The dependence of luminous efficiency on chromatic adaptation

Ocular accommodation and wavelength: The effect of longitudinal chromatic aberration on the stimulus-response curve

The longitudinal chromatic aberration (LCA) of the eye creates a chromatic blur on the retina that is an important cue for accommodation. Although this mechanism can work optimally in broadband illuminants such as daylight, it is not clear how the system responds to the narrowband illuminants used by many modern displays. Here, we measured pupil and accommodative responses as well as visual acuity under narrowband light-emitting diode (LED) illuminants of different peak wavelengths. Observers were able to accommodate under narrowband light and compensate for the LCA of the eye, with no difference in the variability of the steady-state accommodation response between narrowband and broadband illuminants. Intriguingly, our subjects compensated more fully for LCA at nearer distances. That is, the difference in accommodation to different wavelengths became larger when the object was placed nearer the observer, causing the slope of the accommodation response curve to become shallower for shorter wavelengths and steeper for longer ones. Within the accommodative range of observers, accommodative errors were small and visual acuity normal. When comparing between illuminants, when accommodation was accurate, visual acuity was worst for blue narrowband light. This cannot be due to the sparser spacing for S-cones, as our stimuli had equal luminance and thus activated LM-cones roughly equally. It is likely because ocular LCA changes more rapidly at shorter wavelength and so the finite spectral bandwidth of LEDs corresponds to a greater dioptric range at shorter wavelengths. This effect disappears for larger accommodative errors, due to the increased depth of focus of the eye.

Optical modelling of an accommodative light field display system and prediction of human eye responses

The spatio-angular resolution of a light field (LF) display is a crucial factor for delivering adequate spatial image quality and eliciting an accommodation response. Previous studies have modelled retinal image formation with an LF display and evaluated whether accommodation would be evoked correctly. The models were mostly based on ray-tracing and a schematic eye model, which pose computational complexity and inaccurately represent the human eye population's behaviour. We propose an efficient wave-optics-based framework to model the human eye and a general LF display. With the model, we simulated the retinal point spread function (PSF) of a point rendered by an LF display at various depths to characterise the retinal image quality. Additionally, accommodation responses to the rendered point were estimated by computing the visual Strehl ratio based on the optical transfer function (VSOTF) from the PSFs. We assumed an ideal LF display that had an infinite spatial resolution and was free from optical aberrations in the simulation. We tested points rendered at 0-4 dioptres of depths having angular resolutions of up to 4x4 viewpoints within a pupil. The simulation predicted small and constant accommodation errors, which contradict the findings of previous studies. An evaluation of the optical resolution on the retina suggested a trade-off between the maximum achievable resolution and the depth range of a rendered point where in-focus resolution is kept high. The proposed framework can be used to evaluate the upper bound of the optical performance of an LF display for realistically aberrated eyes, which may help to find an optimal spatio-angular resolution required to render a high quality 3D scene.

How well can today's tooth-colored dental restorative materials reproduce the autofluorescence of human teeth? - Ambition and reality!

OBJECTIVES

The autofluorescence of dental hard tissues has been known for over 100 years. Thus, manufacturers add fluorophores to dental restorative materials to improve the esthetic properties of these materials. So far, there has been no study evaluating the ability of these fluorophores to reproduce the autofluorescence of dental hard tissues.

MATERIALS AND METHODS

A total of 240 different color shades representing 17 different brands of fluorescent light-curing RBC and CAD/CAM restorative materials were analyzed with a monochromator-based microplate reader. Additionally, combined enamel-dentin specimens (n = 11) were analyzed as "gold standard". The total fluorescence (TF) and the physiologically relevant luminous efficiency function adjusted total fluorescence (TF_a ) were determined. The differences between the brands and the enamel-dentin specimens were further evaluated and visualized as contour plots.

RESULTS

Merely the TF_a of the brands CERASMART™, Filtek Supreme XTE™, KZR-CAD HD 2, and LuxaCam composite were not significantly different to the enamel-dentin specimens. The analysis of the contour plots revealed that even these four materials showed a fluorescence excess for the excitation wavelengths below about 400 nm and a deficit above this wavelength.

