Sensation and Perception Problem Set Facts

Question 1

What range of photon wavelengths is the human eye sensitive to?

Answer 1

400-700 nm

Question 2

Is the crystalline lens thickest or thinnest when you are looking at a faraway object?

Answer 2

thinnest

Question 3

What is astigmatism?

Answer 3

Defect caused by unequal curving of the cornea or lens in different directions,

Question 4

What is emmetropia?

Answer 4

A condition where the strength of the lens is properly matched to the length of the eye

Question 5

What is hyperopia?

Answer 5

• An image of a distant object becomes focused behind the retina, making objects up close appear out of focus. (farsighted)
• The condition where the lens is too weak for the length of the eye

Question 6

What is accomdation?

Answer 6

The process in which the eye adjusts the thickness of the lens, in order to focus on
objects at various distances

Question 7

How do complex vs simple cells respond to certain orientations?

Answer 7

A simple cell responds to oriented lines at a particular location in its receptive field,

Complex cell responds to oriented lines at any location in its receptive field.

Question 8

At what point in the visual pathway do cells first exhibit spiking responses?

Answer 8

Spiking responses first appear in the collector cells (i.e., horizontal, bipolar, and
amacrine cells).

Question 9

At what point in the visual pathway do cells first exhibit centre surround receptive fields?

Answer 9

Centre-surround receptive fields first occur in the ganglion cells

Question 10

At what point in the visual pathway do cells first exhibit binocular responses and orientation tuning?

Answer 10

Orientation tuning and binocular responses first appear in V1 cells.

Question 11

Describe how accommodation adjusts the crystalline lens in order to focus on objects
at different distances.

Answer 11

The lens is attached to a ring of ciliary muscles by fibers called the zonules of Zinn.

1) In the resting state, the ciliary muscles are relaxed and form a large ring. They stretch
the lens so that it is relatively flat. This is the state of the eye when focusing on faraway
objects.

2) The ciliary muscles can contract inwards to form a smaller ring. This allows the lens to
shrink into a thicker, more spherical shape. This is the state of the eye when focusing on
nearby objects.

Question 12

Explain why contrast sensitivity is lower at high spatial frequencies

Answer 12

In the fovea, cones are spaced about 1/120 degree apart. This means that the cones
cannot accurately represent a sine wave grating with a spatial frequency higher than
around 60 cycles/degree

Question 13

How do the spatial frequencies in an image change as the image moves farther away
from you?

Answer 13

• As sine waves move away from you, the spatial frequency of sine wave increases.
• The contrast sensitivity function shows that above 2 to 4 cycles/degree,
  human visual sensitivity decreases.
• So, as an image moves farther away, the spatial frequencies that make it up move upwards into the spatial frequency region where we are less sensitive, and the object becomes harder to see

Question 14

Suppose that there are three channels of simple cells in V1, with preferred spatial
frequencies of 4, 5, and 6 cycles/degree, at a vertical orientation. When you look at a
vertical sine wave of spatial frequency 5 cycles/degree, what will the relative activation of each channel normally be? (You can either describe the activations verbally, or make up an illustrative number for each channel.)

Answer 14

4 cycle/degree channel activation = 5
5 cycle/degree channel activation = 10
6 cycle/degree channel activation = 5

Question 15

Suppose you adapt to a vertical sine wave of spatial frequency 4 cycles/degree for
several minutes. When you look back at the original vertical sine wave of 5
cycles/degree, what will the relative activation the channels be then? How will this affect the appearance of the original sine wave, if at all?

Answer 15

4 cycle/degree channel activation = 2
5 cycle/degree channel activation = 10
6 cycle/degree channel activation = 5

This is the pattern of activation that would be produced by a sine wave with a
spatial frequency higher than 5 cycles/degree, so the sine wave will appear to
have a higher spatial frequency than 5 cycles/degree.

Question 16

) Suppose that instead of adapting to a single sine wave, you adapt to a complex
pattern that contains vertical sine waves at all spatial frequencies in equal amounts.
When you look back at the original vertical sine wave of 5 cycles/degree, what will the
relative activation of each channel be then? How will this affect the appearance of the
original sine wave, if at all?

Answer 16

4 cycle/degree channel activation = 3
5 cycle/degree channel activation = 6
6 cycle/degree channel activation = 3

The complex pattern will fatigue all channels equally, so their activation from the 5
cycle/degree pattern will be lower overall, but the relative activation of the channels will be the same. The original sine wave may appear dimmer, but its perceived spatial frequency will not be affected.

Question 17

Myopia

Answer 17

an image of a distant object becomes focused in front of the retina, instead of the on the retina making distant objects appear out of focus.