Lecture 6

Question 1

Receptive fields and light inhibition are to be studied on iPad

Answer 1

go to iPad, many slides with notes there

Question 2

who first mapped out the receptive fields of individual retinal ganglion cells

Answer 2

Kuffler on cats

Question 3

explain how on centre cells work

Answer 3

ON-center ganglion cells—excited by light that falls on their center and inhibited by light that falls in their surround.

Question 4

explain how off centre cells work

Answer 4

OFF-center ganglion—inhibited when light falls in their center and excited when light falls in their surround

Question 5

does the size of the light matter when interacting with the on/off receptive feilds

Answer 5

yes, if not perfect it will fire less and less

Question 6

what are mach bands

Answer 6

equal physical intensity of a gradient (grey gets light and lighter each block)

Question 7

what is th ePERCEIVED brightness intensity of mach bands

Answer 7

looks like it is brighter on the left (next to the darker block) than on the right (next to the lighter block)

Question 8

what is edge enhancements

Answer 8

The purpose of the center-surround organisation is to help us perceive the edges of objects

Question 9

why does one side of a block in the act bands look brighter than the other when they are actually they exact dame

Answer 9

the receptive fields that overlap with the edges are centre surround but overlap with some of the darkness AND brightness so lateral (horizontal) cells are inhibited and it makes some areas seem brighter near the edges when contrasting with another shade

Question 10

what is the Hermann grid illusion

Answer 10

the many black boxes (grid) with while lines and the intersections look like there are black dots when there arents

Question 11

how does the Hermann grid illusion work

Answer 11

the lines remain white because the receptive fields have centre light and the surrounding is inhibited by the black lines so all is good
the INTERSECTIONS look as though there are black/grey dots because the centre is light but the surround is also light so the horizontal cells are inhibited and thus so is the cell in general making the contrast difficult and thus having a grey dot

Question 12

if you fixate on an intersection the illusion vanishes in the hermann grid, why

Answer 12

receptive field in foveal vision is much smaller than in peripheral so the light is actually just the right size to make it look all white

Question 13

whatadoes the size of the receptor field depend on

Answer 13

type of bipolar cell

Question 14

what are the types of bipolar cells

Answer 14

Diffuse bipolar cell:

Midget bipolar cell:

Question 15

what are Diffuse bipolar cell

Answer 15

Receives input from multiple photoreceptors.

Question 16

what are Midget bipolar cell:

Answer 16

Receives input from a single cone.

Question 17

are Diffuse bipolar cells mostly in fovea or periphery

Answer 17

periphery

Question 18

are Midget bipolar cell mostly in fovea or periphery

Answer 18

fovea

Question 19

what are the 2 types/pathways of ganglion cells

Answer 19

Parvocellular vs Magnocellular

Question 20

P ganglion cells are connected where

Answer 20

Connect to the parvocellular pathway.

Question 21

M ganglion cells are connected where

Answer 21

Connect to the magnocellular pathway.

Question 22

P ganglion cells: Connect to the parvocellular pathway.

Receive input from where

Answer 22

midget bipolar cells (in fovea)

Question 23

M ganglion cells: Connect to the magnocellular pathway.

Receive input from where

Answer 23

diffuse bipolar cells (in peripheral)

Question 24

Parvocellular pathway is involved in what

Answer 24

fine visual acuity, color, and shape processing; poor temporal resolution but good spatial resolution

Question 25

Magnocellular (“large cell”) pathway is involved in what

Answer 25

motion processing; excellent temporal resolution but poor spatial resolution

Question 26

can you have acuity and light sensitivity

Answer 26

no it is Acuity vs light sensitivity trade-off

Question 27

more convergence of rods/cones to ganglion cells causes what

Answer 27

More convergence causes:
More light sensitivity
Less acuity

Question 28

why does More convergence cause
More light sensitivity
Less acuity

Answer 28

for light sensitivity, there is more chance that the light will be detected if the ganglion cell is connected to many rods or cones (higher receptive field)

for acuity, the ganglion cells are set up the same way: if light activates a photoreceptor with lots of convergence of the ganglion cell, the receptive field is so large and it cannot tell the brain exactly where in the receptive field the light is, just that it is there. And vice versa: if no convergence, there is a smaller receptive field and the ganglion cell can tell the brain exactly where the light is when activated thus higher acuity

Question 29

defineAcuity

Answer 29

The smallest spatial detail that can be resolved.

