Chapter 6

Question 1

What is a photon?

Answer 1

The smallest possible unit of light energy

Question 2

What is the electromagnetic spectrum?

Answer 2

the continuum of energy produced by electric charges and is radiated as waves.

Question 3

How does light travel through the eye?

Answer 3

cornea → pupils → lens → retina → optic nerve

Question 4

What is the point of central focus on the retina?

Answer 4

The fovea. this is where the image should be concentrated.

Question 5

If they don’t send a signal, nothing is seen. what are they?

Answer 5

Retinal cells (rods, cones, retinal ganglion cells)

Question 6

Where are most of our cones located?

Answer 6

On the fovea.

Question 7

Photoreceptors (rods+cones) convert light into _________.

Answer 7

nerve impulses (transduction)

Question 8

What does isomerization do?

Answer 8

triggers transformation of light into electricity in receptors. occurs when retina changes shape, sticking out from the opsin.

Question 9

What is it called when the retina becomes lighter in colour, when light is constant and all the photoreceptors are bleached. + Retinal separates from the opsin. ?

Answer 9

Visual pigment bleaching

Question 10

What is visual pigment regeneration?

Answer 10

As light remains on, more of retinal detaches, but more are regenerated at the same time. Opsin and retinal are rejoined. When sleeping (no light) all visual pigment molecules regenerated. That’s why light seems brighter in the morning.

Question 11

What is the duplexity theory of vision?

Answer 11

Rods and cones are both used for vision, but they are specialized for different tasks.

Question 12

Which cell is better for grayscale, and which for colour?

Answer 12

Rods = grayscale. Cones = colour.

Question 13

What are some characteristics of cones?

Answer 13

• found mostly in fovea
• better for seeing detail (high acuity)
• colour vision
• daytime (photopic) vision
• need lots of light
• 6 million
• no convergence

Question 14

What are some characteristics of rods?

Answer 14

• night (scotopic) vision
• low detail (acuity)
• gray scale vision
• need little light
• more sensitive
• 120 million
• more convergence (ganglion cells receive input from over 120 rod receptors)

Question 15

What are “M and P channels”?

Answer 15

Magnocellular ganglion cells and Parvocellular ganglion cells

Question 16

What are some characteristics of Magnocellular ganglion cells (M channel)?

Answer 16

input largely from rods.
Fast moving channel.
Low acuity, high contrast sensitivity, faster conduction
Motion and grayscale processed
Layers 1-2 carries lighter info like motion

Question 17

What are some characteristics of Parvocellular ganglion cells (P channel)?

Answer 17

input largely from cones.
Slow moving channel.
High acuity
slower conduction
Colour processed
Layers 3-6, carries heavy info like details

Question 18

What is the Mach Band Illusion and what does it show?

Answer 18

optical illusion where same colour rectangle looks darker next to the lighter rectangle and vice versa. Shows how the brain adds contrast & emphasizes borders.

Question 19

What is selective reflection?

Answer 19

some wavelengths are reflected more than others

Question 20

What is selective transmission?

Answer 20

Only some wavelengths pass through the object or substance

Question 21

What is spectral sensitivity?

Answer 21

Our sensitivity to light at each wavelength.

Question 22

How can we measure spectral sensitivity?

Answer 22

To test, would present a monochromatic beam of light to peripheral; vision of participants who would turn it down until they could just barely see it. Much easier for human to detect red, yellow, green. This is a test of both rods and cones together. When rods are tested alone, it was much easier to see short/medium waves of blue and green.

Question 23

What is the Purkinje effect?

Answer 23

Johannes Purkinje noticed he liked red + yellow flowers better during the day and blue ones better at night. This is bc blue appears brighter at night with rods mostly working.

Question 24

What are the 3 kinds of cones?

Answer 24

short (blue), medium (green), and long (red) wavelength cone receptors. Remember most technology uses RGB values for colour.

Question 25

What is protanopia?

Answer 25

colour deficiency where someone is missing the long wavelength (red) pigment. (% of males, 0.2% of females affected)

Question 26

What is deuteranopia?

Answer 26

colour deficiency where someone is missing the medium wavelength (green) pigment. (1% of males affected 0.01% of females)

Question 27

What are the two main theories of colour perception?

Answer 27

Trichromatic theory and Opponent-process theory

Question 28

What is trichromatic theory?

Answer 28

colour vision depends on activity of three different colour receptor types; red, green and blue. All colors can be coded using a pattern of activation across each of the three different cone receptors. Activation indicated by size.

Question 29

What is opponent-process theory?

Answer 29

colour vision is related to opposing responses by blue-yellow and red-green.

Question 30

What is Cerebral Achromatopsia?

Answer 30

colour blindness as a result of damage to the cortex

Question 31

What is the Geniculostriate pathway?

Answer 31

A group of axons that connect neurons in the lateral geniculate nucleus to the primary visual cortex.

Question 31

What does the lateral geniculate nucleus (LGN) do?

Answer 31

Filters the visual input from each eye and sends it to the primary visual areas (V1). Located inside the thalamus.

Question 32

Motion and contrast = __ Channel

Answer 32

Magnocellular

Question 33

Colour and fine detail = __ Channel

Answer 33

Parvocellular

Question 34

What is retinotopic organization?

Answer 34

Each place on the retina corresponds to a place in the LGN and a place in the visual cortex

Question 35

What is cortical magnification and what brain area has it?

Answer 35

A certain % of the cortex is dedicated to a particular area of the visual field. V1 has it.

Question 36

The “where” or “how” pathway

Answer 36

Dorsal stream. controls voluntary movement ex. reaching and grabbing something.

Question 37

The “what” pathway

Answer 37

Ventral stream. Controls conscious perception of objects (colour and shape, used to identify objects)

Question 38

What did DF have?

Answer 38

Visual Agnosia

Question 39

What is Visual Agnosia?

Answer 39

Inability to identify objects as a result of damage to the ventral stream (lateral occipital area). Patients with visual agnosia are still able to act on objects bc their dorsal stream is still intact.

Question 40

What is Optic Ataxia?

Answer 40

the inability to properly act on objects (reach for, grab etc) but ability to identify them remains intact. Caused by damage to the dorsal visual pathway.