Light 2 - Spectral, Sensitivity, Adaptation

What photoreceptors mediate scotopic vision?

Rods mediate scotopic vision.

What photoreceptors mediate photopic vision?

L-, M-, and S-cones mediate photopic vision.

How many opsins does each cone contain?

Each cone contains one opsin.

What are the peak spectral sensitivities of the cone opsins discussed in the lecture?

Cone opsins peak approximately at 420 nm (S-cones), 535 nm (M-cones), and 565 nm (L-cones).

What is the peak spectral sensitivity of rods?

Rods have a peak spectral sensitivity at approximately 507 nm.

What is the peak spectral sensitivity of melanopsin?

Melanopsin has a peak spectral sensitivity around 480 nm.

What is rhodopsin?

Rhodopsin is the photopigment found in rods that mediates scotopic vision.

What are the names of the cone opsins?

The cone opsins are cyanolabe, chlorolabe, and erythrolabe.

Where was melanopsin originally discovered?

Melanopsin was originally discovered in the dermal melanophores (pigment cells) of the African clawed frog.

What is the mathematical relationship between threshold and sensitivity?

Threshold and sensitivity have an inverse mathematical relationship.

What partially determines the photopic and scotopic sensitivity functions?

The photopic and scotopic sensitivity functions partially derive from the opsin absorption/transmission curves.

What does the degree of deviation between sensitivity and absorption curves reflect?

The degree of deviation reflects non-opsin effects.

What is the photochromatic interval?

The photochromatic interval is the difference between scotopic detection of a wavelength and photopic color perception of that wavelength.

What is the Purkinje shift or Purkinje effect?

The Purkinje shift is the shift in peak visual sensitivity from 555 nm under photopic conditions to 507 nm under scotopic conditions.

How does red appear under photopic versus scotopic conditions?

Red appears brighter under photopic conditions, while green appears brighter under scotopic conditions.

Why do spectral sensitivity curves and luminosity functions not look identical?

Spectral sensitivity curves and luminosity functions differ because luminosity functions include additional non-opsin visual processing effects.

Where do cones reach their highest density in the retina?

Cones reach their highest density in the foveola.

Where do rods reach their highest density in the retina?

Rods reach their highest density at the edge of the macula.

What retinal structure lacks photoreceptors and creates a blind spot?

The optic disc lacks photoreceptors and creates the blind spot.

What is meant by the S/M/L mosaic in the retina?

The S/M/L mosaic refers to the spatial distribution of short-, medium-, and long-wavelength cones across the retina.

What is foveal tritanopia?

Foveal tritanopia is the relative absence of S-cones in the foveola, reducing blue sensitivity centrally.

What technology was first used in astronomy and later adapted for retinal imaging?

Adaptive optics was first used in astronomy and later adapted for retinal imaging.

What does AOSLO stand for?

AOSLO stands for adaptive optics scanning laser ophthalmoscopy.

What retinal structures are visualized by AOSLO?

AOSLO visualizes photoreceptor inner segments.

What laser wavelengths were used for pseudocolor imaging in the lecture’s AOSLO example?

The pseudocolor AOSLO image used 543 nm, 680 nm, and 780 nm lasers.

Can humans detect a single photon?

Humans can detect a single photon above chance levels.

What type of light source was used in the single-photon detection experiment?

A quantum optical single-photon light source was used.

How are photon pairs generated in the single-photon experiment?

A high-energy pump photon produces lower-energy signal and idler photon pairs.

What happens to the idler photon in the single-photon experiment?

The idler photon is detected to confirm that the signal photon exists.

What happens to the signal photon in the single-photon experiment?

The signal photon is sent to the subject for detection.

How long were subjects dark adapted before the single-photon experiment?

Subjects were dark adapted for 40 minutes.

How many trials were conducted in the single-photon experiment?

Approximately 30,000 trials were conducted.

How many single-photon events occurred in the experiment?

