Search PubMed⌕ Search

Biomedical subjects

D J Bryant

Publications and source records attributed to D J Bryant.

At least 37 records · Page 2Linked to original sources
PubMed1995

Spatial concepts and perception of physical and diagrammed scenes.

The accessibility of objects in mental spatial frameworks depends on their relation to the spatial axes of the world and people's typical interactions with space. The current study investigated perception of space. Subjects viewed either a physical model of a person surrounded by objects (Exp. 1) or diagrams of scenes (Exp. 2). Subjects named objects at directions from their own external perspective. For physical scenes, subjects were faster to name objects at Above/Below locations, followed by Front/Behind locations, followed by Left/Right locations. This finding indicates that subjects used spatial frameworks to locate objects perceptually. For diagrams, response times to name objects did not conform to this pattern, perhaps because the spatial axes of a diagram do not correspond to stable spatial axes of the world.

Adolescent↗
PubMed1995

Effect of orientation in haptic reproduction of line length.

We investigated the accuracy of haptic reproduction of line length and whether accuracy is influenced by line orientation. 13 blindfolded subjects felt along different line lengths at various orientations in the horizontal plane, then reproduced the line lengths in the same orientation as that felt. Efforts were made to equate learning and reproductive scanning movements. Reproductions of line lengths were a nonveridical power function of their true lengths, but the power function exponents did not differ across spatial orientations. It was concluded that people can encode line lengths across spatial orientations by a common power function if care is taken to equate proprioceptive information across learning and reproduction.

Adult↗
PubMed1995

Effect of functional grade and etiology on in vivo hepatic phosphorus-31 magnetic resonance spectroscopy in cirrhosis: biochemical basis of spectral appearances.

Hepatic phosphorus-31 magnetic resonance spectroscopy (31P MRS) was undertaken in 85 patients with histologically proven cirrhosis of varying etiologies and functional severity. Reference data were acquired from 16 healthy volunteers who had no history or evidence of liver disease or alcohol abuse. In vivo hepatic 31P MR spectra were acquired with pulse angle 45 degrees and repetition times (TR) of 5 and 0.5 seconds. Peak area ratios of phosphomonoesters (PME), inorganic phosphate (Pi), and phosphodiesters (PDE) relative to beta ATP, and of PME relative to PDE were calculated from spectra acquired at TR 5 seconds. Estimates of saturation effects for individual resonances were obtained by dividing the peak height at TR 5 seconds by that at TR 0.5 seconds to yield a T1-related signal height ratio (SHR). When compared with reference values, the patients with liver disease showed a significantly higher PME/ATP (P < .0001), PME/PDE (P < .0001), PME SHR (P < .001), and Pi SHR (P < .02), and a lower PDE/ATP (P < .001) and PDE SHR (P < .001). The magnitude of these changes increased significantly and progressively with increasing functional impairment. In patients with compensated cirrhosis spectral appearances varied with etiology; thus, patients with postviral cirrhosis showed a significantly higher Pi/ATP; those with alcoholic cirrhosis, a significantly lower PDE/ATP; and those with cirrhosis secondary to primary sclerosing cholangitis, a significantly lower Pi/ATP than the healthy volunteers or other etiological groups. However, spectral appearances did not vary with etiology in patients with decompensated disease. In vitro 31P MRS of perchloric extracts of samples of liver tissue obtained from 10 patients with cirrhosis at transplant hepatectomy showed increases in levels of the soluble PME metabolites, phosphorylcholine and phosphorylethanolamine, and reductions in the levels of the soluble PDE metabolites, glycerophosphorylcholine and glycerophosphorylethanolamine. These changes suggest regenerative activity in cirrhotic livers. The increases in soluble phosphomonoesters in the aqueous extracts accounted for the increased PME/ATP ratio seen in the in vivo spectra, and might account for the increase in PME SHR. The reduction in soluble phosphodiesters in the aqueous extracts did not entirely account for the reduction PDE/ATP ratio seen in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1994

Regional variations in cerebral proton spectroscopy in patients with chronic hepatic encephalopathy.

