Showing papers on "Contrast (vision) published in 2002"
20 Apr 2002
TL;DR: A new sensor architecture for making interactive surfaces that are sensitive to human hand and finger gestures that can be integrated within the surface, and which does not suffer from lighting and occlusion problems.
Abstract: This paper introduces a new sensor architecture for making interactive surfaces that are sensitive to human hand and finger gestures. This sensor recognizes multiple hand positions and shapes and calculates the distance between the hand and the surface by using capacitive sensing and a mesh-shaped antenna. In contrast to camera-based gesture recognition systems, all sensing elements can be integrated within the surface, and this method does not suffer from lighting and occlusion problems. This paper describes the sensor architecture, as well as two working prototype systems: a table-size system and a tablet-size system. It also describes several interaction techniques that would be difficult to perform without using this architecture
1,076 citations
TL;DR: In this article, the association between performance on selected tasks of everyday life and impairment in visual acuity and contrast sensitivity was determined, and the relationship of function to the vision measures was mostly linear and receiver operating characteristic curves were not helpful in identifying cutoff points for predicting disabilities.
Abstract: Objective To determine the association between performance on selected tasks of everyday life and impairment in visual acuity and contrast sensitivity. Methods Visual acuity and contrast sensitivity were obtained on a population-based sample of 2520 older African American and white subjects. Performance was assessed on mobility, daily activities with a strong visual component, and visually intensive tasks. Disability was defined as performance less than 1 SD below the mean. Receiver operating characteristic curve analyses were used to evaluate the sensitivity and specificity of thresholds in acuity and contrast loss for determining disability. Results Both visual acuity and contrast sensitivity loss were associated with decrements in function. The relationship of function to the vision measures was mostly linear, therefore, receiver operating characteristic curves were not helpful in identifying cutoff points for predicting disabilities. For mobility tasks, most persons were not disabled until they had significant acuity loss (logMAR visual acuity >1.0 or Conclusions Both contrast sensitivity and visual acuity loss contribute independently to deficits in performance on everyday tasks. Defining disability as deficits in performance relative to a population, it is possible to identify visual acuity and contrast loss where most are disabled. However, the cutoff points depend on the task, suggesting that defining disability using a single threshold for visual acuity or contrast sensitivity loss is arbitrary.
374 citations
TL;DR: The observed attentional benefit is consistent with signal enhancement, and the dependence of the psychometric function on target location, attention improved performance to a similar extent across the visual field.
341 citations
TL;DR: Improvements in contrast sensitivity and visual acuity are demonstrated in white light and in monochromatic light when adaptive optics corrects the eye's higher-order monochromaatic aberrations.
Abstract: The development of technology to measure and correct the eye's higher-order aberrations, i.e., those beyond defocus and astigmatism, raises the issue of how much visual benefit can be obtained by providing such correction. We demonstrate improvements in contrast sensitivity and visual acuity in white light and in monochromatic light when adaptive optics corrects the eye's higher-order monochromatic aberrations. In white light, the contrast sensitivity and visual acuity when most monochromatic aberrations are corrected with a deformable mirror are somewhat higher than when defocus and astigmatism alone are corrected. Moreover, viewing conditions in which monochromatic aberrations are corrected and chromatic aberrations are avoided provides an even larger improvement in contrast sensitivity and visual acuity. These results are in reasonable agreement with the theoretical improvement calculated from the eye's optical modulation transfer function.
285 citations
TL;DR: It is argued that these observations are consistent with changes in the activity within spatial-frequency channels caused by the higher-order phase structure of natural images that is responsible for the presence of edges and specularities.
