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At least 1,765 records · Page 98Linked to original sources
PubMed2003

Deficits of working memory during mental calculation in patients with Parkinson's disease.

Using the dual task paradigm, previous studies have suggested that working memory (WM) deficit is due to depleted attention resources in patients with Parkinson's disease (PD). The aim of this study is to establish whether the WM problems in PD are due to reduced attentional set-shifting resources rather than depletion of attention resources. The task design attempts to eliminate confounding of the deficits in dealing with novel material, a problem documented in PD, by concentrating on WM tasks of mental calculation that are familiar to subjects in daily living. We also administered attention tasks, the Trail Making Test (TMT) that relies primarily on attentional set-shifting and the Kana (Japanese syllabogram) Pick-out Test instead primarily depending on depleted attention resources for allocation. A total of 24 patients with PD and 24 normal controls participated in this study. The PD group showed deficits in mental calculation span and in attentional set-shifting in the TMT-b.Considering the common deficits in alternating processing of mental calculation and TMT-b in PD, the results suggested that the central executive dysfunction in PD during mental calculations was due to reduced attentional set-shifting resources for rapidly alternating operations, rather than the depletion of attentional resources.

Adult↗
PubMed1977

A comparison of aphasic and normal adults in a sentence-verification task.

This study showed that in certain sentence-processing tasks, aphasics fail to perform correctly because they fail to execute particular mental operations. A straightforward information-processing model describes the mental processes that are used in deciding whether a sentence is true or false of an accompanying picture. The aphasics' performance, interpreted in light of the model, indicates what step in their processing is not operating properly in this task.

Aphasia↗
PubMed1994

Handedness and hemispheric differences for feature perturbations.

The influence of handedness on hemispheric differences for feature perturbations was assessed in left- and right-handed normal subjects, with equal numbers of each sex in each group. Stimulus displays consisting of five small squares arranged in a single row were presented tachistoscopically to the left or right of fixation, and the size of the squares was manipulated in different conditions. Subjects were instructed to state in which square a horizontal "tick" mark was located. The handedness of the subjects contributed to the pattern of hemispheric differences for tick mislocations resulting from feature perturbations in the toward-fovea direction. For left-handed subjects, fewer errors occurred when stimuli were presented to the left hemisphere; for right-handed subjects, fewer errors occurred when stimuli were presented to the right hemisphere. Increasing stimulus size tended to enhance the handedness and hemispheric feature perturbation effects. The data suggest that handedness contributes to hemispheric organization of featural extraction processes.

Adult↗
PubMed2000

Dissociating prefrontal and parietal cortex activation during arithmetic processing.

Lesion and brain-imaging studies have implicated the prefrontal and parietal cortices in arithmetic processing, but do not exclude the possibility that these brain areas are also involved in nonarithmetic operations. In the present study, we used functional magnetic resonance imaging to explore which brain areas contribute uniquely to numeric computation. Task difficulty was manipulated in a factorial design by varying the number of operands and the rate of stimulus presentation. Both manipulations increased the number of operations to be performed in unit time. Manipulating the number of operands allowed us to investigate the specific effect of calculation, while manipulating the rate of presentation allowed us to increase task difficulty independent of calculation. We found quantitative changes in activation patterns in the prefrontal and parietal cortices as well as the recruitment of additional brain regions, including the caudate and midcerebellar cortex, with increasing task difficulty. More importantly, the main effect of arithmetic complexity was observed in the left and right angular gyrus, while the main effect of rate of stimulus presentation was observed in the left insular/orbitofrontal cortex. Our findings indicate a dissociation in prefrontal and parietal cortex function during arithmetic processing and further provide the first evidence for a specific role for the angular gyrus in arithmetic computation independent of other processing demands.

Adolescent↗
PubMed1985

The effect of methylphenidate on information processing.

Models of information processing currently popular in cognitive psychology divide the reaction process into a series of discrete separable stages. The distinction between one stage and another is verified by the additive factors method (AFM) as defined by Sternberg (1969). Task factors that do not interact with each other are inferred to affect different stages. The distinction between stimulus evaluation stages and response selection stages has been supported by brain event related potential (ERP) studies. The latency of the P300 component of the ERP is sensitive to changes in stimulus complexity but not to to changes in response complexity. The focus of this research is to determine the effects of stimulant drugs on stages of information processing using both reaction time (RT) and P300 latency within an AFM framework. Four doses of methylphenidate (MP) were used in a within-subjects design to examine the effects of MP on stimulus and response processing. We found that MP speeds RT, and that this effect does not interact with the effect of stimulus complexity on RT. MP dose interacts with response complexity, the dose for optimal speeding varying with the level of complexity. The latency of P300 is increased by stimulus complexity, and not by response complexity, nor is it affected by MP. These results show that the stimulant drug acts on processes involved in response selection, rather than in stimulus evaluation. Individual differences in drug response are dose dependent, but also point to an effect on response processing.

Adult↗
PubMed1995

Constraint satisfaction as a theory of sentence processing.

Various problems with the constraint satisfaction model are discussed. It is argued that the empirical evidence presented in support of the model does not concern predictions of the model that diverge from those of depth-first (one analysis at a time) models. Several methodological problems are also noted. As a theory of sentence processing, the model is inadequate. It fails to account for the assignment of local structure, global structure, structure involving discontinuous dependencies, long-distance dependencies, and adjunct phrases. It makes incorrect predictions about the timing of syntactic analysis. Further, because syntactic structure is available only through activation of syntactic projections stored in the lexical entry of words, the model leaves entirely unexplained the myriad psycholinguistic findings demonstrating independence of lexical and syntactic structure (in Event Related Potential studies, code-switching, pure syntactic priming, etc). Finally, the model is not restrictive or explanatory, providing an account that largely consists of post hoc correlations between frequency counts or subjects' ratings of sentences and processing time data for the same sentences.

Automatism↗