A quiz on the human visual system

Adrian F. Clark

1. What type of cell is responsible for vision in low-light conditions?

   • retina
   • fovea

   • rod

   • cone

   Rods are responsible for low-light vision as they are much more responsive to light than cones. The fovea is a region of the retina, the surface that coats the inside of the eyeball.

2. Where does the "what" pathway run?

   • V2, V3
   • V2, V3, V4, V5

   • V2, V4

   • V2, V5

   This pathway is the ventral stream, running from V2 to V4 (and thence to the inferior temporal cortex). It is associated with recognition of form and objects, and long-term storage.

3. What is the name of the rear surface of the eye?

   • cornea
   • optic nerve
   • fovea

   • retina

   The rear surface of the eye, which is coated in light-sensitive cells, is known as the retina.

4. Roughly, what is the range of wavelengths of visible light?

   • 100--1000 nm

   • 400--700 nm

   • 0--100 nm
   • 1000--5000 nm

   The visible wavelengths lie roughly in the range 400 nm (blue) to 700 nm (red). The red light from a He-Ne laser is about 650 nm, for example.

5. To which of the following do the cells in V1 respond to?

   • orientation, edge
   • edge, motion

   • orientation, edge, motion

   • motion

   V1 cells respond to all three stimuli; finding this out won the Nobel prize in 1950.

6. Where does the "where" or "how" pathway run?

   • V2, V3, V4, V5
   • V2, V4

   • V2, V5

   • V2, V3

   This pathway is the dorsal stream, running from V2 to V5 (and thence to the posterior parietal cortex). It is associated with the representation of objects and control of the eyes and limbs.

7. What type of cell is responsible for colour vision?

   • cone

   • fovea
   • retina
   • rod

   There are three types of cone, with peak responses in the red, green and blue regions of the spectrum; hence, they are the cells that allow humans to sense colour. The fovea is a region of the retina, the surface that coats the inside of the eyeball.

8. Why are the decks of ships usually illuminated using red light at night?

   • Because ships may not show any other colour lights

   • So that the dark-adaption of the rods is affected as little as possible

   • So that only one type of cone is used, leaving the others for looking out
   • To reduce the amount of light pollution from the ship

   The aim is to keep the rods as sensitive as possible; as rods are more sensitive towards the blue, using red light affects them least.

9. What causes the illusion of the Hermann grid?

   • The inhibitory centre and excitatory surround of the ganglion cells

   • The excitatory centre and inhibitory surround of the ganglion cells

   • V5
   • V4

   Galglion cells have an excitatory centre and inhibitory suround, and this appears to be the root cause of the Hermann grid. (This is similar to a Laplacean mask in convolution.)

10. Signals from the eye travel via the optic nerve to which of the following?

    • V1
    • visual striate cortex

    • laterate geniculate nucleus

    • V4

    The optic nerve travels to the laterate geniculate nucleus, though about 10% also go to the superior colliculus, where the signal from the two eyes are mixed.