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Biomedical subjects

M A Just

Publications and source records attributed to M A Just.

At least 19 recordsLinked to original sources
PubMed1999

Plasticity of language-related brain function during recovery from stroke.

BACKGROUND AND PURPOSE: This study was undertaken to correlate functional recovery from aphasia after acute stroke with the temporal evolution of the anatomic, physiological, and functional changes as measured by MRI. METHODS: Blood oxygenation level-dependent contrast and echo-planar MRI were used to map language comprehension in 6 normal adults and in 2 adult patients during recovery from acute stroke presenting with aphasia. Perfusion, diffusion, sodium, and conventional anatomic MRI were used to follow physiological and structural changes. RESULTS: The normal activation pattern for language comprehension showed activation predominately in left-sided Wernicke's and Broca's areas, with laterality ratios of 0.8 and 0.3, respectively. Recovery of the patient confirmed as having a completed stroke affecting Broca's area occurred rapidly with a shift of activation to the homologous region in the right hemisphere within 3 days, with continued rightward lateralization over 6 months. In the second patient, in whom mapping was performed fortuitously before stroke, recovery of a Wernicke's aphasia showed a similar increasing rightward shift in activation recruitment over 9 months after the event. CONCLUSIONS: Recovery of aphasia in adults can occur rapidly and is concomitant with an activation pattern that changes from left to a homologous right hemispheric pattern. Such recovery occurs even when the stroke evolves to completion. Such plasticity must be considered when evaluating stroke interventions based on behavioral and neurological measurements.

Adult↗
PubMed1999

Graded functional activation in the visuospatial system with the amount of task demand.

Two studies examined how the amount and type of computational demand are related to fMRI-measured activation in three bilateral cortical regions involved in the Shepard-Metzler (1971) mental-rotation paradigm. The amount of demand for the computation of visuospatial coordinates was manipulated by presenting mental rotation problems with increasing angular disparity (0, 40, 80, or 120 degrees). Activation in both the left and right intraparietal sulcal regions increased linearly with angular disparity in two separate studies. Activation also occurred in the fusiform gyrus and inferior temporal regions, regions that are primarily associated with the processes of object and object-part identification. By contrast, the demand for object recognition and rotation processes was relatively low, and the demand for executing saccades was high in a control condition that required making a systematic visual scan of two grids. The grid-scanning condition resulted in relatively less activation in the parietal and inferior temporal regions but considerable activation in frontal areas that are associated with planning and executing saccades, including the precentral gyrus and sulcus into the posterior middle frontal region. These data suggest that the amount of activation in the various cortical regions that support visuospatial processing is related to the amount, as well as to the type, of computational demand.

Brain Mapping↗
PubMed1999

A multigene locus containing the Manx and bobcat genes is required for development of chordate features in the ascidian tadpole larva.

The Manx gene is required for the development of the tail and other chordate features in the ascidian tadpole larva. To determine the structure of the Manx gene, we isolated and sequenced genomic clones from the tailed ascidian Molgula oculata. The Manx gene contains 9 exons and encodes both major and minor Manx mRNAs, which differ in the length of their 5' untranslated regions. The coding region of the single-copy bobcat gene, which encodes a DEAD-box RNA helicase, is embedded within the first Manx intron. The organization of the bobcat and Manx transcription units was determined by comparing genomic and cDNA clones. The Manx-bobcat gene locus has an unusual organization in which a non-coding first exon is alternatively spliced at the 5' end of two different mRNAs. The bobcat and Manx genes are expressed coordinately during oogenesis and embryogenesis, but not during spermatogenesis, in which bobcat mRNA accumulates independently of Manx mRNA. Similar to Manx, zygotic bobcat transcripts accumulate in the embryonic primordia responsible for generating chordate features, including the dorsal neural tube and notochord, are downregulated during embryogenesis in the tailless species Molgula occulta and are upregulated in M. occulta X M. oculata hybrids, which restore these chordate features. Antisense experiments indicate that zygotic bobcat expression is required for development of the same suite of chordate features as Manx. The results show that the Manx-bobcat gene complex has a role in the development of chordate features in ascidian tadpole larvae.

Amino Acid Sequence↗
PubMed1997

Aphasic sentence comprehension as a resource deficit: a computational approach.

