How do eyes make the sky look blue, and why do people differ?

"favoring a model of red-green opponency carried by cells whose centers receive input from either L or M cones and whose surrounds receive mixed contributions from both."

"There are three classes of cone photoreceptors ( 2 ): the S cones, the M cones, and the L cones. Each absorbs broadly across the spectrum."

"We now know that there are, in fact, three cone types (L, M, and S) with the predicted wavelength absorption profiles."

"One class of opponent cells (L o and M o ) differences the outputs of the L and M cones, and the other (S o ) differences the output of the S cones from that of the combined L and M cones."

"suggesting that the relative number of L and M cones is a factor that regulates individual variations in red-green color appearance."

"the model predicted mechanisms that would allow color discrimination by comparing activation of L versus M cones (L/M opponency) or by comparing activation of S-cones to the sum of L and M cones (S/L + M opponency)."

"It also increases the amount of blue seen in the 90° to 180° range and decreases the amount of blue in the 180° to 270° range."

"the relative numerosity of the long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) cones and the red-green color appearance, as assessed by means of unique yellow, are stable from fovea to midperiphery (+/- 28 deg nasotemporal)."

"the appearance of each of the four “unique colors” (red—RG; green—GR; yellow—YB; blue—BY) requires a particular mixture of the possible combinations between L/M opponent and S + or S- mechanisms, which are L + S+, M + S−, L + S−, and M + S+, respectively."

"Note that our model predicts, and the data show, that signals arising in the S cones make as large a contribution to the appearance of green as they do to blue."

"As foveal tests decrease in size, unique yellow progressively shifts toward longer wavelengths"

"Importantly, the cone-opponent mechanisms that account for the ability to discriminate colors do not account for color appearance and color perception. Instead, color appearance involves further interactions between the cone-opponent mechanisms (Stage 3, Fig. 1a )."

"We compared color scaling of various isoluminant stimuli by using large spots, which activate all cone types, to that with tiny spots in the central foveola, where S cones, and thus S opponent (S o ) cell activity, are largely or entirely absent."

"Individual differences in unique yellow over a 20-nm range and the relative numerosity of L and M cones can be linked by means of this model"

"It is well known that intraocular scattering tends to increase with age, mostly due to structural changes in the eye lens"

"This amounts to an increase of brightness of order –1 magV/arcsec2 for 80 yr old observers across the whole range of scattering angles, in comparison with young 20 yr old observers."

"The differences caused by pigmentation tend to be more noticeable at mid- to large scattering angles"

"Darum vermutete er drei getrennte chemische Prozesse in der Netzhaut mit je zwei Gegenfarben , mit je einem hemmenden und einem erregenden Anteil, die nach einem Gleichgewicht streben."

"Initially, the normal trichromat is the type in which three colors are required to equal all the other colors: red, blue, and green (Matlin and Foley 1996)."

"the same photoreceptor repertoire can potentially generate different visual outputs depending on retinal circuitry"

"Drei verschiedene Zapfentypen im Auge, die jeweils ihre höchste Empfindlichkeit für kurz (blau)-, mittel (grün)- und langwelliges (rot) Licht haben, liefern Signale an die nachgeschalteten farbopponenten Ganglienzellen der Netzhaut (neuronale Farbkanäle)."

"Die Ursache liegt in den drei Zapfen des Farbsehens. Diese haben ihre Empfindlichkeiten für Blau (S-Zapfen), Grün (M-Zapfen) und Rot (L-Zapfen)."

"since with color blindness, the deficit of one or more of the three cones makes color perception difficult, which makes color contrast low."

"Horizontal cells contribute substantially to spatial and spectral integration by pooling signals from neighboring photoreceptors and providing feedback to the photoreceptor synaptic terminals"

"Auf der neuronalen Ebene werden die Zapfensignale „verschaltet“: „Rot“ und „Grün“ werden subtrahiert, die Differenz wird im Rot-Grün-Kanal weitergeleitet; die Addition von „Rot“ und „Grün“ dagegen ergibt ein Signal, dem die Empfindung von Gelb entspricht; diese Signale werden vom „Blau“-Signal subtrahiert und im Gelb-Blau-Kanal weitergeleitet."

"Um diesen Konflikt von drei oder vier Grundfarben zu entschärfen, teilte Kries den Vorgang des Farbensehens in eine periphere und eine zentrale Zone."

"Bipolar cells transmit photoreceptor-derived information into the inner retina, where amacrine cells introduce additional temporal and spatial processing"

"Obwohl Herings Vorstellungen stark vereinfachend waren, konnten diese drei Prozesse tatsächlich nachgewiesen werden. Seit 1966 bestätigen neurophysiologische Untersuchungsergebnisse, dass es vier grundlegende Farbempfindungen gibt."

"Dabei nimmt die periphere Zone der Sehzellen drei Signale auf. Diese Signale werden in der zentralen Zone, also im Nervensystem, in einem Prozess zu zwei gegensätzlichen Paaren von Grundfarben geformt."

"Ganglion cells represent a major output stage of the retina, transforming local retinal activity into action potentials that are transmitted through the optic nerve to higher visual centers"

"So entstehen, wie auch Hering postulierte, drei Empfindungsdimensionen: 1. Helligkeit, 2. Gelb-Blau-Komponente, 3. Rot-Grün-Komponente, aus denen dann mehrere tausend Farbarten unterschieden werden können."

"Da keine Farbe zugleich rötlich und grünlich oder gleichzeitig Gelb und Blau ist, nahm er komplementäre Wahrnehmungen an, in denen die Farbwahrnehmung aus einem Rot-Grün-, einem Gelb-Blau- und einem Schwarz-Weiß-Ablauf besteht."