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Biomedical subjects

G Jewell

Publications and source records attributed to G Jewell.

5 recordsLinked to original sources
PubMed2000

Pseudoneglect: a review and meta-analysis of performance factors in line bisection tasks.

An exhaustive qualitative (vote-counting) review is conducted of the literature concerning visual and non-visual line bisection in neurologically normal subject populations. Although most of these studies report a leftward bisection error (i.e., pseudoneglect), considerable between-study variability and inconsistency characterize this literature. A meta-analysis of this same literature is performed in which the total quantitative data set, comprising 73 studies (or sub-studies) and 2191 subjects, is analyzed with respect to 26 performance factors. The meta-analytic results indicate a significant leftward bisection error in neurologically normal subjects, with an overall effect size of between -0.37 and -0.44 (depending on integration method), which is significantly modulated to varying degrees by a number of additional task or subject variables. For example, visual bisection tasks, midsagittal-pointing tasks and tactile bisection tasks all lead to leftward errors, while kinesthetic tasks result in rightward errors. Tachistoscopic forced-choice testing methods reveal much greater estimates of bisection error (effect size = -1.32) than do manual method-of-adjustment procedures (effect size= -0.40). Subject age significantly modulates line bisection performance such that older subjects err significantly rightward compared to younger subjects, and to veridical line midpoint. Male subjects make slightly larger leftward errors than do female subjects. Handedness has a small effect on bisection errors, with dextrals erring slightly further to the left than sinistral subjects. The hand used to perform manual bisection tasks modulated performance, where use of the left hand lead to greater leftward errors than those obtained using the right hand. One of the most significant factors modulating bisection error is the direction in which subjects initiate motor scanning (with either eye or hand), where a left-to-right scan pattern leads to large leftward errors while a right-to-left scan pattern leads to rightward errors.

Adult↗
PubMed1999

Visuospatial attention in line bisection: stimulus modulation of pseudoneglect.

Neglect and pseudoneglect are asymmetries of spatial attention which are often assumed to possess a fundamental theoretical and neurological relationship to each other, although this assumption has never been directly tested and there is as yet no unifying quantitative theory. A total of 217 subjects participated in five experiments demonstrating that both the magnitude and direction of bisection errors in normal subjects (pseudoneglect) are modulated by stimulus factors that similarly influence the magnitude and direction of neglect. Stimulus positional uncertainty did not abolish pseudoneglect, indicating that bisection judgements are made within an object-centered frame of reference. Backward masking line stimuli had no influence on the magnitude of pseudoneglect, signifying that pseudoneglect is not a byproduct of covert directional scanning of the line stimulus in iconic or short-term visual memory. Finally, bisection errors are influenced by the direction of contrast gradients imposed on line stimuli, such that perceived line midpoint is drawn toward the lower-contrast line end. The magnitude and direction of pseudoneglect are modulated by stimulus factors that also influence the magnitude and direction of neglect. Both phenomena are succinctly described as biases in attention (i.e., neglect is a right-bias, whereas pseudoneglect is a left-bias). The two phenomena are modulated by stimulus factors as follows. Line length: there is an increased bias with increasing line length for both phenomena, and a cross-over to an reversed bias for short lines. Azimuthal line position: an increasing bias accompanies increasing leftward placement for both phenomena. Line aspect ratio: there is a decreasing bias with increasing line height for both phenomena. Line elevation: there is a decreasing bias with increasing elevation for neglect, and an increasing bias with increasing elevation for pseudoneglect. The only case in which a factor's influence on the two phenomena is discrepant is for elevation, and this difference is explicable. Taken together these congruencies strongly support the notion that neglect and pseudoneglect are phenomena that are twin manifestations of parameter changes in a unitary set of underlying hemispheric attentional asymmetries.

Adult↗
PubMed1994

The effectiveness of vision screening by school nurses in secondary school.

Vision screening of 13 and 15 year old children by school nurses in Oxfordshire has declined in recent years due to the pressure of other commitments. A study was carried out to evaluate the likely consequences of failing to provide vision screening for secondary schoolchildren, in order to make a decision about the future of the service. Parents were also asked to complete a questionnaire about their children's past eye histories. Eight schools that had had no vision screening for at least three years participated in the study. Overall, 3.8% of children between 13 and 15 years old had a visual acuity of worse than 6/12 in one or both eyes, that is they failed vision screening; there was no evidence that this percentage increased significantly across this age range. Less than 1% of children were prescribed and wore spectacles as a consequence of failing vision screening and no new cases of eye pathology were detected. Questionnaire responses suggested that about 50% of children who did not wear spectacles had had an eye examination in the previous two years. The results indicate that vision screening is not the best way to meet the eye/vision needs of secondary schoolchildren. Strategies for targeting the school nursing resource more appropriately are being considered.

Adolescent↗