A5028474518- Visual perception and processing mechanisms
- Color Science and Applications
- Color perception and design
- Retinal Development and Disorders
- Ocular and Laser Science Research
- Neural dynamics and brain function
- Circadian rhythm and melatonin
- Retinal Imaging and Analysis
- Olfactory and Sensory Function Studies
- Ophthalmology and Visual Impairment Studies
- Photoreceptor and optogenetics research
- Image Enhancement Techniques
- Categorization, perception, and language
- melanin and skin pigmentation
- Impact of Light on Environment and Health
- Glaucoma and retinal disorders
- Health, Environment, Cognitive Aging
- CCD and CMOS Imaging Sensors
- Retinal Diseases and Treatments
- Migraine and Headache Studies
- Remote-Sensing Image Classification
- Infrared Target Detection Methodologies
- Optical Imaging and Spectroscopy Techniques
- Multisensory perception and integration
- Neurobiology and Insect Physiology Research
University of Pennsylvania
2016-2025
California University of Pennsylvania
2009-2024
Google (United States)
2018
Heinz Optical Engineering (United States)
2014
Philadelphia University
2014
Prevent Blindness
2013
Penn Presbyterian Medical Center
2013
University of California, Santa Barbara
1996-2010
Institute of Psychology
2005
University of California, San Diego
1999
If color appearance is to be a useful feature in identifying an object, then must remain roughly constant when the object viewed different contexts. People maintain approximate constancy despite variation of nearby objects and spectral power distribution ambient light. Land's retinex algorithm model human constancy. We analyze discuss its general properties. show that too sensitive changes serve as adequate
Several domains of neuroscience offer map-like models that link location on the cortical surface to properties sensory representation. Within visual areas V1, V2, and V3, algebraic transformations can relate position in field retinotopic representation flattened sheet. A limit practical application this structure-function model is cortex, while topologically a two-dimensional surface, curved. Flattening curved plane unavoidably introduces local geometric distortions are not accounted for...
Abstract The illumination of the environment undergoes both intensity and spectral changes during 24 h cycle a day. Daylight power distributions are well described by low-dimensional models such as CIE (Commission Internationale de l’Éclairage) daylight model, but performance this model in non-daylight regimes is not characterised. We measured downwelling irradiance across multiple days two locations North America: One rural location (Cherry Springs State Park, PA) with minimal anthropogenic...
Color constancy is our ability to perceive constant surface colors despite changes in illumination. Although color has been studied extensively, its mechanisms are still largely unknown. Three classic hypotheses that mediated by local adaptation, adaptation the spatial mean of image, or most intense image region. We measure under nearly natural viewing conditions, using a design allows us test these three directly. By suitable stimulus manipulation, we able titrate degree between 11% and...
Direct imaging of the retina by adaptive optics allows assessment relative number long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) cones in living human eyes. We examine functional consequences variation numbers L M (L/M cone ratio) for two observers whose ratios were measured direct imaging. The L/M ratio varied considerably, taking on values 1.15 3.79. Two sets data collected: spectral sensitivity with flicker electroretinogram (ERG) wavelength unique yellow. A genetic...
Most empirical work on color constancy is based simple laboratory models of natural viewing conditions. These typically consist spots seen against uniform backgrounds or computer simulations flat surfaces under spatially illumination. We report measurements made more The experiments were conducted in a room where the illumination was control. Observers used projection colorimeter to set asymmetric matches across spatial gradient. Observers' can be described by either two models. One model...
Most empirical work on color constancy is based simple laboratory models of natural viewing conditions. These typically consist spots seen against uniform backgrounds or computer simulations flat surfaces under spatially illumination. In this study measurements were made more Observers used a projection colorimeter to adjust the appearance test patch until it appeared achromatic. such achromatic settings variety illuminants and when surface was viewed number different backgrounds. An...
Abstract Because of the large number stimulus configurations that may be displayed on a computer controlled color monitor, direct measurement relation between digital input values to frame buffer and output monitor is not possible. To calibrate it necessary make assumptions about monitor's performance. These allow for any set predicted from results feasible calibration measurements. This article describes are sufficient render problem tractable. phosphor constancy, independence, spatial...
We report the results of matching experiments designed to study color appearance objects rendered under different simulated illuminants on a CRT monitor. Subjects set asymmetric matches between standard object and test that were with spectral power distributions. For any illuminant change, we found mapping cone coordinates was well approximated by diagonal linear transformation. In this sense, our are consistent von Kries's hypothesis { Handb. Physiol. Menschen3, 109 ( 1905) [ in Sources...
Significance Our eyes sense bright light using cones (L, M, and S) recently discovered melanopsin-containing ganglion cells. Both S melanopsin respond to blueish (short-wavelength) light. How does interact with the in visual function? We measured response of human pupil isolated stimulation different photoreceptors. work reveals a curious, opponent blue otherwise familiar pupillary response. Increased can cause dilate, but this effect is usually masked by stronger opposite from results have...
Significance Melanopsin-containing retinal cells detect bright light and contribute to reflex visual responses such as pupil constriction. Their role in conscious, cortical vision is less understood. Using functional MRI measure brain activity, we find that melanopsin-directed stimulation reaches the cortex people. Such also produces a distinct perceptual experience. Our results have clinical importance melanopsin function may discomfort some people experience from light.
We compare two methods for measuring the modulation transfer function (MTF) of human eye: an interferometric method similar to that Campbell and Green [ J. Physiol. (London)181, 576 ( 1965)] a double-pass procedure Santamaria et al. Opt. Soc. Am. A4, 1109 1987)]. implemented various improvements in both techniques reduce error estimates MTF. used same observers, refractive state, pupil size (3 mm), wavelength (632.8 nm) methods. In we found close agreement between plane subjective best focus...
Demosaicing is an important part of the image-processing chain for many digital color cameras. The demosaicing operation converts a raw image acquired with single sensor array, overlaid filter into full-color image. In this paper, we report results two perceptual experiments that compare quality output different algorithms. first experiment, found Bayesian algorithm produced most preferred images. Detailed examination data, however indicated good performance was at least in due to fact it...
Using the double pass procedure, Navarro et al. (1993; Journal of Optical Society America A, 10, 201-212) measured monochromatic modulation transfer function (MTF) human eye as a retinal eccentricity. They chose conditions similar possible to those encountered in natural viewing. We report new measurements obtained with chosen instead optimize image quality: we paralyzed accommodation, used 3 mm pupil, and corrected defocus oblique astigmatism at each location. MTFs were estimated tangential...
Background RPE65 is an essential molecule in the retinoid-visual cycle, and gene mutations cause congenital human blindness known as Leber amaurosis (LCA). Somatic therapy delivered to retina of blind dogs with mutation dramatically restores retinal physiology has sparked international interest treatment trials for this incurable disease. An unanswered question how visual cortex responds after prolonged sensory deprivation from dysfunction. We therefore studied RPE65-mutant before therapy....
Color, lightness, and glossiness are perceptual attributes associated with object reflectance. For these representations to be useful, they must correlate physical reflectance properties of objects not overly affected by changes in illumination or viewing context. We employed a matching paradigm investigate the perception lightness under geometric illumination. Stimuli were computer simulations spheres presented on high-dynamic-range display. Observers adjusted diffuse specular components...