Reduced Contrast Sensitivity Function in Central and Peripheral Vision by Disability Glare

Evaluation of the effects of blue-enriched white light on cognitive performance, arousal, and overall appreciation of lighting

Introduction

Light's non-visual effects on the biological clock, cognitive performance, alertness, and mental health are getting more recognized. These are primarily driven by blue light, which triggers specific retinal cells containing melanopsin. Traditionally, research on light has relied on correlated color temperature (CCT) as a metric of its biological influence, given that bluer light corresponds to higher Kelvin values. However, CCT proves to be an inadequate proxy of light's biological effects. A more precise metric is melanopic Equivalent Daylight Illuminance (mel-EDI), which aligns with melanopsin spectrum. Studies have reported positive cognitive impacts of blue-enriched white light. It's unclear if the mixed results are due to different mel-EDI levels since this factor wasn't assessed.

Method

Given recent recommendations from experts to aim for at least 250 mel-EDI exposure daily for cognitive benefits, our aim was to assess if a 50-minute exposure to LED light with 250 mel-EDI could enhance concentration and alertness, without affecting visual performance or comfort compared to conventional lighting producing around 150 mel-EDI. To ensure mel-EDI's impact, photopic lux levels were kept constant across conditions. Conditions were counterbalanced, parameters included subjective sleepiness (KSS; Karolinska Sleepiness Scale), concentration (d2-R test), visual performance (FrACT; Freiburg Visual Acuity and Contrast Test), general appreciation (VAS; Visual Analogous Scale), preferences and comfort (modified OLS; Office Lighting Survey).

Results

The experimental light significantly reduced sleepiness (p = 0.03, Cohen's d = 0.42) and also decreased contrast sensitivity (p = 0.01, Cohen's d = 0.50). The conventional light was found to be more comfortable (p = 0.002, Cohen's d = 0.62), cheerful (p = 0.02, Cohen's d = 0.46) and pleasant (p = 0.005, Cohen's d = 0.55) while the experimental light was perceived as brighter (p = 0.004, Cohen's d = 0.58) and tended to be more stimulating (p = 0.10). Notably, there was a preference for conventional lighting (p = 0.004, Cohen's d=0.56) and concentration was equally improved in both conditions.

Discussion

Despite the lack of further improvement in concentration from exposure to blue-enriched light, given the observed benefits in terms of vigilance, further research over an extended period would be justified. These findings could subsequently motivate cognitive optimization through lighting for workers that would benefit from artificial lighting such as in northern regions.

Contrast sensitivity and comfort levels with different types of polarised glasses under steady glare

The influence of various polarised glasses on visual performance is crucial due to their widespread. This study measured the visual contrast sensitivity (CS) of dominant eyes by quick contrast sensitivity function (qCSF) procedure at 10 spatial frequencies and 3 noise levels under nonglare, steady glare, steady glare with night lenses, and steady glare with day&night lenses, respectively. Later, the second experiment measured the subjects' subjective feelings under these four viewing conditions. The results showed that there was no significant difference in the CS between the two conditions with polarised glasses and the steady glare. However, the subjects reported greater comfort with glasses than without them. These results suggest that there was an underlying bias when people rated the polarised glasses, and the qCSF procedure was a useful tool for evaluating visual performance.

An interaction effect of external noise and exposure duration on the spatial contrast sensitivity function

It has been demonstrated that contrast sensitivity is sensitive to stimulus exposure duration. Here, we investigated how the duration effect on contrast sensitivity was modulated by the spatial frequency and intensity of external noise. Through a contrast detection task, the contrast sensitivity function under 10 spatial frequencies, three external noise, and two exposure duration conditions was measured. The temporal integration effect was defined by the difference in contrast sensitivity or the area under the log contrast sensitivity function between short and long exposure durations. We found that (1) the temporal integration effect was less pronounced in the zero-noise condition than in the low- or high-noise condition; (2) in the zero-noise condition, a stronger temporal integration effect was observed at high spatial frequencies; (3) in the high-noise condition, a stronger temporal integration effect was observed at low spatial frequencies; (4) the spatial-frequency-dependent transient or sustained mechanism is also sensitive to external noise level; and (5) perceptual template model analysis revealed that both decreased additive internal noise and an improved perceptual template accounted for the temporal integration effect, and these two factors were tuned to spatial frequency.

