Helle K. Falkenberg

Acuity, crowding, reading and fixation stability.

People with age-related macular disease frequently experience reading difficulty that could be attributed to poor acuity, elevated crowding or unstable fixation associated with peripheral visual field dependence. We examine how the size, location, spacing and instability of retinal images affect the visibility of letters and words at different eccentricities. Fixation instability was simulated in normally sighted observers by randomly jittering single or crowded letters or words along a circular arc of fixed eccentricity. Visual performance was assessed at different levels of instability with forced choice measurements of acuity, crowding and reading speed in a rapid serial visual presentation paradigm. In the periphery: (1) acuity declined; (2) crowding increased for acuity- and eccentricity-corrected targets; and (3), the rate of reading fell with acuity-, crowding- and eccentricity-corrected targets. Acuity and crowding were unaffected by even high levels of image instability. However, reading speed decreased with image instability, even though the visibility of the component letters was unaffected. The results show that reading performance cannot be standardised across the visual field by correcting the size, spacing and eccentricity of letters or words. The results suggest that unstable fixation may contribute to reading difficulties in people with low vision and therefore that rehabilitation may benefit from fixation training.

Effect of an Oil and Water Emulsion on Tear Evaporation Rate

Dry eye patients have been divided primarily into two categories, evaporative or tear production-deficient.1 In both cases, increased tear evaporation and by extension, evaporation rate, is a significant parameter in the etiology and pathogenesis of dry eye. Paradoxically, the use of tear supplements has been shown to exacerbate tear evaporative loss.2 Theoretically, tear supplements should cause minimal increases in evaporation and ideally, should reduce evaporation of the tear film.

Sampling efficiency and internal noise for motion detection, discrimination, and summation.

By comparing real observers to an ideal observer, previous studies have found that the detection of static patterns is limited by internal noise and by imperfect sampling efficiency. We developed and applied ideal observer models for the detection, discrimination, and summation of oppositely drifting gratings in Gaussian white noise. The three tasks share a common source of internal noise. The sampling efficiencies were on the order of 1-2% except for much lower efficiency in direction discrimination for faster moving gratings. The efficiency of direction discrimination relative to detection systematically declines as the speed is increased from 1 to 6 Hz. These results suggest that observers use mismatched filters tuned to slow speeds regardless of the signal speed. Human visual motion sensing appears to use distorted representations of the incoming signals, and this distortion is a major limitation to visual performance.

The development of global motion discrimination in school aged children

Global motion perception matures during childhood and involves the detection of local directional signals that are integrated across space. We examine the maturation of local directional selectivity and global motion integration with an equivalent noise paradigm applied to direction discrimination. One hundred and three observers (6-17 years) identified the global direction of motion in a 2AFC task. The 8° central stimuli consisted of 100 dots of 10% Michelson contrast moving 2.8°/s or 9.8°/s. Local directional selectivity and global sampling efficiency were estimated from direction discrimination thresholds as a function of external directional noise, speed, and age. Direction discrimination thresholds improved gradually until the age of 14 years (linear regression, p < 0.05) for both speeds. This improvement was associated with a gradual increase in sampling efficiency (linear regression, p < 0.05), with no significant change in internal noise. Direction sensitivity was lower for dots moving at 2.8°/s than at 9.8°/s for all ages (paired t test, p < 0.05) and is mainly due to lower sampling efficiency. Global motion perception improves gradually during development and matures by age 14. There was no change in internal noise after the age of 6, suggesting that local direction selectivity is mature by that age. The improvement in global motion perception is underpinned by a steady increase in the efficiency with which direction signals are pooled, suggesting that global motion pooling processes mature for longer and later than local motion processing.

Contextual modulation of the motion aftereffect.

The authors examined center-surround effects for motion perception in human observers. The magnitude of the motion aftereffect (MAE) elicited by a drifting grating was measured with a nulling task and with a threshold elevation procedure. A surround grating of the same spatial frequency, temporal frequency, and orientation significantly reduced the magnitude of the MAE elicited by adaptation to the center grating. This effect was bandpass tuned for spatial frequency, orientation, and temporal frequency. Plaid surrounds but not contrast-modulated surrounds that moved in the same direction also reduced the MAE. These results provide psychophysical evidence for center-surround interactions analogous to those previously observed in electrophysiological studies of motion processing in primates. Collectively, these results suggest that motion processing, similar to texture processing, is organized for the purpose of highlighting regions of directional discontinuity in retinal images.

Development of radial optic flow pattern sensitivity at different speeds.

