Retinal Pathways

Question 1

Horizontal cells are responsible for:

Answer 1

Lateral inhibition

Question 2

Horizontal cells are specialized retinal cells that run:

Answer 2

Perpendicular to the photoreceptors and make contact with photoreceptors and bipolar cells

Question 3

Amacrine cells have been implicated in:

Answer 3

Contrast enhancement and temporal sensitivity ( detecting light patterns that change over time)

Question 4

Amacrine cells synapse horizontally between:

Answer 4

Bipolar cells and retinal ganglion cells

Question 5

Bipolar cell:

Answer 5

A retinal cell that synapses with one or more rods or cones (not both) and with horizontal cells, and then passes the signals on to ganglion cells

Question 6

Diffuse bipolar cell:

Answer 6

A bipolar cell that receives input from multiple photoreceptors

Question 7

Midget Bipolar cell:

Answer 7

A small bipolar cell that receives input from a single cone

Question 8

P Ganglion Cells:

Answer 8

-Connect to the parvocellular pathway
-Receive input from MIDGET bipolar cells

Question 9

The parvocellular (“small cell”) pathway is involved in:

Answer 9

-Fine visual acuity, color and shape processing.

-Poor temporal resolution, but good spatial resolution

Question 10

M ganglion cells connect to:

Answer 10

The magnocellular pathway

Question 11

M ganglion cells receive input from:

Answer 11

Diffuse bipolar cells

Question 12

Magnoellular “large cell” pathway is involved in:

Answer 12

Motion Processing

Excellent temporal resolution, but poor spatial resolution

Question 13

126 million photoreceptors converge to

Answer 13

1 million ganglion cells

Question 14

Average of 50 rods to

Answer 14

one bipolar cell

Question 15

Average of 6 cones to :

Answer 15

one DIFFUSE bipolar cell

Question 16

Cones in fovea have:

Answer 16

1 to 1 relation to midget bipolar cells

Question 17

All cone foveal vision results in:

Answer 17

high visual acuity

(one to one wiring leads to ability to discriminate details)
(trade off is that cones need more light to respond than rods)

Question 18

Receptive field:

Answer 18

The region on the retina in which stimuli influence a neuron’s firing rate

Question 19

What are the two types of retinal ganglion cells?

Answer 19

Parasol RGC’s (bigger)
Midget RGC’s (smaller)

Question 20

Output of center-surround receptive fields changes depending on area stimulated:

Answer 20

Highest response when only the excitatory area is stimulated

Lowest response when only the inhibitory area is stimulated

Intermediate responses when both areas are stimulated

Question 21

Why center-surround receptive fields?

Answer 21

• each ganglion cell will respond best to spots of a particular size (and respond less to spots that are too big or too small)
  -retinal ganglion cells act like a filter for information coming to the brain

Question 22

Retinal ganglion cells are most sensitive to:

Answer 22

Differences in the intensity of light between center and surround and are relatively unaffected by the average intensity

Question 23

Luminance variations tend to be :

Answer 23

SMOOTH within objects and SHARP between objects

Question 24

Center surround receptive fields help to :

Answer 24

emphasize object BOUNDARIES

Question 25

P (parvocellular) ganglion cells:

Answer 25

Small receptive fields
High acuity
Work best in high luminance situations
Sustained firing

Question 26

P (parvocellular) ganglion cells provide information mainly about:

Answer 26

The CONTRAST in the retinal image

Question 27

M (magnocellular) cells:

Answer 27

Large receptive fields, low acuity, work best in low luminance situations, burst firing

Question 28

M (magnocellular) ganglion cells provide information about:

Answer 28

how an image changes over time

Question 29

Three lightness perception phenomena explained by lateral inhibition:

Answer 29

• The Hermann Grid
• Mach Bands
• Simultaneous Contrast

Question 30

The hermann grid:

Answer 30

seeing spots at an intersection

Question 31

Mach Bands:

Answer 31

Seeing borders more sharply

Question 32

Simultaneous contrast:

Answer 32

Seeing areas of different brightness due to adjacent areas

Question 33

For the Hermann grid effect, signals from __ may cause effect

Answer 33

bipolar cells

Question 34

Explain how the Hermann grid effect happens:

Answer 34

Receptors stimulated by dark areas inhibit the response of neighbouring cells receiving input from white area

The lateral inhibition causes a reduced response which leads to the perception of gray

Question 35

What are Mach Bands?

Answer 35

People see an illusion of enhanced lightness and darkness at borders of light and dark areas
(Actual physical intensities indicate this is not in the stimulus itself)

Question 36

How does lateral inhibition explain our perception of Mach Bands?

Answer 36

The lateral inhibition in our circuit has created a neural
patter that looks like the Mach bands we perceive.
* A circuit similar to this one, but of much greater
complexity, is probably responsible for the Mach bands
that we perceive.

Question 37

What is simultaneous contrast:

Answer 37

People see an illusion of changed brightness or color due to effect of adjacent area

An area that is of the same physical intensity appears:
-lighter when surrounded by a darker area
-darker when surrounded by a light area

Question 38

Explain simultaneous contrast in terms of lateral inhibition?

Answer 38

Receptors stimulated by bright surrounding area send a large amount of inhibition to cells in center –> resulting perception is of a darker area than when this stimulus is viewed alone

Receptors stimulated by dark surrounding area send a small amount of inhibition to cells in center –> resulting perception is of a lighter area than when this stimulus is viewed alone

Question 39

Lateral inhibition __ explain simultaneous contrast

Answer 39

cannot entirely

Question 40

macular degeneration:

Answer 40

damage to photoreceptors at the center of the retina

Question 41

retinitis pigmentosa

Answer 41

gradual degeneration of the photoreceptors over many years–> night blindness