bluuebunny/crossref_metadata_2025 huggingface dataset:
Visual responses to reward‐related cues in inferior parietal lobule
Authors: MacKay W. A. , Blum B. , Mendonça A. J.
Published: December 2007

A sample of 263 neurones was recorded in area 7a of Ihe parietal lobe, in a monkey performing a reach (ask to visual targets displayed on a touch‐sensitive videomonitor. The task had been operantly conditioned on food or juice rewards, and 78 (30%) of the units showed activity changes linked in some way to the reward. For most of these cells, the response was to the approach of the trainer's hand with the food reward. This specific visual response was similar irrespective of the direction of approach. Six cells increased discharge as soon as the task was completed in apparent anticipation of Ihe reward. Another two neurones responded to missing a reward: they fired vigorously if the videoscreen was blanked in mid‐trial because a target was not correctly touched. In many cases (40/78) the same cells responding to some aspect of the reward also responded to visual cues given during the task, especially the presentation of the target location. Reward‐related activity in area 7a probably results from an integration of the visual and limbic inputs to this region, such that visual information which foretells behaviourally important events is emphasized.
Coloured shadows described in a cone contrast space
Authors: Shepherd A. J.
Published: December 2007

Two effects which can modify the appearance of a colour seen in a context compared to isolation are chromatic induction and colour constancy. These effects transform colour in ways which depend on the visual system rather than physical characteristics of light and surfaces. They need not reflect different processes within the visual system, indeed, chromatic induction has been attributed 10 the same processes as those involved in constancy, or, as an error of the visual system attempting to achieve constancy. This hierarchy is not necessary: both constancy and induction may result from the same processes without requiring that one promotes the other or that constancy is a goal of the visual system. This study examines induction in terms of cone contrasts in a coloured shadow display, part of a study to establish a relevant measure of contrast and its role in chromatic induction and colour constancy.
Different spatial tunings for ON and OFF pathway stimulation
Authors: Tyler Christopher W. , Chan Hoover , Liu Lei
Published: December 2007

We compared the spatial tuning of sensitivity to luminance increments and decrements in three types of localized stimulus presentation with a smooth spatiotemporal envelope. The lirst type consisted of spatiotemporal Gabor grating functions with either a positive or a negative bias in luminance, The spatial tuning showed a substantially narrower bandwidth and greater peak sensitivity for the positive Gabors. A similar description could be applied to the results for detection of spots with a 2‐D difference‐of‐Gaussian profile, although the shape of the tuning function differed in several respects. We also used the biased Gabor modulation in n contrast self‐masking paradigm, where the increment (or decrement) was presented against a steady background with the same spatial configuration, over a range of base contrasts. At medium spatial frequencies the biased masking functions were similar to those typically found for unbiased gratings, in showing a threshold facilitation (dipper) at low contrast, and sub‐Weber masking behaviour at higher contrasts. At low spatial frequencies, however, a pronounced asymmetry appeared. Stimuli with a positive bins again showed typical masking behaviour, but a virtually flat masking function was obtained for negative bias stimuli. We conclude that stimuli without abrupt luminance transients reveal pronounced differences in the spatial tuning of responses to positive and negative stimuli, which probably reflect differences in the neural connectivity of the ON and OFF processing systems.
Problems measuring contrast sensitivity in children
Authors: Westall Carol A. , Woodhouse J. Margaret , Saunders Kathryn , Evans Jane , Hughes Belinda
Published: December 2007

A preliminary study measured The contrast sensitivity function (CSF) in 30 children (aged 3 months‐5 years). Preferential looking techniques were used to assess CSF to sine wave gratings displayed on one of two screens. To find a meaningful contrast sensitivity procedure we compared the results with a shorter procedure using an edge stimulus. The following problems were encountered: measuring the contrasts required to detect four or live different spatial frequencies took lime, resulting in boredom and loss of attention in our subjects: there was poor correlation between CSF and edge detection: an interesting artefact resulted in a plateau rather than a low frequency fall‐off in the CSF of live of the children >30 months old. This artefact may have resulted from peripheral rather than central retinal responses and or motion artefacts in the stimulus onset. A follow up study with 41 additional children aged 3–36 months limited the contrast testing to that of the spatial frequency corresponding to the peak of the CSF. The shortened procedure, plus a lot of encouragement, resulted in higher contrast sensitivities in all but the oldest age group and successful monocular contrast measurements. In order to avoid artefacts arising from peripheral vision, children were encouraged to look at each screen before responding.
Dependence of stereomotion on the orientation of spatial‐frequency components
Authors: Wright M. J. , Gurney K. N.
Published: December 2007

It is known that sensitivity to stereoscopic motion in depth is not based upon the fine analysis of static disparities hut instead is based on the binocular combination of motion‐sensitive mechanisms. We show in this paper that an ‘aperture problem’ arises for the analysis of motion in depth, just as ii does for monocular motion sensitivity. We extend Adelson and Movshon's solution to the aperture problem by intersection of perpendicular constraints to the three‐dimensional case, and show that it predicts velocity matches for oblique gratings moving in depth, for orientations close to vertical. We show that binocular plaids give rise to motion in depth when the component orientations match in each eye, and the monocular motions are horizontal. The match velocities are consistent with intersection of erpendicular constraints. In three dimensions intersection of perpendicular constraints may be necessary, but is not a sufficient condition for the perception of coherent stereoscopic motion in depth.
Area 21a in the cat and the detection of binocular orientation disparity
Authors: Wieniawa‐Narkiewicz E. , Wimborne B. M. , Michalski A. , Henry G. H.
Published: December 2007

