Visual Discrimination Capacity Research Articles

Influence of Interocular Differences and Alcohol Consumption on Binocular Visual Performance.

The purpose of this study was to assess the influence of a moderate breath-alcohol content (BrAC of 0.40 mg/L) on binocular visual performance for different visual functions after inducing different levels of interocular differences with the use of filters. A total of 26 healthy young subjects were enrolled. The participants participated in two sessions: one without alcohol consumption and another after alcohol consumption. In each session and for the different filter conditions (subjects were wearing Bangerter foil of 0.8 and BPM2 fog filter on the dominant eye), monocular and binocular visual function was evaluated by measuring visual acuity, contrast sensitivity, visual discrimination capacity (and successively by calculating their corresponding binocular summations) and stereopsis (near and distance stereoacuity). In addition, interocular differences were calculated for different retinal-image quality and straylight parameters. All monocular and binocular visual functions were analyzed and stereopsis was significantly impaired by alcohol and filters (p < 0.05). Interocular differences for different ocular parameters and binocular summations for visual parameters were negatively affected by filters but not alcohol. Significant correlations (averaging all the experimental conditions analyzed) were found, highlighting: the higher the interocular differences, the lower the binocular summation and the poorer the stereopsis and, therefore, the worse the binocular visual performance.

Assessing the influence of cannabis and alcohol use on different visual functions: A comparative study

This study aimed to assess and compare the influence of alcohol intake and cannabis smoking on different visual functions. A total of 64 young and healthy volunteers took part in the study. All undertook several randomised experimental sessions in which different visual functions, namely distance stereopsis, retinal straylight, visual discrimination capacity, and contrast sensitivity, were tested. Cannabis smokers (N = 30) took a baseline session and a session after smoking a cannabis cigarette, whereas alcohol users (N = 34) underwent a baseline session, a session after a low alcohol intake (Alcohol 1), and a session after a moderate to high alcohol intake (Alcohol 2). All visual functions were impaired by cannabis and alcohol use, particularly for the Cannabis and Alcohol 2 groups. The deterioration of all visual variables was higher for the Alcohol 2 than for the Alcohol 1 and Cannabis groups, except for retinal straylight, the deterioration of which was equal for the Cannabis group, and distant stereopsis, which was more impaired for the Cannabis group. The Alcohol 2 group experienced the most impairing conditions, although very similar to the cannabis group, and that factors other than the experimental conditions, such as sex and age, also influenced these visual changes. Alcohol and cannabis use clearly impair vision. The deterioration caused by cannabis is similar to, but slightly lower than, that produced by a moderate to high alcohol intake, with the experimental conditions, sex and age all having an impact on the variability of visual deterioration.

Effect of interocular differences on binocular visual performance after inducing forward scattering

PurposeTo assess binocular visual performance by means of binocular summation on visual function after inducing monocular forward scattering, and to study the influence of interocular differences on ocular parameters.MethodsSeven young healthy subjects were recruited. Four Bangerter foils and five fog filters were used to induce monocular forward scattering. To analyse the impact of the scatter, visual acuity, contrast sensitivity, visual discrimination capacity and distance stereoacuity were measured binocularly with the filter placed over the dominant eye. Additionally, interocular differences were calculated for four ocular parameters: the Objective Scatter Index (OSI), Strehl ratio (SR), modulation transfer function cut‐off (MTF cut off) and straylight (log[s]). Binocular summation was determined for these visual functions.ResultsA statistically significant deterioration in visual acuity, contrast sensitivity and stereoacuity was seen for all of the filter conditions with respect to the natural state (baseline), with the largest change being recorded for the Bangerter foils. Similarly, the interocular difference for the three retinal image quality parameters (OSI, SR and MTF cut‐off) and log(s) increased significantly for the Bangerter foil condition, but not for the fog filters (except log(s)). Binocular summation declined gradually with the Bangerter foils, but not for the fog filters. Statistically significant correlations were found, that is, the greater the interocular differences, the lower the binocular summation of the visual functions and the greater the distance stereoacuity.ConclusionIncreased forward scattering in the dominant eye resulted in interocular differences, which reduced the overall binocular visual performance, including the binocular summation of several visual functions and distance stereoacuity. The results suggest that marked interocular differences in ocular parameters should be avoided in cases of ocular pathology, amblyopia and emmetropisation procedures (such as refractive surgery) or a monovision correction for presbyopia.

