CH 3

Question 1

conduction velocity

Answer 1

signalling fast = magnocellular system
signalling slow= parvocellular system

Question 2

magnocellular system

Answer 2

• signal from retinal magnocellular ganglion cells
• large neurons
• detects luminance, provides info about location of objects

Question 3

parvocellular system

Answer 3

• receiving info from retinal parvocellular ganglion cells in retina
• small neurons
• sensitive to colour, discriminates fine details

Question 4

optic radiation

Answer 4

Axons from the LGN project to primary visual cortex (V1)

Question 5

Organizational Features of V1

Answer 5

a. Topography
b. Cortical magnification
c. Cortical modularity
d. Receptive fields

Question 6

Topography

Answer 6

○ Retinotopic organisation : objects that are close to each other in the visual field are represented close to each other in the primary sensory cortex
○ Losing function in the left visual cortex: can’t see on the right side
○ Damage in the occipital cortex corresponds to location in the visual field

Question 7

cortical magnification

Answer 7

what you focus on: a lot of neurons are responsible for processing that piece of info. Inversement, what I’m not focusing on (parafovially) is being processed by fewer neurons in the occipital cortex

Size is unevenly distributed but our brains make sense of it.

Question 8

Cortical modularity

Answer 8

neurons close by process the same info

Question 9

Off bipolar cells

Answer 9

preserve the sign (+/-) of the cone, are hyperpolarised = produce less glutame by light

Question 10

On bipolar cell

Answer 10

reverse the sign (+/-) of the cone, are depolarised = produce more glutame by light

Question 11

receptive fields

Answer 11

If a stimulus from a certain area of the visual field elicits the strongest response from a specific neuron, then that area of the visual field is the receptive field for the neuron in question. Neurons can also be especially receptive to a certain orientation of a stimulus (tuning curves

they become more and more complex at the
cortex because multiple LGN cells integrate into simple cells in V1, which integrate into complex cells, which integrate into hypercomplex cells.

—> Neurons become more and more specialized higher up in the visual processing stream, for example the fusiform face area and grandmother cells.

Question 12

Dorsal stream

Answer 12

The “where” stream. Primary visual cortexàparietal cortex. Analyses space and motion.

Question 13

Ventral stream

Answer 13

The “what” stream. Primary visual cortexàtemporal cortex. Analyses color and form

Question 14

Perception

Answer 14

product of active visual processing
Can be described by 5 properties:
a. lightness/brightness
b. colour
c. form
d. depth/distance
e. motion

Question 15

Lightness and Brightness

Answer 15

The subjective visual experience with light and dark; not objectively measurable. Driven by knowledge of the world

a. Simultaneous lightness/brightness contrast phenomenon
b. Lateral inhibition
c. The inverse problem

Question 16

Simultaneous lightness/brightness contrast phenomenon

Answer 16

Patches that reflect the same amount of light may appear lighter or darker depending on the lightness of the background because there is more local contrast against a darker background

Question 17

Lateral inhibition

Answer 17

The most active ganglion cells try to inhibit the ones next to them

the center of a receptive field is LESS ACTIVE with lighter backgrounds:
—> for the image with the darker background, retinal ganglia are highly active and do not inhibit the center
—> for the light background, retinal ganglia are less active and inhibit the center.

Question 18

The inverse problem

Answer 18

The visual image on our retina can be the result of many
different sources.
In other words, many different sources can produce the same image on the retina

Question 19

Colour

Answer 19

colours depend on the wavelength of light that is not absorbed, no reflected
seeing colours is based on 3 different types of cones with different properties

colour: created and processed in V4
3 perceptual qualities:
a. hue = actual colour
b. saturation = how colourful something is
c. brightness

Question 20

3 different types of cones

Answer 20

each with their own absorption properties: able to absorb short, medium or long wavelengths

humans are trichromatic: have 3 types of cones
damage to V4: cerebral achromatopsia: can’t see colour

Question 21

colour contrast

Answer 21

the same colour (wavelengths) can be perceived as different depending on the surrounding colours

Question 22

colour constancy

Answer 22

different colours can be perceived as the same depending on the surrounding colours

Question 23

Form

Answer 23

involves perception of :
a. line lengths
b. their orientation
c. their intersections.

—> shape depends on what your brain does, rather than the actual physical properties.

Size: Different sizes of shapes cause different activations of areas in V1. The activation depends on perceived size, not actual size.

Question 24

Distance and depth

Answer 24

we perceive a 3D world from 2D images on the retina

depth perception depends on:
a. monocular component (one eye)
b. binocular components (both eyes)

Question 25

monocular component

Answer 25

depends on learned cues

a. occlusion: shapes in the back are blocked by shapes in the front
b. relationship between size and distance: objects that are far away appear smaller
c. motion parallax: closer objects appear to move faster

Question 26

Binocular component

Answer 26

since our eyes are about 6 cm apart, they create slightly different images from slightly different angles = retinal disparity

Question 27

occlusion

Answer 27

shapes in the back are blocked by shapes in the front

Question 28

relationship between size and distance

Answer 28

objects that are far away appear smaller

Question 29

motion parallax

Answer 29

closer objects seem to move faster

Question 30

binocular rivalry

Answer 30

Each eye receives a completely different
image. The experienced percept is not one that fuses both
images

Question 31

Cyclopean fusion

Answer 31

occurring in V1, brings the images together

Question 32

Motion

Answer 32

The subjective experience when a sequence of different but related images is presented to the retina over a short time
processed in V5

a. aperture problem
b. apparent motion
c. motion aftereffect

Question 33

aperture problem

Answer 33

many different combinations of speed and direction may elicit the same perception of a motion

Question 34

Apparent motion

Answer 34

Similar static images are presented closely in time give the illusion of movement.

Question 35

Motion aftereffect

Answer 35

result of neural adaptation wherein you perceive movement in the opposite direction when looking away from a movement after a relatively long time.

Neurons respond less and less when observing the same movement for a long period of time, so looking away causes non adapted neurons to become more active, creating an illusion of motion in the opposite direction