Visual Function: Ch 3

Under daylight conditions, red and green surface look equally bright. Compared to green surface, red surface most likely emits (less/more/equal) energy?

Under photopic conditions, most sensitive to 550 (green). Need least 550 to see it. Red will be as bright as green if it emits more light. More!

Two patches of light adj to each other under scotopic conditions. One emits 507 nm, other 620 nm. both produce 40 quanta of light. which is brighter?

Under scotopic conditions, 507 nm is most likely to absorb light --> 507 is brighter.

Direct vs indirect

We are indirect scaling: brightness = instensity^constant. Saturation of stimulus in brightness as increases.

Axis of ROC curve

Y: hits = sensitivity: correct when present. X: false positive = 1-specificity Specificity = correct rejects.

serial processing of complex cells

complex cells are direction selective. no excitation or inhibition. stimulus placed anywhere as long as direction

Who has trouble with car breaks?

protands: red is dim.

what is the scotopic threshold reponse?

response from ganglion and amacrine cells: DNMA blocks signal from bipolar to retinal ganglion.

Serial processing of simple cells

simple cells are on and off. when put together (serial processing) then bars of specific widths can stimulate it

Is EOG greater under light or dark adapted conditions?

Greater at light adapted conditions: light rise/dark trough

Which are there more of? Rods or cones?

Rods > Cones

What is found 20 deg from the fovea?

Rods are found where?

Luminosity values

Trichromat: 550 Protans: missing L so shifted a little lower. red is dim: car strugs.

Assume absorption of 10 quanta of 510 nm by an eye that only contains rods result in vision. If wavelengths were 450 nm, how many quanta would need to be absorbed to produce vision?

10 quanta

What wavelengths are most sensitive to small changes?

490 and 590: greens and yellows.

The percentage of cones located in the fovea is

5-10% of this is found in the fovea. Greatest density, but still mainly reside outside of the fovea.

What wavelength appears least saturated for trichromat, protan, and deutan? what about protanomaly and deutanomaly?

570 yellow trichromat 492 (blue-green?) green traffic lights 498 (blue-green?) green traffic lights Protanomaly: 492 will look desaturated but not white, since it doesn't cross the x axis Deuteranomaly: will look desaturated and faded.

What differentiates opia from anomaly? Tritan?

Analmoscope can tell red/green deutan from deutanomoly, plates can't. D15 can test for tritan, ishihara can't.

Rod cone break in dark adaptatio will be least noticeable when stimulus has a wavelength of 500 / 550 / 600 nm

At 600 nm, ____ part of the dark adaptation curve will be least noticable.

Hue contour line

Stimuli that have the same hue. As you increase the intensity of a hue, the wavelength needed to maintain that same hue changes. Hues shorter than 502 nm decrease wavelength as intensity increases Hues longer than 502 nm, inc intensity, increase wavelength

What does the ERG a/b/c wave measure?

ERG measures under dark adapted conditions. a: neg rod/cone. b: pos bipolar/muller c: RPE, in response to bright flashes under dark adapted conditions.

A path of 507 and 620 each bleach 30 rhodopsin molecules. which is brighter?

Equally bright. Bleached the same number of rhodopsin. Probably took more to bleach them, but once it's bleached, it emits light.

Color opposing neurons fire more for what wavelengths and less for what?

Fire more at higher wavelengths above 570 and less for lower.

In the region of the photopic light adaptation function that follows weber's law, as the background intensity increases, absolute sensitivity inc / dec / constant

Following Weber's law as background intensity increases, the foreground intensity has to increase by a factor of 0.14. Contrast remains the same. Sensitivity will decrease : if originally the foreground was 10, now the foreground is 11.4. The stimulus intensity increases, meaning the sensitivity decreases. (check logic)

Payoff: 5$ for every hit, -5 for every miss: strict or lax?

Strict

Additive property

If you add the same thing to two metamers, still matched.

Scalar property

Increase intensity of two metamers by some amount --> same

What cones can be found at the center of the fovea?

L and M cones are found at the center of the fovea.

Payoff: $25 for hit, -5 for miss

Lax

Lesions to the parvo neurons would cause what kinds of changes to wavelength discrimination, spatial frequency, and temporal frequency?

Lesions here would cause dec wavelength disc, dec spat f, no change in temporal

Lesions to the magno neurons would cause what kinds of changes to wavelength discrimination, spatial frequency, and temporal frequency?

Lesions here would cause no change in wavelength disc, dec in low spatial f, dec in high temp f.

Lightness constancy vs color constancy vs simultaneous contrast:

Lightness: weber's law - more light on an optotype doesn't make something more or less easier to see, since it follows the ratio and it's all relative, even though the absolute sensitivity increases (?). Change in lightness looks the same Color: change in lighting color conditions doesn't make things look different (apricots at night, tshirts in the daytime) Simultaneous contrast: brightness depends on the background. A grey box looks different in different backgrounds.

Lax criteria have high? low?

Low misses (false negative), but high false positives.

Associated property

Matched color maintained if one metamer substituted for another

Contrast sensitivity is highest under conditions that are meso, pho, scotopic.

Photopic -- why?

Color plates: who can't see pink? purple? blue?

Protan: can't see pink (red) since red and white cross. Deutan: can't see purple since purple and white cross. Tritan: can't see purple but can see blue.

Spatial frequency changes in cataract? reduced VA?

Reduced VA only at high SF, not low. Cataract is throughout all. 4cpd optimum.

If you remove the RPE, which wave from what kind of measurement do you lose?

Remove RPE, lose c wave in ERG.

Absorption and Spectral sensitivities of rhodopsin/scotopic, cones, and overall photopic system

Rho/sco: 505 nm (green) Photopic: 555 (?) L: 557 559 M: 530 S: 430 However, for cones, we are actually sensitive to 440, 520, 620 due to shifts.

As you increase the intensity of a 480nm wavelength, how do you ensure the same hue?

The wavelength will decrease, so to maintain the same hue, increase the wavelength.

As you increase the intensity of yellow, how does the wavelength change to maintain the same hue?

The wavelength witll increase, so to maintain the same hue, decrease the wavelength.

Where are the S cones round?

These cells are found 0.5 deg away from the center of the fovea

Strict criteria have high ? and low ? Shift FOS up or down?

These criteria tend to have low false positives and low hits, and high correct rejects. Shift FOS curve down.

In full field ERG, a dim flash will result in what kind of wave? what is this called?

This kind of flash gives a slow negative wave, the scotopic threshold response.

Photopic vision compared to scotopic vision is characterized by high/low spatial/temporal summation?

This vision is characterized by low spatial and low temporal summation, compared to the other.

anomaloscope: top / bottom field. what do you change?

Top field: mix of 546 and 670 (green and red) and you can change the wavelength. Bottom field: 590 yellow, you can change the luminance. Dichromat: monochromat at these wavelengths since missing one of the two ML cones.