CONCLUSION

None of the materials analyzed in this study were able to reproduce the natural fluorescence spectrum of the enamel-dentin specimens.

CLINICAL SIGNIFICANCE

Unlike the statements and images of blue fluorescent materials in the manufacturers' brochures, none of the materials examined here is fully capable of reproducing the natural autofluorescence of teeth.

Selection of LED lighting systems for the reduction of the biodeterioration of speleothems induced by photosynthetic biofilms in the Nerja Cave (Malaga, Spain)

Electrical lighting favours the development of photosynthetic biofilms in caves which can induce biodeterioration in the colonized substrates. The use of specific lights as a limiting factor for biofilm growth could be effective in their control and represents an alternative to chemical methods since they can damage the substrate. However, studies about lighting and the photosynthetic activity of organisms in caves are scarce. In order to select the most effective LED light source in reducing photosynthesis and therefore, in reducing the growth rates of microalgae and cyanobacteria, four biofilms in the Nerja Cave were illuminated by several light emitted diodes (LEDs) with different spectral compositions and the photobiological responses were measured both by empirical and theoretical methodologies. The empirical approach was based on the photosynthetic efficiency, by measuring the in vivo chlorophyll a (Chl a) fluorescence and the theoretical approach was based on the photonic assimilation performance related to the proportion of the light quality used for photosynthesis, according to the action spectra for photosynthesis available in the literature. The photobiological responses showed differences between the empirical and theoretical approach mainly in biofilms dominated by cyanobacteria and red algae, probably because the available action spectra were not useful for monitoring these Nerja Cave biofilms. However, the expected spectral responses of photosynthesis were observed in green microalgal biofilms with maximum photosynthetic efficiency in red and blue light although the green light was also unexpectedly high. The high photosynthetic efficiency in green light could be explained by the predictable high chlorophyll content due to a very dark environment. The results were not conclusive enough for all the biofilm types to be able to recommend a specific lighting system for the photocontrol of biofilm expansion. Therefore, new action spectra for photosynthesis of the extremophile organisms of the Nerja Cave are required. This approach, based on theoretical and empirical methodologies, is a useful tool to obtain information to allow the design of the most adequate lighting systems to reduce photosynthetic activity and favour the conservation of the caves.

Restorative CAD/CAM materials in dentistry: analysis of their fluorescence properties and the applicability of the fluorescence-aided identification technique (FIT)

OBJECTIVES

This study investigated the fluorescence properties of the most commonly used fluorescent CAD/CAM materials for monolithic dental restorations and their suitability to perform the fluorescence-aided identification technique (FIT).

MATERIALS AND METHODS

A total of 175 different color shades (n = 1) from 13 CAD/CAM material brands were analyzed with a monochromator-based microplate reader. Additionally, dentin, enamel, and combined dentin-enamel specimens (respectively, n = 11) were analyzed for comparison purposes. The maximum fluorescence intensity, the corresponding excitation and emission wavelength, and the total fluorescence for the wavelength spectrum λ_ex = 395 nm - 415 nm used for FIT were determined.

RESULTS

All assessed CAD/CAM ceramics showed virtually no total fluorescence for the wavelength spectrum λ_ex = 395 nm - 415 nm used for FIT. CERASMART^TM, KZR-CAD HD 2, and LuxaCam Composite displayed total fluorescence values similar to that of the tooth hard substances. All other resin-based CAD/CAM materials showed a significantly higher total fluorescence than the tooth hard substances.

CONCLUSIONS

Apart from the mentioned exceptions, all CAD/CAM materials assessed could be suitable for the FIT, either because they are more fluorescent than hard tooth substances or because they do not fluoresce at all at the respective wavelength of λ_ex = 395 nm - 415 nm.

CLINICAL RELEVANCE

This study provides insight into the not yet well-known fluorescent properties of dental CAD/CAM materials. This knowledge is not only necessary to reproduce the fluorescence properties of natural teeth but also for the applicability of diagnostic fluorescence inducing techniques.

