Biomedical subjects

John R Anderson

Publications and source records attributed to John R Anderson.

29 records · Page 2Linked to original sources

PubMed2004

Partitioning visual displays aids task-directed visual search.

We reduced time to detect target symbols in mock radar screens by adding perceptual boundaries that partitioned displays in accordance with task instructions. Targets appeared among distractor symbols either close to or far from the display center, and participants were instructed to find the target closest to the center. Search time increased with both number of distractors and distance of target from center. However, when close and far regions were delineated by a centrally presented "range ring," the distractor effect was substantially reduced. In addition, eye movement patterns more closely resembled a task-efficient spiral when displays contained a range ring. Results suggest that the addition of perceptual boundaries to visual displays can help to guide search in accordance with task-directed constraints. Actual or potential applications of this research include the incorporation of perceptual boundaries into display designs in order to encourage task-efficient scanpaths (as identified via task analysis and/or empirical testing).

Adult↗

PubMed2004

Differential fan effect and attentional focus.

As people study more facts about a concept, it takes longer to retrieve a particular fact about that concept. This fan effect (Anderson, 1974) has been attributed to competition among associations to a concept. Alternatively, the mental-model theory (Radvansky & Zacks, 1991) suggests that the fan effect disappears when the related concepts are organized into a single mental model. In the present study, attentional focus was manipulated to affect the mental model to be constructed. One group of participants focused on the person dimension of person-location pairs, whereas the other group focused on the location dimension. The result showed that the fan effect with the focused dimension was greater than the fan effect with the nonfocused dimension, which is contrary to the mental-model theory. The number of associations with a concept is indeed crucial during retrieval, and the importance of the information seems to be accentuated with attentional focus.

Attention↗

PubMed2003

Competition and representation during memory retrieval: roles of the prefrontal cortex and the posterior parietal cortex.

In this functional-MRI study we examined the hypothesis that the prefrontal cortex responds differently to the extent of competition during retrieval, whereas the parietal cortex is responsible for problem representation that should not be directly related to the competition. Participants mastered arbitrary person-location pairs, and their recognition memory was tested in a functional-MRI session. The pairs were constructed such that a person was associated with one, two, or three different locations and vice versa. The recognition time increased with the number of associations, reflecting increased competition. A confirmatory analysis of imaging data with prespecified prefrontal and parietal regions showed that, although both regions were highly involved during memory retrieval, only the prefrontal region responded to the levels of competition. This result was consistent with predictions of an information-processing model as well as with an exploratory identification of regions of interest.

Adult↗

PubMed2003

Predicting the practice effects on the blood oxygenation level-dependent (BOLD) function of fMRI in a symbolic manipulation task.

Based on adaptive control of thought-rational (ACT-R), a cognitive architecture for cognitive modeling, researchers have developed an information-processing model to predict the blood oxygenation level-dependent (BOLD) response of functional MRI in symbol manipulation tasks. As an extension of this research, the current event-related functional MRI study investigates the effect of relatively extensive practice on the activation patterns of related brain regions. The task involved performing transformations on equations in an artificial algebra system. This paper shows that the base-level activation learning in the ACT-R theory can predict the change of the BOLD response in practice in a left prefrontal region reflecting retrieval of information. In contrast, practice has relatively little effect on the form of BOLD response in the parietal region reflecting imagined transformations to the equation or the motor region reflecting manual programming.

Adult↗

PubMed2003

The Newell Test for a theory of cognition.

Newell (1980; 1990) proposed that cognitive theories be developed in an effort to satisfy multiple criteria and to avoid theoretical myopia. He provided two overlapping lists of 13 criteria that the human cognitive architecture would have to satisfy in order to be functional. We have distilled these into 12 criteria: flexible behavior, real-time performance, adaptive behavior, vast knowledge base, dynamic behavior, knowledge integration, natural language, learning, development, evolution, and brain realization. There would be greater theoretical progress if we evaluated theories by a broad set of criteria such as these and attended to the weaknesses such evaluations revealed. To illustrate how theories can be evaluated we apply these criteria to both classical connectionism (McClelland & Rumelhart 1986; Rumelhart & McClelland 1986b) and the ACT-R theory (Anderson & Lebiere 1998). The strengths of classical connectionism on this test derive from its intense effort in addressing empirical phenomena in such domains as language and cognitive development. Its weaknesses derive from its failure to acknowledge a symbolic level to thought. In contrast, ACT-R includes both symbolic and sub-symbolic components. The strengths of the ACT-R theory derive from its tight integration of the symbolic component with the sub-symbolic component. Its weaknesses largely derive from its failure, as yet, to adequately engage in intensive analyses of issues related to certain criteria on Newell's list.

Adaptation, Psychological↗

PubMed2003

Stimulus-related priming during task switching.

Task switch cost (the deficit of performing a new task vs. a repeated task) has been partly attributed to priming of the repeated task, as well as to inappropriate preparation for the switched task. In the present study, we examined the nature of the priming effect by repeating stimulus-related processes, such as stimulus encoding or stimulus identification. We adopted a partial-overlap task-switching paradigm, in which only stimulus-related processes should be repeated or switched. The switch cost in this partial-overlap condition was smaller than the cost in the full-overlap condition, in which the task overlap involved more than stimulus processing, indicating that priming of a stimulus is a component of a switch cost. The switch cost in the partial-overlap condition, however, disappeared eventually with a long interval between two tasks, whereas the cost in the full-overlap condition remained significant. Moreover, the switch cost, in general, did not interact with foreknowledge, suggesting that preparation on the basis of foreknowledge may be related to processes beyond stimulus encoding. These results suggest that stimulus-related priming is automatic and short-lived and, therefore, is not a part of the persisting portion of switch cost.

