Vision Science Flashcards
Which retinal cell types undergo graded potentials?
- Photoreceptor cells
- Bipolar cells
- Horizontal cells
Which retinal cell types undergo action potentials?
- Amacrine cells
- Ganglion cells
What is the terms for inability to recognize faces?
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
Akinetopsia
cannot see movement in visual field
* lesion to the middle temporal cortex (MT) which is important for processing of motion stimuli
Color agnosia
Difficulty associating colors with specific objects
What does the Brucke-Bartley effect describe?
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.
What is the Troxler effect?
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.
What happens during the Troxler effect when a patient is tested with the FDT visual field?
The entire field may appear to go gray
Patients should be informed to blink if this occurs.
Which part of the retina is most sensitive to flicker?
The peripheral retina
This sensitivity is due to the magno system, which is known for good temporal resolution.
What is the Granit-Harper law?
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.
Why does the peripheral retina have increased chances of detecting flicker?
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.
What happens to stabilized retinal images at low temporal frequencies?
They are unable to be detected
Blood vessels on the photoreceptors are stable relative to the retina.
What is a Purkinje tree?
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.
Fill in the blank: The peripheral retina is part of the __________ system.
magno
True or False: The Troxler effect can cause a patient to perceive a uniformly-colored large square.
True
What is the primary visual system used in dim illumination?
Scotopic system
The scotopic system is mediated by rods, which provide heightened sensitivity to low light but poor acuity and color vision.
What is the peak spectral sensitivity of the scotopic system?
507 nm
This wavelength indicates the maximum sensitivity of rods in low light conditions.
What is the primary visual system used in bright light?
Photopic system
The photopic system is dominated by cones and allows for high acuity and color discrimination.
What is the peak spectral sensitivity of the photopic system?
555 nm
This wavelength indicates the maximum sensitivity of cones in well-lit conditions.
What is the visual acuity range for scotopic vision?
-20/200
This indicates poor visual acuity under low light conditions.
What is the visual acuity range for photopic vision?
-20/20
This indicates excellent visual acuity under bright light conditions.
What does Ricco’s law state about stimulus detection?
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.
What is the mathematical expression of Ricco’s law?
IA-K
Where I is stimulus intensity, A is stimulus area, and K is a constant.
What does Weber’s Law deal with?
Just noticeable difference
Weber’s Law relates the difference threshold to the original stimulus intensity.
What is the mathematical expression of Weber’s Law?
K = delta I / I
Where K is Weber’s constant, delta I is the difference threshold, and I is the original stimulus intensity.
What does Bloch’s law apply to?
Temporal summation
Bloch’s law relates to stimuli that are separated by time and their combined effects on perception.
What is the critical period for the scotopic system according to Bloch’s law?
100 msec
This is the time frame within which stimuli must be presented to maintain threshold detection.
What is the critical period for the photopic system according to Bloch’s law?
10-50 msec
This shorter time frame reflects the faster processing in bright light conditions.
What is the mathematical expression of Bloch’s law?
I*t = K
Where I is stimulus intensity, t is stimulus duration, and K is a constant. I and t are inversely proportional.
