Generic and customized digital image enhancement filters for the visually impaired

This study compares the effectiveness of various image enhancement filters for improving the perceived visibility of coloured digital natural images for people with visual impairment. Generic filters were compared with Peli's adaptive enhancement and adaptive thresholding and custom-devised filters based on each subject's contrast sensitivity loss. Subjects with low vision made within filter rankings followed by between filter ratings. In general, subjects preferred filters with lower gains. Unsharp masking resulted in a significant increase in perceived visibility for some image types (p < or = 0.05) while Peli's adaptive enhancement, edge enhancement and histogram equalization resulted in borderline improvements. Adaptive thresholding and the custom devised filter did not result in overall improvements in perceived visibility.     

Clinical Assessment of Stereoacuity and 3-D Stereoscopic Entertainment

Abstract

Background/Aims: The perception of compelling depth is often reported in individuals where no clinically measurable stereoacuity is apparent. We aim to investigate the potential cause of this finding by varying the amount of stereopsis available to the subject, and assessing their perception of depth viewing 3-D video clips and a Nintendo 3DS.

Methods: Monocular blur was used to vary interocular VA difference, consequently creating 4 levels of measurable binocular deficit from normal stereoacuity to suppression. Stereoacuity was assessed at each level using the TNO, Preschool Randot®, Frisby, the FD2, and Distance Randot®. Subjects also completed an object depth identification task using the Nintendo 3DS, a static 3DTV stereoacuity test, and a 3-D perception rating task of 6 video clips.

Results: As intraocular VA differences increased, stereoacuity of the 57 subjects (aged 16–62 years) decreased (eg, 110”, 280”, 340”, and suppression). The ability to correctly identify depth on the Nintendo 3DS remained at 100% until suppression of one eye occurred. The perception of a compelling 3-D effect when viewing the video clips was rated high until suppression of one eye occurred, where the 3-D effect was still reported as fairly evident.

Conclusion: If an individual has any level of measurable stereoacuity, the perception of 3-D when viewing stereoscopic entertainment is present. The presence of motion in stereoscopic video appears to provide cues to depth, where static cues are not sufficient. This suggests there is a need for a dynamic test of stereoacuity to be developed, to allow fully informed patient management decisions to be made.     

Visual motion detection sensitivity is enhanced by an orthogonal motion aftereffect

A recent study (H. Takemura & I. Murakami, 2010) showed enhancement of motion detection sensitivity by an orthogonal induced motion, suggesting that a weak motion component can combine with an orthogonal motion component to generate stronger oblique motion perception. Here we examined how an orthogonal motion aftereffect (MAE) affects motion detection sensitivity. After adaptation to vertical motion, a Gabor patch barely moving leftward or rightward was presented. As a result of an interaction between horizontal physical motion and a vertical MAE, subjects perceived the stimulus as moving obliquely. Subjects were asked to judge the horizontal direction of motion irrespective of the vertical MAE. The performance was enhanced when the Gabor patch was perceived as moving obliquely as the result of a weak MAE. The enhancement effect depended on the strength of the MAE for each subject rather than on the temporal frequency of the adapting stimulus. These results suggest that weak motion information that is hard to detect can interact with orthogonal adaptation and yield stronger oblique motion perception, making directional judgment easier. Moreover, the present results indicate that the enhancement effect of orthogonal motion involves general motion integration mechanisms rather than a specific mechanism only applicable to a particular type of illusory motion.     

Visual motion mechanisms under low retinal illuminance revealed by motion reversal

The aim of this study is to determine what kinds of motion mechanisms operate at low luminance levels. We used a motion reversal phenomenon in which the perceived direction of motion is reversed when a blank inter-stimulus interval (ISI) frame is inserted between two image frames of similar mean luminance. At low luminance levels, we found that motion reversal was perceived when the moving pattern was presented in the retinal periphery, but no motion reversal was observed when the stimulus was presented in the central retina. When a large stimulus that covers both central and peripheral visual fields was presented, motion reversal did not occur. We conclude that as retinal illuminance decreases, the relative contribution of a feature-tracking mechanism in the central retina becomes larger, while motion perception in the peripheral retina continues to depend on a biphasic, first-order motion mechanism. When both central and peripheral visual fields are stimulated simultaneously, the motion mechanism that dominates in the central retina determines the perceived direction of motion at low luminance levels.     