Abstract: We examined contrast sensitivity and suprathreshold apparent contrast with natural images. The spatial-frequency components within single octaves of the images were removed (notch filtered), their phases were randomized, or the polarity of the images was inverted. Of Michelson contrast, root-mean-square (RMS) contrast, and band-limited contrast, RMS contrast was the best index of detectability. Negative images had lower apparent contrast than their positives. Contrast detection thresholds showed spatial-frequency-dependent elevation following both notch filtering and phase randomization. The peak of the spatial-frequency tuning function was approximately 0.5–2 cycles per degree (c/deg). Suprathreshold contrast matching functions also showed spatial-frequency-dependent contrast loss for both notch-filtered and phase-randomized images. The peak of the spatial-frequency tuning function was approximately 1–3 c/deg. There was no detectable difference between the effects of phase randomization and notch filtering on contrast sensitivity. We argue that these observations are consistent with changes in the activity within spatial-frequency channels caused by the higher-order phase structure of natural images that is responsible for the presence of edges and specularities.
273 citations
TL;DR: Exposure to unfocused images has previously been shown to influence acuity and contrast sensitivity, and here it is shown that adaptation can also profoundly affect the actual perception of image focus.
Abstract: Blur is an intrinsic feature of retina images that varies widely across images and observers, yet the world still typically appears 'in focus'. Here we examine the putative role of neural adaptation1 in the human perception of image focus by measuring how blur judgments depended on the state of adaptation. Exposure to unfocused images has previously been shown to influence acuity and contrast sensitivity and here we show that adaptation can also profoundly affect the actual perception of image focus.
242 citations
TL;DR: The results show that there was a gradual trend of increasing contrast invariance moving from area V1, which manifested high sensitivity to contrast changes, to the LOC, which showed a significantly higher degree of invariance at suprathreshold contrasts.
Abstract: An important characteristic of visual perception is the fact that object recognition is largely immune to changes in viewing conditions. This invariance is obtained within a sequence of ventral str...
239 citations
TL;DR: The use of a modified prolate intraocular lens during cataract surgery has the potential to improve contrast sensitivity under both mesopic and photopic conditions.
Abstract: PURPOSE: We compare the contrast sensitivity obtained with an anterior surface modified prolate intraocular lens with the contrast sensitivity obtained with a standard spherical intraocular lens. METHODS: Patients presenting for cataract surgery in one eye were randomized to receive either the Tecnis Z9000 intraocular lens (Pharmacia) or the AMO AR40e Opti-Edge intraocular lens (AMO). Sine wave grating contrast sensitivity testing under mesopic and photopic conditions served as the principal outcome measure. RESULTS: The Tecnis Z9000 intraocular lens provided statistically significantly better contrast sensitivity at 1.5 and 3 cycles per degreee under mesopic conditions and at 6, 12 and 18 cycles per degree under photopic conditions. CONCLUSION: The use of a modified prolate intraocular lens during cataract surgery has the potential to improve contrast sensitivity under both mesopic and photopic conditions.
167 citations
TL;DR: It is shown that the noise transmutes the threshold nonlinearity of the input–output relationships into an approximate power law without a threshold within some firing rate range, which implies that, under certain conditions, the tuning of the neuron output is approximately contrast invariant.
Abstract: The width of the orientation tuning curves of the spike response of neurons in V1 is invariant to contrast. This property constrains the possible mechanisms underlying orientation selectivity. It has been suggested that noise circumvents the iceberg effect that would prevent contrast invariance in the purely feedforward mechanism. Here we investigate systematically how noise contributes to the contrast invariance of orientation tuning curves in V1. We study three models of increasing complexity: a simple threshold-linear firing rate model, a leaky integrateand-fire model, and a conductance-based model. We show that the noise transmutes the threshold nonlinearity of the input‐output relationships into an approximate power law without a threshold within some firing rate range. This implies that, under certain conditions which are derived here, the tuning of the neuron output is approximately contrast invariant. In particular we show that this mechanism for contrast invariance requires that the neuron firing rate must not be too large and that increasing or lowering the contrast too much destroys this invariance. We also show that if this mechanism operates in V1, the spike response, R, and average voltage response V of the neurons in V1 should vary with the contrast, C, according to R(C) V(C). The exponent can be estimated from the amount by which the spike tuning curve is sharpened with respect to the voltage tuning curves of the neurons. This prediction does not depend on the specifics of the model and can be tested experimentally.
