Learning representations in a gated prefrontal cortex model of dynamic task switching

The prefrontal cortex is widely believed to play an important role in facilitating people's ability to switch performance between different tasks. We present a biologically‐based computational model of prefrontal cortex (PFC) that explains its role in task switching in terms of the greater flexibility conferred by activation‐based working memory representations in PFC, as compared with more slowly adapting weight‐based memory mechanisms. Specifically we show that PFC representations can be rapidly updated when a task switches via a dynamic gating mechanism based on a temporal‐differences reward‐prediction learning mechanism. Unlike prior models of this type, the present model develops all of its internal representations via learning mechanisms as shaped by the demands of continuous periodic task switching. This advance opens up a new domain of research into the interactions between working memory task demands and the representations that develop to meet them. Results on a version of the Wisconsin card sorting task are presented for the full model and a number of comparison networks that test the importance of various model features. Furthermore, we show that a lesioned model produces perseverative errors like those seen in frontal patients.     

The smoked plastic screen: An alternative to the one-way mirror

A double thickness, smoked plastic screen is presented as an alternative to the one-way mirror. Relative to the glass mirror, the use of the plastic screen provides a safe, nondistracting, durable, light weight, and inexpensive method for unobserved viewing without an appreciable loss in light transmission.     

Differential contributions of set-shifting and monitoring to dual-task interference

It is commonly argued that complex behaviour is regulated by a number of “executive functions”, which work to coordinate the operation of disparate cognitive systems in the service of an overall goal. However, the identity, roles, and interactions of specific putative executive functions remain contentious, even within widely accepted tests of executive function. The authors present two experiments that use dual-task interference to provide further support for multiple distinct executive functions and to establish the differential contributions of those functions in two relatively complex executive tasks—random generation and the Wisconsin Card Sorting Test. Results are interpreted in terms of process models of the complex executive tasks.     

Determinants of fear over the course of avoidance learning

Most theorists have explained attenuation of fear over the course of avoidance learning by assuming that fear extinguishes with repeated nonreinforced avoidance trials. Experiment 1 replicates the finding that rats trained to a criterion of 27 consecutive avoidance responses (CARs) show less fear during the CS than rats trained to a criterion of 3 or 9 CARs. This attenuation of fear cannot, however, be accounted for by simple Pavlovian fear extinction, because yoked partners receiving the exact same pattern of CSs and USs did not show this attenuation and did not differ from yoked partners receiving only reinforced CS presentations. Experiment 2 found that feedback from the master avoidance learner's response is sufficient to produce this attenuation in yoked animals; “control” per se is not necessary. Several possible explanations are discussed regarding the mechanism underlying this role of feedback in diminishing fear of the CS in the avoidance learning context.     

Label training and auditory generalization

To investigate the Miller-Dollard hypothesis (Social learning and imitation, New Haven: Yale University Press, 1941) that verbal labels increase distinctiveness of cues, generalization gradients to pure tones were obtained before and after label training. One group was trained to label all seven tones in an array and another only the middle tone. Three additional groups controlled for nonverbal factors. Before training, gradients were characterized by progressive loss of stimulus control with exposure to the generalization test stimuli. The main effect of possession of labels was to retard this loss, but only in tests where S+ was a labeled stimulus. While the specificity of label effects was in line with the Miller-Dollard hypothesis, the finding that labels did not confer a clear advantage at the start of testing was not. It was suggested that the unlabeled stimuli may have been sufficiently distinct to mask label effects and that interference generated by the test stimuli reduced distinctiveness to levels needed for such effects to emerge.     

