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Biomedical subjects

S Kemper

Publications and source records attributed to S Kemper.

35 records · Page 2Linked to original sources
PubMed1992

Adults' reading comprehension: effects of syntactic complexity and working memory.

Two experiments investigated the relationship between working memory and reading comprehension. In the first, college students, 18 to 26 years of age, and adults, 60 to 92 years of age, were given a battery of tests of working memory, a standard timed reading comprehension test, and a reading test designed to explore how syntactic complexity affects comprehension. In a follow-up study, the adults were retested on a modified version of the syntax comprehension text. Age group declines in working memory and reading comprehension were obtained in Experiment I; age group declines in reading rate but not comprehension were obtained in Experiment II. The results suggest that working memory limitations affect elderly adults' ability to process complex syntactic constructions, lowering comprehension in the timed test (Experiment I) and reducing reading rates in the untimed test (Experiment II).

Adolescent↗
PubMed1991

Syntactic complexity and adults' running memory span.

This study investigated age group differences in adults' running memory span for prose. College students and adults 60 to 94 years of age listened to a prose passage that was interrupted occasionally by pauses. At each pause, the adults attempted to recall the immediately preceding text. The pauses followed either two single-clause sentences, a two-clause right-branching sentence, or a two-clause left-branching sentence. There was a significant Age Group x Syntactic Form x Clause Order interaction such that the age group differences in verbatim recall were exacerbated by the effects of syntactic complexity. The elderly recalled 25% fewer words from the first embedded clause of the left-branching sentences than the college students, whereas they recalled only 4% fewer words from the first of two successive single-clause sentences. Performance on the running memory span task was also correlated with two measures of the adults' working memory: forward digit span and backward digit span. The pattern of correlations indicated that working memory limitations determine adults' running memory span for prose and contribute to age-group deficits in comprehension.

Adolescent↗
PubMed1990

Peroxidation-induced perturbations of erythrocyte lipid organization.

Peroxidation of erythrocyte membrane lipids by hydrogen peroxide perturbs the lipid bilayer and increases phagocytosis by macrophages. This study addresses the underlying mechanism of these processes, and in particular the role of malondialdehyde, a major byproduct of lipid peroxidation. When erythrocytes were treated with hydrogen peroxide or ascorbate/iron to generate malondialdehyde, or with malondialdehyde itself, only those cells treated with hydrogen peroxide showed increased phospholipid spacing and enhanced phagocytosis. This result indicates that the alterations observed are unique to hydrogen peroxide treatment, and that malondialdehyde does not play a role in inducing these changes in surface properties. Comparison of adherence to human umbilical vein endothelial cells and phagocytosis showed that increased phagocytosis was not mirrored by enhanced adherence. This result suggests that two different signals may mediate recognition of erythrocytes by macrophages and by endothelial cells.

Cell Adhesion↗
PubMed1990

Adults' word recall and word repetition.

This experiment investigated age group differences in working memory by examining the effects of word length on adults' recall span and repetition rate. College students and adults, 60 to 94 years of age, recalled lists of one-, two-, or three-syllable words and repeated aloud pairs of one-, two- or three-syllable words. Word recall spans and word repetition rates were computed. Main effects of age group and word length were obtained on both measures, although the interactions were not significant. A second analysis examined the relationship between individuals' recall span and their repetition rate. Across all age groups combined, recall span was a linear function of repetition rate and accounted for 25 percent of the variance on the recall task. A reanalysis of the word repetitions revealed that older adults' word durations and inter-word pauses are longer than young adults'.

Adult↗
PubMed1988

Organ blood flow haemodynamics and metabolism of the albacore tuna Thunnus alalunga (Bonnaterre).

Metabolic haemodynamic, and organ blood flow measurements were made in tabled, partially anaesthetized albacore Thunnus alalunga. Heart rates were 115 +/- 9 beats/min: blood pressure 98/75 mm Hg (systolic/diastolic): cardiac output 36.1 +/- 5 (ml/min/kg): oxygen consumption 3.4 +/- 0.7 (ml O2/min/kg) and cardiac contractility (dP/dt) 6342 +/- 822 mm Hg/s. Organ blood flows were measured with radiolabelled microspheres. The red muscle, kidney, and spleen received the highest flows and the white-muscle the least. There was a flow gradient in the white-muscle with the inner portion near the red-muscle receiving the highest flows. Arterial and venous blood gas measurements showed a reverse temperature effect on arterial PO2 and a P50 of 15.9 Torr corrected to 37 degrees C. Red-muscle temperature was 7 degrees C higher than ambient water temperature. These measurements record the albacore's markedly high cardiovascular capability.