Visual response properties were examined in 115 cells, recorded in area 21a of the cerebral cortex of anaesthetized and paralysed adult cats. Cells were binocular and had receptive fields consisting of a single uniform discharge region which fired with composite ON OFF responses to stationary flashing stimuli. Most cells were sharply tuned for orientation, but this was unaffected by changes in stimulus length. This result is consistent with a model in which the cells of area 2la receive their input from C cells of the striate cortex. Evidence for this was obtained by studying the decline in the responsiveness in area 21a that accompanied the cooling of areas 17 and 18. There was little indication that the cells of area 21a were effective detectors of spatial disparity, hut their sharp monocular orientation tuning and differences in the preferred orientation of ipsilateral and contralateral eyes hinted at a role in the detection of binocular orientation disparity. Our results, however, showed that the recorded binocular disparity curves could be accounted for by summing the two monocular contributions and there was no apparent novel binocular component.
Variability of fixation disparity and accommodation when viewing a CRT visual display unit
Authors: Jaschinski‐Kruza Wolfgang , Schubert‐Alshuth Ewald
Published: December 2007

Fixation disparity and accommodation were measured while subjects viewed a target on a cathode ray tube at a 50cm viewing distance. The psychophysical method of sequential testing was used. For measuring fixation disparity a series of brief dichoptic nonius targets was presented and the direction of perceived misalignment was reported by the subject. From these responses the psychometric function of fixation disparity can be derived which gives not only the mean fixation disparity but also the range of fluctuation during the period of measurement. During a 5 min period, this range was ±1.5min arc averaged over subjects, when expressed as the range in which instantaneous fixation disparity fell with a probability of 68%. Repeated measurements on 5 days within ±2 weeks gave a larger range of ±2min arc. However, individual results can differ considerably from these average values. Repeated measurements and I he analysis of the psychometric function can provide a more complete description of individual binocular status than is obtained with a single adjustment of continuously visible nonius targets. Laser optometry revealed that, compared to the stimulus distance of 50cm, accommodation lagged behind in the range 1–2 D. The two display modes of bright characters on dark background and vice versa gave very similar results.
Meridional profiles of variance—covariance of dioptric power. Part 1. The basic theory
Authors: Harris W. F.
Published: December 2007

It has recently become possible to calculate and represent variation or spread of dioptric power in a meaningful way. This is important for the proper analysis and interpretation of data on dioptric power in a number of areas of the vision sciences. The representation takes the form of a symmetric matrix of six (usually) variances and covariances. Although the matrix is satisfactory for several formal statistical purposes, such as the testing of hypotheses, it does not give an intuitively satisfactory picture of the extent and nature of the variation, nor is it easy to interpret in a way that could be useful to the researcher or clinician. A useful graphical representation of variation can be constructed from the variance–covariance matrix. It Consists of curves that show the meridional dependence of the variation. These meridional profiles of variation give a complete and intuitively satisfactory picture of the nature and extent of the variation of power and are potentially of general use to researcher and clinician. A complete theoretical basis is provided for the construction of meridional profiles of variation of dioptric power, An accompanying paper employs the theory to construct profiles for a number of representative samples of dioptric power.
Analysis of refractive status of Hong Kong Chinese infants
Authors: Harris W. F. , Malan D. J.
Published: December 2007

Recently developed methods of quantifying changing dioptric power are applied to the refractive status of Hong Kong Chinese infants from about 10 to about 40 weeks of age. The analysis confirms that hyperopia decreases during the period and that with‐the‐rule astigmatism predominates, Change, however, is not constant over the period. The rate of decrease of hyperopia slows down and the refractive status becomes more spherical. The mean refractive status is calculated at 10, 20, 30 and 40 weeks. The spread of refractive status is represented by variance‐covariance matrices calculated for each group and 95% confidence ellipsoids on the mean are constructed. The variance‐covariance exhibits little change over the period. The right and left eyes show similar behaviour.
Effects of different ocular fixation conditions on A‐scan ultrasound biometry measurements
Authors: Steele C. F. , Crabb D. P. , Edgar D. F.
Published: December 2007

