Biomedical subjects

Karen Z H Li

Publications and source records attributed to Karen Z H Li.

5 recordsLinked to original sources

PubMed2004

Visual search across the life span.

Gains and losses in visual search were studied across the life span in a representative sample of 298 individuals from 6 to 89 years of age. Participants searched for single-feature and conjunction targets of high or low eccentricity. Search was substantially slowed early and late in life, age gradients were more pronounced in conjunction than in feature search, and all age groups were uniformly affected by eccentricity manipulations. However, developmental and aging trends were distinctly asymmetrical: Children's performance was particularly affected by the mere presence of distractors; whereas in late life, performance was particularly impaired on target-absent trials and with increasing numbers of distractors. The implications for life span theories of cognitive and attentional development and for cognitive-speed and inhibitory-control accounts are discussed.

Adolescent↗

PubMed2004

Selective attention impairments in Alzheimer's disease: evidence for dissociable components.

Tasks emphasizing 3 different aspects of selective attention-inhibition, visuospatial selective attention, and decision making-were administered to subjects with mild Alzheimer's disease (AD) and to healthy elderly control (HEC) subjects to determine which components of selective attention were impaired in AD subjects and whether selective attention could be dissociated into different components. The tasks were administered with easy versus hard levels of difficulty to assess proportional slowing as the key variable across tasks. The results indicated that the inhibitory and visual search tasks showed greater proportional slowing in subjects with AD than in HEC subjects, and that the task involving inhibition was significantly more affected in subjects with AD. Furthermore, there were no significant intertask correlations, and the results cannot be explained simply in terms of generalized cognitive slowing. These results provide evidence that inhibition is the most strikingly affected aspect of selective attention that is observed to be impaired in early stages of AD.

Aged↗

PubMed2002

Age-related changes in task-switching components: the role of task uncertainty.

The present study examined age differences in executive functioning, using an externally cued task-switching paradigm. Two components of task switching were assessed: the ability to maintain and select among task sets (general switch costs) and the ability to switch between task sets (specific switch costs). In contrast to previous findings, we found large age-related differences in specific switch costs, especially when the number of potentially relevant task sets is increased from two to four. Age-related differences in general switch costs were absent when external task cues subserved executive processing in task switching. Generally, the findings suggest that age-related impairments in task-switching components vary as a function of task uncertainty, such as the presence of environmental prompts to behavior.

Adult↗

PubMed2002

Relations between aging sensory/sensorimotor and cognitive functions.

Recent evidence is reviewed to examine relations among sensory, sensorimotor, and cognitive aging. Age-heterogeneous cross-sectional data sets show substantial covariation among sensory, sensorimotor and intellectual abilities, and an increase in covariation from adulthood to old and very old age. Recent longitudinal analyses suggest that changes in sensory and intellectual functioning are interrelated. Experimental studies investigate the interdependence between cognitive and sensory/sensorimotor aging by examining the effects of simulated sensory loss on cognitive performance, or the effects of cognitive load manipulations on sensory or motor performance. Generally, both types of manipulations hinder older adults' performance more than that of younger adults. Theoretically, the age-associated intensification of the links among sensory, sensorimotor and cognitive functions observed both correlationally and experimentally may point to (a). common causes influencing all three functions; (b). an increase in resource overlap, cross-domain resource competition, and compensatory tradeoffs; and (c). a combination of the two. Future research aiming at discerning the relative import of these possibilities would profit from an integration of experimental and correlational research strategies.

Aging↗

PubMed2000

Comparing the effects of aging and background noise on short-term memory performance.

Paired associate recall was tested as a function of serial position for younger and older adults for five word pairs presented aurally in quiet and in noise. In Experiment 1, the addition of noise adversely affected recall in young adults, but only in the early serial positions. Experiments 2 and 3 suggested that the recall of older adults listening to the words in quiet was nearly equivalent to that of younger adults listening in noise. In Experiment 4, we determined the signal-to-noise ratio (S/N) such that, on average, younger and older adults were able to correctly hear the same percentage of words when words were presented one at a time in noise. In Experiment 5, younger adults were tested under this S/N. Compared with older adults from Experiment 3, younger adults in this experiment recalled more words at all serial positions. The results are interpreted as showing that encoding in secondary memory is impaired by aging and noise either as a function of degraded sensory representations, or as a function of reduced processing resources.

Adult↗