About

John S. Werner, Ph.D., is a Distinguished Professor at UC Davis Health, specializing in ophthalmology and vision science. His research focuses on the neurophysiological computations and mechanisms that mediate human vision, particularly changes in color and spatial vision across the lifespan and in association with retinal and optic nerve disease. Dr. Werner's work has demonstrated adaptive modifications of the visual system response to changes in signals due to aging of the eye's optics and retina. His laboratory has developed state-of-the-art methods for imaging the human retina of the living eye at a cellular scale. His studies utilize psychophysical and electrophysiological methods, along with high-resolution retinal imaging techniques such as adaptive optics and optical coherence tomography, to investigate both normal aging and age-related diseases leading to blindness. Dr. Werner's contributions include research on the aging of human short-wave cone pathways, adaptive changes in color vision, and the integrity of central visual pathways in patients with macular degeneration. He has received numerous honors, including the Verriest Medal from the International Colour Vision Society and the Pisart Vision Award from Lighthouse International.

Research topics

• Physics
• Medicine
• Optics
• Ophthalmology

Selected publications

• Melanopsin Stimulation Modulates Blackness Induction

  Color Research & Application · 2026-01-01

  articleOpen accessSenior author

  ABSTRACT A central field will become darker with increasing intensity of a surrounding annulus until it appears uniformly black. We investigated the relation between blackness induction of a central field and the stimulation of melanopsin cells in a surrounding field. Silent substitution was used to selectively modulate melanopsin cells while the tristimulus values were kept constant (melanopic/photopic ratio = 0.51–1.21). Eight participants judged the perceived blackness of the center field using a pairwise comparison method for all visual stimulus combinations. Stimuli were presented monocularly for 0.5 or 5 s with 2‐s inter‐stimulus intervals. Statistical analysis was performed using Scheffé's pairwise comparison method (Nakaya variation). The results showed that perceived blackness of the center decreased significantly under the 5‐s presentation condition with increasing stimulation of melanopsin cells in the surround, although perceived blackness of the center increased with increasing luminance in the surround. In contrast, under the 0.5‐s presentation condition, no significant difference in perceived blackness of the center with stimulus intensity to melanopsin cells was found. These results demonstrate that the stimulation of melanopsin cells of the surround modulates blackness induction of the center at longer stimulus durations.

  PublisherDOI

• AI-Powered Compliance: A RAG-Based System for Product Safety Design Engineering

  2025-05-13 · 1 citations

  article1st authorCorresponding

  This paper presents a Retrieval-Augmented Generation (RAG)-based AI system designed to enhance product safety compliance. By leveraging AI-driven document retrieval, semantic search, and real-time analysis, the system streamlines compliance research, optimizes test planning, and supports regulatory decision-making, significantly improving efficiency, consistency, and accuracy in product safety engineering.

  PublisherDOI

• Training-induced changes in population receptive field properties in visual cortex: Impact of eccentric vision training on population receptive field properties and the crowding effect

  Journal of Vision · 2024-05-21 · 1 citations

  articleOpen accessCorresponding

  This study aimed to investigate the impact of eccentric-vision training on population receptive field (pRF) estimates to provide insights into brain plasticity processes driven by practice. Fifteen participants underwent functional magnetic resonance imaging (fMRI) measurements before and after behavioral training on a visual crowding task, where the relative orientation of the opening (gap position: up/down, left/right) in a Landolt C optotype had to be discriminated in the presence of flanking ring stimuli. Drifting checkerboard bar stimuli were used for pRF size estimation in multiple regions of interest (ROIs): dorsal-V1 (dV1), dorsal-V2 (dV2), ventral-V1 (vV1), and ventral-V2 (vV2), including the visual cortex region corresponding to the trained retinal location. pRF estimates in V1 and V2 were obtained along eccentricities from 0.5° to 9°. Statistical analyses revealed a significant decrease of the crowding anisotropy index (p = 0.009) after training, indicating improvement on crowding task performance following training. Notably, pRF sizes at and near the trained location decreased significantly (p = 0.005). Dorsal and ventral V2 exhibited significant pRF size reductions, especially at eccentricities where the training stimuli were presented (p < 0.001). In contrast, no significant changes in pRF estimates were found in either vV1 (p = 0.181) or dV1 (p = 0.055) voxels. These findings suggest that practice on a crowding task can lead to a reduction of pRF sizes in trained visual cortex, particularly in V2, highlighting the plasticity and adaptability of the adult visual system induced by prolonged training.