Learning and visual discrimination in newly hatched zebrafish

SummaryWith the exception of humans, early cognitive development has been thoroughly investigated only in precocial species, well developed at birth and with a broad behavioral and cognitive repertoire. We investigated another highly altricial species, the zebrafish, Danio rerio, whose embryonic development is very rapid (< 72 h). The hatchlings’ nervous system is poorly developed, and their cognitive capacities are largely unknown. Larvae trained at 8 days post fertilization rapidly learned to associate a visual pattern with a food reward, showing significant performance at 10 days post fertilization. We exploited this ability to study hatchlings’ discrimination learning capacities. Larvae rapidly and accurately learned color and shape discriminations. They also discriminated a figure from its mirror image and from its 90°-rotated version, although with lower performance. Our study revealed impressive similarities in learning and visual discrimination capacities between newborn and adult zebrafish, despite their enormous differences in brain size and degree of development.

Effects of environmental enrichment on recognition memory in zebrafish larvae

Zebrafish (Danio rerio) constitute a useful model for studying memory function and impairment in vertebrates and are now widely used in translational research. On the one hand, the adoption of simple, fast and reliable tests such as novel object recognition (NOR) has increased our knowledge considerable about memory mechanisms in animals. On the other hand, in many model organisms, exposure to environmental enrichment, especially during the early stages of development, affects various cognitive functions. Evidence for the effects of environmental enrichment on zebrafish has been accumulating rapidly, but most of this evidence has been collected in adult subjects. We compared larvae raised in either an enriched or barren environments and measured their memory performance at 14-days post-fertilization. Initially, subjects were allowed to familiarize with two identical novel objects (i.e., pattern of 2D-geometrical figures). After a time interval, larvae faced a two-choice task presenting the same objects paired with a new one. As a measure of recognition memory, we exploit the tendency of individuals to explore a novel object over a familiar one. Our results indicate that larvae from the barren environment spent more time exploring familiar stimuli than novel ones, showing the innate presence of recognition memory capacity in zebrafish larvae. Conversely, subjects bred in a visually enriched environment explore both familiar and novel stimuli almost equally. The increase of exploratory behavior and, consequently, the reduction of avoidance to the novel object may explain the performance shown by larvae exposed to an enrichment environment compared to the larvae bred in a barren environment. Taken together, these results confirm that early-stage zebrafish possess complex visual discrimination capacities and that rearing subjects in a structurally complex environment might hinder memory performance by reducing their neophobic response.

Visual performance after the deterioration of retinal image quality: induced forward scattering using Bangerter foils and fog filters.

We induced and evaluated different levels of retinal-image degradation using Bangerter foils and fog filters. We found increased straylight and an important deterioration in visual performance, assessed by means of visual acuity, contrast threshold, and visual discrimination capacity. Bangerter foils induced forward scattering levels comparable to those observed in mature to severe cataracts, with an important impact of halos and starbursts. Fog filters induced lower levels of intraocular scattering, although luminous veils and circular halos were reported. The visual disturbance index positively correlated with intraocular scattering and straylight. Our results show retinal-image quality has an important influence on night-vision performance.

Intraocular scattering as a predictor of driving performance in older adults with cataracts.

Cataracts can limit a person’s ability to perform vision-dependent tasks safely, affecting the quality of life of older people. This study examines the relationship between visual function and driving, by studying which visual parameters might be important for predicting driving performance in older drivers with and without cataracts, ascertaining whether the objective measurement of intraocular scattering should be considered in assessment procedures for older drivers. This cross-sectional study involved a total of 20 older drivers (10 patients with bilateral cataracts and 10 control subjects). All participants were examined for visual acuity, contrast sensitivity, visual discrimination capacity, and intraocular scattering. Driving performance was also tested using a driving simulator. To study the relationship between visual parameters and driving performance, a correlation analysis and regression model were used. Drivers with cataracts showed a significantly impaired (p<0.05) visual function, with an Objective Scattering Index (OSI) 3.5 times greater than the control group. Driving performance was also significantly worse (p<0.05) in drivers with cataracts, reflected by a notable deterioration in lane keeping. The correlation analysis showed significant associations between driving performance and all the visual parameters studied. Finally, the regression model revealed that the OSI was the best predictor of driving performance, accounting for 51.3% of its variance. Visual function and driving performance are markedly deteriorated when cataracts are present. Our results demonstrate that the objective scattering index (OSI) has a high predictive power when it comes to simulated driving performance in older drivers, both with and without cataracts, suggesting that scatter measurements could be important in helping better understand visual limitations in older drivers.