Methods for determining equiluminance in terms of L/M cone ratios

Heterochromatic flicker photometry (HFP), minimum motion (MM), and minimally distinct border (MDB) settings have often been used to determine equiluminance, a relative intensity setting for two chromaticities that, in theory, eliminates the responses of a luminance or achromatic psychophysical mechanism. These settings have been taken to reflect the relative contribution of the long (L) and medium (M) wavelength cones to luminance, which varies widely across individuals. The present study compares HFP, MM, and MDB using stimuli that do not modulate the short (S) wavelength cones, in both practiced and naïve observers. MDB was performed with both flashed and steadily viewed stimuli. Results are represented in the (∆L/L, ∆M/M) plane of cone contrast space. Considering both practiced and naïve observers, both MM and HFP had excellent within-subject precision and high test–retest reliability, whereas HFP also had low between-subject variability. The MDB tasks were less reliable and less precise. The mean L:M contrast ratios at equiluminance were lower for the two temporal tasks (HFP and MM) compared to the spatial tasks (MDB), perhaps consistent with the existence of multiple luminance mechanisms. Overall, the results suggest that the best method for determining equiluminance is HFP, with MM being a close second.

Fetal eye movements in response to a visual stimulus

INTRODUCTION

In 2D ultrasound, the lens of the fetal eye can be distinguished as white circles within the hypoechoic eyeball, and eye movements can be visualized from about 15 weeks' gestation. It has been shown that from 31 weeks gestational age the fetal sensory system is capable of directed vision if enough light is available.

METHODS

We have developed a light source for delivering visual stimuli to be seen by the fetal eye, using laser dot diodes emitting at 650 nm. The 2D component of 94 fetal ultrasound scans (mean gestational age 240 days), where the light stimulus was presented, was coded to determine whether the eyes moved in response to the stimuli independent of any head movement.

RESULTS

The light stimulus significantly provoked head and eye movements, but after the light was withdrawn the head stopped moving, yet the eyes continued to move.

CONCLUSION

This provides evidence for visual attention mechanisms that can be controlled through eye movements that are independent of head movements prior to birth.

A hierarchical model of perceptual multistability involving interocular grouping

Ambiguous visual images can generate dynamic and stochastic switches in perceptual interpretation known as perceptual rivalry. Such dynamics have primarily been studied in the context of rivalry between two percepts, but there is growing interest in the neural mechanisms that drive rivalry between more than two percepts. In recent experiments, we showed that split images presented to each eye lead to subjects perceiving four stochastically alternating percepts (Jacot-Guillarmod et al. Vision research, 133, 37-46, 2017): two single eye images and two interocularly grouped images. Here we propose a hierarchical neural network model that exhibits dynamics consistent with our experimental observations. The model consists of two levels, with the first representing monocular activity, and the second representing activity in higher visual areas. The model produces stochastically switching solutions, whose dependence on task parameters is consistent with four generalized Levelt Propositions, and with experiments. Moreover, dynamics restricted to invariant subspaces of the model demonstrate simpler forms of bistable rivalry. Thus, our hierarchical model generalizes past, validated models of binocular rivalry. This neuromechanistic model also allows us to probe the roles of interactions between populations at the network level. Generalized Levelt's Propositions hold as long as feedback from the higher to lower visual areas is weak, and the adaptation and mutual inhibition at the higher level is not too strong. Our results suggest constraints on the architecture of the visual system and show that complex visual stimuli can be used in perceptual rivalry experiments to develop more detailed mechanistic models of perceptual processing.

Model of parafoveal chromatic and luminance temporal contrast sensitivity of humans and monkeys

Rhesus monkeys are a valuable model for studies of primate visual contrast sensitivity. Their visual systems are similar to that of humans, and they can be trained to perform detection tasks at threshold during neurophysiological recording. However, the stimulus dependence of rhesus monkey contrast sensitivity has not been well characterized. Temporal frequency, color, and retinal eccentricity affect the contrast sensitivity of humans in reasonably well-understood ways. To ask whether these factors affect monkey sensitivity similarly, we measured detection thresholds of two monkeys using a two-alternative, forced-choice task and compared them to thresholds of two human subjects who performed the same task. Stimuli were drifting Gabor patterns that varied in temporal frequency (1-60 Hz), L- and M-cone modulation ratio, and retinal eccentricity (2°-14° from the fovea). Thresholds were fit by a model that assumed a pair of linear detection mechanisms: a luminance contrast detector and a red-green contrast detector. Analysis of model fits indicated that the sensitivity of these mechanisms varied across the visual field, but their temporal and spectral tuning did not. Human and monkey temporal contrast sensitivity was similar across the conditions tested, but monkeys were twofold less sensitive to low-frequency, luminance modulations.

