Lecture 2 (pres 2 up to slide 105)

Question 1

If a person only has ONE photopigment, what variable can be adjusted to allow the observer to match ANY wavelength in the spectrum?

Answer 1

INTENSITY

-adjusting only that can allow a monochromat to see two colors as being identical (recall: dichromat on anomaloscope)

Question 2

WHAT type of info is lost once isomerization (11-cis to all trans) has occurred? What is this principle called?

-which two pathological conditions present w/ only ONE photopigment?

Answer 2

• SPECTRAL info is lost once photons absorbed/isomerization happens
• aka principle of UNIVARIANCE

-Rod monochromatism, and S-cone monochromatism

Question 3

T/F: under MESOPIC conditions, which type of monochromatism has a slight advantage?

Answer 3

mesopic: both rods/cones working, but neither working OPTIMALLY
- S-cone monos have slight advantage (might see some hues/colors)

Question 4

T/F: In DIchromats, intensity is irrelevant in determining the difference between two wavelength? If true, why? Based on what variable instead of intensity?

Answer 4

True. B/c the RATIOS b/w the responses of each photopigment remains the SAME, and it’s the RATIO information that’s used to discrimate one wavelength (color) from another

-trichromats works the same way, but having three photopigments allows discrimination b/w ALL wavelengths

Question 5

In color deficient individuals (like Tim) his system can SEE all colors - so what’s the problem?

Answer 5

for certain colors, the RATIOS are similar - makes it tough to see certain wavelengths/colors as separate

Question 6

Grassman’s law of SCALAR INVARIANCE states that if the intensity of one half is changed by K, then the two fields can be matched (recall, the fields are metamers) by change the intensity on the other half by K - what does this mean, practically?

Answer 6

If you increase intensities of BOTH fields by the SAME amt, the metamerism won’t be disrupted

Question 7

Grassman’s law of ADDITIVITY states what?

Answer 7

If light is added to one field, then the two fields can be matched by adding the SAME light to the OTHER field (makes sense) - two colors seen will still be metamers

Question 8

ADDITIVE color mixing of blue and yellow creates what color?

SUBTRACTIVE color mixing of blue and yellow creates what color? How does subtractive work? Think of paint.

Answer 8

additive: white - LIGHT (projector)
subtractive: green - PAINT (art)
subtractive: blue paint absorbs L wavelengths, reflects Short wavelengths (blue). Yellow paint absorbs Short and reflects long (red) Combo blue and yellow paint absorbs blue and red, and reflects only GREEN

Question 9

So: mixing LIGHT causes ____ wavelenghts (more/less) wavelengths are reflected.
-Mixing PIGMENT causes what?

Answer 9

LIGHT: ADDITIVE: MORE wavelengths reflected (white)
PIGMENT: SUBTRACTIVE: LESS wavelengths reflected (green)

-Note: additive IS possible w/ pigments (think of small paint spots seen as a whole)

Question 10

A BLUE filter transmits only WHAT wavelength light?

Answer 10

SHORT wavelength light ONLY (hence, you’ll only see blue) - other colors are absorbed

Question 11

Which type of cell makes connection with ONLY cones, range in number from 7-36 cone connections/cell (depending on retinal eccentricity), and provide fdbk to neighboring cones?

Which SPECIFIC type receive input from L and M cones?

White SPECIFIC type receive input from mostly S cones, but also some L and M?

Do they transmit signal vertially?

Answer 11

HORIZONTAL cells

H1: L- and M-

H2: mostly S-, some L/M

NO!! ONLY horizontal signal transmission (no vertical)

Question 12

Horizontal cells have two other responsibilities: passing the signal onto which cell type? And do they respond more to spatial or temporal changes?

Answer 12

bipolar

Trick question: they respond well to BOTH spatial AND temporal!

Question 13

Three types of BIPOLAR cells (although 9-10 exist)? What is the MAIN thing each one detects?

Answer 13

1) Midget: On/Off C/S of RED/GREEN
2) Diffuse: On/Off C/S of LUMINANCE
3) S-cone: S-cone CENTER, L/M surround of BLUE/YELLOW

Question 14

T/F: midget bipolar cells are 1:1 Center/surround orientation in the fovea, but can have MULTIPLE:1 cell orientation in the surround

Answer 14

TRUE! That’s what allows precise spatial orientation!

Question 15

Role of amacrine cells? Differentiating feature over Horizontal cells?

Answer 15

Role: unknown - transmit signals both VERTICALLY AND HORIZONTALLY b/w bipolar cells

Question 16

Three types of GANGLION cells (although ~17 exist)? Receive input from which cells?

Answer 16

1) On/off midget bipolar–> on/off MIDGET ganglion
2) On/off diffuse bipolar–> on/off PARASOL ganglion
3) On S-cone bipolar–> On-only or OFF-only center SMALL BISTRATIFIED GC (no surround/no spatial antagonism)

Question 17

Midget GCs send R/G info to WHAT cell in the LGN? More sensitive to (longer/shorter) wavelengths?

Answer 17

Midget GC–> PARVOcellular layers [L-M] –> sensitive to LONG wavelengths

Question 18

Parasol GCs send achromatic info to WHAT cell in the LGN? More sensitive to (longer/shorter) wavelengths?

Answer 18

Parasol GC–> MAGNOcellular (motion) layers [L+M] - max sensitivity! –> most sensitive to SHORT wavelengths

Question 19

What are the three attributes of color space? What do they each mean?

Answer 19

Hue (color), Saturation (vivid/rich), Luminance (bright)

-Computers use either the RGB system or the HSB system (hue/sat/brightness)

Question 20

On the CIE chromaticity diagram, what is the SPECTRAL LOCUS?

-what’s special about all the colors on this line?

Answer 20

spectral locus: all the wavelengths which are plotted on the OUTER line
-all the wavelengths along the outer line are MONOCHROMATIC colors

Question 21

Negative values in color matching fxns were d/t which color? CIE modified the table by making a graph with 1) a spectral locus and 2) which other property?

Answer 21

red - had to switch it to other side of equation d/t negative slope

1) spectral locus and 2) line of purples (complimentary to green, but NOT monochromatic! It’s a combination product!)

Question 22

What’s important to remember specifically about LUMINANCE w/ respect to the color space?

Answer 22

Luminance is a vector that’s VERTICAL to the color space

i.e. brightness INCREASES as you go higher in the color space

Question 23

The “neutral” or ‘white’ point on the color space is at what locus?

Answer 23

0. 33, 0.33

- allows CONSISTENCY of colors, i.e. for traffic lights worldwide

Question 24

T/F: the DOMINANT wavelength of two mixed wavelengths (colors) can be determined by using the color space. If so, how?

Answer 24

TRUE - by drawing another point @ the WHITE point and crossing it thru the line of combined pigments