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Biomedical subjects

R Parasuraman

Publications and source records attributed to R Parasuraman.

At least 19 recordsLinked to original sources
PubMed1994

Cognition in Alzheimer's disease: disorders of attention and semantic knowledge.

Alzheimer's disease leads to a selective decline of cognitive skills, particularly semantic knowledge and visuospatial attention. Recent advances suggest that, although the two systems responsible for these skills can interact, the semantic memory deficit seen in Alzheimer's disease cannot be solely attributed to attention or retrieval deficiencies. This is consistent with a modular view of cognition, which postulates that disruption to these systems is selective in Alzheimer's disease. Cortico-cortical disconnection of association areas may disrupt widespread networks mediating attention and semantic knowledge in Alzheimer's disease.

Alzheimer Disease↗
PubMed1993

Changes in visuospatial attention over the adult lifespan.

Shifts of visual attention elicited by spatial cues were examined for detection and letter-discrimination tasks in 90 normal adults ranging in age over each decade from the 20s to the 70s. Spatial cues were valid, invalid, or neutral in indicating probable target location and were presented either centrally at fixation or peripherally 6.7 degrees to the left or right of fixation. Stimulus-onset asynchrony (SOA) between cue and target was varied between 200, 500 and 2000 msec. Reaction time (RT) costs and benefits associated with spatial cueing did not vary with age for: (1) the detection task; (2) the letter-discrimination task with peripheral cues; and (3) the letter-discrimination task with central cues at a short (200 msec) SOA. RT costs and benefits increased with age only for SOAs greater than 200 msec with central cueing in the discrimination task. In general, the efficiency of cue-based shifts of visuospatial attention appears relatively resistant to the effects of adult age up to 79 years. When an age effect was found, RT costs and benefits increased steadily across all age decades, the correlation with age being 0.25 and 0.38 for the 500 and 2000 msec SOAs, respectively. The findings suggest a qualitative difference in the influence of normal adult aging and effects of dementia noted in previous studies; normal aging has only a weak influence on voluntary attention shifts, whereas dementia affects both voluntary and involuntary modes of attention shifting.

Adult↗
PubMed1993

Attention and driving. Assessment in elderly individuals with dementia.

Older drivers with dementia are involved in more crashes than healthy older drivers. Some investigators, therefore, have proposed that a diagnosis of dementia (DAT or other type) should lead to the automatic revocation of a driver's license. In the authors' view, however, renewal of license should be based on criteria related to driving competence rather than solely on chronologic age or a medical diagnosis. Unfortunately, current competency testing procedures do not assess the attentional factors discussed herewith that have been found to be important for safe driving. As the studies reviewed in this article reveal, there is good evidence that a skill test that predicts crash involvement in older drivers should incorporate attentional measures, in particular tests of attentional shifting based on dichotic listening and related tests. There is also evidence that attention-shifting measures are diagnostic of attention impairment in the early stages of Alzheimer-type dementia. Further research is needed to determine whether other attentional skills, such as sustained and divided attention, also need to be assessed. Additional work also is needed to refine attention tests for ease of use in the clinical setting. Lastly, although these attention measures account for only some of the variance contributing to crash involvement, they may allow for better predictive capability when combined with measures of other skills involved in driving. Driver training programs can complement driver testing procedures in serving the dual requirement for reducing crash risk among drivers with dementia while continuing to be responsive to their mobility needs. Information on the role of attention and other cognitive skills in safe driving should be made available, so that drivers (or their family members) who think they may have declining skills can seek further evaluation. Organizations such as automobile associations and retired persons groups can provide self-assessment inventories for completion by older drivers or referral for medical and neuropsychological evaluation. Finally, training techniques for improving attentional skills in drivers with DAT need to be developed and tested.

Adult↗
PubMed1992

Visuospatial attention in dementia of the Alzheimer type.