An Automated Water Task to Test Visual Discrimination Performance, Adaptive Strategies and Stereotyped Choices in Freely Moving Mice.

We describe an automated training/testing system for adult mice that allows reliable quantification of visual discrimination capacities, adaptive swimming strategies, and stereotyped choices with minimal human intervention. The experimental apparatus consists of a hexagonal swimming pool with an internal decision zone leading to three interior arms with two software-controlled platforms inside of each arm. Each experimental trial consists in projecting a “positive” conditioned discriminative stimulus (SD) in one randomly chosen arm, whereas the other two arms project non-reinforced stimuli (the delta stimuli, SΔ). By employing a classical behavioral training schedule, the mice learn to swim toward the arm that displays the SD, because it predicts the presence of two elevated platforms located symmetrically to the left and right side of the projecting monitor. Separate behavioral components for discriminative and stereotyped choice behavior can be identified through this geometric arrangement. In addition, the projection in real-time of either static or dynamic visual stimuli allows the usage of training programs contingent on current behavioral performance. We validated the system by characterizing the visual acuity and contrast sensitivities in a group of trained mice. By employing pharmacological manipulations, we found that the mice required an intact functioning of the primary visual cortex (V1) to solve the hexagonal pool. Overall, the automated training system constitutes a reliable, rapid, and inexpensive method to quantify visual capacities of mice. It can be used to characterize visual and non-visual factors of choice behavior. It can also be combined with manipulations of visual experience and pharmacological micro-infusions to investigate integrated brain function and learning processes in adult mice over consecutive days.

Stereopsis Simulating Small-Aperture Corneal Inlay and Monovision Conditions.

To analyze stereoscopic vision under a broad range of experimental conditions simulating small-aperture corneal inlay and monovision conditions. A total of 10 patients participated in the study. The anisocoria generated by corneal inlays was simulated by using a small-aperture contact lens fitted on the non-dominant eye. Visual acuity, contrast sensitivity function, visual discrimination capacity (halo perception), and stereoacuity tests were performed under natural conditions or when the non-dominant eye wore the small-aperture contact lens under two conditions: induced anisocoria and induced anisocoria combined with monovision (using two add-powers: +0.75 and +1.25 diopters [D]). Stereoscopic vision and binocular summation were analyzed under those experimental conditions and for far, intermediate, and near vision. The results showed a deterioration in stereoacuity with respect to natural conditions, being significant mainly for near and intermediate distances. Results with other visual functions showed a deterioration of the binocular summation and therefore of visual performance, although not in a generalized way for all distances. Binocular visual acuity under the conditions that used the small-aperture contact lens was comparable to that of the natural eye. The deterioration of stereopsis and other binocular functions found in this study may be acceptable for patients who had this surgical technique because it is similar to the deterioration found in other surgical procedures of emmetropization. [J Refract Surg. 2018;34(7):482-488.].

Visual Search Performance in Patients with Vision Impairment: A Systematic Review

ABSTRACTPurpose: Patients with visual impairment are constantly facing challenges to achieve an independent and productive life, which depends upon both a good visual discrimination and search capacities. Given that visual search is a critical skill for several daily tasks and could be used as an index of the overall visual function, we investigated the relationship between vision impairment and visual search performance.Methods: A comprehensive search was undertaken using electronic PubMed, EMBASE, LILACS, and Cochrane databases from January 1980 to December 2016, applying the following terms: “visual search”, “visual search performance”, “visual impairment”, “visual exploration”, “visual field”, “hemianopia”, “search time”, “vision lost”, “visual loss”, and “low vision”. Two hundred seventy six studies from 12,059 electronic database files were selected, and 40 of them were included in this review.Results: Studies included participants of all ages, both sexes, and the sample sizes ranged from 5 to 199 participants. Visual impairment was associated with worse visual search performance in several ophthalmologic conditions, which were either artificially induced, or related to specific eye and neurological diseases.Conclusions: This systematic review details all the described circumstances interfering with visual search tasks, highlights the need for developing technical standards, and outlines patterns for diagnosis and therapy using visual search capabilities.