A‐scan readings must he taken along the visual axis for accurate axial length measurement. Various fixation targets, which ideally should not induce accommodation, are used to limit eye movements. In this study results using the Humphrey biometer under different fixation conditions were compared to establish the most suitable target. We also investigated corneal applanation effects by comparing optical and ultrasonic measurements of anterior chamber depth. We examined 12 randomly selected normal eyes of 12 young subjects. Three A‐scans were recorded for each of five fixation conditions: spotlight at 6 m: Snellen letter at 6 m; solid probe's built‐in green fixation target; Snellen letter at 6m viewed through a –4.00 DS lens: spotlight at d m under cycloplegia (the comparison condition I. Variability ‘within’ each fixation condition. estimated by the standard deviation for each subject, was equal throughout the 12 subjects for each fixation condition. Also variation was independent of size of the ocular dimension. The good agreement between the comparison condition and optical anterior chamber depth measurements indicated that the solid probe produced little applanation. Differences ‘between’ fixation conditions were investigated. It was concluded that a spotlight or letter at 6 m provides a suitable fixation target for biometry. Built‐in fixation targets can produce significant errors.
Accommodative responses to eccentric and laterally‐oscillating targets
Authors: Hung George K. , Ciuffreda Kenneth J.
Published: December 2007

There is little information on the accommodative response to stimuli having naturalistic motion on the retina. In the present experiment, the steady‐state accommodative response al various dioptric levels was assessed with a Hartinger coincidence optometer as sinusoidal frequency of a small target was systematically altered across the horizontal foveal region (±2°). The steady‐state accommodative response became less accurate as target oscillation frequency increased, approaching the tonic accommodation level when the frequency was between 0.5 and 1 Hz (corresponding to peak velocities of 6.3 and 12.6 deg s−1, respectively). These results suggest that the accommodation system is reasonably robust to naturally‐occurring retinal‐image motion.
Colour vision anomalies following experimental glaucoma in monkeys
Authors: Kalloniatis Michael , Harwertah Ronald S. , Smith Earl L. , DeSantis Louis
Published: December 2007

Spectral sensitivity defects, associated with chronic elevated intraocular pressure (IOP) produced by Argon laser trabeculoplasty, were studied in monkeys. Increment‐threshold spectral sensitivity (ITSS) and threshold versus intensity (TVI) functions were measured using a behavioural model. Elevated IOP resulted in slum wavelength (SW) sensitivity losses characteristic of many ocular diseases. The amount of SW sensitivity loss for ITSS functions depended upon the intensity level and chromatic composition of the background field. The optimum condition identifying the greatest SW sensitivity reduction was a yellow background of moderate intensity (100–100 Td). In the early stages of experimental glaucoma. The cone mechanisms and the rod mechanism typically showed decreased test and field sensitivities. The SW cone pathway has slightly greater threshold elevation (∼0.3 log unit) compared to the rod and cone pathways. On the other hand, in the advanced stages of experimental glaucoma, the largest sensitivity losses were in the longer‐wavelength, red‐green opponent mechanism, with the rod and SW cone pathways showing smaller losses. The similarities of the colour vision anomalies in this animal model with those of patients with glaucoma, provides support for its use as an experimental model for human glaucoma.
Astigmatism, accommodation, the oblique effect and meridional amblyopia
Authors: Charman W. N. , Voisin Linda
Published: December 2007

The variation with accommodation in the dimensions of the geometrical blur ellipse that is formed on the retina of the astigmatic eye is explored in relation to orientation dependence of the corresponding line‐spread function (LSF) and modulation transfer function (MTF). It is shown that if θ is the orientation of the line or grating with respect to the more powerful meridian of an eye having C dioptres of astigmatism, the optimal accommodation response varies as 0.5C c cos2θ. The analysis is extended to include the effects of diffraction. Even at optimal focus, the diffraction‐limited MTF at 45° to the principal meridians of an eye with small amounts of astigmatism is substantially degraded. For example, with a 3 mm pupil and only 0.50 DC of astigmatism, the first zero in monochromatic modulation transfer at 555 nm occurs at ∼32c/deg in the oblique meridian as compared with 94c/deg in the principal meridians. The results arc used as the basis of a discussion of the possible role of infant and juvenile astigmatism in the development of the oblique effect and of meridional amblyopia.
Explanation of isogyre formation by the eye lens
Authors: Pierscionek Barbara K.
Published: December 2007

The eye lens is considered to be birefringent and this properly is thought to be responsible for the image of a cross which is formed within the lens when it is placed between crossed polarizers. This paper presents an alternative explanation for the pattern, as a phenomenon of refraction.
Deformable spectacle lenses
Authors: Pateras E. S. , Fowler C. W. , Chandrinos A. B.
Published: December 2007

Although there are many designs of progressive power multifocal lenses commercially available, they all follow the same basic design concept, with the lens power varying across their aperture as a result of using one aspheric lens surface. An alternative approach was tried on an experimental basis, where the variation in power is produced by a liquid‐filled deformable lens.
Open trial of subjective precision tinting: a follow‐up of 55 patients
Authors: Maclachlan Anne , Yale Sheila , Wilkins Arnold
Published: December 2007

We gave glasses, tinted using new techniques, to 55 patients with visual discomfort and a range of associated complaints. The techniques permitted the patients to adjust the colour and saturation of tint for maximum clarity and comfort when viewing text. Benefit was experienced by 45 patients (82%) who were still using them more than 10 months later. Of these, 40 presented with a perceptual distortion of text that the glasses alleviated: 86% reported migraine in the family. An independent series of 74 children with reading difficulty was examined using coloured plastic sheets placed upon a page of text. Of those reporting beneficial effects of colour, 60% had migraine in the family, as compared with 31% of those for whom colour was of no benefit.
Notch in contrast sensitivity function of optical origin: diffraction effects of acrylic filters
Authors: Irving Elizabeth L. , Woo George C. , Charman W. Neil
Published: December 2007