Occupational wage differentials among university educated technical personnel in a developing economy

Data taken in 1970–1971 from three university-trained occupational groups (2796 engineers, 1430 economists/business-administrators, and 162 basic scientists) in São Paulo's manufacturing industries are used in a path analysis to draw interoccupational comparisons concerning the antecedents of occupational wage differentials. The worker's total hourly wage is the dependent variable. A new variable, occupational influence level, is employed as immediately antecedent to wage, as in job experience (years in the present job). Years of advanced education, age, and seniority in the firm are treated as exogenous variables. Similarities and differences among occupations are discussed. As a whole the analysis illustrates a strategy of comparative occupational analysis.     

Measuring the importance of information in judgment: Individual differences in weighting ability and effort

Measuring the importance of cues in social judgment has been a longstanding problem. Past research has shown individual differences in the impact of ability and study effort on judgments of student performance. This research examined the hypothesis that the individual differences are due to the weight given to the information as opposed to the perceived extremity of the values of the information. Subjects judged the performance of hypothetical students described by ability, study effort, and effort during an exam. Individual differences in the impact of the three types of information were obtained and were predictable from self-reports of the relative importance of information. Different values of weights were necessary to account for the differences in the impact of information, although there were also differences in the perceived extremity of the information. The theoretical and applied significance of distinguishing the weight given to information in judgment from its subjective value are discussed. On the basis of a new review of the literature, as well as the present results, it is concluded that self-reports of the relative importance of information are predictive of individual differences in information use in judgment, but that they may reflect the total impact of information rather than only the weight.     

The effects of onset and offset warning and post-target stimuli on the saccade latency of children and adults

Two studies, involving children (mean age = 10 years) and adults, investigated the effects of visual stimulus onsets and offsets on the latency of saccades to peripheral targets. Saccade latency was reduced when foveal stimulus onsets or offsets preceded the target. When stimulus onset occurred 100 msec after target onset, the stimulus interfered with responding, with this interference effect significantly greater for children than for adults. When stimuli were presented in the peripheral visual field facilitation and interference effects were similar for children and adults. These results were interpreted as indicating that oculomotor processes are similar in children and adults while the stimulus intake processes that follow stimulus onset at the point of fixation have a greater interference effect on children's than on adults' eye movements.     

Competence and processing in children's grammar of relative clauses

We report two toy-manipulation experiments investigating 4–5-year-old children's interpretations of relative clauses. In the first experiment we show that the frequency with which relatives modifying the matrix direct object are interpreted as referring to the matrix subject is sensitive to the nature of the material in the relative. Animacy of the relative direct object leads to an increase in subject coreference errors for relatives; a similar effect of animacy was not found for infinitival complements. We propose that such errors arise when the child's sentence processor is taxed. In our second experiment we compare children's interpretations of relatives to their interpretations of temporal participial complements. Children eschewed coreference between the complement and the object of a passive prepositional phrase in the case of temporal participials but not in the case of relatives. We interpret this result as evidence that children are capable of analyzing relatives as constituents of the NP node, and hence that this node is recursive in their grammars. We discuss the results of both experiments in the context of a two-stage parsing model, arguing that our data fit a picture of children's linguistic abilities in which the 4-year-old has a sophisticated competence grammar and a parsing mechanism of essentially the same structure as the adult's. We compare our approach to a number of other approaches to children's relative clause interpretations in the literature, arguing that these alternatives are too structure-specific and can lead to underestimations of the child's competence grammar. We conclude that our analysis is compatible with a picture of acquisition in which the child's competence grammar of relatives is not qualitatively different from the adult's.     

Judging similarity among strings described by hierarchical trees

The paper compares the tree-theoretical model of similarity judgement (in which the similarity between two objects is a function of the distance between them in a conceptual tree) with an averaging model of similarity judgement that is drawn jointly from information integration theory and from current research indicating the prevalence of anchoring and adjustment mechanisms in judgement. Results of an experiment are presented that suggest that even when subjects organize conceptual material as a hierarchical tree, judgments of similarity among the objects are better accounted for by an averaging mechanism than by distances in the tree. These data are discussed in terms of the differences between the representation in which knowledge is encoded and the processes that operate on the represented information.