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Biomedical subjects

Alastair D Smith

Publications and source records attributed to Alastair D Smith.

16 recordsLinked to original sources
PubMed2006

Eye remember you two: gaze direction modulates face recognition in a developmental study.

The effects of gaze direction on memory for faces were studied in children from three different age groups (6-7, 8-9, and 10-11 years old) using a computerized version of a task devised by Hood, Macrae, Cole-Davies and Dias (2003). Participants were presented with a sequence of faces in an encoding phase, and were then required to judge which faces they had previously encountered in a surprise two-alternative forced-choice recognition test. In one condition, stimulus eye gaze was either direct or deviated at the viewing phase, and eyes were closed at the test phase. In another condition, stimulus eyes were closed at the viewing phase, with either direct or deviated gaze at the test phase. Modulation of gaze direction affected hit rates, with participants demonstrating greater accuracy for direct gaze targets compared to deviated gaze targets in both conditions. Reaction times (RT) to correctly recognized stimuli were faster for direct gaze stimuli at the viewing phase, but not at the test phase. The age group of participants differentially affected these measures: there was a greater hit rate advantage for direct gaze stimuli in older children, although RTs were less affected by age. These findings suggest that while the facilitation of face recognition by gaze direction is robust across encoding and recognition stages, the efficiency of the process is affected by the stage at which gaze is modulated.

Age Factors↗
PubMed2006

The effects of fluoride on the nanostructure and surface pK of enamel crystals: an atomic force microscopy study of human and rat enamel.

Atomic force microscopy (AFM) studies have revealed 30-40 nm-wide regular positively charged bands across maturation-stage rat enamel crystals. Low pH resolved these into positively charged spherical domains of approximately 30 nm diameter. Crystal surface pK values from adhesion force titrations were approximately 6.5. The effect of fluoride on this pK value and on the nanostructure of fluorosed human enamel crystals has not been reported. The nanostructure and surface chemistry (pK) of normal and fluorotic human and of fluoride-treated rat maturing enamel crystals was examined. Enamel was sectioned and polished, prior to examination, using AFM in height and friction modes. High-resolution height images revealed 30 nm-diameter spherical domains within crystals, arranged as layers of hexagons or as a shallow spiral. Fluorotic enamel showed similar, but less well ordered, nanodomains. These could represent an arrangement of original initiation sites or binding sites for modulating matrix proteins. Surface pK was derived from adhesion-force measurements between functionalized tips (OH or COOH) and crystal surfaces between pH 2 and pH 10. pK values of approximately 6.5 for normal crystals were reduced to approximately 5.5 after fluoride treatment. Reduction in surface pK by fluoride might indicate lowered protonation with possible effects on matrix protein binding.

Amelogenesis↗
PubMed2005

Drawing from childhood experience: constructional apraxia and the production of oblique lines.

We report the performance of two patients (ECR and RA) with constructional apraxia on a drawing task previously used to test the development of planning abilities in children. Patients and controls were required to produce both oblique and horizontal/vertical lines that formed a right angle. Planning demands were manipulated across conditions by providing additional spatial information to constrain the drawing. Both patients produced drawings that were less accurate than controls. In addition, ECR was particularly poor at producing oblique lines compared to both RA and controls, even under conditions with minimal planning demands. This pattern of performance is qualitatively similar to that of children under eight years (see Broderick and Laszlo, 1988). Taken together these results provide further evidence that constructional apraxia is not a unitary disorder (with differential performance between patients) and that those differences are not necessarily related to laterality of damage (as both patients had right-hemisphere lesions). We argue for a more quantitative approach to the study of drawing abilities in neuropsychological testing in order to facilitate a finer grained analysis of the disorder and of comparison between patients.

Aged↗
PubMed2005

Children's search behaviour in large-scale space: developmental components of exploration.