Assessing visual activities of daily living in the visually impaired

Purpose:  Visual function assessment questionnaires ask people to rate the difficulty they have performing visual activities of daily living (ADLs). This study examines the relationship between self-reported difficulty and actual performance in such ADLs.
Methods:  Twenty four subjects with established bilateral visual impairment initially self-reported their difficulty with 4 ADLs (reading newsprint, reading medicine labels, identifying coins and entering a PIN). Subjects' performance in variants of these ADLs was then assessed by measuring the time taken; by an observer rating subjects' performance; and by the subject rating their perceived difficulty with each specific task. Clinical visual function parameters were also assessed.
Results:  Varying the assessed ADL task changed how well the task correlated with self-reported difficulty. Clinical visual function, rate of task completion and observer rating of difficulty all correlated significantly with self-reported difficulty, explaining up to 69% of the variance in self-reported difficulty. However, despite replicating the ADLs as closely as possible in the clinical environment the perceived difficulty of the clinic tasks was rated as being less than the initial self-reported difficulty of the real-world task.
Conclusions:  The task variant used is important when assessing functional visual performance directly. Timed and observer-rated methods of assessment can be appropriate for assessing functional vision. In this small study, the disconnect between self-reported visual difficulty and perceived or assessed difficulty suggests that functional performance is not the only factor influencing self-report, and responses to visual function assessment questionnaires should be interpreted in this light.     

Visual quality assessment after presbyopic laser in-situ keratomileusis

AIM: To assess visual quality after presbyopia correction using an aspheric ablation profile and a micro-monovision protocol. METHODS: This is a retrospective interventional study. Fifty-four eyes of 27 patients (mean age, 50.2±7.5y) who underwent presbyopia correction with an aspheric micro-monovision protocol were enrolled. The values of modulation transfer function (MTF) cutoff frequency, Strehl ratio, objective scattering index (OSI) and accommodation range were quantitatively assessed using the HD analyzer. Preoperative and postoperative contrast sensitivity (CS) at far (2.5 m) and near (40 cm) distance and higher-order aberrations (HOAs) were analyzed. Subjective visual satisfaction was evaluated by self-reported questionnaire regarding optical visual symptoms. RESULTS: One year after presbyopia correction, no significant differences were found in the MTF cutoff frequency, Strehl ratio and OSI, however, the HD analyzer accommodation range significantly differed postoperatively (P=0.004). Postoperative CS at 12 and 18 cpd at near showed statistically significant improvement (P=0.020 and 0.008, respectively). Visual performance by self-reported questionnaire revealed satisfactory results in terms of subjective visual quality improvement. CONCLUSION: Objective optical quality parameters show good visual outcomes. Subjective visual quality assessed by self-reported questionnaire in the presbyopia correction group show satisfactory results.     

【In Press】 Visual quality assessment after presbyopic laser in-situ keratomileusis

AIM: To assess visual quality after presbyopia correction using an aspheric ablation profile and a micro-monovision protocol. METHODS: This is a retrospective interventional study. Fifty-four eyes of 27 patients (mean age, 50.2±7.5y) who underwent presbyopia correction with an aspheric micro-monovision protocol were enrolled. The values of modulation transfer function (MTF) cutoff frequency, Strehl ratio, objective scattering index (OSI) and accommodation range were quantitatively assessed using the HD analyze. Preoperative and postoperative contrast sensitivity (CS) at far (2.5 m) and near (40 cm) distance and higher-order aberrations (HoAs) were analyzed. Subjective visual satisfaction was evaluated by self-reported questionnaire regarding optical visual symptoms. RESULTS: One year after presbyopia correction, no significant differences were found in the MTF cutoff frequency, Strehl ratio and OSI, however, the HD analyzer accommodation range significantly differed postoperatively (P=0.004). Postoperative CS at 12 and 18 cpd at near showed statistically significant improvement (P=0.020 and 0.008, respectively). Visual performance by self-reported questionnaire revealed satisfactory results in terms of subjective visual quality improvement. CONCLUSION: Objective optical quality parameters show good visual outcomes. Subjective visual quality assessed by self-reported questionnaire in the presbyopia correction group show satisfactory results.     