A series of retinal image degrading filters was evaluated by measuring the contrast sensitivity function of four human subjects through the litters (residual CSF). The acrylic filters, with regularly spaced cross‐hatches, produced progressively more reduction in the residual CSF as the density of the cross hatching increased. For some of the fillers there was a selective toss of a narrow band of spatial frequencies as a result of diffraction effects. This experiment serves to further emphasize the need to rule out optical causes of such notches in the CSF before making a diagnosis of neurological dysfunction.
Calibration of the Canon Autoref R‐1 for continuous measurement of accommodation
Authors: Davis Brett , Collins Michael , Atchison David
Published: December 2007

The Canon Autoref R‐1 is an infrared optometer which allows free‐space viewing. Pugh and Winn described hardware modifications necessary to convert the Autoref R‐1 from an instrument capable of taking single static measurements of the eye's accommodative (refractive) status to an instrument capable of continuous measurement of the accommodative status of the eye. We describe two methods of calibrating the Autoref R‐1 for continuous measurement of accommodation for any individual eye. The assumptions and sources of error underlying these calibration techniques are discussed. We also describe further hardware modifications to simplify signal acquisition from, the Autoref R‐1.
Clinical norms for amplitude of accommodation in Chinese
Authors: Edwards M. H. , Law L. F. , Lee C. M. , Leung K. M. , Lui W. O.
Published: December 2007

Amplitude of accommodation was measured in 121 Hong Kong Chinese subjects between the ages of 11 and 65 years, using the ‘push‐up’ method and the results compared with those previously obtained for Caucasian subjects. The results confirm and quantify clinical experience that Chinese people have lower amplitudes of accommodation than Caucasians. If presbyopia is considered to commence when the amplitude of accommodation declines to less than 5 D, then presbyopia in the Chinese race occurs between the ages of 36 and 40 years. By early in the second decade of life the amplitude of accommodation in the Chinese is already lower than that of Caucasians. This suggests that reduced amplitude of accommodation may he due, at least in part, to factors other than longterm environmental effects.
Tonic vergence, age and clinical presbyopia
Authors: Ciuffreda Kenneth J. , Ong Editha , Rosenfield Mark
Published: December 2007

The relative contribution of tonic vergence to the maximum near vergence response as a function of age and the development of presbyopia has received little attention. Tonic vergence position was measured subjectively in a group of 50 subjects between 20 and 68 years of age. While there was no progressive trend with age. tonic vergence did exhibit a small but consistent convergent increase after 40 years of age, Thus, tonic vergence showed a slight change, possibly of a motor adaptive nature, concurrent with increasing age and the development of clinical presbyopia.
Role of heredity in the genesis of myopia
Authors: Yap M. , Wu M. , Liu Z. M. , Lee F. L , Wang S. H.
Published: December 2007

Previous studies suggest that myopia in parents may influence the genesis of myopia in their offspring. In this study, we surveyed 2888 children of Chinese descent in China and Hong Kong to determine the relationship between the refraction state of parents and their children. The age range of the children was 7–17 years, Refraction was measured using a Canon R‐22 objective infrared autorefractor and a survey on family history of ametropia was conducted using a questionnaire. We found that children with myopic parents are more likely to be myopic.
Off‐axis measurements of a plano distance power progressive addition lens
Authors: Atchison David A. , Kris Michy
Published: December 2007

To test that the Humphrey Lens Analyzer can be used validly to measure off‐axis powers of progressive addition lenses of low distance power, we made measurements of a piano distance progressive power tens with both a conventional focimeter and the Humphrey Lens Analyzer. The use of the Humphrey Lens Analyzer in two modes, one in which the lens related about a point corresponding to the centre‐of‐rotation of the eye (mode 1) and one in which (he lens rotated about its back surface centre of curvature (mode 2), gave off‐axis power measurements which were similar to those of conventional measurements. In addition, the Humphrey Lens Analyzer in mode I gave prism measurements which were similar to conventional measurements. The Humphrey Lens Analyzer in mode 2 gave prism measurements which were less than those of conventional measurements, but the prism contours were similar and the differences were < 1 Δ within 20 mm of the lens centre.
Colour vision screening in glaucoma: the Tritan Album and other simple tests
Authors: Heron Gordon , Erskine Niall A. , Farquharson Elaine , Moore Ann T. , White Helen
Published: December 2007

Results from simple colour vision tests used for the detection of (he Type III colour vision deficiency in glaucoma and ocular hypertension are presented. We assessed 49 patients with primary open angle glaucoma. 16 ocular hypertensives, 54 age matched normals and 50 young normal observers using six established tests and the recently introduced Tritan Album. This lest was introduced specifically for acquired colour vision deficiencies. Results show in general that individual tests have low sensitivity and poor screening efficiency. The best screening efficiency was achieved by the City University Colour Vision Test and the AO HRR plate test, no acquired tritan defects were identified by the Farnsworth F2 plate, and the Tritan Album had very low sensitivity (the lowest excluding the F2 plate). Best results were obtained from a combination of City University and HRR test scores and this combination could provide useful additional data on colour vision in a glaucoma screening programme.
Refraction referral criteria for Hong Kong Chinese preschool children
Authors: Chan Osbert Y. C. , Edwards Marion
Published: December 2007