The Effect of Bangerter Filters on Visual Acuity and Contrast Sensitivity With External Noise

It is critical to address the relationship between density label of Bangerter filters and expected visual acuity, and how filters modulate contrast sensitivity (CS) at different spatial frequency and external noise levels. In the current study, the monocular visual acuity and CS at ten spatial frequencies and three noise levels were measured in normal subjects wearing no filters, 0.8, 0.4, or 0.2 Bangerter filters. Compared with the baseline condition (no filter worn), Bangerter filters degraded both visual acuity and contrast sensitivity function (CSF) in zero-noise conditions, but the reduction of both visual functions did not correlate with each other at any filter level. In addition, the stronger the filter was, the worse both visual functions became. In contrast, when external noise was present, filters improved the contrast sensitivity at low frequencies but deteriorated it at intermediate and high spatial frequencies. The perceptual template model was used to reveal the corresponding mechanism accounted for filter-induced visual function changes. Although the internal process in visual system should not be affected by the filters, the measurement of parameters was biased. To be specific, (1) the internal additive noise was elevated at all frequencies; (2) the perceptual template was improved at low spatial frequencies but impaired at intermediate spatial frequencies; and (3) the changes in both factors were highly dependent on filter intensity. We conclude that Bangerter filters influence visual acuity and contrast sensitivity differently and that their effect on contrast sensitivity depends on spatial frequency and noise.

Acute Alcohol Intake Affects Internal Additive Noise and the Perceptual Template in Visual Perception

A reduction in visual performance is among the serious consequences of acute alcohol intake. Contrast sensitivity (CS) is a fundamental feature of visual function. Here, we investigated the negative effect of a moderate dose of alcohol on CS across a wide range of spatial frequencies and with multiple levels of external noise and clarified the corresponding mechanisms in the context of a perceptual template model (PTM). To avoid the effect of alcohol washout, a quick contrast sensitivity function (qCSF) method was used to assess the visual performance of subjects before and 30 min after a moderate dose of alcohol intake. We found that (1) CS was significantly disrupted by acute alcohol intake; (2) alcohol-induced CS loss was dependent on spatial frequency and external noise; and (3) increased internal additive noise and an impaired perceptual template accounted for alcohol-induced CS loss. These results help us better understand the negative effect of alcohol consumption and provide guidance for driver safety studies.

Lower Internal Additive Noise and Better Perceptual Template Characterize Binocular Contrast Sensitivity Summation

Binocular summation is generally defined as the superiority of binocular over monocular performance. Here, we investigated how external noise modulates the effect of binocular summation on the contrast sensitivity function (CSF) and clarified the corresponding mechanisms with a perceptual template model (PTM). The contrast sensitivity (CS) over 10 spatial frequencies and three external noise levels was assessed under one binocular and two monocular viewing conditions. The binocular summation ratio (BSR) was calculated by dividing the area under the log CSF (AULCSF), or the CS of using both eyes, by that of only using the "good eye" (BSRG) or the "bad eye" (BSRB), respectively. We found that: (1) based on the AULCSF, the BSRB was higher than the BSRG; (2) based on the AULCSF, the BSR was more pronounced under zero-noise than under low-noise conditions, but the BSR was not higher than 1 under high-noise conditions due to a large individual difference; (3) based on the CS, with increasing spatial frequencies, the BSRB steadily increased; (4) both decreased internal additive noise and an improved perceptual template accounted for the gain in binocular summation. These results help us better understand the features of binocular CS and shed light on the clinical studies on populations with monocular CS loss.