4.2 Vision I: The Eyes and the Brain Convert Light Waves to Neural Signals

Question 1

What is Visual Acuity?

Answer 1

Defined as the ability to see fine detail

Question 2

Who designed the 20/20 vision measurement?

Answer 2

Hermann Snellen;

It is the smallest line of letters that a typical person can read from a distance of 20 feet.

Question 3

What is Visible Light?

Answer 3

The portion of the electromagnetic spectrum that we can see, (which is an extremely small slice)!

Question 4

What is the range, in nanometres which Visible Light falls under?

Answer 4

400-700nm

Question 5

What are the shortest waves on the Visible Light spectrum?

Answer 5

Ultraviolet Rays

Question 6

What are the longest waves on the Visible Light spectrum?

Answer 6

Infrared Waves

Question 7

What does “wavelength” mean?

Answer 7

The distance between peaks of waves

Question 8

What aspect of a wave determines the colour a human will see?

Answer 8

The LENGTH of a lightwave determines hue/color

Question 9

What aspect of a wave determines the brightness a human will see?

Answer 9

The AMPLITUDE (height of the peaks) of a wave

Question 10

What aspect of a wave determines the saturation or richness of colour a human will see?

Answer 10

The PURITY (number of distinct wavelengths that make up the light)

Question 11

What’s the first part of the eye which light passes through?

Answer 11

The Cornea, which is a clear, smooth, outer tissue.

The Cornea bends the light coming in,

Question 12

Where does the light go after it’s past the Cornea?

Answer 12

The Pupil, which is a hole in the coloured part of the eye

Question 13

What are the three properties of light waves?

Answer 13

Purity

Wavelength

Amplitude

Question 14

What is the name of the part of the eye which controls the size of the pupil? Why does it do this?

Answer 14

The Iris. By changing the size of the Pupil, the amount of light that can enter the eye changes

Question 15

Retina

Answer 15

A layer of light-sensitive tissue lining the back of the eyeball

Question 16

Define “Accomodation”:

Answer 16

The process whereby the eye maintains a clear image on the retina; the process by which infants revise their schemas in light of new information

Question 17

What’s “Myopia”?

Answer 17

If the eyeball is too long, images are focused in front of the retina, leading to nearsightedness

You can see objects near to you clearly, but objects farther away are blurry

Question 18

What’s “Hyperopia”?

Answer 18

If the eyeball is too short, images are focused behind the retina, and the result is farsightedness

You can see objects far away clearly, but objects up close are blurry

Question 19

Two types of photoreceptor cells in the retina contain light-sensitive pigments that transduce light into neural impulses

What are the two types of photoreceptor cells in the retina, and what do they do?

Answer 19

Cones

Rods

They contain light-sensitive pigments that transduce light into neural impulses

Question 20

These photoreceptor cells allow us to detect colour, operate under normal daylight conditions, and focus on fine detail

Answer 20

Cones

Question 21

What do “Rods” do for our vision?

Answer 21

They become active under low-light conditions for night vision

Question 22

What shades of colour do Rods produce?

Answer 22

None. They all contain the same pigment, which is perceived to us as shades of grey

Question 23

Which photoreceptor is more sensitive?

Answer 23

Rods are more sensitive

However this comes at a cost, as they produce no information about colour

Question 24

An area of the retina where vision is the clearest and there are no Rods at all

Answer 24

Fovea

Question 25

How many Rods are distributed more or less evenly around each retina except in the very centre?

Answer 25

120 million

Question 26

How many Cones are contained inside each Retina? Is it less or more than Rods?

Answer 26

6 Million, which is much less than Rods (120 million)

Question 27

How can a lack of Rods in the Fovea influence how astronomers view bright stars?

Answer 27

By looking slightly off to the side of a target (star), the image won’t fall on the Rod-free Fovea.

Looking directly at a reduced-light target would make things blurry

Question 28

Why are objects in our Peripheral Vision less clear?

Answer 28

Cones are densely packed in the Fovea, but are much more sparse in areas of the Retina off to the side. This affects our Visual Acuity

Light reflecting from those peripheral objects is less likely to land in the Fovea, making the resulting image less sharp

Question 29

What kind of neurons can be found in the outermost layer of the Retina?

Answer 29

Retinal Ganglion Cells (RGC’s)

Question 30

What cells connect neural signals from photoreceptor cells and transmit them to RGC’s?

Answer 30

Bipolar Cells

Question 31

What do Retinal Ganglion Cells do?

Answer 31

They organize signals and send them to the brain

Question 32

How is the Optic Nerve formed by RGC’s?

Answer 32

The axon of a Retinal Ganglion Cell connects with other RGC axons

Question 33

How many RGC axons can be found in a single eye?

Answer 33

1.5 Million

Question 34

A location in the visual field that produces no sensation on the retina

Answer 34

Blind Spot

Question 35

How does light register in the brain? What is the process?

Answer 35

Streams of action potentials (neural impulses) containing information encoded by the retina travel to the brain along the optic nerve

Question 36

Where is the Lateral Geniculate Nucleus located?

Answer 36

It’s a relay centre located in the Thalamus

Question 37

Where does the Optic Nerve travel to in the brain?

Answer 37

Lateral Geniculate Nucleus, and then on to the Visual Cortex (which is part of the Occipital Lobe)

Question 38

What is the relationship between our visual field and the retina stimulation?

Answer 38

Objects in our left visual field will stimulate the right half of our retina’s and vice versa

Question 39

Where does visual information end up in our brains relative to our eyes?

Answer 39

Info from our left visual field will travel into the right hemisphere of our brains (via the Thalamus)

Question 40

What are the three types of cones, and what are they each good for?

Answer 40

The three types are long, medium, and short wavelength. Each is used for blueish, greenish, and reddish light, respectively

Each type is most sensitive to a narrow range of wavelengths in the visible spectrum

Question 41

What percentage of men inherit conditions in which either the red or the green photoreceptors do not transduce light properly

Answer 41

Around 5%

Question 42

What is Colour-opponent System?

Answer 42

States that pairs of visual neurons work in opposition: red-sensitive cells against green-sensitive and blue-sensitive cells against yellow-sensitive). The colour-opponent system explains colour aftereffects

Question 43

Describe the VENTRAL stream:

Answer 43

Travels across the occipital lobe into the lower levels of the temporal lobes and includes brain areas that represent an object’s shape and identity—in other words, what it is, essentially a “what” pathway…

Question 44

Describe the DORSAL stream:

Answer 44

travels up from the occipital lobe to the parietal lobes (including some of the middle and upper levels of the temporal lobes), connecting with brain areas that identify the location and motion of an object—in other words, where it is. Known as the “how” pathway

Allows us to perceive spatial relations

Question 45

Define “Visual Agnosia”

Answer 45

The inability to recognize objects by sight