Animals↗
PubMed1987

Life-span changes in syntactic complexity.

Adults' diaries were examined for age-related changes in syntactic complexity. The diaries in the longitudinal sample were kept by 8 adults, born between 1856 and 1876, for seven or more decades. The diaries in the cohort-sequential sample were kept by 10 adults born between 1820 and 1829 and recorded during 1860 to 1869 or during 1900 to 1909 and 10 adults born between 1860 and 1869 and recorded during 1900 to 1909 and again in 1940 to 1949. Sentences from the two longest, usable entries from each half-decade were analyzed. The analysis determined the incidence of left- and right-branching embeddings and of coordinate and subordinate phrases and sentence fragments as well as the mean length of sentences in words and in clauses. The analysis revealed an age-related decline in the syntactic complexity of adults' sentences.

Adult↗
PubMed1970

Endo-N-acetyl-glucosaminidase from Clostridium perfringens, lytic for cell wall murein of gram-negative bacteria.

An endo-N-acetyl-glucosaminidase which degrades the murein (peptidoglycan) sacculi of the cell walls of Escherichia coli and Spirillum serpens, but not those of Micrococcus lysodeikticus and Sarcina lutea, is present as a contaminant in a "phospholipase C" from Clostridium perfringens. The specificity of enzyme action was elucidated by reduction of liberated glycosidic groups with NaBH(4) and identification of glucosaminol as the reduction product. This finding contradicts previous reports associating cell wall breakdown with specific phospholipase action.

Acyltransferases↗
PubMedDate not supplied

Age differences in implicit and explicit associative memory: exploring elaborative processing effects.

Research in memory processes suggests implicit memory is more resistant to the effects of aging than explicit memory. Two experiments examined how variations in level of processing affect memory for novel word-pair associations across age groups. The results indicate that new learning may rely on some degree of elàborate and even explicit processing and that older adults show deficits in any form of new learning. Explicit associative memory benefited from elaborative processing for both age groups and age differences appeared to relate to overall working-memory capacity rather than effective use of elaborative processes. These results support a model of associative memory that distinguishes automatic unconscious processes versus conscious controlled processes in which older adults exhibit deficits in associative memory tasks that actually rely on consciously controlled processes.

Adult↗
PubMedDate not supplied

Cognitive construct measurement in small samples of younger and older adults: an example of verbal working memory.

An important issue in experimental aging research is the accurate measurement of cognitive constructs, particularly in small-sample studies. Latent variable modeling approaches to assessing age-based construct similarity are difficult to implement in smaller-scale studies, which tend to have small samples and measurement of a single construct. We discuss factor score comparison methods for assessing age-based construct similarity that may be more appropriate for small-scale studies. We then examine these methods for a series of single-factor models of verbal working memory (VWM) based on data from three separate studies in which small samples of younger and older adults' completed VWM-based tasks. Our single-factor models accounted well for the associations among the sets of VWM tasks. This construct was also measured well across age groups and different samples. Our analyses suggest that factor score comparison methods may be useful for small-scale studies that require assessment of age-based measurement similarity in cognitive constructs.

Adult↗
PubMedDate not supplied

Syntactic complexity and elderly adults' prose recall.

Elderly adults in their 70s and 80s and middle-aged adults in their 40s and 50s recalled a series of paragraphs made up of single-clause sentences and sentences with right-branching or left-branching embedded or subordinate clauses. Overall, the middle-aged adults recalled 65% of the propositions regardless of syntactic form. While the elderly adults recalled 43% of the propositions from the single-clause sentences, they recalled 60% of the propositions from the right-branching clauses but only 22% of the propositions from the left-branching clauses. These results, in conjunction with prior research on elderly adults' production and imitation of complex syntactic constructions, demonstrate age-related changes in syntactic processing.

Adult↗
PubMedDate not supplied

Age differences in summarizing descriptive and procedural texts.

This study compared young and older adults' summaries of expository texts under the hypothesis that older adults would be more experienced, hence more accurate, at summarizing texts. Two types of expository texts were used: procedural and descriptive texts. The texts were read by a panel of judges who wrote summaries of each text and identified the central ideas of each text; the judges' summaries were used to prepare lists of the central ideas of each text and to write standard summaries of each text. The participants read four texts, two orally and two silently, and then wrote summaries, which were limited to 50 words. Words-per-minute reading times were collected and the summaries were scored on two measures of content, how many ideas were reproduced from the original texts and the proportion of central ideas that were reproduced, and two measures of length, the number of sentences and the number of words. Although the older adults read more slowly than the young adults, the older adults reproduced more total and central ideas than the young ideas.

Adult↗