Study guide Exam #2 Chapter 9

Question 1

1. Define sensation and perception. How do they differ?

Answer 1

sensation- registration of physical stimuli
from the environment by the sensory organs.

perception- subjective interpretation of
sensations by the brain.

Sensation helps you determine the difference between rough or smooth, hot or cold, perception helps you interpret what is rough or hot and if it hurts.

Question 2

2. What is the stimulus for vision? What is the range of light for humans?

Answer 2

vision- light energy- chemical energy

work in a range of light intensities from very bright to very dim. These cells afford visual precision sufficient for us to see a human hair lying on the page of this book from a distance of 18 inches.

Question 3

3. Explain how the brain analyzes sensory information detected by the receptors of the eye.

Answer 3

NOT SURE

Question 4

4.     How does the eye work? What is the role of the:
Cornea-
Lens-
Retina-
Optic disk-
Fovea-

Answer 4

• the eye’s clear outer covering
• focuses light.
• light-sensitive surface at the back of the eye consisting of neurons and photoreceptor cells
• NOT SURE
• region at the center of the retina that is specialized for high acuity; its receptive fields are at the center of the eye’s visual field

Question 5

5. Describe colorblindness, what are the 4 types of colorblindness

Answer 5

Achromatopsia - fully colorblind - Rods only - See shades of grey

Protanopia- lack of red - difficulty with blue/green red/green

Deuteranopia - Lack of Green cones - difficulty with red/purple and green/purple - most common - 5% of mean and .4% women

Tritanopia- lack of blue - difficulty yellow/green and blue/green

Question 6

6. What is sensory coding (firing rates). How do action potentials code different sensations?

Answer 6

-After it has been transduced, all sensory information from all sensory systems is encoded
by action potentials
-then travel along peripheral nerves in the somatic nervous system
-then they enter the spinal cord or brain
-and, from there, on nerve tracts within the central nervous system
-Every bundle carries the same kind of signal. The presence of a stimulus can be encoded by an increase or decrease in the discharge rate of a neuron, and the amount of increase or decrease can encode stimulus intensity.
-As detailed in Section 9-4, qualitative visual changes, such as from red
to green, can be encoded by activity in different neurons or even by different levels of
discharge in the same neuron (for example, more activity might signify redder and less
activity greener). (p.285)

Question 7

7. What is a receptive field at the retinal ganglion cell level?

Answer 7

-A retinal ganglion cell (RGC) responds to stimulation of small circular patch of retina=cell’s receptive field
-Coding location
-Light shone in one place on the retina will activate one ganglion cell
-Light shone in another place will activate a different ganglion cell
Receptive-Field Hierarchy (302) Figure 9-23
-Each ganglion cell tells the brain about the amount of light hitting a certain spot on the retina compared with the rest of the retina

Question 8

8. Describe the process by which the visual system converts light energy into neural activity.

Answer 8

For vision, light energy is converted into chemical energy in the photoreceptors of the retina, and the chemical energy is in turn converted into action potentials.(p.283)

Question 9

9. What are the differences between rods and cones?

Answer 9

rod - photoreceptor specialized for functioning at low light levels.
cone - photoreceptor specialized for color and high visual acuity.

Question 10

9a. Types of cones and light sensitivity of each?

Answer 10

• 419 nm “blue” or short wavelength
• 531 nm “green” or middle wavelength
• 559 nm “red” or long wavelength

Question 11

9b. What is the distribution of the rods and cones?

Answer 11

• Cones - highest at the fovea and decrease precipitously towards the periphery
• No rods the fovea
• Rods increase in number around the fovea
• Rods decrease gradually in number towards the periphery
• No Rods and cones in blind spot
• Ganglion cell axons exit to brain and blood vessels
• (remember the eye is a sphere and has 3 dimensions)

Question 12

10. Describe optic flow.

Answer 12

Optic Flow - streaming of visual stimuli that accompanies an observer’s forward movement through space.

-Steam of visual stimuli- forward movement. We have holes in our vision but the brain files in the gaps.

Question 13

11. Describe the neural pathways for vision and their function (including anatomical structures and type of information processes in each pathway)

Answer 13

NOT SURE

Question 14

11a. Geniculostriate (dorsal and ventral and type of information processed in each) Figure 9-14 geniculostriate pathway (296)

Answer 14

Geniculostriate system projections from the retina to the lateral geniculate nucleus to the visual cortex. Helps you arrive at the WHAT

Question 15

11b. Tectopulvinar system

Answer 15

Projections from the retina to the superior colliculus to the pulvinar (thalamus) to the parietal and temporal visual areas. Helps you arrive at the HOW OR WHERE

Question 16

11c. What types of visual information is important for each pathway

Answer 16

NOT SURE

Question 17

10. Compare and contrast the dorsal and ventral visuals pathways.

Answer 17

Dorsal Visual Stream
-Originates in occipital cortex- parietal cortex
-the “WHERE OR HOW” pathway (how action is guided toward objects)
-Also called where pathway
Ventral Visual Stream
-Originates in the occipital cortex - temporal cortex
-the “WHAT” pathway (identifies what an object is)

Question 18

11. What is retinotopic organization or retinotopic map?

Answer 18

Areas of visual cortex are sometimes defined by their retinotopic boundaries, using a criterion that states that each area should contain a complete map of the visual field.