Cue-directed shifts of spatial attention were examined for a letter-discrimination task in 15 patients with mild to moderate dementia of the Alzheimer type (DAT) and 15 healthy, age-matched controls. Spatial cues were valid, invalid or neutral in indicating probable target location and were presented either centrally at fixation or peripherally 6.7 degrees to the left or right of fixation. Stimulus-onset asynchrony (SOA) between cue and target was varied between 200 ms and 2000 ms. Reaction time (RT) benefits conferred by valid cues did not differ between the DAT group and the controls. However, RT costs incurred by invalid cues were significantly greater in the DAT group than in the control group. Group differences in RT costs plus benefits occurred at short SOAs (less than 500 ms) for peripheral cues and at long SOAs (greater than 500 ms) for central cues. Reaction time costs plus benefits were correlated with right-left asymmetry in resting levels of cerebral glucose metabolism in the superior parietal lobe for DAT patients but not for controls. The results indicate that focusing of attention to spatial location is intact in early DAT, whereas the disengagement of visuospatial attention is impaired. Automatic attention shifts elicited by peripheral cues reveal abnormalities earlier than attention shifts initiated 'effortfully' by central cues. Intact focusing and impaired disengagement of visuospatial attention may be linked to dysfunction in early DAT of cortico-cortical networks linking the posterior parietal and frontal lobes.

Aged↗
PubMed1991

Divided attention and metabolic brain dysfunction in mild dementia of the Alzheimer's type.

The relationship between reaction time (RT) measures under single-task and dual-task conditions and resting levels of brain metabolism, as measured by positron emission tomography (PET), was examined in patients with mild dementia of the Alzheimer type (DAT) and age- and educationally-matched controls. Slowing of RT in dual-task but not single-task conditions correlated with reductions in brain metabolism in right premotor and right parietal association areas only for the mild DAT patients. The results suggest a relation between divided attention deficits and metabolic dysfunction of right frontal and parietal lobes in mild DAT patients.

Aged↗
PubMed1991

Skill development in vigilance: effects of event rate and age.

Thirty-six young (19-27 years), middle-aged (40-55 years), and old (70-80 years) adults performed a 30-min vigilance task at low (15 per min) and high (40 per min) event rates for 20 sessions. Skill-acquisition curves modeled on power, hyperbolic, and exponential functions were predicted. With extensive practice, hit rates increased and false-alarm rates decreased to virtually asymptotic levels. Skill development was best described by the hyperbolic function. Practice reduced but did not eliminate the vigilance decrement in all subjects. The event-rate effect--the decrease in hit rate at high event rates--was reduced with practice and eliminated in young subjects. Hit rates decreased and false-alarm rates increased with age, but there was little attenuation of age differences with practice. Implications for theories of vigilance, skill development, and cognitive aging are discussed.

Adult↗
PubMed1991

Sustained attention following mild closed-head injury.

The sustained-attention performance of patients with mild closed-head injury (CHI) was examined within one month of injury using a high-event rate, digit-discrimination vigilance task with two levels of stimulus degradation (undegraded, highly degraded). Under undegraded stimulus conditions, vigilance performance for mild CHI subjects, uninjured case-matched control subjects, and college students was highly accurate and remained so across the entire task period. When stimuli were presented in degraded fashion, however, all three groups showed a similar decline over time (i.e., vigilance decrement) in hit rates and d' scores. Although mild CHI did not lead to a greater rate of deterioration in vigilance performance in the degraded stimulus condition, it did produce lower overall levels of sensitivity (d') in target detection. These results suggest that, during the first month after mild CHI, vigilance performance is unimpaired under normal task conditions, but may fall short under task conditions that require sustained effortful processing. These findings join a growing body of evidence showing that mild CHI can lead to measurable deficits in cognitive functioning.

Adolescent↗
PubMed1991

Attention and driving skills in aging and Alzheimer's disease.

The number of older drivers with dementia is rising with the aging of the adult population. A public health issue is growing because of concerns about the motor vehicle accident risk posed by drivers with dementia of the Alzheimer's type (DAT) and other progressive, degenerative dementias. However, little is known about the specific perceptual/cognitive deficits contributing to impaired driving in DAT. The present paper proposes, on both theoretical and empirical grounds, that attentional skills in relation to driving should be examined in older adults with and without DAT. Such investigations should focus on normal older adults and those in the mild, early stages of dementia because the latter are the most likely among the dementia population to be still driving. Evidence is presented indicating (1) that motor vehicle accident rates are related to performance on information-processing measures of different components of attention; (2) that this relationship is greatest for measures of the switching of selective attention and less for that of divided and sustained attention (vigilance); and (3) that many of these same attentional functions, and particularly the switching of visual selective attention, are impaired in the early stages of DAT and thus may contribute to increased accident risk. Further studies of cognitive and driving performance in older drivers are necessary to establish that the attentional impairments found in mild DAT contribute to increased accident risk. Implications of these findings for driver assessment, education, and training are discussed.