  PublisherOA PDFDOI

• Touch Temperature Safety Standards and their Impact on Server Design

  2024-05-28

  article

  High server heat loads result in excessive exhaust air and surface temperatures for given server airflows. Increasing surface temperatures are restricted by safety standards that govern how hot surfaces can be such that they can be safely handled. Handling of hot surfaces and components must be considered as part of the server design process as parts in the rear of the server, facing into the hot aisle, often need to be serviced during operation. This paper will focus on reviewing trends in server and data center temperature and air flow as well as the International Electrotechnical Commission (IEC) touch safety standards and requirements. This paper will also discuss a server design that highlights how caloric analyses of air heating through the server can lead to a significant under-prediction of surface temperatures on touch points and surfaces due to non-uniform airflow and heating within the server. This paper also seeks to help educate the community on the importance of touch safety standards and how such standards can significantly impact server design and potentially limit the ability to lower fan speeds to improve energy and air usage in servers and data centers.

  PublisherDOI

• Warm and cool reheated

  Color Research & Application · 2023-08-29 · 7 citations

  articleOpen access

  Abstract Among more conventional perceptual attributes, such as hue brightness and saturation, color is universally assigned a value along a warm/cool dimension. The source of this aspect of color experience is uncertain and a subject of current debate in color science. An unpublished study from the late twentieth century has recently appeared in an online archive that makes publicly available the results of an extensive set of measurements that document the variation of warm/cool values throughout color space and shows that they relate simply to the sum of the red‐green and blue‐yellow opponent‐color activations (red+yellow vs. blue+green), which the authors suggest is consistent with a sensory basis for this distinction.

  PublisherOA PDFDOI

• Perception of brown with variation in center chromaticity and surround luminance

  Journal of the Optical Society of America A · 2023-01-23 · 1 citations

  articleSenior author

  Brown is a contrast color that depends on complex combinations of chromatic and achromatic signals. We measured brown perception with variations in chromaticity and luminance in center-surround configurations. In Experiment 1, the dominant wavelength and saturation in terms of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mi>S</mml:mi></mml:mrow></mml:math> -cone stimulation were tested with five observers in a fixed surround luminance ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mn>60</mml:mn></mml:mrow><mml:mspace width="thickmathspace"/><mml:mrow class="MJX-TeXAtom-ORD"><mml:msup><mml:mrow class="MJX-TeXAtom-ORD"><mml:mi mathvariant="normal">c</mml:mi><mml:mi mathvariant="normal">d</mml:mi><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>/</mml:mo></mml:mrow><mml:mi mathvariant="normal">m</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:math> ). A paired-comparison task required the observer to select the better exemplar of brown in one of two, simultaneously presented, stimuli (1.0° center diameter; annulus of 9.48° outer-diameter). In Experiment 2, the same task was tested with five observers in which surround luminance was varied (from 13.1 to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mn>99.6</mml:mn></mml:mrow><mml:mspace width="thickmathspace"/><mml:mrow class="MJX-TeXAtom-ORD"><mml:msup><mml:mrow class="MJX-TeXAtom-ORD"><mml:mi mathvariant="normal">c</mml:mi><mml:mi mathvariant="normal">d</mml:mi><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>/</mml:mo></mml:mrow><mml:mi mathvariant="normal">m</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:math> ) for two center chromaticities. The results were a set of win–loss ratios for each stimulus combination and converted to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mi>Z</mml:mi></mml:mrow></mml:math> -scores. An ANOVA did not reveal a significant main effect of the observer factor but revealed a significant interaction with red/green ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>a</mml:mi><mml:mo>∗</mml:mo></mml:msup></mml:math> ) [but not with the dominant wavelength and the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mi>S</mml:mi></mml:mrow></mml:math> -cone stimulation (or <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>b</mml:mi><mml:mo>∗</mml:mo></mml:msup></mml:math> )]. Experiment 2 revealed observer variation in interactions with surround luminance and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mi>S</mml:mi></mml:mrow></mml:math> -cone stimulation. The averaged data plotted in 1976 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>L</mml:mi><mml:mo>∗</mml:mo></mml:msup><mml:msup><mml:mi>a</mml:mi><mml:mo>∗</mml:mo></mml:msup><mml:msup><mml:mi>b</mml:mi><mml:mo>∗</mml:mo></mml:msup></mml:math> color space indicate that high <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow class="MJX-TeXAtom-ORD"><mml:mi>Z</mml:mi></mml:mrow></mml:math> -score values widely distribute in the area of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>a</mml:mi><mml:mo>∗</mml:mo></mml:msup></mml:math> from 5 to 28 and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>b</mml:mi><mml:mo>∗</mml:mo></mml:msup></mml:math> over 6. The balance of the strength between yellowness and blackness differs among observers owing to the amount of induced blackness required for the best brown.

