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J Metcalfe

Publications and source records attributed to J Metcalfe.

At least 37 records · Page 2Linked to original sources
PubMed1991

Composite models never (well, hardly ever) compromise: reply to Schooler and Tanaka (1991)

With respect to the influence of postevent information, Schooler and Tanaka (1991) made a useful distinction between composite recollections--in which subjects retrieve "items from both the original and the postevent sources" (p.97)--and compromise recollections--in which subjects retrieve" at least one feature that cannot be exclusively associated with either the original or the postevent sources, but which reflects some compromise between [the] two" (p.97). Schooler and Tanaka argued that only the latter constitutes good evidence for blend-memory representations of the CHARM-type. As it turns out, Schooler and Tanaka's intuitions (and Metcalfe & Bjork's, initially) are faulty. Compromise recall--defined as a preference for an intervening alternative over either of the actually presented alternatives--is not normally a prediction of CHARM and may not be a prediction of composite-trace models in general. Only under specialized conditions--a systematic displacement of the test alternatives or a systematic shift attributable to assimilation to prior semantic knowledge--will computer simulations of CHARM produce unimodal compromise recollection. Equally surprising is the fact that separate-trace models, under a different set of conditions, can predict compromise recollection.

Association Learning↗
PubMed1991

Representations, predictions, and remembrances in CHARM: a reply to Lindsay (1991)

Lindsay (1991), in his comment CHARMed, but not Convinced: Comment on Metcalfe (1990), acknowledged that distributed models of human memory using the construct of a composite memory trace, such as the Composite Holographic Associative Recall Model (CHARM), are able to account for most of the findings within the eyewitness-testimony paradigm. Despite this success, Lindsay found CHARM to be of limited usefulness as a model of eyewitness suggestibility. The reasons stated for this peculiar conclusion are discussed in this rebuttal.

Attention↗
PubMed1991

Recognition failure and the composite memory trace in CHARM.

The relation between recognition and recall, and especially the orderly recognition-failure function relating recognition and the recognizability of recallable words, was investigated using a composite holographic associative recall-recognition memory model (CHARM). Ten series of computer simulations are presented. Analysis of CHARM and comparisons to other models indicate that the recognition-failure function depends on (a) both recognition and recall being similar (convolution-correlation) processes such that an interpretable representation is retrieved in both tasks and (b) the information underlying both recall and recognition being stored in the same composite memory trace. It is of considerable interest that constructs central to the distributed nature of CHARM are responsible for the model's adherence to the recognition-failure function.

Attention↗
PubMed1990

Prenatal oxidative stress: I. Malondialdehyde in hypoxic and hyperoxic chick embryos.

Evidence suggests a positive correlation between metabolic rate (VO2), or ambient oxygen (O2) tension, and the rate of formation of free radicals from O2. We have previously demonstrated that the rates of growth, VO2, protein and DNA accumulation, and the activity of cytochrome oxidase (a key mitochondrial respiratory enzyme), are increased significantly by exposing the chick embryo to 72 h of hyperoxia (60% O2) late in incubation. To test the hypothesis that the chick embryo responds to a prenatal alteration in O2 availability in such a way as to protect its tissues from oxidative damage, we have used the thiobarbituric acid assay to estimate lipid peroxidation (a major form of free radical damage) in selected organs from chick embryos exposed to altered O2 availability. We found significantly higher concentrations of malondialdehyde (MDA, a secondary product of lipid peroxidation) in liver than in chorioallantoic membrane, brain, or heart. However, embryos exposed to brief (72 h) hypoxia (15% O2) or hyperoxia (60% O2) late in incubation, or 48 h of such exposure followed by 24 h of incubation in pure O2, exhibited no significant difference in MDA levels compared to normoxic (21% O2) controls in any of the tissues examined. We conclude that the increase in aerobic metabolism induced in the chick embryo by 3 days of hyperoxia is not accompanied by an increase in lipid peroxidation. We postulate that the chick embryo adapts to hyperoxia in such a way as to escape additional free radical damage, perhaps by increasing the capacity of its antioxidant defenses to compensate for a potential increase in the rate of free radical generation.

Animals↗
PubMed1990

Composite holographic associative recall model (CHARM) and blended memories in eyewitness testimony.