Sensitivity to S-Cone Stimuli and the Development of Myopia

Purpose

Longitudinal chromatic aberration (LCA) is a color signal available to the emmetropization process that causes greater myopic defocus of short wavelengths than long wavelengths. We measured individual differences in chromatic sensitivity to explore the role LCA may play in the development of refractive error.

Methods

Forty-four observers were tested psychophysically after passing color screening tests and a questionnaire for visual defects. Refraction was measured and only subjects with myopia or hyperopia without severe astigmatism participated. Psychophysical detection thresholds for 3 cyc/deg achromatic, L-, M-, and S-cone-isolating Gabor patches and low-frequency S-cone increment (S+) and decrement (S-) blobs were measured. Parametric Pearson correlations for refractive error versus threshold were calculated and nonparametric bootstrap 95% percentage confidence intervals (BCIs) for r were computed.

Results

S-cone Gabor detection thresholds were higher than achromatic, L-, and M-cone Gabors. S-cone Gabor thresholds were higher than either S+ or S- blobs. These results are consistent with studies using smaller samples of practiced observers. None of the thresholds for the Gabor stimuli were correlated with refractive error (RE). A negative correlation with RE was observed for both S+ (r = -0.28; P = 0.06; BCI: r = -0.5, -0.04) and S- (r = -0.23; P = 0.13; BCI = -0.46, 0.01) blobs, although this relationship did not reach conventional statistical significance.

Conclusions

Thresholds for S+ and S- stimuli were negatively related to RE, indicating that myopes may have reduced sensitivity to low spatial frequency S-cone stimuli. This reduced S-cone sensitivity might have played a role in their failure to emmetropize normally.

Excellent luminous efficiency and high thermal stability of glass-in-LuAG ceramic for laser-diode-pumped green-emitting phosphor

A kind of glass-in-LuAG (GIP) ceramic with excellent luminous efficiency and high thermal stability was fabricated by solid-state sintering for laser diode (LD)-pumped green-emitting phosphor. The GIP ceramic employing particularly designed borosilicate glass as adhesive exhibits high thermal conductivity (2.8  W/m·K at 80°C) and remarkable improvement in thermal stability (T_g=711°C) and reliability (luminous flux has only a 0.5% drop after 100 h at 300°C). When the GIP ceramic is pumped by 455 nm blue LDs (14.5  W/mm²), a luminous efficacy of 205 lm/W was achieved. More importantly, the GIP ceramic did not have luminescence saturation even under a higher power density (17.1  W/mm²) excitation. The novel GIP ceramic, possessing good optical and thermal properties, is promising for LD-pumped green-emitting phosphor.

Hue opponency: chromatic valence functions, individual differences, cortical winner-take-all opponent modeling, and the relationship between spikes and sensitivity

Neural spike rate data are more restricted in range than related psychophysical data. For example, several studies suggest a compressive (roughly cube root) nonlinear relationship between wavelength-opponent spike rates in primate midbrain and color appearance in humans, two rather widely separated domains. This presents an opportunity to partially bridge a chasm between these two domains and to probe the putative nonlinearity with other psychophysical data. Here neural wavelength-opponent data are used to create cortical competition models for hue opponency. This effort led to creation of useful models of spiking neuron winner-take-all (WTA) competition and MAX selection. When fed with actual primate data, the spiking WTA models generate reasonable wavelength-opponent spike rate behaviors. An average psychophysical observer for red-green and blue-yellow opponency is curated from eight applicable studies in the refereed and dissertation literatures, with cancellation data roughly every 10 nm in 18 subjects for yellow-blue opponency and 15 subjects for red-green opponency. A direct mapping between spiking neurons with broadband wavelength sensitivity and human psychophysical luminance yields a power law exponent of 0.27, similar to the cube root nonlinearity. Similarly, direct mapping between the WTA model opponent spike rates and psychophysical opponent data suggests power law relationships with exponents between 0.24 and 0.41.