This article describes a new computational model of aphasic sentence comprehension. The model is based on the premise that all aphasics, however different, share a common deficit which determines a considerable amount of the individual variation observed in their sentence comprehension performance. This common deficit is construed as a pathological reduction in the activation resources of a working memory system that subserves sentence comprehension (Miyake, Carpenter, & Just, 1994). To test the theoretical feasibility of the resource reduction hypothesis, a new computer model of aphasic sentence comprehension was developed and tested. We describe the model as well as some initial simulation results, indicating that the model can account for some of the sentence complexity and severity effects that have been reported in the aphasia literature.

Aphasia↗
PubMed1996

Brain activation modulated by sentence comprehension.

The comprehension of visually presented sentences produces brain activation that increases with the linguistic complexity of the sentence. The volume of neural tissue activated (number of voxels) during sentence comprehension was measured with echo-planar functional magnetic resonance imaging. The modulation of the volume of activation by sentence complexity was observed in a network of four areas: the classical left-hemisphere language areas (the left laterosuperior temporal cortex, or Wernicke's area, and the left inferior frontal gyrus, or Broca's area) and their homologous right-hemisphere areas, although the right areas had much smaller volumes of activation than did the left areas. These findings generally indicate that the amount of neural activity that a given cognitive process engenders is dependent on the computational demand that the task imposes.

Adolescent↗
PubMed1996

The capacity theory of comprehension: new frontiers of evidence and arguments.

A capacity theory of comprehension (M.A. Just & P.A. Carpenter, 1992) has provided an integrated account of several central aspects of sentence comprehension, such as the processing of syntactic ambiguity, complex embeddings, syntactic (non) modularity, and individual differences, in terms of the working-memory capacity for language. Some of the evidence supporting the theory is questioned by G.S. Waters and D. Caplan (1996a). This article identifies some of Waters and Caplan's errors about the empirical support in Just and Carpenter (1992), evaluates Waters and Caplan's alternative hypothesis, and presents the results of a new neuroimaging study that supports capacity theory and not Waters and Caplan's separate resources hypothesis.

Arousal↗
PubMed1995

Constraints on the processing of rolling motion: the curtate cycloid illusion.

When a wheel rolls along a flat surface, a point on its perimeter traces a cycloid trajectory, forming a sequence of adjacent semicircle-like scallops. However, when mentally visualizing this point's trajectory, participants erroneously describe the point's path as looping back on itself between each scallop or phase of the cycloid, a phenomenon called the curtate cycloid illusion. The studies supported the hypothesis that the curtate cycloid illusion occurs because the cognitive system sometimes does not have sufficient resources for simultaneously processing 2 components of the motion: its translation and its rotation about its current instant center. Four experiments using computer-animated rolling wheels found that participants who were high in spatial ability were less susceptible to the curtate cycloid illusion than were low-spatial participants, that high-spatial participants were not susceptible to the illusion if they could control the animated wheel display, and that the illusion was substantially decreased if the opportunity to compute instant centers was reduced.

Form Perception↗
PubMed1993

The intensity dimension of thought: pupillometric indices of sentence processing.

This article explores the intensity of processing during sentence comprehension by measuring pupillary response during reading. Two experiments contrast the processing of simpler versus more complex sentences. The two more complex sentence types, object-relative center-embedded sentences and filler-gap sentences, not only take longer to process than their simpler counterparts, but they also produce a larger change in pupil diameter. We propose that the pupillary response is an indicator of how intensely the processing system is operating. The more complex sentences evoke some intense processing at the point in the sentence where a syntactic complexity is first encountered. The gaze durations at these points are elevated, indicating the immediate response to the demand of the syntactic processing. The pupil then starts to dilate, reaching a maximal diameter approximately 1.3 s later. The results from these various performance measures are integrated within a resource-limited computational model of comprehension. The paper develops a model of comprehension that includes an intensity dimension of thought, drawing a correspondence between the computational model's consumption of resources and the human pupillary response.

Adult↗
PubMed1992

Working memory constraints on the processing of syntactic ambiguity.