The major types of ametropia and visual problems for Hong Kong Chinese and Caucasian children are different. Consequently, the referral criteria developed for Caucasian children may not be applicable to Hong Kong children. Results of our study suggested that the referral criteria for Hong Kong children should be set as hyperopia of ≥+ 2.0 D, myopia of ≥ 1.0 D, anisometropis of ≥ 1.0 D and anisometropia of ≥ 1.25 D. Sensitivity using only these criteria for abnormal refraction in identifying children with amblyopia. Esotropia, exotropia and subnormal vision (< 6/12) was respectively 100%, 84.6%, 45.2% and 95.7%. The overall sensitivity for the identification of visual problems was 86.1 % and the overall specificity was 76%. If a cover test or a Hirschberg test was introduced into the screening battery so that all the strabismic cases were identified, the overall sensitivity would increase to 98.6%.
Non‐compliance in general health care
Authors: Claydon Bridget E. , Efron Nathan
Published: December 2007

An increased interest in non‐compliance has been demonstrated by the great number of papers recently published on the subject, A review of the relevant literature shows a pattern emerging of at least one third of clients being non‐compliant. This can result in a hazard to health, a waste of health resources and much frustration for practitioners and clients in many areas of health care. There are multiple factors which appear to he related to non‐compliance in a complex and interdependent way. These factors can be described under three main headings: the client, the treatment and disorder, and the clinic interactions. Compliance is summarized as the shared responsibility of practitioner and client in a health care partnership. The purpose of this paper is to review the extensive literature on compliance in general health care and to present a set of guidelines for the enhancement of compliance in the form of a general model.
Tonic accommodation: a review. II. Accommodative adaptation and clinical aspects
Authors: Rosenfield Mark , Ciuffreda Kenneth J. , Hung George K. , Gilmartin Bernard
Published: December 2007

Part I of this review considered basic aspects of tonic accommodation (TA). i.e. the accommodative response observed under degraded stimulus conditions. Part II considers accommodative adaptation, i.e. the apparent change in TA following periods of sustained fixation, and clinical aspects of both baseline TA and accommodative adaptation. It is suggested that the apparent post‐task shift in TA reflects the slow rate of decay of the stimulus‐mediated adaptive accommodative response, while the actual level of tonic innervation to the ciliary muscle remains relatively constant. The clinical implications of both TA and accommodative adaptation are discussed with regard to night, space and instrument myopia and refractive error development, notably nearwork‐induced myopia. It is concluded that the evidence for any association between this form of myopia and either TA or accommodative adaptation is equivocal, and furthermore it seems likely that TA plays only a minor role in influencing the closed‐loop steady‐state accommodative response.
Calculation method for retinal irradiance from extended sources
Authors: Campbell C.
Published: December 2007

A method is given for calculating retinal irradiance from an extended source, whether the source is focused on the retina or not. Both the refractive state of the eye and the source distance from the eye are taken into consideration. Examples for emmetropic and ametropic eyes are given.
Three month study of changes in the cornea after computer‐determined and conventionally‐determined contact lens fitting
Authors: Lam Andrew K. C. , Douthwaite W. A.
Published: December 2007

The conventional rigid‐lens fitting method uses fluorescein to assess the tear layer beneath a trial lens on the corneal surface. A more advanced technique, which uses a computer program to determine the back surface specifications of a contact lens from a pre‐set tear layer thickness, has been studied. No significant difference was found in terms of corneal physiological changes between the conventionally determined contact lenses and computer‐determined contact lenses after a three‐month wearing period. The results suggest that there is little difference in the two methods of fitting. However, the computer determined method was found to be more efficient in terms of chair time, and also can aid inexperienced rigid lens practitioners to select the appropriate lens back surface curves.
Repeatability of post‐task regression of accommodation in emmetropia and late‐onset myopia
Authors: Strang Niall C. , Winn Barry , Gilmartin Bernard
Published: December 2007