Wavelength and ambient luminance dependence of laser eye dazzle

A series of experiments has been conducted to quantify the effects of laser wavelength and ambient luminance on the severity of laser eye dazzle experienced by human subjects. Eight laser wavelengths in the visible spectrum were used (458-647 nm) across a wide range of ambient luminance conditions (0.1-10,000  cd·m^-2). Subjects were exposed to laser irradiance levels up to 600  μW·cm^-2 and were asked to recognize the orientation of optotypes at varying eccentricities up to 31.6 deg of visual angle from the laser axis. More than 40,000 data points were collected from 14 subjects (ages 23-64), and these were consolidated into a series of obscuration angles for comparison to a theoretical model of laser eye dazzle. Scaling functions were derived to allow the model to predict the effects of laser dazzle on vision more accurately by including the effects of ambient luminance and laser wavelength. The updated model provides an improved match to observed laser eye dazzle effects across the full range of conditions assessed. The resulting model will find use in a variety of laser safety applications, including the estimation of maximum dazzle exposure and nominal ocular dazzle distance values.

Circuitry to explain how the relative number of L and M cones shapes color experience

The wavelength of light that appears unique yellow is surprisingly consistent across people even though the ratio of middle (M) to long (L) wavelength sensitive cones is strikingly variable. This observation has been explained by normalization to the mean spectral distribution of our shared environment. Our purpose was to reconcile the nearly perfect alignment of everyone's unique yellow through a normalization process with the striking variability in unique green, which varies by as much as 60 nm between individuals. The spectral location of unique green was measured in a group of volunteers whose cone ratios were estimated with a technique that combined genetics and flicker photometric electroretinograms. In contrast to unique yellow, unique green was highly dependent upon relative cone numerosity. We hypothesized that the difference in neural architecture of the blue-yellow and red-green opponent systems in the presence of a normalization process creates the surprising dependence of unique green on cone ratio. We then compared the predictions of different theories of color vision processing that incorporate L and M cone ratio and a normalization process. The results of this analysis reveal that—contrary to prevailing notions--postretinal contributions may not be required to explain the phenomena of unique hues.

Spatial properties of fundus reflectance and red-green relative spectral sensitivity

We investigated the spatial characteristics of the diffuse light in the eye at two different wavelengths and the extent to which this may affect red-green relative spectral sensitivity. The fundus reflectance of six subjects was measured for different field sizes ranging from a 0.18° to 7.28° radius and for two different wavelengths, 560 and 650 nm. The experimental setup consisted of having an instrument project uniform disks on the fundus and recording their retinal images after a double pass through the eye. Additionally, the relative spectral sensitivity for the same wavelengths was measured using heterochromatic flicker photometry for a stimulus of a 0.4° radius with and without the presence of a synchronously flickering concentric annulus. We concluded that although light backscattered from the fundus contributes to vision, the effect is not strong and can only be observed under appropriate laboratory conditions. This suggests that diffuse light from deeper fundus layers is unlikely to have a practical relevance to vision.

Macular pigment optical density measured by heterochromatic modulation photometry

Purpose

To psychophysically determine macular pigment optical density (MPOD) employing the heterochromatic modulation photometry (HMP) paradigm by estimating 460 nm absorption at central and peripheral retinal locations.

Methods

For the HMP measurements, two lights (B: 460 nm and R: 660 nm) were presented in a test field and were modulated in counterphase at medium or high frequencies. The contrasts of the two lights were varied in tandem to determine flicker detection thresholds. Detection thresholds were measured for different R:B modulation ratios. The modulation ratio with minimal sensitivity (maximal threshold) is the point of equiluminance. Measurements were performed in 25 normal subjects (11 male, 14 female; age: 30±11 years, mean ± sd) using an eight channel LED stimulator with Maxwellian view optics. The results were compared with those from two published techniques – one based on heterochromatic flicker photometry (Macular Densitometer) and the other on fundus reflectometry (MPR).