Attention↗

PubMed2003

An information-processing model of the BOLD response in symbol manipulation tasks.

Two imaging experiments were performed--one involving an algebraic transformation task studied by Anderson, Reder, and Lebiere (1996) and the other an abstraction symbol manipulation task studied by Blessing and Anderson (1996). ACT-R models exist that predict the latency patterns in these tasks. These models require activity in an imaginal buffer to represent changes to the problem representation, in a retrieval buffer to hold information from declarative memory, and in a manual buffer to hold information about motor behavior. A general theory is described about how to map activity in these buffers onto the fMRI blood oxygen level dependent (BOLD) response. This theory claims that the BOLD response is integrated over the duration that a buffer is active and can be used to predict the observed BOLD function. Activity in the imaginal buffer is shown to predict the BOLD response in a left posterior parietal region; activity in the retrieval buffer is shown to predict the BOLD response in a left prefrontal region; and activity in the manual buffer is shown to predict activity in a motor region. More generally, this article shows how to map a large class of information-processing theories (not just ACT-R) onto the BOLD response and provides a precise interpretation of the cognitive significance of the BOLD response.

Brain↗

PubMed2002

The transformation of anthers in the msca1 mutant of maize.

In normal anther development in maize (Zea mays L), large hypodermal cells in anther primordia undergo a series of proscribed cell divisions to form an anther containing microsporogenous cells and three distinctive anther wall layers: the tapetum, the middle layer and the endothecium. In homozygous msca1 mutants of maize, stamen primordia are initiated normally and large hypodermal cells can be detected in developing anthers. However, the normal series of cell division and differentiation events does not occur in msca1 mutant plants. Rather, structures containing parenchymal cells and ectopic, nonfunctional vascular strands are formed. The epidermal surfaces of these structures contain stomata, which are normally absent in maize anthers. Thus, all of the cell layers of the "anther" have been transformed in mutant plants. The filaments of the mutant structures are normal, and all other flower parts are normal. The msca1 mutation does not affect female fertility, but transformed "stamen" structures remain associated with mature ovules rather than aborting as in normal ear development. The msca1 mutation is distinctive in that only one part of a single (male) reproductive organ is transformed. The resulting structure has general vegetative features, but cannot be conclusively identified as a particular vegetative organ.

Fertility↗

PubMed2002

Neural mechanisms of planning: a computational analysis using event-related fMRI.

To investigate the neural mechanisms of planning, we used a novel adaptation of the Tower of Hanoi (TOH) task and event-related functional MRI. Participants were trained in applying a specific strategy to an isomorph of the five-disk TOH task. After training, participants solved novel problems during event-related functional MRI. A computational cognitive model of the task was used to generate a reference time series representing the expected blood oxygen level-dependent response in brain areas involved in the manipulation and planning of goals. This time series was used as one term within a general linear modeling framework to identify brain areas in which the time course of activity varied as a function of goal-processing events. Two distinct time courses of activation were identified, one in which activation varied parametrically with goal-processing operations, and the other in which activation became pronounced only during goal-processing intensive trials. Regions showing the parametric relationship comprised a frontoparietal system and include right dorsolateral prefrontal cortex [Brodmann's area (BA 9)], bilateral parietal (BA 40/7), and bilateral premotor (BA 6) areas. Regions preferentially engaged only during goal-intensive processing include left inferior frontal gyrus (BA 44). The implications of these results for the current model, as well as for our understanding of the neural mechanisms of planning and functional specialization of the prefrontal cortex, are discussed.

Adult↗

PubMed2002

Why do children learn to say "Broke"? A model of learning the past tense without feedback.

Learning the English past tense is characterized by a U-shaped learning function for the irregular verbs. Existing cognitive models often rely on a sudden increase in vocabulary, a high token-frequency of regular verbs, and complicated schemes of feedback in order to model this phenomenon. All these assumptions are at odds with empirical data. In this paper a hybrid ACT-R model is presented that shows U-shaped learning without direct feedback, changes in vocabulary, or unrealistically high rates of regular verbs. The model is capable of learning the default rule, even if regular forms are infrequent. It can also help explore the question of why there is a distinction between regular and irregular verbs in the first place, by examining the costs and benefits of both types of verbs.

Child↗

PubMed2002

Comprehending anaphoric metaphors.

In this study we investigate the comprehension of various kinds of anaphoric metaphors in context. We describe an experiment that manipulated the metaphoricity of simple noun + verb + ending sentences by using either a metaphoric noun or a metaphoric verb or both. Our results show that metaphoric nouns affect sentence comprehension to a greater extent than do metaphoric verbs. Thus, even though there were no sentence-reading time differences between metaphoric and literal targets, metaphoric nouns were read more slowly than were literal nouns, and they also affected the reading time of the following verb. Moreover, in trials involving metaphoric-noun targets, participants read the endings of the targets faster and made more mistakes in answering posttrial questions than they did in literal-noun trials. We argue that these results suggest a comprehension deficit for anaphoric noun metaphors even when they are preceded by a context.

Adult↗