The characteristics of post‐task regression of accommodation to pre‐task ionic accommodation (TA) levels have been examined in a number of studies to clarify the nature of the within‐task facility for accommodative adaptation. Of special interest is the recent observation that significant attenuation of post‐task regression occurs in late‐onset myopes (LOMs) when compared with emmetropes(EMMs). These findings have led to speculation that such attenuation may reflect a deficit in inhibitory sympathetic innervation to ciliary smooth muscle in late‐onset myopia and hence a predisposition to sustained accommodative adaptation which then acts as a precursor to the induced myopia. A consequence of this study was that post‐task regression may have some value in predicting those individuals who may be susceptible to post‐task accommodative hysteresis. A pre‐requisite for such a predictive value is that for a given individual the variation in inter‐trial regression patterns is not significant. The aim of this study is principally to Investigate the inter‐trial variability of post‐task regression for individual subjects following a sustained near vision task, and to confirm further differences that have been reported between EMMs and LOMs with respect to the time course of post‐task regressions, A modified Canon Rl infrared optometer was used to measure accommodation objectively throughout a near task and for 2 min post‐task. Accommodative level was measured following 3 min fixation of a high contrast photopic Maltese cross target placed 3 D above the subject's baseline TA. Repeatability of post‐task regression in 10 EMMs and 10 LOMs was assessed by taking measurements on three separate occasions, A significant difference in the post‐task regression patterns between EMMs and LOMs was observed which supports previously reported work; the rate of regression to pre‐task TA being slower in the LOMs. Within‐subject analysis showed that for both EMMs and LOMs the differences between time‐course of post‐task regressions were not significant. The repeatability of post‐task regression patterns thus justifies their use as indices of within‐task adaptation.
Vision screening, eye examination and risk assessment of display screen users in a large regional teaching hospital
Authors: Jackson A. J. , Barnett E. S. , Stevens A. B. , McClure M. , Patterson C. , McReynolds M. J.
Published: December 2007

In January 1993 the Royal Group of Hospitals Trust, which employs approximately 5000 staff, implemented the Health and Safety (Display Screen Equipment) Northern Ireland Regulations (1992). During 1994 all regular display screen equipment users were offered a vision screening test. In total 571 employees were screened using computerized vision screening software (City Visual Systems Ltd). Risk assessments were completed for 293 display screen work‐stations. One hundred and twelve full eye examinations, carried out by optometrists, were performed on those who failed vision screening and on those who specifically requested an optometric assessment. Results indicate that whereas the proportion of users experiencing visual and general symptoms differed markedly from department to department (28–82%), the median number of individuals failing the screening test was 25% (range 9–40%), Those involved in uninterrupted display screen equipment work for prolonged periods reported visual and general work‐related symptoms twice as frequently as those who spent less time working with DSE. The outcome of full eye examinations confirmed that less than 5% of display screen users required spectacles solely for display screen use. Work‐station analysis indicated that ergonomic problems were common. The authors conclude that the successful management of health risks from display screen equipment requires simultaneous attention to work‐place design, working patterns and eye care.
Assessment of Left Ventricular Dyssynchrony in Patients With Heart Failure and Normal QRS Duration
Authors: Narayan Vidya , Varadarajan Padmini , Pai Ramdas G.
Published: December 2007

Cardiac resynchronization therapy (CRT) is an important component of heart failure therapy in patients with a left ventricular ejection fraction <35%, class III or ambulatory class IV symptoms, and a QRS duration >120 ms. The QRS duration criterion for patient selection is imperfect. About 30% of patients with an increased QRS duration are nonresponders to CRT and many with a normal QRS duration with mechanical dyssynchrony respond to CRT. The authors review the currently available echocardiographic tools for the assessment of ventricular dyssynchrony in patients with heart failure.
FRACTURE ANALYSIS IN THE DETERMINATION OF SUB‐UNCONFORMITY STRUCTURE: A PHOTOGEOLOGICAL STUDY
Authors: Norman J. W. , Partridge T. C.
Published: December 2007

This is a record of an attempt to understand the geological structure of an area of several thousand square kilometres where the main interest lies in formations concealed under some 750 to 2500m of unconformable terrestrial sediments. Various fracture trace techniques have been used in an attempt to understand the stress system in the underlying rocks, and to distinguish between movements caused by horizontal and vertical forces. The study resulted in the interpretation of possible anticlines, domes, and drape folds in the underlying rocks, whereas the surface rocks were found to be mainly deformed by differential compaction during diagenesis.
STRUCTURAL DEVELOPMENT IN THE NORTHERN NORTH SEA
Authors: Hay J. T. C.
Published: December 2007

The Northern North Sea basin is a relatively narrow, grabenal or half‐grabenal, northsouth trending feature. The trapping structures are tilted fault blocks. In the southern part of the basin these are mainly westwards tilted blocks formed by down to the east throw faults trending north‐south, parallel to the basin margins. This could fit with general plate tectonic theory, but in the northern part of the area this faulting is complicated by a pronounced NE‐SW trend. This is parallel to the old Caledonian trend and it is postulated that strike‐slip faulting may have been reactivated during the Mesozoic. This strike‐slip movement on the NE‐SW fault trend gave a tendency for individual fault block rotation resulting in a variety of block tilt directions in the northern part of the basin.

The overall half‐graben feature probably started forming in early Triassic, but the faulting leading to the individual fault block formation mainly started during the Middle Jurassic, continuing through the Upper Jurassic. A further period of fault movement occurred during the Upper Cretaceous, but this is not associated with any tilt.
NATURAL GAS IN THE ARCTIC ISLANDS: DISCOVERED RESERVES AND FUTURE POTENTIAL
Authors: Waylett D. C.
Published: December 2007

The Canadian Arctic Islands are underlain by the Cambrian‐Devonian Franklinian geosyncline, which is exposed in several areas, including the Parry islands fold belt, a part of the Paleozoic Arctic fold belt; and by the Mississippian‐Tertiary Sverdrup successor basin. Since 1969, one oilfield has been found in the Parry Islands fold belt and seven gasfields have been found in the Sverdrup basin. Only the gasfields are considered here.