We propose a model that explains how the working-memory capacity of a comprehender can constrain syntactic parsing and thereby affect the processing of syntactic ambiguities. The model's predictions are examined in four experiments that measure the reading times for two constructions that contain a temporary syntactic ambiguity. An example of the syntactic ambiguity is The soldiers warned about the dangers . . . ; the verb warned may either be the main verb, in which case soldiers is the agent; or the verb warned may introduce a relative clause, in which case soldiers is the patient of warned rather than the agent, as in The soldiers warned about the dangers conducted the midnight raid. The model proposes that both alternative interpretations of warned are initially activated. However, the duration for which both interpretations are maintained depends, in part, on the reader's working-memory capacity, which can be assessed by the Reading Span task (Daneman & Carpenter, 1980). The word-by-word reading times indicate that all subjects do additional processing after encountering an ambiguity, suggesting that they generate both representations. Furthermore, readers with larger working-memory capacities maintain both representations for some period of time (several words), whereas readers with smaller working-memory capacities revert to maintaining only the more likely representation.

Adult↗
PubMed1992

A capacity theory of comprehension: individual differences in working memory.

A theory of the way working memory capacity constrains comprehension is proposed. The theory proposes that both processing and storage are mediated by activation and that the total amount of activation available in working memory varies among individuals. Individual differences in working memory capacity for language can account for qualitative and quantitative differences among college-age adults in several aspects of language comprehension. One aspect is syntactic modularity: The larger capacity of some individuals permits interaction among syntactic and pragmatic information, so that their syntactic processes are not informationally encapsulated. Another aspect is syntactic ambiguity: The larger capacity of some individuals permits them to maintain multiple interpretations. The theory is instantiated as a production system model in which the amount of activation available to the model affects how it adapts to the transient computational and storage demands that occur in comprehension.

Concept Formation↗
PubMed1990

What one intelligence test measures: a theoretical account of the processing in the Raven Progressive Matrices Test.

The cognitive processes in a widely used, nonverbal test of analytic intelligence, the Raven Progressive Matrices Test (Raven, 1962), are analyzed in terms of which processes distinguish between higher scoring and lower scoring subjects and which processes are common to all subjects and all items on the test. The analysis is based on detailed performance characteristics, such as verbal protocols, eye-fixation patterns, and errors. The theory is expressed as a pair of computer simulation models that perform like the median or best college students in the sample. The processing characteristic common to all subjects is an incremental, reiterative strategy for encoding and inducing the regularities in each problem. The processes that distinguish among individuals are primarily the ability to induce abstract relations and the ability to dynamically manage a large set of problem-solving goals in working memory.

Adult↗
PubMed1989

Changes in activation levels with negation.

Three experiments investigated the effects of negation during on-line language processing. It was hypothesized that negation of a noun (e.g., no bread) would affect the activation level of the mental representation of that noun. Experiment 1 manipulated the location of the negation in sentences that were followed by a probe recognition task. Subjects were slower to indicate that a probe had been in the sentence when the probe corresponded to a negated noun. Experiment 2 replicated these results with a probe naming task. Experiment 3 replicated the result that reading the phrase no bread inhibits responses to bread in the probe task but found no evidence of inhibition of the response to an associate probe, such as butter. The results of these three studies suggest that negation affects the discourse focus of a noun phrase, and hence the activation level of its representation.

Adult↗
PubMed1982

Paradigms and processes in reading comprehension.

This article compares several methods of presenting text, including a new paradigm that produces reading-time data with many of the characteristics of naturally occurring eye-fixation data. In the new paradigm, called the moving window condition, a reader presses a button to see each successive work in a text, and the previous work is removed when a new work appears. The words appear in the same position that they would in normal test, and word-length information is available in peripheral vision. The results are qualitatively and quantitatively compared to the results obtained by monitoring the eye fixations of subjects reading normal text. The word-level effects are generally similar. Readers pause longer on longer words, on less frequent words, on words that introduce a new topic, and at ends of sentences. The results suggest that readers initiate thr processing of each word as soon as they encounter it rather than buffer words and delay processing. Also considered are two other reading-time paradigms, one in which words are cumulatively displayed on the screen and one in which each successive word is presented at the same location on the screen. Finally, we consider how the tendency to immediately process text might interact with other techniques for text presentation, such as the rapid serial visual presentation (RSVP) condition, and we generate predictions about the nature and limits of the method.

Eye Movements↗