152 citations
TL;DR: In two experiments it is found that contrast sensitivity increases following extensive practice at detecting briefly presented sinusoidal luminance gratings and that learning is maintained after six months.
131 citations
TL;DR: A new flow suppression method has been proposed for the acquisition of blood‐suppressed (black‐blood) images in combination with administration of a positive contrast agent using the quadruple inversion‐recovery (QIR) preparative pulse sequence.
Abstract: A new flow suppression method has been proposed for the acquisition of blood-suppressed (black-blood) images in combination with administration of a positive contrast agent. The technique employs the quadruple inversion-recovery (QIR) preparative pulse sequence, which consists of two double-inversion modules followed by two delays. Within each double inversion, a nonselective RF pulse is immediately followed by a slice-selective one. The time intervals of the sequence can be calculated using an algorithm based on minimization of the variation of a signal equation over an entire range of T(1) occurring in blood before and after contrast administration. QIR is highly insensitive to variations of T(1), providing efficient suppression of a flow signal with T(1) in a range of 200-1200 ms. The technique utilizes identical scan parameters for pre- and postcontrast acquisition, and thus allows reliable quantitative interpretation of contrast enhancement (CE). The clinical application of QIR was demonstrated in high-resolution, contrast-enhanced, black-blood imaging of atherosclerotic plzzaque.
TL;DR: In this article, a new absolute thermal contrast method is proposed for pulsed infrared thermography, which is based on the computations of reconstructed defect-free images so that no a priori knowledge of a sound area on the sample is necessary.
Abstract: In this paper, a new absolute thermal contrast method is proposed for pulsed infrared thermography. It is based on the computations of reconstructed defect-free images so that no a priori knowledge of a sound area on the sample is necessary. Moreover, a correction is applied to take into account possible delays in the acquisition time. Results are presented both on Plexiglas and graphite-epoxy specimens. Comparisons with Pulsed Phase Thermography phase images are also presented along with a discussion on the advantages of the proposed method.
TL;DR: The results suggest that suppressive spatial interactions in amblyopic vision extend over larger distances than in normal foveal vision, similar to peripheral vision of non-amblyopic observers, for targets of the same size.
Patent•
15 Mar 2002
TL;DR: In this paper, an LCD has an adaptive luminance intensifying function and driving method of a timing controller, which checks features of externally provided image data, and when they are found to be moving pictures, outputs a predetermined luminance signal.
Abstract: Disclosed is an LCD having an adaptive luminance intensifying function and driving method thereof A timing controller checks features of externally provided image data, and when they are found to be moving pictures, it determines a luminance level required from the image data and outputs a luminance level control signal, and when they are found to be still images, outputs a predetermined luminance signal A backlight driver outputs a high-potential backlight driving voltage to the backlight unit when a luminance control signal of high-luminance level driving is provided by the timing controller, and outputs a constant level luminance signal when a constant luminance signal is input As a result, by selecting a plurality of portions of the displayed screen and tracking and monitoring the changes of the image data, features of the images are defined and application conditions of the luminance intensifying function are determined to control the luminance level of the backlight and outputs of gamma voltage levels Accordingly, the contrast of a display screen is improved and the power consumption is
TL;DR: The results of the present study considerably extend knowledge about the multisensory integration, by showing in humans the existence of an integrated visuoauditory system with functional properties similar to those found in animals.