A total of 12.0 Tcf of proved and probable marketable gas reserves has been established in Early Jurassic and Triassic sandstones of the Sverdrup basin. These are mainly in structural traps, although some stratigraphic trapping has been established. Two of the fields–Hecla and Drake Point–are giants. Most of the gas reserves are in the Early Jurassic Borden Island Formation. Prospects for the future, largely offshore, are considered to be very good.
THE GEOLOGY OF THE AREA BETWEEN WADI WARDAN AND WADI GHARANDAL, EAST CLYSMIC RIFT, SINAI, EGYPT
Authors: Thiébaud C. E. , Robson D. A.
Published: December 2007

The area between Wadi Wardan and Wadi Gharandal lies within the rift of the Gulf of Suez, the Clysmic rift, and is part of an elongated zone of outcropping Miocene deposits which show considerable persistence in a NNW to SSE direction, but which undergo frequent and rapid facies changes from W to E. The rocks are folded into a series of asymmetrical anticlinal flexures and synclines, sometimes faulted, whose axes trend NNW to SSE. They prove to be drape structures overlying pre‐Miocene blocks which are generally tilted. Block faulting began during Oligocene times and persisted through Miocene into the post‐Miocene period. The blocks dip westwards, towards the centre of the rift, and are generally bounded by antithetic faults. The structures described in this paper are typical for the whole region of the Clysmic rift. There are no beds of Oligocene age and no igneous rocks, either of extrusive or of intrusive origin, occur in association with Miocene or later deposits.

The area has proved to be important economically. Three oilfields have been discovered there–Sudr (which lies some kilometres N of Wadi Wardan) in 1946, Ras Metarma in 1948, and Asl in 1949. In each case, the reservoir rock is found near the base of the Miocene or in Eocene limestone at or near the top of a Wdipping block of pre‐Miocene strata. Marls and gypsum or anhydrite deposits invariably form the capping rock.
THE MYTH OF A VAST OCEANIC TETHYS, THE INDIA‐ASIA PROBLEM AND EARTH EXPANSION
Authors: Crawford A. R.
Published: December 2007

Common belief in a vast oceanic Tethys is mistaken and results from attempts to reconstruct Pangaea on an Earth of constant dimensions. Tethys was an epicontinental sea, much longer than it was wide. India was simultaneously attached to Asia and formed part of Gondwanaland. This is possible only if, as Carey suggests, the Earth has expanded and the Indian Ocean formed as continents separated. Such separation was a single controlled event.
PETROLEUM GEOLOGY IN THE PALEOZOIC CLASTICS OF THE MIDDLE AMAZON BASIN, BRAZIL
Authors: Carozzi Albert V.
Published: December 2007

Paleoenvironmental maps of all the stratigraphic units of the Middle Amazon Basin from Ordovician to Early Carboniferous are analysed in terms of their source‐rock and reservoir potentials. These maps were obtained by applying the following techniqes; detailed petrography of diamictites, sandstones and siltstones including measurements of index of clasticity; analysis of early and late diagenetic cementation processes; environmental interpretation of sedimentary structures; geochemistry of trace elements and lateral variations of clay mineral assemblages based on X‐ray diffraction data. Five distinct sedimentary models were recognized. Fluvio‐deltaic model consisting of fluvial, deltaic, distal deltaic and offshore subenvironments. Tidal flat model consisting of marshes, intertidal flat, shoreface and offshore subenvironments. Beach model consisting of dunes (inferred), beach, shoreforce and offshore subenvironments. Glacial model (Nhamundá time, Early Silurian), consisting of glacial (tillites), fluvial, beach, shoreface and offshore subenvironments. Glacial model (Curiri time, Late Devonian) consisting of glacial (tillites with subglacial sandstone channels and interglacial braided streams), shoreface and offshore subenvironments.

From the association of these depositional models, the direction and intensity of the supply of coarse clastics was determined in a semi‐quantitative manner for each stratigraphic unit. The time andspace distribution of the detritalsupplies and of the areas of coarse clastic sedimentation indicates a continuous synsedimentary tectonic control of the depocenters by the differential subsidence of the underlying Precambrian basement in the shape of large blocks limited by a system of NW‐SE and NE‐SW lineaments. By using an index of synsedimentary tectonic activity it is possible to define three major episodes of coarse clastic sedimentation which have the best reservoir potential: Early Silurian fluvio‐glacial systems, Early Devonian progmding deltas and Late Devonian fluvio‐glacial systems. The tmps for hydrocarbons are mainly stmtigmphic but enhanced by the weak structures of the basin and result from the relationship between the coarse clastics and two intervening sequences of mature black shales.
RELATIONSHIP OF FACIES AND RESERVOIR QUALITY IN ROTLIEGENDES DESERT SANDSTONES, SOUTHERN NORTH SEA REGION
Authors: Nagtegal P. J. C.
Published: December 2007

