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Quiz: Vision

Test your understanding of Chapter 5. Choose the best answer, then click Show Answer to check.

Question 1

Which type of photoreceptor is far more numerous in the human retina and works best in dim light?

  1. Cones
  2. Rods
  3. Retinal ganglion cells
  4. Bipolar cells
Show Answer

The correct answer is B. The retina has about 120 million rods and only about 6 million cones. Rods are very sensitive and handle dim light, but they give low detail and no color. Cones (A) handle bright light, detail, and color. Ganglion and bipolar cells are retinal neurons, but they are not photoreceptors.

Concept Tested: Rods and Cones Bloom's Level: Remember

Question 2

At the optic chiasm, which nerve fibers cross to the opposite side of the brain?

  1. Fibers from the temporal half of each retina
  2. All fibers from the left eye
  3. Only fibers from the fovea
  4. Fibers from the nasal half of each retina
Show Answer

The correct answer is D. Fibers from the nasal (inner) half of each retina cross at the chiasm, and fibers from the temporal half stay on the same side. A common mistake is thinking a whole eye crosses (B), but each hemisphere gets input from both eyes about the opposite visual field.

Concept Tested: Optic Chiasm Bloom's Level: Remember

Question 3

In which lobe of the brain is the primary visual cortex (V1) found?

  1. Occipital lobe
  2. Temporal lobe
  3. Parietal lobe
  4. Frontal lobe
Show Answer

The correct answer is A. V1 lies in the occipital lobe at the back of the brain. The temporal (B) and parietal (C) lobes receive visual information later, through the ventral and dorsal streams, but they are not where it first reaches the cortex.

Concept Tested: Primary Visual Cortex Bloom's Level: Remember

Question 4

What happens inside a rod when it absorbs light?

  1. Sodium channels open, and the rod fires an action potential
  2. The rod depolarizes and releases more glutamate
  3. Sodium channels close, the rod hyperpolarizes, and it releases less glutamate
  4. The rod releases dopamine onto the optic nerve
Show Answer

The correct answer is C. In the dark, sodium channels in the rod are open, so it is depolarized and releases glutamate steadily. Light changes the shape of retinal in rhodopsin, which triggers a chain reaction that closes those channels. Options A and B describe how most neurons respond to a stimulus. Photoreceptors do the opposite, which is why they surprise people.

Concept Tested: Sensory Transduction Bloom's Level: Understand

Question 5

Why does an on-center retinal ganglion cell respond only weakly when its entire receptive field is lit evenly?

  1. Excitation from light on the center is largely canceled by inhibition from light on the surround
  2. Ganglion cells respond only to colored light, not white light
  3. Even light saturates the cell so it cannot fire
  4. The surround is made of rods, which do not work in light
Show Answer

The correct answer is A. Center-surround receptive fields have opposite zones. Light on the center excites an on-center cell, while light on the surround inhibits it, so even light mostly cancels out. This is why the retina mainly signals edges and contrast. Option C confuses ganglion cells with rods, which do saturate in bright light.

Concept Tested: Receptive Field Bloom's Level: Understand

Question 6

Why is red-green color blindness much more common in males than in females?

  1. Males have fewer cones in the fovea
  2. Testosterone damages the green cone pigment
  3. Males are missing rods in the center of the retina
  4. The genes for the red and green cone pigments are on the X chromosome
Show Answer

The correct answer is D. Males have one X chromosome, so a single faulty red or green pigment gene causes color blindness. Females have two X chromosomes, and a working copy usually makes up for a faulty one. Option C is true of everyone (rods are absent from the fovea), so it can't explain a difference between the sexes.

Concept Tested: Color Vision Bloom's Level: Understand

Question 7

A 70-year-old woman has a stroke in her right occipital lobe. Which visual field defect is she most likely to have?

  1. Blindness in the right eye only
  2. Loss of the left half of the visual field in both eyes, often with the center spared
  3. Loss of the outer half of the visual field in each eye
  4. Loss of the right half of the visual field in both eyes
Show Answer

The correct answer is B. Behind the chiasm, the right side of the brain handles the left visual field from both eyes, so damage there causes a left homonymous hemianopia. Occipital strokes often spare central (macular) vision. Option A is a common misconception: brain damage behind the chiasm does not blind one eye.

Concept Tested: Visual Field Defect Bloom's Level: Apply

Question 8

After brain damage, a patient cannot name or describe common objects by sight, or say how a slot is tilted. Yet she reaches for objects accurately and turns a card to fit through the slot. Which part of the visual system is most likely damaged?

  1. The dorsal stream
  2. The optic chiasm
  3. The ventral stream
  4. The rods of the retina
Show Answer

The correct answer is C. The ventral ("what") stream, running into the lower temporal lobe, is needed to recognize objects. Her accurate reaching shows that the dorsal ("where/how") stream to the parietal lobe still works. This matches the famous patient D.F. Damage to the dorsal stream (A) would impair reaching, the opposite of what she shows.

Concept Tested: Ventral and Dorsal Streams Bloom's Level: Apply

Question 9

A 47-year-old driver keeps bumping into door frames on both sides. He can read an eye chart normally. Testing each eye separately shows that the left eye has lost the left half of its field and the right eye has lost the right half. What is the most likely cause?

  1. A stroke in the left occipital lobe
  2. Damage to the left optic nerve
  3. Damage to Meyer's loop in the temporal lobe
  4. A pituitary tumor pressing on the optic chiasm
Show Answer

The correct answer is D. Losing the outer (temporal) half of each eye's field is bitemporal hemianopia. The only place where both nasal retinas' crossing fibers meet is the middle of the optic chiasm, which sits just above the pituitary gland. A left occipital stroke (A) would remove the right half of the field in both eyes, not the outer halves.

Concept Tested: Pituitary Tumor Bloom's Level: Analyze

Question 10

A patient has completely lost vision in the left eye, but the right eye's visual field is normal. Where along the visual pathway is the lesion most likely to be?

  1. Left optic nerve
  2. Optic chiasm
  3. Right optic tract
  4. Left occipital cortex
Show Answer

The correct answer is A. Only structures in front of the chiasm carry fibers from just one eye, so a one-eye loss points to the eye or its optic nerve. Lesions at or behind the chiasm (B, C, D) affect fibers from both eyes and change the visual field of both eyes.

Concept Tested: Optic Nerve Bloom's Level: Analyze