The idea that compositing or blending occurs in human episodic memory stems from two sources: (a) distributed memory models and (b) studies on the errors that occur in eyewitness testimony. These two traditions of research--theoretical and empirical--have been independent and distinct. Here, data from the eyewitness testimony paradigm are simulated by the distributed model CHARM (Composite Holographic Associative Recall Model). Of focal concern are Loftus's studies, which have been interpreted in favor of the blending hypothesis, and McCloskey and Zaragoza's studies, which have been interpreted as refuting Loftus's position. Both of these seemingly contradictory results, as well as recent findings with yes/no recognition, fall out of the model. Finally, the model predicts empirically found color shifts and provides specifications for when blends and memory impairments will and will not be expected.

Association Learning↗
PubMed1989

O2 effect on composition of chick embryonic heart and brain.

Heart ventricles from chick embryos incubated in 60% O2 (hyperoxia) on the 16th through the 18th days of incubation were 21% heavier than those from control embryos maintained in 21% O2 (normoxia). Heart ventricles from embyros incubated in 15% O2 (hypoxia) were 8% lighter than controls. Changes in ventricular weight were accompanied by proportional changes in protein content (21% more in hyperoxic ventricles; 8% less in hypoxic ventricles). Ventricular tissue DNA content showed a significant increase in hyperoxia. Tissue protein/DNA ratios were significantly higher in hyperoxia and lower in hypoxia. These data suggest that increased O2 availability led to hypertrophy of chick embryo ventricular cells and an increase in the level of DNA synthesis. Cytochrome oxidase activity per mg DNA was 15-25% higher in hyperoxic ventricles than in hypoxic ventricles. This result is consistent with our previous findings that alterations in O2 availability affect the O2 consumption rate of the chick emryo in ovo, and it provides direct evidence that a phenomenon repeatedly observed in vitro is of importance in vivo. In contrast to the heart, O2 availability did not affect the wet weight, protein or DNA contents, or cytochrome oxidase activity of the chick embryo brain.

Animals↗
PubMed1988

Diurnal variations in the concentration, arteriovenous difference, extraction ratio, and uptake of 3-hydroxybutyrate and plasma free fatty acids in the hind limb of lactating sheep.

Four lactating sheep were used to study diurnal variations in the concentration, arteriovenous concentration difference, extraction ratio, and uptake of 3-hydroxybutyrate and plasma free fatty acids by the hind limb of the lactating sheep. The arterial and venous concentrations of 3-hydroxybutyrate showed significant diurnal variations, which appear to be related to the feeding regimen, since values declined after feed withdrawal and rose after refeeding. Throughout the experimental period uptake of 3-hydroxybutyrate by the hind-limb was consistent and none of the small variations in arteriovenous difference, extraction ratio, or uptake of 3-hydroxybutyrate by the hind limb was statistically significant. By contrast, free fatty acid concentrations in arterial blood rose steadily after feed withdrawal. Except at feeding time, there was an output of free fatty acid by the hind limb.

3-Hydroxybutyric Acid↗
PubMed1987

Modulation of growth and metabolism of the chick embryo by a brief (72-hr) change in oxygen availability.

Growth of the chick embryo is accelerated by brief (72-hr) exposure to 60% O2 beginning on day 16 of incubation, and acute (2-3 hr) hyperoxia stimulates oxygen consumption (VO2). However, the increment in VO2 that accompanies acute exposure to 60% O2 is only about half that required to account for the degree of growth acceleration observed during 72 hr of hyperoxia. We tested the hypothesis that the magnitude of the oxygen-induced change in embryonic metabolism depends on the length of exposure by making daily measurements of embryonic VO2 during brief (72-hr) exposure to 60% or 15% O2. White leghorn eggs were incubated in 21% O2 for 15 days. On day 16 the experimental eggs were switched to 60% or 15% O2; control eggs were maintained in 21% O2. Oxygen consumption and CO2 production (VCO2) were measured daily. Embryo and organ weights were compared on day 18. Wet and dry weights of briefly hyperoxic embryos were significantly greater than those of normoxic controls. The relative increase in wet weight was significant for the heart and liver but not the brain. Oxygen consumption increased 7% relative to control after 24 hr of hyperoxia and 17% after 72 hr; VO2/gm embryo was 9% greater than control on day 18. Normal growth deceleration was exaggerated by hypoxia; mean wet and dry weights of the briefly hypoxic embryos were significantly less than those of controls. Organ wet weights also showed growth retardation, although the relative decrease in brain weight was not significant. Body water concentration increased in briefly hypoxic embryos. Oxygen consumption was 13% less than control after 24 hr and 17% less after 72 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Aortic function during normal human pregnancy.

