Fourier Analysis and Temporal Factors in Vision - Visual Neurophysiology and Perception Spring 2026

maximum contrast sensitivity

The Pelli-Robson Chart estimates what?

1

Letters on the Pelli-Robson Chart are about ____ logMAR when tested at 1m

Patient will read down the chart until 2 letters are missed. Contrast sensitivity will be marked on the score sheet

How to test contrast sensitivity function with Pelli-Robson chart?

No

On a unaffected patient, will there be a low frequency roll off when testing with the Pelli-Robson chart (letters)?

at x intercept

Where is the VA indicated on this chart (See pic)?

yes

There are commercial tests that use a sine-wave grating (like the CSV-1000) at different spatial frequencies. Will there be a low frequency roll off in this type of test?

Similar design to the Pelli-Robson but these cards are hand held and tested at 40cm

Describe Mars Contrast Sensitivity Cards

-digital test that uses calibrated letters of different contrast

-uses testing algorithm to graph out CSF in a few min

Describe qCSF (quick contrast sensitivity function)

better

**more light, more sight

With higher ambient illumination, one has (better/worse) contrast sensitivity

will not

Increasing illumination on printed contrast sensitivity chart (will/will not) change the contrast of the letters

to the right & gets higher

With increasing illumination, the peak of the CSF curve will shift where?

to the right

With increasing illumination, the x intercept (acuity) of the CSF curve will shift where?

not much change in CS to low spatial frequencies

Under photopic conditions, will there be a large change to the CSF function in low spatial frequencies with different illumination?

Yes -- big reduction at all frequencies

Under scotopic conditions, will there be a large change to the CSF function with different illumination?

YES

BIG PICTURE SUMMARY: Is there more to visual function than just high-contrast visual acuity?

true

BIG PICTURE SUMMARY:

True or False:

Patients use their vision for other tasks besides resolving fine detail, and this can be esp important for a patient's quality of life and their overall mobility

low and middle

BIG PICTURE: Diseases/conditions can affect the CSF at the ___ and ___ spatial frequencies to a greater extend

not as much

BIG PICTURE: Do diseases/conditions usually affect high spatial frequencies of CSF

That different cells/channels are mediating information for the different spatial frequencies

BIG PICTURE: The fact that different conditions affect different spatial frequencies provides evidence of what?

true

True or False:

Having good contrast sensitivity is very important for mobility (walking and driving)

yes

Could one easily argue that having good contrast sensitivity is more important than having good VA?

true

True OR False:

There are lots of different RGCs with different sizes of their center-surround receptive fields throughout the retina and they serve areas throughout the visual field

when their center receptive field is roughy the same width of 1/2 of a cycle of the grating (the width of the light bar or the dark bar)

When are cells going to respond best to a certain sine wave grating?

Medium-Large parasol RGCs

Low frequency sine waves stimulate which RGCs most?

Small-Medium Midget RGCs

High frequency sine waves stimulate which RGCs most?

FALSE -- they respond to a narrow range of spatial frequencies

True or False:

Each cell (bipolar or RGC) will have a receptive field that responds to a wide range of spatial frequencies

Log Contrast Sensitivity vs Log Spatial Frequency Graph (Pic)

Log Contrast Sensitivity vs Log Spatial Frequency Graph (Pic)

"upper envelope" of the mini-contrast sensitivity functions that are "tuned" to narrow ranges of spatial frequencies

The overall contrast sensitivity function for the human eye is the "upper envelope" of what?

for the responses of the center-surround receptive fields of corresponding sizes

The sine wave in an index for what?

they will adapt

Cells with receptive fields similar in width to the gratings will be what with prolonged viewing of these gratings?

that there are center-surround units of different sizes and they can adapt separately

There will be selective adaptation near the adapting frequency. What does this show?

Fourier analyzer

It was proposed in the 1960s that the visual system acts as a ________

There is processing of spatial frequencies rather than particular features of the visual world. The visual world is pieced together like a puzzle, and somewhere along the pathway, the various spatial frequencies in a given image are put together in a way analogous to the mathematical technqiue of Fourier analysis

Why was it proposed that the visual system acts like a Fourier Analyzer?

into a series of sine waves of appropriate amplitudes and phases -- sine waves as building blocks that can be added together to make more complicated stimuli

Fourier showed that any repetitive waveform can be broken down into what?

true

True or False:

Any image can be broken down into component since waves of various frequencies and contrast (also phase and orientation)

Yes

Can a square wave be constructed by adding together sine waves?

Fundamental frequency wave + Odd Order Harmonics

Square wave = _____ + ______

3F, 5F, 7F -- "harmonic frequencies"

What are the harmonic frequencies that can be added to a fundamental frequency in order to create a square wave from a sine wave?

Square wave = Fundamental Frequency + Odd-Order Harmonics (Pic)

Square wave = Fundamental Frequency + Odd-Order Harmonics (Pic)

true

True or False:

The Fourier spectrum of a stimulus can be re-combined to retrieve the original stimulus (fundamental frequency)

Yes

Does Fourier Analysis/Synthesis apply to letters (such as Snellen)?

high -- high order harmonics

A little bit of blur on the Snellen E results in (low/med/high) spatial frequencies being lost

high and medium -- more harmonics

A moderate amount of blur on the Snellen E results in (low/med/high) spatial frequencies being lost

all spatial frequencies & all harmonics

An extreme amount of blur on the Snellen E results in (low/med/high) spatial frequencies being lost

Yes

When there is an extreme amount of blur present, does the fundamental frequency still remain in an image?

Normal vision is limited by blur. More blur = more contrast sensitivity loss.

What is the effect of blur on a CSF function?

Contrast Sensitivity Function for Sine Waves (Pic)

Contrast Sensitivity Function for Sine Waves (Pic)

linear

Linear falloff in a contrast sensitivity function is a function of the ______ function

d/t the optics of the eye

What is the linear falloff in a contrast sensitivity function d/t in a normal patient?

-participants adapt (by staring) at a 6 cycle/degree square wave

-stimulates the channels that respond best to the fundamental frequency (6 cycle/degree) and the harmonics (3F, 5F)

To prove that the retina acts as a Fourier analyzer, researchers did what?

Yes

Did study results show adaptation at both the fundamental and 3rd order harmonics, which supported the hypothesis that the visual system was indeed functioning as a Fourier analyzer?

large

(Large/small) retinal ganglion cells respond to the fundamental frequency

Small

(Large/small) retinal ganglion cells respond to the harmonics

Yes

BIG PICTURE: Do center-surround receptive fields in bipolars and RGCs contribute to contrast sensitivity function?

higher

BIG PICTURE: With smaller receptive fields, midget RGCs are tuned into the (higher/lower) spatial frequencies

lower

BIG PICTURE: With larger receptive fields, parasol RGCs are tuned into the (higher/lower) spatial frequencies

resolution acuity

BIG PICTURE: The high frequency cut-off of contrast sensitivity function relates to what?

Yes

BIG PICTURE: Can any image be deconstructed into its spatial frequency components?

high

BIG PICTURE: Midget RGCs relay (high/low) spatial frequency info

low

BIG PICTURE: Parasol RGCs relay (high/low) spatial frequency info

changes

The visual system is geared towards detecting _______ in the environment

luminance

In addition to changes in luminance over space (spatial vision), the visual system is concerned with changes in _____ over time

temporal vision

Changes in luminance over time

No

Does the eye ever sit still?

micro-saccades, slow drifts, tremors

What are the involuntary movements of the eye?

sameness

Neurons will adapt to ________

The response will fade over time

When neurons adapt to sameness, what happens?