permian Rotliegendes desert sandstones cored in two wells in the southern North Sea were grouped as wadi, adhesion‐ripple, dune‐base and dune‐top sandstones on the basis of sedimentary structure and grains‐size characteristics. The porosities of these sandstones differ significantly. Those of wadi origin have the lowest values (φav.=5.5%) and the dune‐top sandstones have the highest (φav.=14.6%). The present study is amied at explaining these differences. The sandstones, which have been buried to a depth of approx. 4.000 m. have a complex diagenetic history marked by envirnment‐and depth‐related changes. Apart from authigenic ferric oxide, dolomite, anhydrite, K‐feldspar and quartz, they are characterised by well‐developed pressure solution and well‐crystallised authigenic illite and chlorite. The chlorite has a pore‐bridging growth habit which disturbs the porosity‐permeability relationship.

On the basis of thin‐section petrographic point‐count analyses and porosity and permeability measurements, and by means of multivariate analysis, the nature and the small‐scale distribution of sorting in each of the sandstone facies types are ultimatly isolated as the main variables explaining the porosity differences. These sandstones thus display porosity differences which correlate with primary sedimentary structure. This relationship was not destroyed even at deep burial and marked diagenetic change.
UTILIZATION AND DOCUMENTATION OF VERTICAL OIL MIGRATION IN DEEP BASINS
Authors: Price Leigh C.
Published: December 2007

Use of the model of a hot, deep, origin of oil places rigid constraints on the migration and entrapment of crude oil. Specifically, oil originating from depth migrates vertically up faults and is emplaced in traps at shallower depths. Review of petroleum‐producing basins worldwide shows oil occurrence in these basins conforms to the restraints of this hypothesis. Most of the world's oil is found in the very deepest sedimentary basins, and production over or adjacent to the deep basin is cut by, or directly updip from, faults dipping into the basin deep. Generally, the greater the fault throw, the greater the reserves.

Fault‐block highs next to deep sedimentary troughs are the best target areas by the present concept. Traps along major basin‐forming faults are quite prospective.

The structural style of a basin governs the distribution, types, and amounts of hydrocarbons expected, and hence the exploration strategy. Production in delta depocenters (Niger) is in structures cut by or updip from major growth faults, and structures not associated with such faults are barren. Production in block‐fault basins in on horsts next to deep sedimentary troughs (Sirte, North Sea). In basins whose sediment thickness, structure and geologic history are known to a moderate degree, the main oil occurrences can be specifically predicted by analysis of fault systems and possible hydrocarbon migration routes.

Use of the concept permits the identification of significant targets, which have either been downgraded or ignored in the past, such as production in or just updip from thrust belts, stratigraphic traps over the deep basin asociated with major faulting, production over the basin deep, and regional stratigraphic trapping updip from established production along major fault zones.
PETROLEUM GEOLOGY OF THE MASCARENE RIDGE, WESTERN INDIAN OCEAN
Authors: Kamen‐Kaye M. , Meyerhoff A.A.
Published: December 2007

The Mascarene Ridge, more than 2,000 km long, has an arcuate shape, convex to ward the east. The ridge is interpreted here to be a relict island arc which ceased to be active in late Proterozoic or early Paleozoic time during the tectonic and orogenic events of the Panafrican tectogenesis. Precambrian granite is exposed at the northern end of the arc (Seychelles Bank) and recent volcanoes are at the southern end of the arc (Rhunion Island). Between the two extremities is a Tertiary basin with 2,432m (in the Saya de Malha no. 1 well) of Paleocene‐Pleistocene carbonate rocks, and more than 830 m of basaltic volcanic rocks of unknown age. Although drilling to date has been discouraging, the amount and depth of drilling are insufficient to determine theprospectivity of the area. At least one well should be drilled below the volcanic sequence in order to determine whether the Saya de Malha‐Nazareth Bank basin has petroleum potential.
COMPARISON OF POROSITY‐DEPTH RELATIONSHIPS OF SHALE AND SANDSTONE*
Authors: Magara Kinji
Published: December 2007

The rate of shale compaction or porosity reduction decreases with increase in burial or compaction. This may be caused by decreasing shale permeability and increasing water viscosity, thus decreasing rate of fluid expulsion with increasing compiction. For a given increase in overburden pressure, the pressure or stress applied to a given grain‐to‐grain contact area decreases with burial becaused the contact area increases with compaction and concomitant grain deformation. This may also cause the reduced rate of compaction with increase in burial. The above abservations may suggest that the shale compaction is primarily controlled by physical forces of sedimentary rocks.

On the contrary, the rate of sandstone porosity reduction is known to be relatively constant throughout the burial diagenetic history in many regions provided ther was no significant secondary porosity developed by leaching and fracturing. For a given increase in overburden pressure, the grain‐to‐grain contact area. Yet, rate of porosity reduction for the sandstones is realtively constant, whether they are at a shallow or deep burial depth. This suggests that, for the sandstones, the physical forces have been of secondary importance in reducing the porosity. Chemical and mineralogical agents are believed to have been more significant in sandstones. Numerous regional petrographic studies confiirm the importance of diagenetic cements.