Arterial rupture and dissection have been observed in both normal and complicated pregnancies. To understand how arterial mechanical properties might change during pregnancy, we measured aortic root diameter by M-mode echocardiography and obtained simultaneous cuff blood pressures during systole and diastole at rest and during isometric exercise. Measurements were obtained in 19 women at the end of normal gestation and again 3 to 6 months post partum. The aorta is larger and more compliant during normal human pregnancy, and these changes may not revert to prepregnant levels post partum. Increased aortic compliance, combined with decreased vascular resistance, may enhance left ventricular performance in normal pregnancy. Conversely, the presumed structural alterations leading to increased compliance may weaken diseased vessels leading to dissection or rupture during pregnancy.

Adolescent↗
PubMed1985

Exercise dynamics in late gestation: effects of physical training.

Heart rate and stroke volume were measured serially in subjects at rest in the sitting position and at the onset and end of a 6-minute period of upright bicycle exercise. Twenty-three subjects with normal pregnancy were studied in late gestation and again post partum. Rest and exercise cardiac outputs in late gestation were not different from those in the postpartum period. Heart rate was higher at rest and stroke volume lower during exercise in late gestation than post partum. At the end of exercise, stroke volume fell dramatically in late gestation but not post partum. Ten women prospectively identified as physically fit had responses that were not different from those of the nonfit cohort in late gestation. Post partum, the physically fit women had exercise responses typical of trained persons and different from those of the nonfit cohort. In late gestation, rest and exercise hemodynamics in subjects in the sitting position appeared to be dominated by factors influencing venous return, independent of physical fitness.

Birth Weight↗
PubMed1985

Stimulatory and persistent effect of acute hyperoxia on respiratory gas exchange of the chick embryo.

The hypothesis that oxygen availability limits growth of the normal chick embryo late in development predicts that an increase in oxygen availability would accelerate the rate of growth and, therefore, metabolism. We tested the prediction concerning metabolism by comparing the oxygen consumption (VO2) and carbon dioxide production (VCO2) of 14-18 day embryos acutely exposed to either 50% or 100% O2 with those of normoxic (21% O2) controls. Two hours of hyperoxia produced increases in both VO2 and VCO2; however, repeated measurements over time in normoxia also demonstrated a significant increase in gas exchange, presumably due to normal growth of the embryos. After correcting for the increase in VO2 due to growth, there was no effect of 60% O2 on day 14. Thereafter the stimulatory effect of 60% O2 increased gradually, reaching 6.1% on day 18. VCO2 was 4 to 6% higher in embryos acutely exposed to 60% O2 than in normoxic controls throughout the observation period, although the difference was significant only on day 18. The VO2 of embryos acutely exposed to 100% O2 was not significantly different from that observed in 60% O2, and was still significantly elevated 3 h after the eggs were returned to 21% O2. We conclude that acute hyperoxia late in incubation elicits an increase in embryonic VO2 and VCO2, with little or no effect on the respiratory exchange ratio, and that the stimulation of gas exchange by 100% O2 persists after the embryo is returned to normoxic conditions. These findings support the hypothesis that oxygen availability limits growth and metabolism of the normoxic chick embryo late in development.

Animals↗
PubMed1985

Monosaccharide uptake by erythrocytes of the embryonic and adult chicken.

Rates of monosaccharide uptake by adult and 10-18 day old embryonic chicken erythrocytes were quantitated. The rate of carrier-mediated, stereospecific transport decreased 28% from day 10 to day 14 of incubation and was unchanged thereafter. At no time, however, did the rate of carrier-mediated transport by embryonic erythrocytes differ significantly from that of the adult cells. The rate of transfer by simple diffusion was 3-5 fold faster in embryonic than in adult erythrocytes. Uptake by simple diffusion decreased slightly as the embryo developed. Chronic hyperoxic incubation (70% O2) had little influence on total monosaccharide uptake by embryonic erythrocytes.

3-O-Methylglucose↗
PubMed1985

Exercise during pregnancy.

Theoretical arguments suggest that cardiovascular fitness would be desirable during pregnancy but that high-intensity exercise should be avoided; both notions require rigorous testing. Moderate exercise, by normal women with uncomplicated pregnancy, does not appear to affect fetal health. Coexisting maternal medical or obstetrical complications may contraindicate exercise.

Animals↗