Regional variations in proton magnetic resonance spectroscopy (MRS) were assessed in 26 patients and 14 healthy volunteers using a two dimensional chemical shift imaging technique. Patients were classified as being neuropsychiatrically unimpaired, or as having subclinical or overt chronic hepatic encephalopathy (CHE). Peak area ratios of choline (Cho), glutamine and glutamate (Glx) and N-acetylaspartate (NAA) relative to creatine (Cr) were measured. Significant reductions in mean Cho/Cr and elevations in mean Glx/Cr were observed in the patient population, which correlated with the severity of CHE. There were significant regional variations in these metabolite ratios with the mean Cho/Cr lowest in the occipital cortex and the mean Glx/Cr highest in the basal ganglia. NAA/Cr remained relatively constant in all areas of the brain analysed. The regional variation in the metabolite ratios suggests that spectral information from more than one voxel may be useful in the assessment of patients with CHE.

Adult↗
PubMed1994

Subjective landmarks in perception and memory for spatial location.

Four experiments investigated the use of cognitive strategies for encoding spatial location in visual figures. Subjects reproduced the position of a dot in a square figure that had distance markers placed along two sides. Subjects' responses were biased toward imaginary points of intersection formed by the distance markers when subjects responded from memory (Experiment 1) or while viewing the figures (Experiment 2). Dots located at an intersection point were reproduced more accurately than those located off an intersection. These findings demonstrate that empty regions of a figure can serve as subjective landmarks for spatial localization. In Experiment 3, dot relocation was found to be similarly distorted toward physical cross marks placed at the intersections of distance markers, supporting the landmark hypothesis. The attraction of dots to intersection points depends on the viewer employing a strategy of mentally projecting from distance markers to form imaginary intersections, which makes intersection points salient landmarks for coding location of nearby stimulus dots. In Experiment 4, attraction toward intersection points was observed only when subjects employed the projection strategy and not when instructed to use a different encoding strategy.

Adult↗
PubMed1994

Cerebral phosphorus-31 magnetic resonance spectroscopy in patients with chronic hepatic encephalopathy.

Cerebral phosphorus-31 magnetic resonance spectroscopy was undertaken in 33 patients with biopsy-proven cirrhosis: 6 had no evidence of neuropsychiatric impairment on standard clinical, psychometric and electrophysiological testing; 8 had evidence of subclinical hepatic encephalopathy; and 19 were classified as having overt hepatic encephalopathy. The reference population comprised 15 healthy volunteers. Unlocalized spectra were acquired from the entire head with a 45-degree pulse angle and repetition times of 1 and 5 sec. Spectra localized to the basal ganglia were acquired with a 45-degree pulse angle and a repetition time of 1 sec. Peak area ratios of phosphomonoesters, inorganic phosphate, phosphodiesters and phosphocreatine relative to beta-ATP were measured in the spectra acquired. We noted no consistent change in the ratios of inorganic phosphate to ATP and phosphocreatine to ATP. Mean values of the ratios of phosphomonoesters to ATP and phosphodiesters to ATP were significantly lower in the total patient population than in the reference population, and they correlated with the patients' neuropsychiatric status. Thus we found no significant reductions in the mean ratios of phosphomonoesters to ATP and phosphodiesters to ATP in patients who were neuropsychiatrically unimpaired, but significant reductions were observed in the mean ratios of phosphomonoesters to ATP and phosphodiesters to ATP in patients with both subclinical and overt hepatic encephalopathy. The most marked reductions in these metabolite ratios were observed in patients with overt encephalopathy.

Adult↗
PubMed1993

Proton spectroscopy of the neonatal brain following hypoxic-ischaemic injury.