Age Factors↗
PubMed1989

Sustained-attention capacity in young and older adults.

The sustained-attention capacity of young (21-29 years) and older (65-78 years) adults was examined using a high-event rate digit-discrimination vigilance task presented at three levels of stimulus degradation. Increased stimulus degradation led to a reduction in the hit rate and to a greater decline in hit rate over blocks (increased vigilance decrement). Sensitivity (d') declined over blocks only at the highest level of stimulus degradation. Older adults had a lower hit rate and showed greater vigilance decrement than young adults, particularly when stimuli were highly degraded. However, both age groups showed the same pattern of stability in sensitivity when stimulus degradation was moderate, and sensitivity decrement over time when stimulus degradation was high. The results suggest that the process of sustained allocation of capacity--as reflected in temporal changes in sensitivity--operates similarly in young and older adults.

Adult↗
PubMed1988

Alcohol intoxication reduces visual sustained attention.

Effects of alcohol intoxication on visual sustained attention were studied using a vigilance task entailing detection of degraded target stimuli. Data were obtained in separate sessions under four ethanol doses, ranging from 0 (placebo) to 1.05 g/kg lean body weight, with periodic maintenance dosing of 0.12 g/kg. Intoxication lowered the overall level of detection performance, and in addition produced dose-related increases in the rate of performance decrement over time. Analysis of performance data using techniques derived from Signal Detection Theory indicated that the decrements were due specifically to alterations in perceptual sensitivity. Examination of eye movements and blinks indicated that the effects of ethanol were not mediated peripherally. Rather, alcohol appears to have deleterious effects on central processing capacity and the availability of capacity over time. The alcohol-related failure of sustained attention may contribute to increased accident risk in tasks requiring continuous performance.

Adult↗
PubMed1987

Alcohol intoxication in humans: effects on vigilance performance.

Effects of ethanol on vigilance in tasks requiring continuous performance are reviewed. Evidence is presented to indicate that ethanol has adverse effects on both the overall level of performance and the rate of performance decrement over time. The effects on performance level are attributed to nonspecific sedative properties of ethanol whereas the effects on rate of decrement are interpreted as a more specific loss in cognitive processing capacity.

Alcoholic Intoxication↗
PubMed1983

Visual sustained attention: image degradation produces rapid sensitivity decrement over time.

Perceptual sensitivity to a visual target presented in a random continuous sequence of targets and nontargets decreased rapidly over time when stimuli were highly degraded visually but not when moderately degraded or undegraded. Large declines in sensitivity, independent of changes in response criterion, were found after only 5 minutes of observation. These rapid decrements of sensitivity to degraded targets seem to result from demands on the limited capacity of visual attention.

Adolescent↗
PubMed1980

Brain events underlying detection and recognition of weak sensory signals.

Through the use of a quantitative extension of signal detection theory, the brain events associated with the detection and recognition of weak acoustic signals were examined by recording brain event-related potentials. The early N100 componenet of the event-related potential varied only with detection, whereas the late P300 component varied with both detection and recognition. P300 amplitude accurately predicted recognition performance on a trial-by-trial basis. The results suggest that detection and recognition are partially concurrent processes in perception and demonstrate that the electrocortical events occurring during the perception of sensory stimuli are closely associated with both detection and recognition of these stimuli by the nervous system.

Acoustic Stimulation↗
PubMed1979

Memory load and event rate control sensitivity decrements in sustained attention.

The capacity to sustain attention at an efficient level deteriorates over time in discrimination and monitoring tasks. This "vigilance decrement" results from a decrement in perceptual sensitivity only if (i) target discrimination loads memory and (ii) stimulus events occur rapidly; otherwise, the decrement reflects temporal changes in response criteria. These results provide a basis for distinguishing between the perceptual and response processes underlying the vigilance decrement that may be generalized across a range of tasks.

Attention↗