Psy 256 Vision lecture

Question 1

What is Sensation?

Answer 1

-Sensation is the detection and translation of stimulus energy into neural activity

Question 2

What is perception?

Answer 2

-perception is the organization and interpretation of sensory info/activity

Question 3

What is transduction?

Answer 3

-transduction is process through which something changes in specific way

Question 4

What kind of environmental energy produces sensation in the 5 classic senses?

Answer 4

-vision (electromagnetic energy) (light)
-hearing (mechanical energy) (from sound pressure waves)
-smell and taste (chemical compounds)
-touch (mechanical energy) (pressure)

Question 5

What are the three main dimensions of light (names and stimulus features)?

Answer 5

-Hue: wavelength/color
-Brightness: intensity
-saturation: purity

Question 6

What & where is the retina? the fovea?

Answer 6

• the retina is the light-sensitive layer of tissue at the back of the eyeball
  -the fovea is a tiny pit in the macula, a small structure located in the center of the retina, the light
  sensitive tissue that lines the back of the eye

Question 7

What is the blindspot? Why do we have it? Why aren’t we aware of it (3 reasons)?

Answer 7

-there are no photoreceptors (rods & cones) at the optic disc, where the optic nerve exits the eyeball.
Creates a blind spot in our vision.
-our brain automatically fills in the blind spot with a simple extrapolation of the image surround the
blind spot

Question 8

What are the main differences between the two classes of photoreceptors (rods and cones)?

Answer 8

-there are around 120 million rods, most in periphery, B&W, high sensitivity (can see in dim light), poor
acuity
-there are around 6 million cones, most in fovea, color, low sensitivity, (need bright light), good acuity
(details)

Question 9

What and where are bipolar and ganglion cells? What are the 2 main types of ganglion cells?

Answer 9

-bipolar cells, form synapses with photoreceptors, some info integration
-ganglion cells, axons form optic nerve, thus creating blind spot
-2 types: based on the LGN cells which they synapse
-magnocellular (large b&w)
-parvocellular (small, color)

Question 10

What wavelengths and colors are associated with the 3 types of cones?

Answer 10

-color perception is based on 3 types of cones:
-Short (blue) cones
-Medium (green) cones
-Long (red) cones

Question 11

Describe and name the two visual pathways that go from the eyes to the brain

Answer 11

-two main visual pathways are retino-geniculo-striate pathway (which mediates high-level cortical
vision) and retino-tecto-pulvinar pathway (mediates more reflexive aspects of vision)

Question 12

Where are the temporal and nasal portions of the retina?

Answer 12

-temporal (outside) portions of each retina project ipsilaterally while nasal (inside) portions project
contralaterally

Question 13

Where is the optic chasm and what happens there?

Answer 13

-optic chiasm is located at the base of the brain inferior to the hypothalamus and superior to the
pituitary gland, part of the brain where optic nerves cross and therefore is primary importance to
visual pathway

Question 14

Where is the
superior colliculus and suprachiasmatic nucleus; what do they do?

Answer 14

-superior colliculus in the midbrain, mediates visual reflexes (attention), suprachiasmatic nucleus in the
hypothalamus and mediates sleep-wake cycles

Question 15

How many layers are there in the LGN?

Answer 15

6 layers in Lateral Geniculate Nucleus

Question 16

Which photoreceptors and what kind of light is processed by the magnocellular, parvocellular, &
koniocellular layers of the LGN.

Answer 16

-magnocellular (M) layers are mainly fed by rods and mediate b&w vision
-parvocellular (P) layers are mainly fed by cones and mediate color (green & red)
-koniocellular (K) sublayer mediates short wavelength (blue) light

Question 17

What are ocular dominance columns, where are they located, and what do they do?

Answer 17

-are stripes of neurons in visual cortex of certain mammals (including humans) that respond
preferentially to input from one eye to other, laid out across the surface of the striate cortex (V1)

Question 18

Where is the striate cortex? Why is it called this? What are the three other names for it?

Answer 18

-area of visual cortex that receives the sensory input from the lateral geniculate nucleus is primary visual
cortex, V1, Brodmann area 17, or striate cortex

Question 19

How is the striate cortex organized (what parts of the visual field go where?)

Answer 19

-divides into five different areas (V1 to V5) based on function and structure

Question 20

What are receptive fields? Give examples for touch and vision.

Answer 20

-receptive fields of a neuron is the area of space (body surface or retinal location) in which a stimulus
may alter the activity of that neuron
-touch receptors on skin have receptive fields that reflect the distribution of their dendrites on the
surface of skin
-photoreceptors have receptive fields, there is a neuron devoted to processing just that relative
location

Question 21

How do center-surround (dot detector) cells combine to create “line detectors” in V1?

Answer 21

-using LGN neurons as intermediate step, retinal ganglion “dot detectors” can be combined to form “line
detectors” in V1. Such arrangements of neurons can be configured in many ways, allowing detection
of lines of different orientation

Question 22

What are center-surround ON & OFF cells in the LGN, and how do they work?

Answer 22

-ON-center cells with this organization increase their firing rate when light falls on the center of their
receptive field, but decreases their firing rate when light falls into periphery of their field
-Off-center cells show the opposite characteristics, increasing their firing when light falls in their
periphery but decreasing when light hits their center

Question 23

Describe the trichromatic & opponent-process theories of color vision. Which is correct?

Answer 23

-trichromatic theory: based on additive (light based) color mixing, proposed three types of color
receptors (blue, green, and red)
-partially were correct but 3 cones alone cant explain afterimages & certain forms of color blindness

-opponent process theory is competing theory that proposed the existence of (ganglion) cells with
antagonistic color pairs (blue-yellow) & (red-green)
-both theories are correct but at different places

Question 24

What & where are the what & where visual streams? What other terms describe these two pathways?

Answer 24

-where pathway, “occipitoparietal” “dorsal pathway”, localization of objects in space, control of
movement, vision-for-action
-the what pathway, “occipitotemporal”” ventral pathway”, object identification (features, colors,
shapes, complex objects” vision-for-perception

Question 25

What is blindsight?

Answer 25

-Blindsight is the ability to correctly identify or respond to visual stimuli, despite having no conscious
awareness of them, usually due to damage to primary visual cortex ( area V1, aka BA17)

Question 26

What is achromatopsia?

Answer 26

-Achromatopsia is “cortical color blindness” from damage to the color processing area V4

Question 27

What is semi-spatial neglect?

Answer 27

-hemi spatial neglect is the failure to attend to objects in the side of space opposite to the brain lesion

Question 28

What is agnosia?

Answer 28

-agnosia refers to the inability to recognize (identify) objects even though basic sensation & perception
is intact

Question 29

What are the two main forms of agnosia? What behavioral characteristics distinguish between them?

Answer 29

-apperceptive agnosia: most severe, unable to identify basic/low level features of objects, must use
other senses
-associative agnosia: perception without meaning, basic perception intact, but unable to recognize
objects by vision