BIOPSYCH - Chapter 5 - Vision

What term refers to the fact that rubbing your eyes makes you see something?

Law of specific nerve energies

The fictional character Superman is said to have x-ray vision. What would happen if your eyes could send out x-rays?

You would increase other people’s cancer risk.

What is the route from retinal receptors to the brain?

Receptors connect to bipolars, which connect to ganglion cells, which send axons to the brain

What axons form the optic nerve?

Axons from the ganglion cells

Why is vision most acute at the fovea?

Receptors in the fovea connect to midget ganglion cells.

Why does vision in the periphery have high sensitivity to faint light?

Toward the periphery, the retina has more convergence of input.

Why do some people have greater than average sensitivity to brief, faint, or rapidly changing visual stimuli?

They have more axons from the retina to the brain.

Compared to many birds, what is true of human color vision, and why?

Humans are color-vision deficient, because we do not see ultraviolet radiation.

Suppose you perceive something as red. According to the trichromatic theory, what is the explanation?

Light from the object has excited your long-wavelength cones more strongly than your other cones.

An object that reflects all wavelengths equally would ordinarily appear gray, but it may appear yellow, blue, or any other color, depending on what?

Contrast with surrounding objects

Color vision deficiency demonstrates which fundamental point about perception?

Color is in the brain and not in the light itself.

What do horizontal cells in the retina do?

They inhibit neighboring bipolar cells.

In humans, what crosses to the contralateral hemisphere at the optic chiasm?

Half of each optic nerve, the part representing the nasal half of the retina

What is the function of lateral inhibition in the retina?

To sharpen borders

Suppose light strikes the retina in a circle, surrounded by dark. Which bipolar cells will exhibit the greatest response, and which the least?

Bipolar cells connected to the receptors just inside the circumference of the circle respond most. Those connected to receptors just outside the circumference respond least.

Parvocellular cells are specialized to respond to what?

Color and detail

Magnocellular cells are specialized to respond to what?

Movement

Which of these is true of visual imagery?

it starts in language or memory areas and spreads to V1.

Which of the following is responsible for many if not all cases of blindsight?

Connections to cortical areas outside V1

How do complex cells in the visual cortex differ from simple cells?

Complex cells make the same response after a stimulus moves.

After you stare at a waterfall or other steadily moving display, you see stationary objects as moving in the opposite direction. That observation is evidence in favor of which of the following?

Feature detectors

If a kitten has one eye shut for its first few weeks of life, its visual cortex becomes insensitive to that eye. Why?

Activity from the active eye inhibits synapses from the inactive eye.

If someone has dense cataracts on both eyes, and the cataracts are removed years later, what happens?

The person has continuing limitations in depth and motion perception.

The dorsal stream of the visual system is specialized for what?

Coordinating vision with movement

What happens to receptive fields as we progress from V1 to V2, V3, and beyond?

They become larger and more complicated.

What is distinctive about visual perception in the inferior temporal cortex?

Cells respond to an object regardless of the angle of view.

The fusiform gyrus is specialized for what?

Recognizing faces and other highly familiar objects

If someone has trouble recognizing faces, what pathway in the nervous system is probably deficient?

Connections between the fusiform gyrus and part of the occipital cortex

What happens after damage limited to area MT?

Motion blindness

Why is it difficult to watch your own eyes move when looking in the mirror?

During saccadic eye movements, activity decreases in area MT.

In many ways the eye is analogous to a camera. The light sensitive surface in the back of the eye that would correspond to the film in a camera is the____

Retina

Where are the rods and cones of the eye located?

Retina

The fovea is the part of the retina

with the greatest perception of detail.

If you want to see something in fine detail, you should focus the light on which part of your retina?

Fovea

Anatomically, which of the following types of cell in the retina is located closest to the pupil?

Ganglion cells.

Rods and cones make direct synaptic contact with __________ and __________.

bipolar cells, horizontal cells

The optic nerve, which conveys visual information to the brain, is composed of axons from which kind of cell?

Ganglion cells.

Why is the blind spot of the retina blind?

It is the point where the optic nerve leaves the retina and there are no rods or cones.

The point at which the optic nerve leaves the retina is known as the

blind spot.

The two kinds of receptors in the retina are

rods and cones.

The optic nerves from the two eyes

meet to form the optic chiasm, where half of the axons from each eye cross to the other side.

The occipital lobe of the cerebral cortex receives visual information directly from

the lateral geniculate of the thalamus.

In comparison to the rods, the cones of the retina are

more sensitive to detail.

Walking down a dark alley at night, Nathan is startled by the movement of a cat that he sees out of the "corner of his eye". He is unable to see the cat when he looks directly at it because

cones are less sensitive to dim light.

The perception of color depends on

cones.

In comparison to the cones, the rods are

more sensitive to dim light.

Why are humans unable to distinguish colors in their extreme peripheral vision?

The periphery of the retina contains only rods.

Retinal ganglion cells form two classes, based on characteristics of their receptive fields: 1) "on centre off surround" cells, 2) "off centre on surround" cells. A light moves across type 2, so that it FIRST hits the periphery (surround) and THEN the centre, one would note the following changes in the firing frequency of this ganglion cell:

an increase of the frequency, followed by a reduction falling under the original level.

The range of wavelengths detected by the human eye is approximately

400 700 nm.