The range of stereoscopic perception: influence of binocular summation, interocular differences in optical quality and halo perception

The study of the visual function and optical quality of the eye has become a fundamental aim in the characterization of visual performance, especially in binocular vision, as this is our natural state of visual perception and because of its importance in clinical applications. Interocular asymmetry affects visual performance, and therefore its effect on different visual functions and stereopsis is of interest. In this work, we analyse interocular differences in optical quality (higher order aberrations and Strehl ratio) on the maximum disparity (the total range of stereoscopic perception) under mesopic conditions. We also analyse the relationship between the maximum disparity and the visual-discrimination capacity (halo perception) or binocular summation. The results in normal observers show a deterioration of the range of stereoscopic perception with the interocular differences in optical quality and with a higher perception of halos. Regarding the binocular summation for the visual functions studied, a positive correlation with the maximum disparity is found.

Visual Discrimination Increase by Yellow Filters in Retinitis Pigmentosa.

The objective of this study was to evaluate, by halometry and under low illumination conditions, the effects of short-wavelength light absorbance filters on visual discrimination capacity in retinitis pigmentosa patients. This was an observational, prospective, analytic, and transversal study on 109 eyes of 57 retinitis pigmentosa patients with visual acuity better than 1.25 logMAR. Visual disturbance index (VDI) was determined using the software Halo 1.0, with and without the interposition of filters which absorb (totally or partially) short-wavelength light between 380 and 500 nm. A statistically significant reduction in the VDI values determined using filters which absorb short-wavelength light was observed (p < 0.0001). The established VDIs in patients with VA logMAR <0.4 were 0.30 ± 0.05 (95% CI, 0.26-0.36) for the lens alone, 0.20 ± 0.04 (95% CI, 0.16-0.24) with the filter that completely absorbs wavelengths shorter than 450 nm, and 0.24 ± 0.04 (95% CI, 0.20-0.28) with the filter that partially absorbs wavelengths shorter than 450 nm, which implies a 20 to 33% visual discrimination capacity increase. In addition, a decrease of VDI in at least one eye was observed in more than 90% of patients when using a filter. Short-wavelength light absorbance filters increase visual discrimination capacity under low illumination conditions in retinitis pigmentosa patients. Use of such filters constitutes a suitable method to improve visual quality related to intraocular light visual disturbances under low illumination conditions in this group of patients.

Binocular summation and visual function with induced anisocoria and monovision.

The advances in new techniques for correcting presbyopia, such as a small aperture combined with monovision, require an in-depth study of binocular aspects. In this work, we have studied binocular visual performance of 12 subjects after inducing different degrees of anisocoria combined with two different add powers in the non-dominant eye. We have analysed visual performance in terms of the visual-discrimination capacity (a function to evaluate the strength of bothersome halos) and the contrast-sensitivity. The results show a deterioration of the binocular vision when inducing anisocoria and with any add power, with a higher perception of halos, a lower contrast sensitivity and poorer binocular summation of these visual functions on increasing anisocoria. This deterioration is clinically acceptable in the case of low add power, since positive binocular summation is maintained in contrast sensitivity, and visual discrimination is not altered.