Abstract: Cross-modal spatial integration between auditory and visual stimuli is a common phenomenon in space perception. The principles underlying such integration have been outlined by neurophysiological and behavioral studies in animals (Stein & Meredith, 1993), but little evidence exists proving that similar principles occur also in humans. In the present study, we explored such possibility in patients with visual neglect, namely, patients with visuospatial impairment. To test this hypothesis, neglect patients were required to detect brief flash of light presented in one of six spatial positions, either in a unimodal condition (i.e., only visual stimuli were presented) or in a cross-modal condition (i.e., a sound was presented simultaneously to the visual target, either at the same spatial position or at one of the remaining five possible positions). The results showed an improvement of visual detection when visual and auditory stimuli were originating from the same position in space or at close spatial disparity (16°). In contrast, no improvement was found when the spatial separation of visual and auditory stimuli was larger than 16°. Moreover, the improvement was larger for visual positions that were more affected by the spatial impairment, i.e., the most peripheral positions in the left visual field (LVF). In conclusion, the results of the present study considerably extend our knowledge about the multisensory integration, by showing in humans the existence of an integrated visuoauditory system with functional properties similar to those found in animals.
TL;DR: The neural basis for spatial color contrast and temporal color contrast in primary visual cortex (V1) of the alert macaque is explored and the remarkable degree of specialization shown by cells in V1, especially that of the double-opponent color cells, is discussed.
Abstract: We explored the neural basis for spatial color contrast (red looks redder surrounded by green) and temporal color contrast (red looks redder if preceded by green) in primary visual cortex (V1) of the alert macaque. Using pairs of stimuli, we found a subset of neurons that gave stronger responses to sequences of red and green spots and stronger responses to adjacent red and green spots. These cells combined their cone inputs linearly: for a red-ON-center cell, the sum of the OFF response to green and the ON response to red predicted the peak response to red preceded by green. These 'color' cells, which could underlie hue discrimination because they show cone opponency, could mediate spatial and temporal color contrast. In contrast, the majority of cortical cells, which do not show overt cone opponency but which are often orientation tuned and/or direction selective, are by themselves incapable of mediating hue discrimination. The remarkable degree of specialization shown by cells in V1, especially that of the double-opponent color cells, is discussed.
TL;DR: The post‐LASIK nonpermanent depression in contrast sensitivity was probably due to optical factors, and was greater for higher amounts of myopia.
Abstract: Purpose To determine whether contrast sensitivity measurement, a more sensitive test of visual function than visual acuity, better characterizes visual outcomes after laser in situ keratomileusis (LASIK). Setting Hong Kong Laser Eye Centre, Hong Kong, China. Methods Contrast sensitivity was monitored in 41 LASIK patients for 1 year. Seven spatial frequencies (0.3, 0.8, 1.5, 3.4, 6.9, 10.3, and 20.5 cpd) were tested with 15 sequences per spatial frequency, and a staircase technique was used for target presentation. Results There was a general depression in the contrast sensitivity function after LASIK; 1.5 cpd and 3.4 cpd were the most affected frequencies. Recovery took at least 6 months. The reduction in contrast sensitivity was greater for higher amounts of myopia. Conclusion The post-LASIK nonpermanent depression in contrast sensitivity was probably due to optical factors.
TL;DR: The adaptive optics visual simulator is a powerful, non-invasive tool to evaluate how aberrations affect vision and can be used for the interactive design and testing of new ophthalmic devices, and for the simulation of visual outcomes in customized refractive surgery.