  PublisherDOI

• Color Vision 2023: Introduction by the feature editors

  Journal of the Optical Society of America A · 2023-02-14 · 2 citations

  article1st authorCorresponding
  PublisherDOI

• Sunlight exposure cannot explain “grue” languages

  Scientific Reports · 2023-02-01 · 4 citations

  letterOpen access

  Recently in this journal, Josserand et al. 1 argued that high exposure to UV-B light is an important factor in a language's failing to lexically distinguish green and blue.As noted previously 2,3 , there is a correlation, globally, between (1) societies living in areas with high levels of exposure to UV-B light and (2) the tendency for languages in those societies to lack separate basic color terms for green and blue.Such languages, instead, have either a single term spanning green and blue, referred to as a "grue" term, or a term that merges green and blue with black and other dark shades.It has been proposed that this correlation is caused in part by premature lens aging.While this hypothesis is attractive at first glance, given that UV-B exposure can lead to more rapid yellowing of the eye's crystalline lens, it overlooks two well-established facts, one about color vision and one about color naming.First, chromatic adaptation in the visual system compensates for a wide range of prevailing illuminations, ensuring that the perceived color of objects remains relatively constant across different lighting conditions.This phenomenon, known as color constancy 4,5 , is particularly robust at the level of color categorization 6 , which is the level that is important for color naming.Chromatic adaptation and other perceptual mechanisms that support color constancy compensate for changes in the overall retinal illuminance caused by aging of the ocular media of the eye (i.e., "lens brunescence"), as well.The same neural mechanisms that ensure that a green apple appears green in the middle of the day or at sunset ensure that the apple appears green to a young child and an older adult.Hardy et al. 7 demonstrated that optical media (crystalline lens, cornea, etc.) brunescence is thoroughly compensated at the level of color naming across the age span of normal, healthy adults.In this study, younger (mean age = 23.2) and older (mean age = 73.9)adults were asked to name a range of standardized color samples.Across the 41-fold range of optical media opacity for participants in this sample, use of the English color term "blue" remained constant (R 2 = 0.009, p = 0.89).These findings indicate that even a very large amount of lens brunescence is insufficient to affect color naming in the manner suggested by Josserand et al. 1 Second, Berlin and Kay 8 , based on color naming data collected from 20 languages and examination of 78 additional cases from the published literature, concluded that there is a predictable progression through which most languages develop basic color terms.The specific account of color term evolution proposed there has since been significantly modified and simplified, mainly on the basis of color naming data collected in situ from 110 (at the time) unwritten languages 9 .But the initial qualitative finding of Berlin and Kay, namely that there exist substantial predictable regularities across languages in their color naming systems, has been corroborated.For example, no known language has distinct words for blue and green and yet fails to have distinct terms for red and yellow.These cross-language patterns of color naming have been explained in terms that do not rely on lens brunescence but instead on the similarity of colors, communicative need, or a combination of the two [10][11][12][13] .Therefore, a more parsimonious explanation for why some languages lack a particular set of color terms is based in need: such a distinction may not be sufficiently important to have arisen in that culture.According to Berlin and Kay 8 , "as a culture becomes technologically more complex, speakers have more frequent need to distinguish objects by their colors" (p.512).With an increase in the number and variety of trade goods and other objects available in a society, accompanying, for example, the advent of manufacturing, and contact with languages of previously industrialized societies, there is increased pressure on the language used in that society to add color terms.This argument is supported by the observation that distance from the equator (and thus low UV-B exposure), level of technology, and number of basic color terms are positively correlated [14][15][16] .Thus, the correlation of grue terms with high levels of UV-B exposure could simply reflect the fact that grue terms tend to occur in less technologically complex societies, which tend to be spoken in high UV-B areas.An appeal to lens brunescence is not necessary to explain the geographical distribution of languages with grue terms.One final consideration concerns historical language change.For example, Old Japanese had a grue term, ao(i), probably appearing between 500 and 650 CE, which now serves as the common term for blue.The