Question 19

12. Explain how the off-center and on-center ganglion cells influence the perception of shapes.

Answer 19

(A) In the receptive field of an Retinal Ganglion Cell (RGC) with an ON-CENTER and off-surround, a spot of light shining on the center excites the neuron, a spot of light in the surround inhibits it. When the light in the surround is turned off, firing rate increases briefly—an “offset” response. A light shining in both the center and the surround would produce a weak increase in firing.
(B) In the receptive field of an RGC with an OFF-CENTER and on-surround, light in the center produces inhibition, light on the surround produces excitation, and light across the entire field produces weak inhibition.(p.304)

Question 20

12a. On-off receptivity

Answer 20

Respond-presence or absence of light in receptive field (Center and surround) Figure 9-26 (304)
On-Center cells
-Excited when light falls on the center
-Inhibited when wight falls on the surround
-Light across whole receptive field - weak excited

Question 21

12b. Role of overlapping receptive fields

Answer 21

Overlapping Receptive Fields (305) Figure 9-27

• The receptive fields of retinal ganglion cells overlap extensively
• so any two adjacent fields look at almost the same part of the world

Question 22

12c. How do they detect edges

Answer 22

Figure 9-28 Activity at the Margins (305) -
Luminance Contrast: the amount of light reflected by an object relative to its surroundings.
Ganglion cells provide information about edges…It’s all about the edges.
-This allows input from Retinal Ganglion Cells (RGC’s) to tell the brain about shape

Question 23

12d. What is the receptive field of simple cells? Complex cells? Hypercomplex cells?

Answer 23

Figure 9-29 Typical Receptive Fields for Simple Visual-Cortex Cells V1 (306)
Processing shape in V!
Cells are orientation detectors
excited by bars of light oriented in particular directions
Simple Cells
Receptive field with a rectangular on-of arrangement
(Referring to Figure 9-29)
Simple cells respond to a bar of light in a particular orientation, such as (A) horizontal or (B) oblique. The position of the bar in the visual field is important, because the cell either responds (ON) or does not respond (OFF) to light in adjacent regions of the visual field.

Complex Cells Figure 9-30 (307) - Unlike a simple cell’s on–off
response pattern, a complex cell in the visual cortex shows the same response throughout
its circular receptive field, responding best to bars of light moving at a particular angle. The
response is reduced or absent with the bar of light at other orientations.

Hypercomplex Cells Figure 9-31 (307) - A hypercomplex cell in the visual cortex responds to a moving bar of light in a particular orientation (horizontal, e.g.) anywhere in the excitatory (ON) part of its receptive field. If most of the bar extends into the inhibitory area (OFF), however, the response is inhibited.

Question 24

13. Columnar organization

a. V1 – ocular dominance and line orientation.

Answer 24

ocular-dominance column (306) - functional column in the visual cortex maximally responsive to information coming from one eye.

Question 25

13b. Area TE – shape columns

Answer 25

NOT SURE

Question 26

14. Describe the regions of visual cortex and the type of information each region processes?

Answer 26

visual field

• vertical & horizontal meridia
• blind spots
• left & right hemifields

Principle of lateralization (left-hemifield -> right hemisphere and vice versa)

LGN (anatomy and physiology)

• magnocellular and parvocellular layers
• center-surround receptive fields

retinotopic maps

V1 (anatomy and physiology)

• simple cells, complex cells, and hypercomplex cells
• orientation- and direction-selectivity
• orientation and ocular dominance columns

amblyopia

Question 27

15. Explain how the brain perceives color. Compare and contrast the two theories of color vision.

Answer 27

LOOKING INTO IT

Question 28

15a. Trichromatic theory of vision

Answer 28

Trichromatic theory: explanation of color vision based on the coding of three primary colors: red, green, and blue.
three colors- red, green, and blue
color determined- relative responses of cone type
explain color blindness
limitation: four basic colors, red, blue, green and yellow can’t explain afterimage

Question 29

13b. Opponent color contrast theory of color

Answer 29

Opponent Processing theory (310) explanation of color vision that emphasizes the importance of the apparently opposing pairs of colors: red versus green and blue versus yellow.

Question 30

Possible test questions:(what is this and how does it work? good exam question, why do we need both theories: need the three cones and we need yellow and we get it through…)

Answer 30

Opposition of colors
Red vs Green
Blue vs Yellow
Opponent processing in retinal ganglion cells
on/off center-surround receptive fields
~60% of retinal ganglion.