Abstract: PURPOSE: To develop a prototype instrument that uses adaptive optics to introduce virtually any desired aberration profile in a subject’s eye. At the same time, the instrument could be used to evaluate the subject’s spatial vision for each controlled aberration profile. This “aberration testing station” or “visual simulator” allows us to study the relationship between specific aberrations and visual quality. METHODS: The apparatus uses infrared light to measure the wavefront aberration of the system plus the eye with a Hartmann-Shack wavefront sensor. Defocus is added (or removed) with a computer-controlled, motorized optometer, while higher order aberrations are introduced by a 37-channel membrane deformable mirror. A parallel viewing channel is used for visual testing with the instrument. Visual acuity, contrast sensitivity, and other visual tests are performed under normal viewing for each desired aberration profile. RESULTS: The range of defocus that can be added is nearly unlimited, while the maximum amount of other aberration modes is restricted to approximately 0.5 µm, depending on mode. Pure modes or any selected combination of modes can be produced with high repeatability and precision (usually better than 0.05 µm), and the system works for pupil diameters up to 6 mm (with a natural pupil). CONCLUSIONS: The adaptive optics visual simulator is a powerful, non-invasive tool to evaluate how aberrations affect vision. In addition, it can be used for the interactive design and testing of new ophthalmic devices, and for the simulation of visual outcomes in customized refractive surgery. [J Refract Surg 2002;18:S634-S638]
TL;DR: The results suggest that optical measurements could be used for clinical testing of ophthalmic optics and studied the correlation between optical parameters and psychophysical estimates of the visual performance for larger ranges of defocus.
Abstract: Purpose. To evaluate how ocular optical image quality and psychophysical estimates of visual performance compare to each other as a function of defocus. Methods. We measured the optical modulation transfer function using a double-pass apparatus and psychophysical estimates of visual performance: contrast sensitivity function (CSF) and visual acuity. Both sets of data were obtained under the same optical conditions. Results. We measured optical and psychophysical parameters as a function of defocus. We studied the correlation between optical parameters (Strehl ratio and the logarithm of the volume in the double-pass image (log_Vol D-P)) and psychophysical parameters (the area under the fitted CSF represented in a logarithmic scale with the spatial frequency in linear scale (Area CSF-log_lin) and visual acuity) for different values of defocus. Conclusions. Strehl ratio is well correlated with the psychophysical estimates of the visual performance for moderate amount of defocus (within 1 D), whereas the other parameter (log_Vol D-P) is well correlated for larger ranges of defocus (within 2 D) and for different pupil diameters. These results suggest that optical measurements could be used for clinical testing of ophthalmic optics. (Optom Vis Sci 2002;79: 60-67)
TL;DR: The density difference of fibrils in breast cancer as measured by absorption images correlate well with the density difference derived from refraction angle images of DEI, and theDEI apparent absorption image and the image obtained with the DEI system at the top of the reflectivity curve have much greater contrast than that of the normal radiograph.
Abstract: We have investigated the contrast mechanisms of the refraction angle, and the apparent absorption images obtained from the diffraction enhanced imaging technique (DEI) and have correlated them with the absorption contrast of conventional radiography. The contrast of both the DEI refraction angle image and the radiograph have the same dependence on density differences of the tissues in the visualization of cancer; in radiography these differences directly relate to the contrast while in the DEI refraction angle image it is the density difference and thickness gradient that gives the refraction angle. We show that the density difference of fibrils in breast cancer as measured by absorption images correlate well with the density difference derived from refraction angle images of DEI. In addition we find that the DEI apparent absorption image and the image obtained with the DEI system at the top of the reflectivity curve have much greater contrast than that of the normal radiograph (×8 to 33-fold higher). This is due to the rejection of small angle scattering (extinction) from the fibrils enhancing the contrast.
15 Mar 2002
TL;DR: The concept of Thermographic Signal Reconstruction (TSR) is introduced as a means of enhancing defect to background contrast while reducing the amount of data that must be stored by an order of magnitude, and the mechanisms for the resulting performance improvements are considered.
Abstract: Visualization and analysis of pulsed thermographic data for NDT has generally been based on simple image averaging, subtraction or slope operations. Quantitative contrast methods, based on comparison to a defect free reference point or region, have also been used to a lesser extent. Despite their widespread use, all of these methods are highly susceptible to noise, nonlinearity of the IR camera response, and the presence of surface features on the sample. More importantly, the ability of any of these methods to significantly improve the ability to retrieve deep or weak subsurface features beyond the original unmodified image is limited. In a previous paper, we introduced the concept of Thermographic Signal Reconstruction (TSR) as a means of enhancing defect to background contrast while reducing the amount of data that must be stored by an order of magnitude. The TSR method increases the depth range over which pulsed thermography can be applied, and also reduces the amount of blurring due to lateral diffusion that is typical of thermographic imaging. In this paper we compare TSR with conventional thermographic approaches and consider the mechanisms for the resulting performance improvements.