Results

We were able to estimate MPOD with HMP using a modified theoretical model that was fitted to the HMP data. The resultant MPOD_HMP values correlated significantly with the MPOD_MPR values and with the MPOD_HFP values obtained at 0.25° and 0.5° retinal eccentricity.

Conclusions

HMP is a flicker-based method with measurements taken at a constant mean chromaticity and luminance. The data can be well fit by a model that allows all data points to contribute to the photometric equality estimate. Therefore, we think that HMP may be a useful method for MPOD measurements, in basic and clinical vision experiments.

Action video game playing is associated with improved visual sensitivity, but not alterations in visual sensory memory

Action video game playing has been experimentally linked to a number of perceptual and cognitive improvements. These benefits are captured through a wide range of psychometric tasks and have led to the proposition that action video game experience may promote the ability to extract statistical evidence from sensory stimuli. Such an advantage could arise from a number of possible mechanisms: improvements in visual sensitivity, enhancements in the capacity or duration for which information is retained in visual memory, or higher-level strategic use of information for decision making. The present study measured the capacity and time course of visual sensory memory using a partial report performance task as a means to distinguish between these three possible mechanisms. Sensitivity measures and parameter estimates that describe sensory memory capacity and the rate of memory decay were compared between individuals who reported high evels and low levels of action video game experience. Our results revealed a uniform increase in partial report accuracy at all stimulus-to-cue delays for action video game players but no difference in the rate or time course of the memory decay. The present findings suggest that action video game playing may be related to enhancements in the initial sensitivity to visual stimuli, but not to a greater retention of information in iconic memory buffers.

The biological basis of a universal constraint on color naming: cone contrasts and the two-way categorization of colors

Many studies have provided evidence for the existence of universal constraints on color categorization or naming in various languages, but the biological basis of these constraints is unknown. A recent study of the pattern of color categorization across numerous languages has suggested that these patterns tend to avoid straddling a region in color space at or near the border between the English composite categories of "warm" and "cool". This fault line in color space represents a fundamental constraint on color naming. Here we report that the two-way categorization along the fault line is correlated with the sign of the L- versus M-cone contrast of a stimulus color. Moreover, we found that the sign of the L-M cone contrast also accounted for the two-way clustering of the spatially distributed neural responses in small regions of the macaque primary visual cortex, visualized with optical imaging. These small regions correspond to the hue maps, where our previous study found a spatially organized representation of stimulus hue. Altogether, these results establish a direct link between a universal constraint on color naming and the cone-specific information that is represented in the primate early visual system.

How inherently noisy is human sensory processing?

Like any physical information processing device, the human brain is inherently noisy: If a participant is presented with the same sensory stimulus multiple times and is asked to press one of two buttons in response to some property of the stimulus, the response may vary even though the stimulus did not. This response variability can be used to estimate the amount of so-called internal noise-that is, noise that is not present in the stimulus (such as random dynamic dots on the screen) but in the participant's brain. How large is this internally generated noise? We obtained >400 independent estimates on 40 participants for a range of protocols (yes/no, two-, four-, and eight-alternative forced choice), modalities (auditory and visual), attentional state, adaptation state, stimulus types (static, moving, stereoscopic), and other parameters (timing, size, contrast). Our final estimate at ~1.3 (units of external noise standard deviation) is generally somewhat larger than that previously inferred from smaller and less varied data sets. We discuss the impact of high levels of internal noise on a number of experimental and computational efforts aimed at understanding and characterizing human sensory processing.

Reduced attentional capture in action video game players

Recent studies indicate that playing action video games improves performance on a number of attention-based tasks. However, it remains unclear whether action video game experience primarily affects endogenous or exogenous forms of spatial orienting. To examine this issue, action video game players and non-action video game players performed an attentional capture task. The results show that action video game players responded quicker than non-action video game players, both when a target appeared in isolation and when a salient, task-irrelevant distractor was present in the display. Action video game players additionally showed a smaller capture effect than did non-action video game players. When coupled with the findings of previous studies, the collective evidence indicates that extensive experience with action video games may enhance players' top-down attentional control, which, in turn, can modulate the negative effects of bottom-up attentional capture.