The development of sensitivity to radial optic flow discrimination was investigated by measuring motion coherence thresholds (MCTs) in school-aged children at two speeds. A total of 119 child observers aged 6-16years and 24 young adult observers (23.66+/-2.74years) participated. In a 2AFC task observers identified the direction of motion of a 5° radial (expanding vs. contracting) optic flow pattern containing 100 dots with 75% Michelson contrast moving at 1.6°/s and 5.5°/s and. The direction of each dot was drawn from a Gaussian distribution whose standard deviation was either low (similar directions) or high (different directions). Adult observers also identified the direction of motion for translational (rightward vs. leftward) and rotational (clockwise vs. anticlockwise) patterns. Motion coherence thresholds to radial optic flow improved gradually with age (linear regression, p<0.05), with different rates of development at the two speeds. Even at 16years MCTs were higher than that for adults (independent t-tests, p<0.05). Both children and adults had higher sensitivity at 5.5°/s compared to 1.6°/s (paired t-tests, p<0.05). Sensitivity to radial optic flow is still immature at 16years of age, indicating late maturation of higher cortical areas. Differences in sensitivity and rate of development of radial optic flow at the different speeds, suggest that different motion processing mechanisms are involved in processing slow and fast speeds.

Reduction in direction discrimination with age and slow speed is due to both increased internal noise and reduced sampling efficiency.

PURPOSE Sensitivity to moving structure decreases with age and slow speeds may be selectively impaired. This loss could be caused by elevated internal noise in the responses of motion sensors or a reduction in the efficiency with which motion responses are integrated. We adapt an equivalent noise paradigm to analyze the perception of slow and fast speed motion as a function of normal aging. METHODS A total of 70 observers (20 to 89 years) identified the direction of global motion in a two-alternative forced choice task. In a central 8° aperture, 100 dots of 10% Michelson contrast were moving at 1.6 or 5.5°/s. The direction of each dot was drawn from a Gaussian distribution whose mean and SD were adaptively changed. Internal noise and sampling efficiency were estimated from direction discrimination thresholds as a function of external direction noise, speed, and age. RESULTS Direction sensitivity was significantly worse for slow speeds at all ages (paired t-test, P < 0.05) and decreased approximately 2% per year (linear regressions, P < 0.01). This aging deficit was due to significant changes in internal noise (5.5°/s) and sampling efficiency (1.6°/s) (linear regression, P < 0.05). CONCLUSIONS There is motion sensitivity loss with age that arises from an increase in internal noise in the responses of directional sensors and a decrease in responses that contribute to the global decision. Differences in the rates of progression at each speed indicate that motion is processed by independent systems tuned to different speeds, and that the channel for slow speed may be more vulnerable to normal age-related changes.

Development of sampling efficiency and internal noise in motion detection and discrimination in school-aged children.

The aim of this study was to use an equivalent noise paradigm to investigate the development and maturation of motion perception, and how the underlying limitations of sampling efficiency and internal noise effect motion detection and direction discrimination in school-aged children (5-14 years) and adults. Contrast energy thresholds of a 2c/deg sinusoidal grating drifting at 1.0 or 6.0 Hz were measured as a function of added dynamic noise in three tasks: detection of a drifting grating; detection of the sum of two oppositely drifting gratings and direction discrimination of oppositely drifting gratings. Compared to the ideal observer, in both children and adults, the performance for all tasks was limited by reduced sampling efficiency and internal noise. However, the thresholds for discrimination of motion direction and detection of moving gratings show very different developmental profiles. Motion direction discrimination continues to improve after the age of 14 years due to an increase in sampling efficiency that differs with speed. Motion detection and summation were already mature at the age of 5 years, and internal noise was the same for all tasks. These findings were confirmed in a 1-year follow-up study on a group of children from the initial study. The results support suggestions that the detection of a moving pattern and discriminating motion direction are processed by different systems that may develop at different rates.

Happy Living in Darkness! Indoor Lighting in Relation to Activities of Daily Living, Visual and General Health in 75-Year-Olds Living at Home

ABSTRACT Lighting has been identified as a significant environmental attribute for promoting vision and general health among older people, enabling successful aging at home, but it has received little attention in the literature. Indoor lighting levels, self-reported vision and general health, and activities of daily life were measured in 114 healthy 75-year-old Norwegians. Despite very low levels of indoor lighting, the subjects were happy and healthy. There is a large discrepancy between self-assessed health and recommended lighting levels, and low awareness of the effect of lighting on age-related vision loss or daily living in the future. Knowledge of how to utilize indoor lighting to ensure healthy and safe aging in the home is needed.

Lighting old age--how lighting impacts the ability to grow old in own housing, part one.

A functionally optimized housing development designed to meet the demands in different phases of living (universal design) may result in the elderly living longer in their own homes. In this study a total of 165 healthy persons were included out of a total of approximately 320 persons turning 75 years of age in 2009 living in Drammen municipality. They went through a quantitative, questionnaire-based interview (including VAS and SF-36) and 20 participants were then selected for a qualitative in depth interview. The lighting conditions in the kitchen, living room, bathroom, bedroom and staircase were measured according to a simplified procedure. The overall lighting conditions were evaluated to be rather low, with means between 35 and 121 Lux, but the quantitative interviews showed that on most questions the scores were rather low, indicating that the overall thriving is good regardless of rather low lighting values.