TL;DR: Photorefractive keratectomy can induce significant reductions in contrast sensitivity under mesopic conditions, even though the photopic contrast sensitivity function is normal.
Abstract: PURPOSE To evaluate contrast sensitivity under mesopic conditions in patients who had undergone uncomplicated excimer laser photorefractive keratectomy (PRK) for myopia. METHODS Monocular contrast sensitivity function was measured with the Stereo Optical F.A.C.T. chart in 26 patients who had received PRK using the Nidek EC-5000 excimer laser system. Mean preoperative refractive error was -6.23 +/- 1.69 D (range, -4.00 to -8.25 D); postoperatively, mean refractive error was -0.36 +/- 0.58 D (range, -0.75 to +0.50 D). Contrast sensitivity function was measured 6 months after surgery using four different chart luminances: 85, 5.0, 2.5, and 0.1 cd/m2, the first being a photopic level and the rest mesopic. A control group of eight emmetropic subjects was also studied to allow comparison of results for statistical purposes. RESULTS Logarithmic values of contrast sensitivity at each spatial frequency were used for statistical analysis and normalized values were used for graphical representation. The results showed a statistically significant reduction (P .01 for all frequencies). CONCLUSION Photorefractive keratectomy can induce significant reductions in contrast sensitivity under mesopic conditions, even though the photopic contrast sensitivity function is normal.
TL;DR: Among this cohort of patients with AMD, visual acuity, contrast sensitivity, and color vision defects are significant predictors of computer task performance.
01 May 2002
TL;DR: Iridigm has produced the first color MEMS based reflective display as mentioned in this paper, which exhibits good contrast and high brightness with response times of 35 microseconds at extremely low power consumption.
Abstract: Iridigm has produced the first color MEMS based reflective display. With dimensions of 240 × 160 pixels at 100 dpi, it exhibits good contrast and high brightness. Response times of 35 microseconds have been achieved at exceptionally low power consumption, and there is no active matrix. The status of this technology will be discussed.
TL;DR: In early glaucoma, the reduction in contrast sensitivity to stimuli which isolate the magnocellular pathway was not significantly different compared with the reduction to stimuli that isolate the parvocellular pathways.
Abstract: Aim: The psychophysical evaluation of selective cell loss in early glaucoma and ocular hypertension.
Methods: Contrast sensitivity was measured for the detection of luminance modulated gratings at a range of spatial (0.5, 2, 8 c/deg) and temporal (0, 16 Hz) frequency combinations in three groups of age matched patients (primary open angle glaucoma, ocular hypertension, normal controls; n=16). Stimuli of 5° were presented foveally and at 15° along the nasal horizontal meridian under photopic conditions.
Results: Fovea: Compared to the normal group, the thresholds for the glaucoma patients were significantly elevated at all spatial and temporal frequencies (p 0.1). There was no difference in contrast sensitivity between the normals and OHTs (p>0.10). Periphery: The thresholds of the glaucoma patients were elevated compared to the normal controls (p 0.10).
Conclusions: In early glaucoma, the reduction in contrast sensitivity to stimuli which isolate the magnocellular pathway (0.5 c/deg, 16 Hz) was not significantly different compared with the reduction in contrast sensitivity to stimuli that isolate the parvocellular pathway. These findings are not consistent with the hypothesis that the magnocellular pathway is selectively damaged in early glaucoma.
TL;DR: In this paper, delay-time and aging effects on contrast and sensitivity have been investigated and a general correlation between sensitivity and contrast has been established for various pre-exposure and postexposure treatments for 20, 50, and 100 kV exposures.