Visual Performance and Optical Quality after Implantation of a New Generation Monofocal Intraocular Lens

PurposeTo evaluate the performance of two intraocular lenses (IOLs). The new monofocal IOL using a higher-order aspheric optic (Tecnis Eyhance ICB00) was compared to a standard monofocal IOL (Tecnis monofocal ZCB00) of the identical platform and material.MethodsThe medical records of the patients who had undergone cataract surgery with implantation of either the ZCB00 or the ICB00 in the dominant eye from March 2020 to August 2020 and with available data from the 3-month visit were reviewed. Subjects with ocular comorbidities or corneal astigmatism greater than 1.00 diopters were excluded. The uncorrected near, intermediate, distance visual acuity and corrected distance visual acuity were the main outcome measures. Optical quality parameters measured using an optical quality analysis system, clinical records including age, sex, laterality, ocular dominance, and information related to refractory errors was also collected. Parameters related to the refractory errors were all uniformly based on the Barrett Universal II formula.ResultsOf the 197 recruited patients, 111 and 86 were implanted with the ICB00 and ZCB00, respectively. No statistically significant differences in baseline parameters were observed between the two groups. While no statistically significant differences in distance visual acuity or optical quality were found between the two groups, compared to the ZCB00 group, the ICB00 group showed significantly higher intermediate visual acuity (p < 0.001) and near visual acuity (p < 0.05) 3 months postoperatively.ConclusionsICB00 provided superior intermediate vision and comparable distance performance and photic phenomena compared to a standard monofocal IOL.     

Neural latencies do not explain the auditory and audio-visual flash-lag effect

A brief flash presented physically aligned with a moving stimulus is perceived to lag behind, a well studied phenomenon termed the Flash-Lag Effect (FLE). It has been recently shown that the FLE also occurs in audition, as well as cross-modally between vision and audition. The present study has two goals: to investigate the acoustic and cross-modal FLE using a random motion technique; and to investigate whether neural latencies may account for the FLE in general. The random motion technique revealed a strong cross-modal FLE for visual motion stimuli and auditory probes, but not for the other conditions. Visual and auditory latencies for stimulus appearance and for motion were measured with three techniques: integration, temporal alignment and reaction times. All three techniques showed that a brief static acoustic stimulus is perceived more rapidly than a brief static visual stimulus, while a sound source in motion is perceived more slowly than a comparable visual stimulus. While the results of these three techniques agreed closely with each other, they were exactly opposite that required to account for the FLE by neural latencies. We conclude that neural latencies do not, in general, explain the flash-lag effect. Rather, our data suggest that neural integration times are more important.     

Motion perception during dichoptic viewing of moving random-dot stereograms

The relation between binocular and monocular motion perception was investigated. A random-dot stereogram (30 X 30 deg arc), containing a central figure seen in front of the background in stereoscopic vision, was viewed dichoptically by human subjects without a fixed visual frame of reference. The images seen by the right and left eye were moved laterally according to a triangular wave form, in counterphase, but with variable amplitude ratios. Under this condition only purely lateral movement and no motion in depth of the stereogram as a whole was perceived, while stereoscopic vision of the figure-background relation was maintained. The magnitude of the binocularly perceived lateral motion, signalled by manual tracking of the perceived displacement, equalled the algebraic mean of the monocular motion percepts. As a special case, when the two images forming the stereogram were moved with equal velocities but in opposite directions they were perceived as a completely stationary, fused image in stereoscopic depth. Only the addition of a stationary reference (a bar or grating seen by both eyes) resulted in the perception of motion in depth. We conclude that a visual frame of reference is essential for perception of motion in depth but not for perception of lateral movements. Moreover, it seems likely that not absolute binocular disparity (retinal locus differences) but relative binocular disparity (differences in angular distance between two or more corresponding features in the two retinal images) is a cue for perception of depth.     

Visual function and ocular status of children with hearing impairment in Oman: A case series

Visual functions of children with hearing disability were evaluated in a school of Muscat, Oman in 2006. Two hundred and twenty-three children were tested for near vision, distant vision, contrast sensitivity, color vision, field of vision, motion perception and crowding. Profound and severe hearing loss was noted in 161 and 63 students respectively. Thirty-five (81%) students with refractive error were using spectacles. Color vision and field of vision was defective in one student each. In 286 (64.1%) eyes, contrast sensitivity was defective. Abnormal contrast sensitivity was not associated with the severity of hearing loss [RR = 1.04 (95% CI 0.91 to 1.29)]. Children with hearing impairment should be assessed for visual functions. Refractive error and defect in contrast sensitivity were unusually high among these children. In addition to visual aids, we recommend environmental changes to improve illumination and contrast to improve the quality of life of such children with double disability.     