There were 2,420 single-photon events.

What was the correct response probability for single-photon detection?

The correct response probability was 0.516.

What response probability was achieved for high-confidence observations of single photons?

High-confidence observations had a response probability of 0.60.

What effect does a priming photon have on single-photon detection?

A priming photon increases the probability of detecting a single photon.

Why was the priming photon effect thought not to result from temporal summation?

The interval was too long for temporal summation, suggesting the effect involved attention.

What process enables the exquisite sensitivity of rods?

Regeneration of photopigments during dark adaptation enables exquisite rod sensitivity.

What happens to sensitivity during dark adaptation?

Sensitivity recovers over time as photopigments regenerate.

What is the cone plateau in dark adaptation?

The cone plateau is the early stage of dark adaptation where cone sensitivity stabilizes before rods dominate.

What is the rod plateau in dark adaptation?

The rod plateau is the later stage of dark adaptation where rod sensitivity reaches maximum levels.

What is the rod-cone break?

The rod-cone break is the point during dark adaptation when rod sensitivity surpasses cone sensitivity.

What is the approximate size of the photochromatic interval in dark adaptation?

The photochromatic interval is approximately 3 log units.

What overall increase in sensitivity occurs during dark adaptation?

Dark adaptation results in approximately a 100,000-fold increase in sensitivity.

What is cone bleaching?

Cone bleaching is the temporary loss of cone photopigment sensitivity after exposure to bright light.

How quickly do cones recover 50% sensitivity after bleaching?

Cones recover approximately 50% sensitivity in 1.5 minutes.

What visual phenomenon can result from cone bleaching?

Cone bleaching can produce temporary afterimages.

Can cone bleaching be color-specific?

Yes, cone bleaching can be incomplete and color-specific.

What happens to rhodopsin during bleaching?

Rhodopsin becomes transparent during bleaching.

What is rhodopsin saturation?

Rhodopsin saturation occurs when all rod photopigment is bleached.

How quickly does rhodopsin recover 50% after bleaching?

Rhodopsin recovers approximately 50% in 5 minutes.

Why does the rod-cone break occur after about 90% rhodopsin recovery rather than 50% recovery?

The rod-cone break occurs after about 90% rhodopsin recovery because rod saturation limits sensitivity until most Na⁺ channels recover.

What is an incremental threshold measurement?

An incremental threshold measurement determines the smallest detectable increase in light intensity above a background illumination.

Why are incremental threshold measurements used?

They are used to isolate rod or cone system responses.

What is dark light?

Dark light is the intrinsic visual noise present in the absence of external light.

What is the slope of the threshold-versus-background function in darkness?

The slope is flat in darkness.

What is the DeVries-Rose law?

The DeVries-Rose law states that detection threshold increases with the square root of background luminance.

What limits detection under the DeVries-Rose law?

Detection is limited by background quantal fluctuations.

What slope characterizes the DeVries-Rose law?

The DeVries-Rose law has a slope of 1/2.

What does the DeVries-Rose region represent?

The DeVries-Rose region represents ideal light detection limited by photon noise.

What is Weber’s Law in vision science?

Weber’s Law states that the detection threshold remains a constant proportion of background luminance.

What slope characterizes Weber’s Law?

Weber’s Law has a slope of 1.

What is contrast constancy or invariance?

Contrast constancy is the maintenance of a constant relative detection threshold across illumination levels.

What is Weber’s constant or fraction?

Weber’s constant is the constant ratio of detectable contrast relative to background luminance.

What is the Weber fraction for scotopic vision?

The Weber fraction for scotopic vision is approximately 0.14.

What is the Weber fraction for photopic vision?

The Weber fraction for photopic vision is approximately 0.015.

What is the Weber fraction for S-cones?

The Weber fraction for S-cones is approximately 0.09.

Why does the visual system regulate sensitivity according to Weber’s Law?

The visual system regulates sensitivity to maintain a constant relative detection threshold despite changes in illumination.