Abstract: Hydrogen silsesquioxane (HSQ) has been shown to behave as a negative tone inorganic e-beam resist with a resolution better than 20 nm established. In this article, delay-time and aging effects on contrast and sensitivity have been investigated. The effect of a 1 week delay in air between softbake and exposure is much larger than either the aging effect or the effect of the softbake temperature. A pre-exposure delay in air seems to decrease the sensitivity and to enhance the contrast of HSQ. A general correlation between sensitivity and contrast has been established for various pre-exposure and postexposure treatments for 20, 50, and 100 kV exposures. The possible causes for the various delay-time effects are discussed.
Journal Article•
TL;DR: Reduced contrast sensitivity may be important in indicating the level of driving skills for individuals with glaucoma, who have normal or near-normal visual acuity and mild to moderate visual field loss.
Abstract: The purpose of this study was to determine the relationship between clinical measures of visual function and driving-related skills in patients with glaucoma who had good visual acuity in at least one eye and mild to moderate visual field loss. METHODS: Twenty-five patients with glaucoma and twenty-nine age-equivalent normally sighted control subjects were included in the study. We tested each patient on an interactive driving simulator and collected vision data, including Lighthouse visual acuity, Goldmann and Humphrey visual fields, and Pelli-Robson contrast sensitivity. Information about real-world accident history for the previous 5-year period was obtained. RESULTS: The glaucoma patients did not have significantly more simulator or real-world accidents than the normally sighted group. There were no significant differences between the groups in performance on seven of the eight simulator indexes that were measured. Of the clinical visual function measures, only lower contrast sensitivity in the eye with better contrast sensitivity correlated with driving skills, including slower speeds (r(24) = 0.58, p Language: en
TL;DR: It is concluded that early cone-specific regulation of sensitivity cannot be responsible for the change in perceived colour, and chromatic induction takes place after contrast gain control, and the more colourful surroundings had considerably less influence on subjects' colour judgments.
Abstract: Judgments of the colour of a surface are influenced by the colour of the surrounding. To determine whether only the average colour of the surrounding matters, or also the chromatic variability, judgments in colourful scenes are often compared with ones in which a target is surrounded by a plain background that provides the same average physical illumination of the retina as the colourful scene. The variability sometimes makes a difference (eg Shevell and Wei, 1998 Vision Research 38 1561-1566), and sometimes it does not (eg Brenner and Cornelissen, 1998 Vision Research 38 1789-1793). Is this because of the nonlinearity in cone responses? We designed scenes that stimulated the cones in an equivalent manner, both on average and in terms of variability, and yet differed markedly in chromatic variability. The more colourful surroundings had considerably less influence on subjects' colour judgments. We conclude that early cone-specific regulation of sensitivity cannot be responsible for the change in perceived colour, and deduce that chromatic induction takes place after contrast gain control.
TL;DR: This study clearly demonstrates that diffuse luminance flicker increases optic nerve head blood flow and increased neural activity in the retina has no effect on choroidal blood flow, which appears to be largely independent of alterations in retinal metabolism.
Abstract: Purpose. In the retina there is general agreement that blood flow adapts in response to different conditions of light and darkness including diffuse luminance flicker. By contrast, regulation of choroidal blood flow in response to different light conditions is still a matter of controversy. Thus, we investigated the effect of diffuse luminance flicker on choroidal and optic nerve head blood flow. Methods. In a group of 14 healthy volunteers, choroidal blood flow and ocular fundus pulsation amplitude were assessed with laser Doppler flowmetry and laser interferometry, respectively. Measurements were done before, during and after stimulation with diffuse luminance flicker. Furthermore, the response of optic nerve head blood flow (ONHBF) to flicker stimulation was measured. Flicker stimuli were generated by a Grass® PS2 photostimulator, stimulating at a frequency of 8 Hz. Flicker light consisted of light flashes at a wavelength below 550nm and produced a retinal irradiance of 140 µW/cm 2. Blood pressure and ...