Visual and psychomotor performance of elite,intermediate and novice table tennis competitors

The purpose of this cross-sectional study was to determine whether measures on a selected groups of visual and psychomotor variables distinguished between groups of elite, intermediate and novice table tennis players. The variables included commonly of Melbourne measured clinical functions such as static visual acuity, extent of visual field and oculomotor balance and more experimental visual tasks such as recognition of, peripheral targets, saccadic latency and dynamic visual acuity. Psychomotor performance was assessed by measures of simple reaction time, choice response time and hand movement time. Although elite level competitors had significantly better dynamic visual acuity, a wider visual field and superior recognition of peripheral targets compared to less skilled competitors, the magnitude, or practical significance of these differences was not great and individually accounted for less than 5 per cent of population variance. Elite competitors had significantly faster psychomotor responses than novice players with die skill variables individually accounting for between 21 per cent and 62 per cent of population variance in psychomotor performance. These results indicate that the psychomotor parameters could be a useful part of a test battery for talent identification amongst table tennis players.     

Second-order motion shifts perceived position

Many studies have documented that first-order motion influences perceived position. Here, we show that second-order (contrast defined) motion influences the perceived positions of stationary objects as well. We used a Gabor pattern as our second-order stimulus, which consisted of a drifting sinusoidal contrast modulation of a dynamic random-dot background; this second-order carrier was enveloped by a static Gaussian contrast modulation. Two vertically aligned Gabors had carrier motion in opposite directions. Subjects judged the relative positions of the Gabors' static envelopes. The positions of the Gabors appeared shifted in the direction of the carrier motion, but the effect was narrowly tuned to low temporal frequencies across all tested spatial frequencies. In contrast, first-order (luminance defined) motion shifted perceived positions across a wide range of temporal frequencies, and this differential tuning could not be explained by differences in the visibility of the patterns. The results show that second-order motion detection mechanisms contribute to perceived position. Further, the differential spatial and temporal tuning of the illusion supports the idea that there are distinct position assignment mechanisms for first and second-order motion.     

The effect of retinal illuminance on visual motion priming

The perceived direction of a directionally ambiguous stimulus is influenced by the moving direction of a preceding priming stimulus. Previous studies have shown that a brief priming stimulus induces positive motion priming, in which a subsequent directionally ambiguous stimulus is perceived to move in the same direction as the primer, while a longer priming stimulus induces negative priming, in which the following ambiguous stimulus is perceived to move in the opposite direction of the primer. The purpose of this study was to elucidate the underlying mechanism of motion priming by examining how retinal illuminance and velocity of the primer influences the perception of priming. Subjects judged the perceived direction of 180-deg phase-shifted (thus directionally ambiguous) sine-wave gratings displayed immediately after the offset of a primer stimulus. We found that perception of motion priming was greatly modulated by the retinal illuminance and velocity of the primer. Under low retinal illuminance, positive priming nearly disappeared even when the effective luminance contrast was equated between different conditions. Positive priming was prominent when the velocity of the primer was low, while only negative priming was observed when the velocity was high. These results suggest that the positive motion priming is induced by a higher-order mechanism that tracks prominent features of the visual stimulus, while a directionally selective motion mechanism induces negative motion priming.     

The impact of image degradation and temporal dynamics on sustained attention

Many clinical populations that have sustained attention deficits also have visual deficits. Therefore, it is necessary to understand how the quality of visual input and different forms of image degradation can contribute to worse performance on sustained attention tasks, particularly those with dynamic and complex visual stimuli. This study investigated the impact of image degradation on an adapted version of the gradual-onset continuous performance task (gradCPT), where participants must discriminate between gradually fading city and mountain scenes. Thirty-six normal-vision participants completed the task, which featured two blocks of six resolution and contrast levels. Subjects either completed a version with gradually fading or static image presentations. The results show decreases in image resolution impair performance under both types of temporal dynamics, whereas performance is only impaired under gradual temporal dynamics for decreases in image contrast. Image similarity analyses showed that performance has a higher association with an observer''s ability to gather an image''s global spatial layout (i.e. gist) than local variations in pixel luminance, particularly under gradual image presentation. This work suggests that gradually fading attention paradigms are sensitive to deficits in primary visual function, potentially leading to these issues being misinterpreted as attentional failures.     

