Our simulation results also found that the TD algorithm can subserve learning in delayed-reversal tasks.     

A rational account of pedagogical reasoning: Teaching by,and learning from,examples

Much of learning and reasoning occurs in pedagogical situations—situations in which a person who knows a concept chooses examples for the purpose of helping a learner acquire the concept. We introduce a model of teaching and learning in pedagogical settings that predicts which examples teachers should choose and what learners should infer given a teacher’s examples. We present three experiments testing the model predictions for rule-based, prototype, and causally structured concepts. The model shows good quantitative and qualitative fits to the data across all three experiments, predicting novel qualitative phenomena in each case. We conclude by discussing implications for understanding concept learning and implications for theoretical claims about the role of pedagogy in human learning.     

The long-term effect of relational information in classification learning

This study examines the long-term effect of mutual information in the learning of Shepardian classifications. Mutual information is a measure of the complexity of the relationship between features because it quantifies how the features relate to each other. For instance, in various categorisation models, Type VI concepts—originally studied by Shepard, Hovland, and Jenkins (1961)—are unanimously judged to be the most complex kind of 3-D Boolean concepts. This has been largely confirmed by empirical data. Yet, it is apparently inconsistent with the fact that this concept entails the greatest amount of mutual information of all the 3-D Boolean concepts. The present study was aimed at verifying whether individuals can use relational information, in the long run, to devise easier strategies for category learning. Subject performance was measured repeatedly for 1 hour on either successive Type VI concepts (using different features between problems) or successive Type IV concepts. The results showed that shortly after the second problem, Type VI concepts became easier to learn than Type IV ones. The gap between the mean per-problem error rates of the two concepts continued to increase as the number of problems increased. Two other experiments tended to confirm this trend. The discussion brings up the idea of combining different metrics in categorisation models in order to include every possible way for subjects to simplify the categorisation process.     

Working memory in children: a time-constrained functioning similar to adults

Within the time-based resource-sharing (TBRS) model, we tested a new conception of the relationships between processing and storage in which the core mechanisms of working memory (WM) are time constrained. However, our previous studies were restricted to adults. The current study aimed at demonstrating that these mechanisms are present and functional before adulthood. For this purpose, we investigated the effect on maintenance of the duration of the attentional capture induced by processing. In two experiments using computer-paced WM span tasks, 10-year-olds were asked to maintain letters while performing spatial location judgments. The duration of this processing was manipulated by varying either the discriminability between target locations or the contrast between targets and background. In both experiments, longer processing times resulted in poorer recall, as we observed previously in adults. These findings suggest that the core mechanisms of WM described by the TBRS model are already settled during childhood.     

Short-term memory and working memory as indices of children's cognitive skills

In the current literature, empirical and conceptual distinctions have been drawn between a more or less passive short-term memory (STM) system and a more dynamic working memory (WM) system. Distinct tasks have been developed to measure their capacity and research has generally shown that, for adults, WM, and not STM, is a reliable predictor of general cognitive ability. However, the locus of the differences between the tasks has received little attention. We present data from children concerning measures of matrices reasoning ability, reading, and numerical skill along with forward and backward order serial recall of WM, STM, and STM with articulatory suppression tasks. As indices of children's cognitive skills, STM and WM are shown to be rather similar in terms of memory per se. Neither the opportunity for rehearsal nor task complexity provides satisfactory explanations for differences between memory tests.     

Short-term memory and working memory as indices of children's cognitive skills

In the current literature, empirical and conceptual distinctions have been drawn between a more or less passive short-term memory (STM) system and a more dynamic working memory (WM) system. Distinct tasks have been developed to measure their capacity and research has generally shown that, for adults, WM, and not STM, is a reliable predictor of general cognitive ability. However, the locus of the differences between the tasks has received little attention. We present data from children concerning measures of matrices reasoning ability, reading, and numerical skill along with forward and backward order serial recall of WM, STM, and STM with articulatory suppression tasks. As indices of children's cognitive skills, STM and WM are shown to be rather similar in terms of memory per se. Neither the opportunity for rehearsal nor task complexity provides satisfactory explanations for differences between memory tests.     

Searching for serial refreshing in working memory: Using response times to track the content of the focus of attention over time

One popular idea is that, to support the maintenance of a set of elements over brief periods of time, the focus of attention rotates among the different elements, thereby serially refreshing the content of working memory (WM). In the research reported here, probe letters were presented between to-be-remembered letters, and response times to these probes were used to infer the status of the different items in WM. If the focus of attention cycles from one item to the next, its content should be different at different points in time, and this should be reflected in a change in the response time patterns over time. Across a set of four experiments, we demonstrated a striking pattern of invariance in the response time patterns over time, suggesting either that the content of the focus of attention did not change over time or that response times cannot be used to infer the content of the focus of attention. We discuss how this pattern constrains models of WM, attention, and human information processing.     

Binding serial order to representations in working memory: a spatial/verbal dissociation

Verbal information is coded naturally as ordered representations in working memory (WM). However, this may not be true for spatial information. Accordingly, we used memory span tasks to test the hypothesis that serial order is more readily bound to verbal than to spatial representations. Removing serial-order requirements improved performance more for spatial locations than for digits. Furthermore, serial order was freely reproduced twice as frequently for digits as for locations. When participants reordered spatial sequences, they minimized the mean distance between items. Participants also failed to detect changes in serial order more frequently for spatial than for verbal sequences. These results provide converging evidence for a dissociation in the binding of serial order to spatial versus verbal representations. There may be separable domain-specific control processes responsible for this binding. Alternatively, there may be fundamental differences in how effectively temporal information can be bound to different types of stimulus features in WM.     

Psychometric intelligence dissociates implicit and explicit learning

The hypothesis that performance on implicit learning tasks is unrelated to psychometric intelligence was examined in a sample of 605 German pupils. Performance in artificial grammar learning, process control, and serial learning did not correlate with various measures of intelligence when participants were given standard implicit instructions. Under an explicit rule discovery instruction, however, a significant relationship between performance on the learning tasks and intelligence appeared. This finding provides support for Reber's hypothesis that implicit learning, in contrast to explicit learning, is independent of intelligence, and confirms thereby the distinction between the 2 modes of learning. However, because there were virtually no correlations among the 3 learning tasks, the assumption of a unitary ability of implicit learning was not supported.     

Aging, working memory, and discrimination learning

Older adults easily learn probabilistic relationships between cues and outcomes when the predictive event is the occurrence of a cue, but have greater difficulty when the predictive event is the nonoccurrence of a cue (Mutter & Pliske, 1996; Mutter & Plumlee, 2004; Mutter & Williams, 2004). This study explored whether this age-related deficit occurs in a simpler learning context and whether it might be related to working memory (WM) decline. We gave younger and older adults simultaneous discrimination tasks that allowed us to compare their ability to learn deterministic relationships when either the occurrence (feature positive; FP) or the nonoccurrence (feature negative; FN) of a distinctive feature predicted reinforcement. We also included a group of younger adults who performed the discrimination tasks under a concurrent WM load. Both age and WM load had a detrimental effect on initial FP and FN discrimination; however, these effects persisted only in FN discrimination after additional learning experience. Learning predictive relationships requires inductive reasoning processes that apparently do not operate as efficiently in individuals with reduced WM capacity. The impact of WM decline may ultimately be greater for negative cue-outcome relationships because learning these relationships requires more difficult inductive reasoning processes, which place greater demands on WM.