Toward a new computer-based and easy-to-use tool for the objective measurement of motivational states in humans: a pilot study

The experimental methods currently used for assessing motivational processes in humans have two major limitations. Some of them rely on global subjective assessments while others evaluate these processes using food-related tasks often coupled with functional neuroimaging techniques that have however limited availability and important associated costs. Here we propose a novel experimental computer-generated and easy-to-use tool primarily based on the presentation of food images and designed to provide a quantitative and objective measurement of motivational states in humans. Two tasks evaluating respectively visual and time discrimination capacities were developed and tested on a sample of 30 healthy subjects. The subjects were asked to compare a food stimulus (food picture in color) and its devalued counterpart (same image in grayscale), at each trial, assessing either the size (task A) or the duration of presentation (task B). Geometric figures presented in color or grayscale were used as controls. The subjects were invited to perform tasks A and B during three separate experimental sessions, one under fasting and two under satiety. Relative to their devalued counterparts, the food images were judged significantly greater in size and shorter in time of presentation in fasting than in satiety. In fasting, the size and the time of presentation for the food images were respectively estimated significantly greater and shorter than for the control images when compared to their respective devalued counterparts. Conversely, there was no overall change in the perception of size or duration of presentation for the control images between fasting and satiety conditions. Our findings support that hunger specifically affects the perception of visual food stimuli, and suggest that this novel computer-based test is potentially useful for the study of motivational states in human diseases that are characterized by serious disturbances in reward processing.

Retinal-image quality and night-vision performance after alcohol consumption.

Purpose. To evaluate the influence of alcohol consumption on the retinal-image quality and visual performance under surrounding low-illumination conditions. Methods. A volunteer sample of 67 subjects was analyzed. Optical quality of the eye was evaluated by means of the Strehl ratio, the Objective Scattering Index (OSI), and the tear-film quality. We used the visual disturbance index (VDI) to evaluate visual performance under low-illumination conditions and we measured the pupil size under these conditions. The tear-film volume was also measured. All measurements were made before and after alcohol consumption and patients were classified into two groups depending on their breath alcohol content (BrAC): low-alcohol (BrAC < 0.25 mg/L) and high-alcohol content (BrAC ≥ 0.25 mg/L). Results. The VDI was significantly higher after alcohol consumption: the higher the BrAC, the higher the deterioration of the visual discrimination capacity. The pupil size increased significantly for the high-BrAC group. Parameters evaluating optical quality deteriorated after alcohol consumption. Conclusion. The visual performance under low-illumination conditions and the retinal-image quality were deteriorated after alcohol consumption, especially for the high-alcohol group. Furthermore, some physiological changes were observed under effects for high-alcohol contents, such as an increase in the pupil size and disturbances in the tear film, which deteriorated optical quality.

Controlled variations in stimulus similarity during learning determine visual discrimination capacity in freely moving mice

The mouse is receiving growing interest as a model organism for studying visual perception. However, little is known about how discrimination and learning interact to produce visual conditioned responses. Here, we adapted a two-alternative forced-choice visual discrimination task for mice and examined how training with equiprobable stimuli of varying similarity influenced conditioned response and discrimination performance as a function of learning. Our results indicate that the slope of the gradients in similarity during training determined the learning rate, the maximum performance and the threshold for successful discrimination. Moreover, the learning process obeyed an inverse relationship between discrimination performance and discriminative resolution, implying that sensitivity within a similarity range cannot be improved without sacrificing performance in another. Our study demonstrates how the interplay between discrimination and learning controls visual discrimination capacity and introduces a new training protocol with quantitative measures to study perceptual learning and visually-guided behavior in freely moving mice.

Quantifying age-related differences in visual-discrimination capacity: Drivers with and without visual impairment

The aim of this study is to examine the effects of aging as well as visual impairment on retinal-image quality and visual performance in drivers. We use a new visual test called Halo v1.0 software for quantifying the discrimination capacity, an important visual function for evaluating the visual disturbances perceived by the observer. The study included 55 subjects with normal vision and 15 older subjects with cataracts. All subjects were examined for visual acuity, contrast sensitivity, visual-discrimination capacity and optical quality. Subjects also completed a subjective Driving Habits Questionnaire (DHQ). Older drivers with and without visual impairment showed significantly (p < 0.05) worse visual performance and deteriorated retinal-image quality, even when their binocular visual acuity was ≥20/25. In conclusion, some visual functions are considerably diminished in older drivers, even when visual acuity is sufficient to get or renew a driver's license. Halo software enables easy quantification of night-vision disturbances such as halos, which could impede the detection of pedestrians, cyclists, or traffic signals, thereby making this system advisable in clinical practice, e.g. in the requirements for a driver's license, particularly for older drivers.