Proton magnetic resonance spectroscopy was used to examine, within the first month of life, the brains of 11 infants born at term--10 with signs of hypoxic-ischaemic encephalopathy (HIE) and one who was neurologically normal at birth. All the infants had peak resonances on their spectra which could be assigned to N-acetyl-aspartase (NAA), choline-containing compounds (Cho) and creatine plus phosphocreatine (Cr). When neurodevelopmental outcome at one year was correlated with initial spectroscopy findings, the NAA/Cho and NAA/Cr ratios reflected clinical outcome. This study suggests that proton spectroscopy not only provides new information about biochemical changes occurring in the brains of infants with HIE, but also may help to predict outcome within the first month of life.

Brain↗
PubMed1993

Strategic and perceptual factors producing tilt contrast in dot localization.

Encoding spatial location in a frame of reference is often biased by both perceptual and strategic factors. For example, tilt contrast occurs when a line presented in the frame of horizontal and vertical axes appears to be repulsed from the nearest axis, including the diagonal axis of symmetry, due to symmetry perception mechanisms. Research has demonstrated, however, that people can adopt particular viewing strategies that eliminate this effect. In Experiment 1, a similar tilt contrast effect was observed when subjects reproduced from memory the position of a single dot in this reference frame. It was hypothesized that this effect resulted from a combination of strategic and perceptual factors. Specifically, people employ an origin strategy, coding the location of the dot relative to the origin of the horizontal and vertical axes, thereby establishing a virtual line that appears tilted away from the axes due to the same perceptual processes affecting physically present lines. Two additional experiments support this hypothesis. In Experiment 2, no clear tilt contrast effect was observed in a perception condition, indicating that the tilt effect for dots cannot be accounted for by purely perceptual processes. In Experiment 3, the tilt contrast effect was found to be contingent upon the use of the origin strategy as opposed to a different strategy. The results demonstrate the importance of a viewer's strategy in determining the pattern of distortion observed in spatial encoding.

Adolescent↗
PubMed1992

Phosphorus-31 magnetic resonance spectroscopy of the human liver using chemical shift imaging techniques.

Phosphorus-31 magnetic resonance spectroscopy of the human liver was undertaken in 28 healthy adult individuals and in 49 patients with liver disease of varying aetiology. Data localised to the liver were obtained using chemical shift imaging techniques. The mean (+/- 1 S.D.) of the peak area ratio phosphomonoesters (PME)/phosphodiesters (PDE) in healthy adult individuals, from spectra obtained with pulse angle 45 degrees and repetition time 1 s, was 0.24 +/- 0.07. The intra-examination variability of this ratio was 20%, the intra-subject variability 27% and the inter-subject variability 32%. An increase in the PME/PDE was observed in the 31P hepatic MR spectrum from primary or secondary tumours in all 17 patients studied, which invariably represented an increase in PME/ATP and, in some cases, a reduction in PDE/ATP. The spectra did not show aetiological characteristics. A non-specific elevation in PME/PDE was also observed in the 31P hepatic MR spectra of 10 (40%) of 25 patients studied who had diffuse liver diseases, such as cirrhosis and infiltrating malignancies. The spectral pattern did not distinguish between diseases of varying aetiologies, but there was a linear correlation between increasing PME/PDE and a reduction in plasma albumin concentrations (p = 0.03). In three patients with hepatic malignancy and abnormal hepatic 31P-MRS, marked spectral changes were observed after successful treatment to debulk the tumour. Only minor changes were observed in the abnormal spectrum of a fourth patient in whom treatment was unsuccessful. Hepatic 31P-MR spectroscopy may prove useful for monitoring disease processes and treatment effects in well characterised patient populations.

Adenocarcinoma↗
PubMed1992

Fat suppression in magnetic resonance imaging at low field strength using binomial pulse sequences.

The use of binomial pulse sequences for fat suppression in MRI at low field strength (0.15 T) was investigated. Both spin-echo and inversion-recovery sequences were used and images obtained of the limbs, head and neck, and pelvis of volunteers and patients. Good fat suppression was seen particularly in small fields of view. Despite technical problems, chemical shift selective techniques can be applied at low field strength.

Adipose Tissue↗
PubMed1991

Exceptions to recognition failure as a function of the encoded association between cue and target.