What happens to absolute threshold as illumination increases?

Absolute threshold increases as illumination increases.

What happens when rods become saturated?

Rod saturation occurs when approximately 10% rod bleach closes the maximum number of Na⁺ channels.

Why is 90% rhodopsin recovery required before the rod-cone break?

Because rod Na⁺ channels remain saturated until most rhodopsin recovers.

What is contrast ratio?

Contrast ratio is the ratio of maximum luminance to minimum luminance in a display system.

What formula defines contrast ratio?

Contrast ratio is defined as Lmax/Lmin.

How is contrast ratio commonly expressed?

Contrast ratio is commonly expressed as a proportion such as 1000:1.

What does contrast ratio describe?

Contrast ratio describes the maximum brightness capability of a system relative to its darkest black level.

What applications best use contrast ratio?

Contrast ratio is best used for evaluating display monitors, televisions, and projectors.

What is Michelson contrast?

Michelson contrast measures the modulation of a periodic signal relative to its average luminance.

What formula defines Michelson contrast?

Michelson contrast is defined as (Lmax − Lmin)/(Lmax + Lmin).

What range of values can Michelson contrast take?

Michelson contrast ranges from 0 (no contrast) to 1 (maximum contrast).

What applications best use Michelson contrast?

Michelson contrast is best used for periodic patterns, visual gratings, and optical charts with equal bright and dark areas.

What is Weber contrast?

Weber contrast measures the relative luminance difference between a feature and its background.

What formula defines Weber contrast?

Weber contrast is defined as (Lfeature − Lbackground)/Lbackground.

What applications best use Weber contrast?

Weber contrast is best used for isolated small targets such as letters on an eye chart.

Why does Weber contrast stem from Weber’s Law?

Weber contrast measures relative luminance differences against a uniform background, consistent with Weber’s Law of constant proportional detection.

Can Weber contrast have negative values?

Yes, Weber contrast can have negative values for darker objects on a brighter background.

What is root-mean-square (RMS) contrast?

RMS contrast is the standard deviation of pixel luminances relative to the mean luminance.

What applications best use RMS contrast?

RMS contrast is best used for complex natural scenes, photographs, and random-dot patterns.

Why is RMS contrast useful in vision science?

RMS contrast is useful for calculating visual efficiency and neural responses.

What are the three major luminance adaptation ranges of vision?

The three adaptation ranges are scotopic, mesopic, and photopic.

Can rods contribute to vision under photopic conditions?

Yes, evidence suggests rods can drive responses even under photopic conditions.

What happens to rod contrast sensitivity at high irradiance levels?

Rod contrast sensitivity is initially strongly reduced at high irradiances.

What happens to rod contrast sensitivity after prolonged high irradiance?

Rod contrast sensitivity progressively recovers, allowing responses to moderate contrast stimuli.

What mechanisms underlie rod recovery at high irradiance?

Phototransduction gain adjustments and bleaching adaptation underlie rod recovery.

How do retinal ganglion cell responses behave in coneless retinas at mesopic ranges?

Retinal ganglion cell responses shut down at mesopic ranges in coneless retinas.

How do retinal ganglion cell responses behave in photopic ranges in coneless retinas?

Retinal ganglion cell responses become even larger in photopic ranges in coneless retinas.

What genetic modification was made in the Opn1mwR transgenic mouse line?

The mouse M-opsin coding sequence was replaced with the human long-wavelength-sensitive L-opsin sequence.

What adaptation and stimulus colors were used in the rod-cone interaction experiment?

Subjects adapted to violet light and were presented with blue, cyan, and red stimuli.

How did S-opsins respond to blue, cyan, and red stimuli?

S-opsins showed low responses to all three stimuli.

How did L-opsins respond to blue, cyan, and red stimuli?

L-opsins responded to all three stimuli.

How did rod opsins respond to red stimuli?

Rod opsins showed low responses to red stimuli.