Neural correlates of intra-saccadic motion perception

Retinal motion of the visual scene is not consciously perceived during ocular saccades in normal everyday conditions. It has been suggested that extra-retinal signals actively suppress intra-saccadic motion perception to preserve stable perception of the visual world. However, using stimuli optimized to preferentially activate the M-pathway, Castet and Masson (2000) demonstrated that motion can be perceived during a saccade. Based on this psychophysical paradigm, we used electroencephalography and eye-tracking recordings to investigate the neural correlates related to the conscious perception of intra-saccadic motion. We demonstrated the effective involvement during saccades of the cortical areas V1-V2 and MT-V5, which convey motion information along the M-pathway. We also showed that individual motion perception was related to retinal temporal frequency.     

Matching convolved images to optically blurred images on the retina

Convolved images are often used to simulate the effect of ocular aberrations on image quality, where the retinal image is simulated by convolving the stimulus with the point spread function derived from the subject''s aberrations. However, some studies have shown that convolved images are perceived far more degraded than the same image blurred with optical defocus. We hypothesized that the positive interactions between the monochromatic and chromatic aberrations in the eye are lost in the convolution process. To test this hypothesis, we evaluated optical and visual quality with natural optics and with convolved images (on-bench, computer simulations, and visual acuity [VA] in subjects) using a polychromatic adaptive optics system with monochromatic (555 nm) and polychromatic light (WL) illumination. The subject''s aberrations were measured using a Hartmann Shack system and were used to convolve the visual stimuli, using Fourier optics. The convolved images were seen through corrected optics. VA with convolved stimuli was lower than VA through natural aberrations, particularly in WL (by 26% in WL). Our results suggest that the systematic decrease in visual performance with visual acuity and retinal image quality by simulation with convolved stimuli appears to be primarily associated with a lack of favorable interaction between chromatic and monochromatic aberrations in the eye.     

How do visual skills relate to action video game performance?

It has been claimed that video gamers possess increased perceptual and cognitive skills compared to non-video gamers. Here, we examined to which extent gaming performance in CS:GO (Counter-Strike: Global Offensive) correlates with visual performance. We tested 94 players ranging from beginners to experts with a battery of visual paradigms, such as visual acuity and contrast detection. In addition, we assessed performance in specific gaming skills, such as shooting and tracking, and administered personality traits. All measures together explained about 70% of the variance of the players’ rank. In particular, regression models showed that a few visual abilities, such as visual acuity in the periphery and the susceptibility to the Honeycomb illusion, were strongly associated with the players’ rank. Although the causality of the effect remains unknown, our results show that high-rank players perform better in certain visual skills compared to low-rank players.     

Motion-form interaction: Motion and form aftereffects induced by distorted static natural scenes

Spatially varying distortions (SVDs) are common artifacts of spectacles like progressive additional lenses (PALs). To habituate to distortions of PALs, the visual system has to adapt to distortion-induced image alterations, termed skew adaptation. But how this visual adjustment is achieved is largely unknown. This study examines the properties of visual adaptation to distortions of PALs in natural scenes. The visual adaptation in response to altered form and motion features of the natural stimuli were probed in two different psychophysical experiments. Observers were exposed to distortions in natural images, and form and motion aftereffects were tested subsequently in a constant stimuli procedure where subjects were asked to judge the skew, or the motion direction of an according test stimulus.Exposure to skewed natural stimuli induced a shift in perceived undistorted form as well as motion direction, when viewing distorted dynamic natural scenes, and also after exposure to static distorted natural images. Therefore, skew adaptation occurred in form and motion for dynamic visual scenes as well as static images. Thus, specifically in the condition of static skewed images and the test feature of motion direction, cortical interactions between motion-form processing presumably contributed to the adaptation process.In a nutshell, interfeature cortical interactions constituted the adaptation process to distortion of PALs. Thus, comprehensive investigation of adaptation to distortions of PALs would benefit from taking into account content richness of the stimuli to be used, like natural images.