Question 30

There are several ways to measure visual acuity. give example

Answer 30

Eye doctors use distance to characterize visual acuity, as in “20/20 vision.”

Question 31

explain the numbers in “20/20 vision.”

Answer 31

Your distance/Normal vision distance
The patient is typically placed at 20 feet from the letters
20/20 means that, when placed at 20 feet from the letters, the smallest letter that you can read is the smallest letter that the average person can read at 20 feet
20/15 means that, when placed at 20 feet from the letters, the smallest letter that you can read is the smallest letter that the average person can read at 15 feet
20/40 means that, when placed at 20 feet from the letters, the smallest letter that you can read is the smallest letter that the average person can read at 15 feet

Question 32

how do Vision scientists define acuity

Answer 32

Smallest visual angle of a cycle of grating.

Question 33

Vision scientists: Smallest visual angle of a cycle of grating.
thus, The smaller the visual angle at which you can identify a cycle of a grating…

Answer 33

the better your vision

basically this can be tested by having black and white alternating lines (either hormonally or vertically this is a grate) and the smaller and smaller the scientists makes it, you will eventually just see grey and this help to determine your acuity and visual angle

Question 34

for grating:
Vision scientists: Smallest visual angle of a cycle of grating.
The smaller the visual angle at which you can identify a cycle of a grating, the better your vision.
The limit is determined primarily by what

Answer 34

the spacing of photoreceptors on the retina.

Question 35

how many cones do you need to determine the difference between the black and white grating

Answer 35

at least 2 cones

Question 36

what is Spatial frequency

Answer 36

Cycles of a grating per unit of visual angle (in degrees).

Another way to think of spatial frequency is as the number of times a pattern repeats per unit area

Question 37

what kind of graph is used to display spatial frequency

Answer 37

sine waves/grafs

so the iage is a blurry grate (blurry white and black lines) because it is not really a sharp up and down that happens

Question 38

what are Gabor patches

Answer 38

another way to display the sin graph (for spatial frequency)

the farther spread the ripples, the lower the spatial frequency and vice versa

Question 39

Why sine gratings?

for visual acuity

Answer 39

Patterns of stripes with fuzzy boundaries are quite common.
(reality) Trees in a forest, books on a bookshelf, pencils in a cup.

Any black-and-white image can be described in terms of a weighted combination of different frequencies with different orientations.

Question 40

Low frequencies display what

Answer 40

general image

Question 41

High frequencies display what

Answer 41

details

Question 42

do Ganglion cells with center-surround receptive fields respond preferentially to certain frequencies.

Answer 42

absolutely

Question 43

Ganglion cells with center-surround receptive fields respond preferentially to certain frequencies.– explain the response of lw frequency

Answer 43

weak response

will look like very large blurry line

Question 44

Ganglion cells with center-surround receptive fields respond preferentially to certain frequencies.– explain the response of medium frequency

Answer 44

strong response

will look more solid…

Question 45

Ganglion cells with center-surround receptive fields respond preferentially to certain frequencies.– explain the response of high frequency

Answer 45

weak response (will look like very small and blurry lines)

Question 46

Ganglion cells with center-surround receptive fields respond preferentially to certain frequencies.

what else is also important

Answer 46

Phase

Question 47

what is Phase

Answer 47

The phase of a grating refers to its position within a receptive field

Question 48

define Contrast:

Answer 48

intensity difference between the lightest and darkest portions of the patch

Question 49

is it easier to see gabor patches with high or low contrast

Answer 49

high

Question 50

what is Contrast sensitivity function

Answer 50

Visibility of a pattern as a function of spatial frequency and contrast