Ivar Lie

Visual detection and resolution as a function of retinal locus

Abstract Area-threshold functions for detection and resolution thresholds were compared at various retinal eccentricities. The shape of the two functions differs in several respects, but remains invariant of locus under both photopic and scotopic conditions, changing only position on the size axis. Under photopic conditions the relationship between the two functions is invariant with stimulus eccentricity. This covariance of detection and resolution thresholds is shown to imply shape identity of detection and resolution sensitivity profiles of the retina. The results are interpreted in terms of the multiple-channel theory of receptive field organization and the cortical magnification factor.

Oculomotor factors in the aetiology of occupational cervicobrachial diseases (OCD)

SummaryThe traditional posture-ergonomic perspective on the aetiology of Occupational Cervicobrachial Disease (OCD) is discussed and criticized in the light of present knowledge of oculomotor strain during sustained visual work at short distances.Two experiments on ocularly induced neck muscular tension are reported. In both experiments EMGs were taken from six different muscles in the head, neck and shoulder region during a visual discrimination task. In Experiment 1, accommodation and fusion requirements were systematically varied by changing viewing distance in combination with the application of minuslenses and base-out prisms. EMG was shown to increase as a function of accommodation and fusion load. In Experiment 2, a clinical population with severe and long lasting neck and shoulder problems and inappropriate optical corrections was studied with the same experimental design. EMG was shown to decrease when habitual corrections were replaced by more apppropriate ones.

Visual functions and acute ingestion of alcohol

In a placebo‐controlled experiment comprising 22 healthy men (mean age 27.4 years), we investigated the influence of three breath levels of blood alcohol (BrAC; 0.0%, 0.05% and 0.1%) upon distant visual acuity, stereoacuity, contrast sensitivity, accommodation, resting focus of accommodation and binocular vision. Positive (PRA) and negative accommodation (NRA) and resting focus of accommodation showed no significant changes with increasing BrAC. Compared to the placebo condition, visual acuity and refraction were only significantly affected at a breath alcohol level of 0.1%. Contrast sensitivity, stereoacuity and binocular vision were affected both at BrAC 0.05% and BrAC 0.1%. Only the higher spatial frequencies of contrast sensitivity were affected.

Visual detection and resolution as a function of adaptation and glare

Abstract Area-threshold curves for detection and resolution thresholds are compared at different adaptation levels and glare intensities. The shape of the curve for detection thresholds remains unaffected, whereas the shape of the resolution curve varies with adaptation and glare conditions. The curves are displaced along the size axis with variation of adaptation, and along both axis with variation of glare. The results are interpreted in terms of a multiple-channel theory suggesting that receptive fields are functionally organized as a contrast-luminance tuned magnification system.

VDU-screen filters: remedy or the ubiquitous Hawthorne effect?

Abstract The claim that visual display units (VDU)-screen filters improve health by reducing exposure to electrical fields and/or improving screen legibility was investigated by introducing VDU screen filters into an office environment. The study design was quasi-experimental, with the first part conducted according to a simulated control group design with one intervention and one control group. In the second part, which served as a partly switched replication, the control group also received screen filters. The first group continued their use. The dependent measures were sick leave, productivity. subjective symptoms, and musculoskeletal condition. Subjectively reported symptom improvement was found in the group that received screen filters during the initial part of the study, but that was followed by an aggravation of symptoms during the second part for the same group. No effect was observed in the control group in either part of the study. The discontinuity observed between the study parts indicates that factors other than VDU-screen filter use were responsible for the results. However, the results appear to be explained by subject reactivity, i.e. the Hawthorne effect. The results caution against premature conclusions drawn from short-term interventions and emphasise the need for a better understanding of the various psychological and task-related factors that influence subjects. Relevance to industry Visual display units (VDU) are widely used in industry. Knowledge of potential VDU-related health hazards can improve workers health and performance.

VDU work, contrast adaptation, and visual fatigue

Abstract Prolonged VDU work leads to a number of detrimental changes in visual performance and to frequent complaints about asthenopia, musculoskeletal, and other symptoms. The relationship between changes in contrast adaptation at five spatial frequencies and workrelated symptoms were studied in an experimental approach with two groups, one working 2 h (n=13) and the other 4 h (n = 17). Both groups showed a significant reduction in visual acuity and contrast sensitivity, but there were no significant differences between working two or four hours. The relationship between contrast adaptation and symptoms showed a mixed pattern. For the 2 h group there was significant positive correlation between symptoms and all spatial frequencies. For the 4 h group there were mixed correlations between symptoms and contrast adaptation. The results offer only partial support to Lunn and Banks hypotheses on contrast adaptation, accommodation control and visual fatigue symptoms. Contrast adaptation saturates after 1-2 h a...

Accommodation/vergence/fixation disparity and synergism of head, neck and shoulders

The integration of scanning eye movements with head and body movements as well as the synergetic interaction of accommodation and convergence have been known for a long time. Surprisingly, little interest, if any, has been devoted to the possible interaction between vergence/accommodation and other body muscles. Experimental evidence suggesting the existence of an eye-head-body focusing programme for maintenance of clear and single vision was published by Lie and Watten in 1987. In the present paper, these results are summarised and the two-step vergence model of Schor (1980) is extended to account for an ocular motor/body muscle interaction. New evidence of the existence of very large fixation disparities suggesting a dynamic interplay between motor and sensory compensation of angular misalignment is presented. Binocular eye movement registrations are performed while prism induced vergence capacity is measured. In extreme cases prism induced angular deviations up to 15 degrees are seen to be substituted in full by disparity changes. Possible implications of these findings for our vergence-body muscle interaction model is discussed and some preliminary EMG results are mentioned.

On Replacement and Problem Solving Potentials of Spatial Aids for the Blind

The functional usefulness of prosthetic aids is of ultimate interest for rehabilitation. However, the simulation of visual processing and the use of strategies for solving practical problems represent two alternative approaches to evaluation and development of technological aids for the blind. Some basic problems associated with both approaches are briefly outlined and discussed.