Vision Science

Question 1

Which retinal cell types undergo graded potentials?

Answer 1

1. Photoreceptor cells
2. Bipolar cells
3. Horizontal cells

Question 2

Which retinal cell types undergo action potentials?

Answer 2

1. Amacrine cells
2. Ganglion cells

Question 3

What is the terms for inability to recognize faces?

Answer 3

Prosopagnosia

• inferotemporal (IT) cortex plays a role in facial recognition
• visual area 4 and IT are close proximity and very common for a patient with prosopagnosia to also suffer from achromatopsia

Question 4

Akinetopsia

Answer 4

cannot see movement in visual field
* lesion to the middle temporal cortex (MT) which is important for processing of motion stimuli

Question 5

Color agnosia

Answer 5

Difficulty associating colors with specific objects

Question 6

What does the Brucke-Bartley effect describe?

Answer 6

A flickering stimulus at 10 Hz appears brighter than a non-flickering light with the same average luminance

This effect also applies to stimulus presentation duration.

Question 7

What is the Troxler effect?

Answer 7

A phenomenon where surrounding background blends together when fixating on a point in space

This effect can cause a perceived disappearance of a smaller square when fixating on an ‘X’ in its center.

Question 8

What happens during the Troxler effect when a patient is tested with the FDT visual field?

Answer 8

The entire field may appear to go gray

Patients should be informed to blink if this occurs.

Question 9

Which part of the retina is most sensitive to flicker?

Answer 9

The peripheral retina

This sensitivity is due to the magno system, which is known for good temporal resolution.

Question 10

What is the Granit-Harper law?

Answer 10

As the log of the area of the stimulus increases, the critical flicker fusion frequency also increases

This law explains why larger stimuli are more likely to be perceived as flickering.

Question 11

Why does the peripheral retina have increased chances of detecting flicker?

Answer 11

Larger stimuli take up more area of the retina, increasing chances of detection due to increased summation

The peripheral retina’s receptors exhibit increased summation.

Question 12

What happens to stabilized retinal images at low temporal frequencies?

Answer 12

They are unable to be detected

Blood vessels on the photoreceptors are stable relative to the retina.

Question 13

What is a Purkinje tree?

Answer 13

The shadows cast by blood vessels on the retina when a penlight is rapidly moved against the eyelid

The penlight must move to visualize the shadows due to sufficient temporal frequency.

Question 14

Fill in the blank: The peripheral retina is part of the __________ system.

Answer 14

magno

Question 15

True or False: The Troxler effect can cause a patient to perceive a uniformly-colored large square.

Answer 15

True

Question 16

What is the primary visual system used in dim illumination?

Answer 16

Scotopic system

The scotopic system is mediated by rods, which provide heightened sensitivity to low light but poor acuity and color vision.

Question 17

What is the peak spectral sensitivity of the scotopic system?

Answer 17

507 nm

This wavelength indicates the maximum sensitivity of rods in low light conditions.

Question 18

What is the primary visual system used in bright light?

Answer 18

Photopic system

The photopic system is dominated by cones and allows for high acuity and color discrimination.

Question 19

What is the peak spectral sensitivity of the photopic system?

Answer 19

555 nm

This wavelength indicates the maximum sensitivity of cones in well-lit conditions.

Question 20

What is the visual acuity range for scotopic vision?

Answer 20

-20/200

This indicates poor visual acuity under low light conditions.

Question 21

What is the visual acuity range for photopic vision?

Answer 21

-20/20

This indicates excellent visual acuity under bright light conditions.

Question 22

What does Ricco’s law state about stimulus detection?

Answer 22

Threshold number of quanta is constant

Ricco’s law describes the reciprocal relationship between stimulus intensity and stimulus area for detection below a critical diameter.

Question 23

What is the mathematical expression of Ricco’s law?

Answer 23

IA-K

Where I is stimulus intensity, A is stimulus area, and K is a constant.

Question 24

What does Weber’s Law deal with?

Answer 24

Just noticeable difference

Weber’s Law relates the difference threshold to the original stimulus intensity.

Question 25

What is the mathematical expression of Weber’s Law?

Answer 25

K = delta I / I

Where K is Weber’s constant, delta I is the difference threshold, and I is the original stimulus intensity.

Question 26

What does Bloch’s law apply to?

Answer 26

Temporal summation

Bloch’s law relates to stimuli that are separated by time and their combined effects on perception.

Question 27

What is the critical period for the scotopic system according to Bloch’s law?

Answer 27

100 msec

This is the time frame within which stimuli must be presented to maintain threshold detection.

Question 28

What is the critical period for the photopic system according to Bloch’s law?

Answer 28

10-50 msec

This shorter time frame reflects the faster processing in bright light conditions.

Question 29

What is the mathematical expression of Bloch’s law?

Answer 29

I*t = K

Where I is stimulus intensity, t is stimulus duration, and K is a constant. I and t are inversely proportional.