  PublisherOA PDFDOI

• Aging of visual mechanisms

  Progress in brain research · 2022-01-01 · 5 citations

  articleSenior authorCorresponding
  PublisherDOI

• Progress in measurements and interpretation of light-evoked retinal function using OCT based optoretinography (ORG)

  2021-12-09

  article

  The development of functional retinal imaging is of great interest to clinical and experimental ophthalmology, because it should provide more sensitive tools for ocular diseases diagnostic that would go beyond current gold standard of simple evaluation of the static retinal morphology. In this presentation we will review our recent progress in measurements and interpretation of OCT-based optoretinograms (ORG) i.e., the paradigm of using NIR OCT to measure in vivo bleaching-induced changes in retinal morphology (transient changes in volume of individual neurons, or thickness of retinal layers). Specifically, comparison between different instrumentations used to acquire ORGs and between results acquired using clinical (human) and experimental (animal) systems will be presented. Additionally, intensity-based and phase-based ORG extraction framework will be presented. Finally, we will discuss our findings in the context of current understanding of measured process, being a result osmotically driven water movements between the photoreceptors, and other retinal neurons and its surroundings.

  PublisherDOI

Recent grants

• Vision Science Training Program: Cornea to Cortex

  NIH · $4.7M · 2003–2028

• Structure and Function of the Chorioretinal Complex in Age-Related Macular Degene

  NIH · $2.4M · 2014–2020

• NIH Grant R23AG004058

  NIH · $50k · 1987

• NIH Grant R01AG004058

  NIH · $3.3M · 2017

• NIH Grant R37AG004058

  NIH · $2.9M · 2011

Frequent coauthors

• D. Blöch

  Institut Pluridisciplinaire Hubert Curien

  441 shared

• E. Conte

  Institut Pluridisciplinaire Hubert Curien

  354 shared

• J. Andreä

  Institut Pluridisciplinaire Hubert Curien

  349 shared

• C. Collard

  Institut Pluridisciplinaire Hubert Curien

  343 shared

• E. C. Chabert

  Institut Pluridisciplinaire Hubert Curien

  329 shared

• G. Hamel de Monchenault

  Université Paris-Saclay

  318 shared

• M. Lethuillier

  Institute of Nuclear Physics of Lyon

  297 shared

• P. Verdier

  Institute of High Energy Physics

  292 shared

Education

• PhD, Ophthalmology

  University of California Davis

Awards & honors

• Verriest Medal, International Colour Vision Society, 2015
• Pisart Vision Award, Lighthouse International (New York), 20…
• Jules and Doris Stein Research to Prevent Blindness Professo…
• Ninetieth Annual Distinguished Research Lecture, University…
• Alexander von Humboldt Foundation, Humboldt-Preis, 1994