Visual quality after monovision correction by laser in situ keratomileusis in presbyopic patients

To evaluate visual quality after laser in situ keratomileusis (LASIK) performed to achieve monovision in presbyopic patients. Laboratory of Vision Sciences and Applications, Department of Optics, University of Granada, Granada, and Clínica Novovisión, Madrid, Spain. Cohort study. Laser in situ keratomileusis was performed with the Allegretto Wave Eye-Q 400 Hz laser. The dominant eye was corrected for far vision and the nondominant eye for near vision by targeting -1.25 diopters of myopia. The F-CAT algorithm was programmed targeting a postsurgical corneal asphericity of -0.80 in the dominant eye and -1.00 in the nondominant eye. Visual acuity, contrast sensitivity function, ocular aberrations, stereoacuity, the scattering index, and the visual-discrimination capacity were analyzed preoperatively and 3 months postoperatively. The study enrolled 25 patients (50 eyes) with a mean age of 49.3 years ± 4.5 (SD). Postoperatively, more than 90% of patients had a binocular uncorrected distance and near visual acuity of 0.0 logMAR or better, although the contrast sensitivity function diminished, especially in the nondominant eye and with binocular vision. Stereoacuity was significantly worse in all patients (P<.001). The visual discrimination capacity declined in nondominant eyes and under binocular conditions (P<.005); no significant changes occurred in dominant eyes (P=.614). In all eyes, the mean objective scatter index value increased postoperatively, but not significantly (P>.05). Monovision correction by LASIK improved functional near vision in presbyopic patients. Although visual acuity was good for far vision, contrast sensitivity and stereoacuity diminished significantly.

Optical Quality and Visual Discrimination Capacity After Myopic LASIK With a Standard and Aspheric Ablation Profile

To determine whether the eye's optical quality is correlated to the visual discrimination capacity of patients treated with LASIK using two different ablation algorithms. Visual discrimination was evaluated by the disturbance index under low illumination (Halo v1.0 software, Laboratory of Vision Sciences and Applications) in two groups of patients who underwent LASIK with two different ablation algorithms using the Allegretto Wave Eye-Q 400 Hz laser (WaveLight AG). In the first group (standard group; 30 eyes), corneal ablations were performed with the standard algorithm (preoperative spherical equivalent refraction -3.20±1.70 diopters [D]). In the second group (Q-optimized group; 38 eyes; spherical equivalent refraction -3.40±1.90 D), the ablations were made with the Q-optimized (F-CAT) algorithm. Optical quality of the eye was calculated by the Strehl ratio measured with a double-pass device (OQAS, Visiometrics SL). After LASIK, both the Strehl ratio as well as visual discrimination capacity diminished in both groups, although the changes were significantly greater in the standard group than in the Q-optimized group. A high correlation was found between the Strehl ratio and the disturbance index in patients who underwent LASIK, regardless of the ablation algorithm applied. Optical and visual deterioration were greater after standard ablation.

Transient interference of right hemispheric function due to automatic emotional processing

We examined the effects of emotional stimuli on right and left hemisphere detection performance in a hemifield visual discrimination task. A group of 18 healthy subjects were asked to discriminate between upright and inverted triangles (target). Targets were randomly presented in the left or right visual hemifield (150 ms target duration). A brief emotional picture (pleasant or unpleasant; 150 ms stimulus duration) or neutral picture selected from the International Affective Picture System was randomly presented either in the same (47%) or the opposite (47%) spatial location to the subsequent target. Emotional or neutral stimuli offset 150 ms prior to the subsequent target. Subjects were instructed to ignore the pictures and respond to the targets as quickly and accurately as possible. Independent of field of presentation, emotional stimuli prolonged reaction times ( P<0.01) to LVF targets, with unpleasant stimuli showing a greater effect than pleasant stimuli. The current study shows that brief emotional stimuli selectively impair right hemispheric visual discrimination capacity. The findings suggest automatic processing of emotional stimuli captures right hemispheric processing resources and transiently interferes with other right hemispheric functions.