The relation of the recognition failure of recallable words to overall recognition rates is largely invariant across conditions that influence both recall and recognition separately. In two experiments, the influence of the integration of the members of A-B word pairs on this relation was investigated. In Experiment 1, it was found that deviations of observed recognition failure from predictions of the Tulving-Wiseman function (Tulving & Wiseman, 1975) were produced by shallow, nonsemantic encoding. In Experiment 2, the association of category-to-instance pairs was varied. It was found that weak associates caused larger deviations of observed recognition failure from predicted recognition failure than did strong associates. Such results suggest that a strongly encoded association between cue and target elements of A-B pairs is a necessary condition for the adherence of data to the Tulving-Wiseman function. The implications of these findings for general models of memory are discussed.

Cognition↗
PubMed1990

31P magnetic resonance spectroscopy of the human paediatric liver.

Localized 31P NMR spectroscopy was used to study the developing human liver in three neonates and one infant, all with neonatal intracranial problems, but normal liver function. A prominent resonance was present in the phosphomonoester (PME) region of the spectrum of the neonates; the PME/ATP ratio was 1.0 +/- 0.4 (repetition time 1 s), compared to the mean adult liver value of 0.2 +/- 0.1. The saturation factor of PME in the neonates was large, indicating that the increase in PME/ATP reflected an increase in relative PME concentration. The chemical shift of the PME peak in the neonatal liver (6.8 +/- 0.1) was similar to that found in neonatal brain, suggesting that phosphorylethanolamine may be a major constituent. The phosphodiester (PDE)/ATP ratio in these patients (0.4 +/- 0.1) was decreased compared with the mean adult value (1.3 +/- 0.2), and the saturation factor of PDE was small. The results from the infant were different from both the neonates and adults; PME/ATP was decreased compared to the neonates, but increased compared to adults. The saturation factor of PDE was increased compared to neonates. The biochemical implications of the observed changes in PME and PDE in paediatric liver are discussed in relation to membrane turnover.

Brain Diseases↗
PubMed1990

Implicit associative responses influence encoding in memory.

In list-learning experiments, the orienting question asked of one item may influence the processing of, and memory for, later items in the list. Four experiments demonstrated that words that are not related to their own orienting question, but that are semantically related to the question asked of a previous item, are better recalled than are words that are not related to any question in the list. Factors that influence this memory enhancement include the number of times relevant orienting questions appear during study, as well as the retention interval. Experiment 4 revealed that this effect is contingent upon conscious awareness: Item-category relations do not enhance recall if the subject is not aware of them. The results of the four experiments imply that semantic categories can be primed as implicit associative responses to words, which influence memory.

Adult↗
PubMed1989

Use of ultralong echo time imaging to assist in measuring the velocity of perfused flow in vivo.

The measurement of the velocity of perfused flow in tissue in vivo is complicated by the presence of stationary as well as moving spins and by a variety of dephasing phenomena which affect signal amplitudes. This paper describes a technique by which, using flow-sensitized spin-echo sequences with a set of very long TE times, the velocity of the moving component can be assessed.

Blood Circulation↗
PubMed1989

Problems with achieving saturation using methods based on bursts of rf pulses with spoilers in magnetic resonance imaging.

Attempts at saturation by nonselective rf pulses, followed by gradient spoiler pulses, are sometimes used as the basis of a method of measuring T1 in magnetic resonance imaging, because a method of this type is perceived as being less affected by slice shape artifact than partial saturation methods. This note suggests that, unless care is taken, this assumption can be quite erroneous.

Evaluation Studies as Topic↗
PubMed1989

31P magnetic resonance spectroscopy of the normal human brain: approaches using four dimensional chemical shift imaging and phase mapping techniques.

The use of four-dimensional chemical shift imaging to monitor phosphorus metabolites within the human brain is illustrated. Saturation effects are described, and acquisition conditions are discussed in relation to quantification and sensitivity. The effects of magnetic field variations on spectral parameters are assessed and the use of a field mapping technique is illustrated.

Adult↗