Video game players show more precise multisensory temporal processing abilities

Recent research has demonstrated enhanced visual attention and visual perception in individuals with extensive experience playing action video games. These benefits manifest in several realms, but much remains unknown about the ways in which video game experience alters perception and cognition. In the present study, we examined whether video game players' benefits generalize beyond vision to multisensory processing by presenting auditory and visual stimuli within a short temporal window to video game players and non-video game players. Participants performed two discrimination tasks, both of which revealed benefits for video game players: In a simultaneity judgment task, video game players were better able to distinguish whether simple visual and auditory stimuli occurred at the same moment or slightly offset in time, and in a temporal-order judgment task, they revealed an enhanced ability to determine the temporal sequence of multisensory stimuli. These results suggest that people with extensive experience playing video games display benefits that extend beyond the visual modality to also impact multisensory processing.

Grouping puts figure-ground assignment in context by constraining propagation of edge assignment

Figure-ground organization involves the assignment of edges to a figural shape on one or the other side of each dividing edge. Established visual cues for edge assignment primarily concern relatively local rather than contextual factors. In the present article, we show that an assignment for a locally unbiased edge can be affected by an assignment of a remote contextual edge that has its own locally biased assignment. We find that such propagation of edge assignment from the biased remote context occurs only when the biased and unbiased edges are grouped. This new principle, whereby grouping constrains the propagation of figural edge assignment, emerges from both subjective reports and an objective short-term edge-matching task. It generalizes from moving displays involving grouping by common fate and collinearity, to static displays with grouping by similarity of edge-contrast polarity, or apparent occlusion. Our results identify a new contextual influence on edge assignment. They also identify a new mechanistic relation between grouping and figure-ground processes, whereby grouping between remote elements can constrain the propagation of edge assignment between those elements. Supplemental materials for this article may be downloaded from http://app.psychonomic-journals.org/content/supplemental.

Novel mutations and electrophysiologic findings in RGS9- and R9AP-associated retinal dysfunction (Bradyopsia)

PURPOSE

To examine the phenotypes of 8 patients with evidence of cone dysfunction and normal color vision (characteristic features of both oligocone trichromacy and bradyopsia), and subsequently to screen RGS9 and R9AP for disease-causing mutations.

DESIGN

Retrospective case series.

PARTICIPANTS

Eight affected individuals from 7 families.

METHODS

Ophthalmologic examination, color vision testing, fundus photography, and detailed electrophysiologic assessment were undertaken. Blood samples were taken for DNA extraction from affected subjects and, where possible, unaffected relatives. Mutation screening of RGS9 and R9AP was performed.

MAIN OUTCOME MEASURES

Detailed clinical, electrophysiologic, and molecular genetic findings.

RESULTS

All 8 patients had normal ocular examination results, with visual acuity ranging from 6/12 to 6/18. Four subjects were found to harbor mutations in RGS9 or R9AP, with 3 of the identified sequence variants being novel. Three subjects, 2 Pakistani sisters and an Afghani female, had mutations in R9AP. A novel homozygous nonsense mutation, p.G205fs, was identified in the simplex case, and a second novel homozygous in-frame deletion, p.D32_Q34del, was found in the 2 sisters. The remaining patient, a British male, had a compound heterozygous mutation in RGS9 (p.R128X/p.W299R). The mutation p.R128X represents the first nonsense mutation reported in RGS9. The 4 mutation-positive subjects had concordant characteristic previously described electrophysiologic findings that were not present in the 4 individuals in whom mutations were not identified. Novel findings associated with these mutation-positive patients included that they all showed electroretinogram evidence of severe cone system dysfunction under photopic conditions but normal cone function to a red flash under scotopic conditions. Such findings seem unique for the disorder.

CONCLUSIONS

This is the first report describing a nonsense mutation in RGS9. We have established novel electrophysiologic observations associated with RGS9 and R9AP mutations, including those relating to dark-adapted cone function and S-cone function. Patients with either RGS9/R9AP mutations (bradyopsia) or oligocone trichromacy have very similar clinical phenotypes, characterized by stationary cone dysfunction, mild photophobia, normal color vision, lack of nystagmus, and normal fundi. The distinctive electrophysiologic features associated with RGS9 and R9AP mutations enable directed genetic screening.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.