It has been argued that visual-search tasks provide a valid model for foraging behaviour. However, Gilchrist et al (2001 Perception 30 1459-1464) demonstrated that, whilst some aspects of behaviour transferred to large-scale egocentric search, there were substantially fewer revisits to previously searched locations than would be expected from the visual-search literature. This difference might be a result of the greater effort required to search in a large-scale egocentric context. Here, we present a novel, automated paradigm, for examining the effect of effort on egocentric search behaviour by manipulating the motor difficulty of the task. Children searched for a hidden target amongst a randomised display of lights by activating a switch at each potential location. The motor difficulty of the task was manipulated by requiring children to search with either their dominant or their nondominant hand. We found that when children searched with their nondominant hand, they made significantly more revisits to previously checked locations than they did when using their dominant hand. This suggests that, when the motor response was more effortful, children were less able to efficiently guide their search behaviour. Individuals with a greater visuo-spatial short-term memory span performed the task more quickly than those with a lower span. However, search latencies were unrelated to general fluid intelligence. This highlights the role of spatial working memory in the development of efficient exploration of large-scale space.

Child↗
PubMed2005

Gastrointestinal hemorrhage due to complicated gastroduodenal ulcer disease in liver transplant patients taking sirolimus.

Sirolimus is emerging as a popular immunosuppressive agent for patients undergoing solid organ and pancreatic cell transplantation. Here, we report the clinical courses of three patients receiving sirolimus who developed aggressive gastroduodenal ulcer disease. One patient died from massive gastrointestinal bleeding, and ulcers in the other two patients healed only after discontinuation of sirolimus. We propose that the mechanism underlying this severe ulcer diathesis, and poor ulcer healing, was linked to the well-known inhibitory effects of sirolimus on wound healing. We propose that sirolimus should be used carefully (or even withheld) in patients with known or previous ulcer disease, and further that it should be used prudently and/or in conjunction with aggressive prophylaxis therapy in those at risk for ulcer disease.

Adult↗
PubMed2004

Does intravenous glucagon improve common bile duct visualisation during magnetic resonance cholangiopancreatography? Results in 42 patients.

INTRODUCTION: Magnetic resonance cholangiopancreatography (MRCP) has been demonstrated as a reliable, non-invasive means of biliary tract imaging among patients with suspected choledocholithiasis. The aim of this study was to establish the impact of intravenous glucagon administration (IVGA) upon visualisation of the common bile duct (CBD) and ampulla of Vater during MRCP. MATERIALS AND METHODS: Forty-two consecutive, non-diabetic subjects with a working diagnosis of symptomatic choledocholithiasis were scanned, pre- and post-IVGA using the half-Fourier, single shot, turbo-spin-echo (HASTE) sequence. Maximum intensity projections (optimised for the extra-hepatic biliary tree and ampulla of Vater) were reviewed blindly by three consultant radiologists. The CBD images were graded (0-3) according to the length of duct seen. The ampullary images were graded according to whether to it was visualised clearly (1), or not (0). RESULTS: Following IVGA the CBD was visualised at grade 3 (75-100% of length seen) in 14 additional patients compared with images prior to IVGA. Furthermore, ampullary visualisation was considered diagnostic in 18 additional patients post-IVGA. No glucagon-associated adverse effects were observed. CONCLUSION: These results demonstrate that IVGA improved visualisation of the CBD and ampulla of Vater during magnetic resonance cholangiopanctreatography. This may reduce the requirement for repeat investigation or recourse to invasive diagnostic procedures (e.g. endoscopic retrograde cholangiopancreatography (ERCP)).

Adult↗
PubMed2002

Common bile duct compression by an abdominal aortic aneurysm: an unusual cause of biliary tract dilatation.

Extra-hepatic bile duct compression is encountered commonly among patients with pancreatic disease, primary sclerosing cholangitis, and cholangiocarcinoma. However, in an elderly lady with predominantly cholestatic liver test abnormalities, magnetic resonance cholangiopancreatography (MRCP) demonstrated a large abdominal aortic aneurysm that was causing extra-hepatic bile duct compression and concomitant proximal bile duct dilatation. This unusual and uncommon finding was almost certainly the explanation for her liver test dysfunction. This report draws attention to the increasing role for MRCP as an accurate, but non-invasive means of appraisal of the pancreatico-biliary tree. In addition, an unusual and uncommon cause of extra-hepatic bile duct compression is discussed.

Aged↗