2.04 spatial vision

Question 1

what is spatiotemporal vision

Answer 1

Spatiotemporal vision is about how we perceive patterns defined by luminance variation over space (spatial variation) and time (temporal variation)

Question 2

What is the Michelson equation for contrast?

Answer 2

contrast = lmax - lmin / lmax + lmin

Question 3

Greater contrast means….

Answer 3

bigger increment and decrement about the mean luminance

Question 4

what does one cycle of a sine wave grating consist of

Answer 4

one dark stripe and one light stripe

Question 5

What is the frequency of a grating

Answer 5

the number of cycles that can fit within a degree of visual angle

Question 6

What do the bars look like when there is low spatial frequency vs high spatial frequency

Answer 6

low spatial frequency = bars are wider
high spatial frequency = bars are narrower

Question 6

How do we measure the quality of an optical system

Answer 6

image contrast/ object contrast

perfect system = ratio should be 1 as no loss of contrast

Question 7

How do you work out sensitivity

Answer 7

1 / threshold

Question 8

What is the peak sensitivity

Answer 8

around 3-10 cycles per degree

sensitivity falls at low and high frequencies

Question 9

what does low and high frequency roll off mean

Answer 9

the loss in contrast sensitivities for low and high spatial frequencies

Question 10

what is the max value for contrast threshold

Answer 10

100%

Question 11

what is the minimum contrast sensitivity

Answer 11

1

it is also known as acuity limit or high frequency cut off which is 50CPD and any spatial frequency above this will not be detected.

Question 12

what are the differences in the different letter acuity charts

Answer 12

visual acuity chart - contrast is high, letter size is varied

Pelli-robinson chart - contrast varied, letter size is fixed

low contrast bailey-lovie - contrast is low and fixed, letter size is varied

Question 13

How does retinal illuminance affect contrast sensitivity

Answer 13

calculated by doing luminance of light falling on cornea x area of pupil

As retinal illuminance changes:
- spatial freq of peak contrast sensitivity shifts to lower spatial frequency
- the high freq cut off shifts to low spatial freq
- the low freq roll of disappears when retinal illuminance is very low

Question 14

How does retinal eccentricity affect contrast sensitivity

Answer 14

As it increases the CSF shifts leftwards ( towards lower spatial freq and peak is reduced)

Question 15

Is the CSF improved when using both eyes or one

Answer 15

CSF is improved if we use both eyes

Question 16

binocular view improves what 2 things and by how much

Answer 16

improves VA by 10%
improves contrast sensitivity by 40%

Question 17

what is a receptive field

Answer 17

• a region within visual field in which stimulation can affect the neurons response
• it can range from few minutes of arc to tens of degrees
• RF increases with processing stage
• Receptive fields also increases with retinal eccentricity
• fovea has the smallest receptive field

Question 18

what the differences between having a small or large receptive field

Answer 18

Large receptive fields have poor spatial resolution. Ability to resolve fine details is reduced

Question 19

On centre ganglion cells

Answer 19

• This is excited by light falling on its centre
• increases firing rate when light falls on centre
• decreases firing rate when light falls on surround

Question 20

off centre ganglion cell

Answer 20

• this is inhibited by light falling on its centre
• increases firing rate when light falls on surround
• decreases firing rate when light falls on centre

Question 21

which kind of spatial frequencies are most informative for identification of faces and general objects

Answer 21

intermediate spatial frequencies

Question 22

A ganglion cell responds best to gratings with a spatial frequency that…

Answer 22

…matches the size of its receptive field
i.e bright bar falls on centre
dark bar falls on surround

Question 23

how to work out the logmar visual acuity when given cycles per degree

Answer 23

(0.5/cycles) x 60
thats your MAR
then do log mar