Topic 3: The Visual Cortex and Beyond

Question 1

What occurs at the optic chiasm?

Answer 1

Some axons cross to the opposite side of the brain from the eye that they came from.

Result = right visual field goes to the left side; left visual field goes to the right side (contralateral processing)

Question 2

What are visual fields determined by?

Answer 2

Where a person is fixating; Anything to the right of center vs. anything to the left of center

Question 3

How are signals divided after partial crossover at the optic chiasm?

Answer 3

Approximately 90% of the signals will proceed to the lateral geniculate nucleus (LGN)

Other 10% proceeds to the superior colliculus

Question 4

Thalamic nuclei; “Sensory relay station”

Answer 4

Lateral geniculate nucleus (LGN)

Question 5

Midbrain (tectum) nuclei; Eye movements, orienting movements

Answer 5

Superior colliculus

Question 6

Primary visual receiving area in the occipital lobe

Answer 6

Striate cortex; V1

Question 7

Describe the pathway of visual signals to the occipital lobe.

Answer 7

Visual signals leave the back of both eyes as the optic nerves, which then meet at the optic chiasm.

At the optic chiasm, some axons cross to the opposite side of the brain from the eye that they came from.

After meeting, and partially crossing, at the optic chiasm, most signals will proceed to the lateral geniculate nucleus (LGN), while a smaller portion proceed to the superior colliculus

From LGN, signals travel to the occipital lobe (V1)

Question 8

Describe what Hubel and Wiesel (1965) found regarding perceptual fields in the visual cortex.

Answer 8

Flashing spots of light on different places in the retina, found cells in V1 with receptive fields that, like the RGCs in the retina, have excitatory and inhibitory areas

Unlike the circular receptive fields in the retina, the areas are side-by-side

Question 9

A neuron in the visual cortex that responds best to bars of a particular orientation

Answer 9

Simple cortical cells

Question 10

Graph in which orientation (degrees) is plotted against firing rate (impulses per second)

Answer 10

Orientation tuning curve

Question 11

Neurons in the visual cortex that respond best to moving bars with a particular orientation

Answer 11

Complex cortical cells

Question 12

Neurons that respond best to lines of a specific length, that are moving in a particular direction

Answer 12

End-stopped cells

Question 13

What are the three types of feature detectors?

Answer 13

Simple cortical cells
Complex cortical cells
End-stopped cells

Question 14

Where does evidence that feature detectors in our visual cortex play a role in our perception come from?

Answer 14

Selective rearing experiments

Question 15

Describe selective rearing experiments

Answer 15

Procedure in which animals are raised in special environments that contain only certain types/features of stimuli

Neurons that respond to that feature will become more prevalent

Neurons that respond to features that aren’t present will not develop

Question 16

What characteristic of the nervous system do selective rearing experiments demonstrate?

Answer 16

Neural plasticity or experience-dependent plasticity; “Use it or lose it”

Question 17

Horizontal/vertical orientations are perceived more easily than other orientations

Answer 17

Oblique effect

Question 18

A map on a structure in the visual system that corresponds to locations on the retina

Answer 18

Retinotropic map

Question 19

How do locations on the retina relate to locations in V1?

Answer 19

Locations adjacent to each other on the retina are represented by locations that are adjacent to each other on V1

Question 20

What does it mean to say the fovea is “overrepresented” in V1?

Answer 20

More of the space on V1 is dedicated to the fovea than to the peripheral retina

Question 21

Occurs when a disproportionately large area on the cortex is activated by stimulating a much smaller area on the receptor surface (e.g. overrepresentation of the fovea)

Answer 21

Cortical magnification

Question 22

Describe the topographic organization of V1

Answer 22

Fovea = posterior
Periphery = anterior
Top of visual field = bottom of V1 (the opposite is true as well)

Question 23

Describe the organization of V1 in terms of location, orientation, and ocular dominance columns.

Answer 23

Neurons in V1 have receptive fields at roughly the same location on the retina

Preferred orientation is also the same

Each orientation and each location will have one column for the left eye and one for the right eye

Question 24

Name the areas of the extrastriate cortex and their functions.

Answer 24

V2: Initial processing of color, shape, motion; moves to V3, V4, or V5 depending on the processing required

V3: shapes of objects (particularly, when in motion)

V4: Color

V5: Motion

Question 25

Areas of the occipital lobe aside from V1

Answer 25

Extrastriate cortex

Question 26

Describe the role of the temporal lobe in terms of its visual stream function.

Answer 26

Ventral pathway/what pathway

Object recognition

Question 27

Describe the role of the parietal lobe in terms of its visual stream function.

Answer 27

Dorsal pathway/where and how pathway

Location and direction

Question 28

Describe the pathway of signals as they travel beyond the visual cortex.

Answer 28

Signals from the striate cortex (V1) travel to the extrastriate cortex (V2-V5)

Signals then leave the occipital lobe & continue through the ventral pathway (temporal lobe; what) and the dorsal pathway (parietal lobe; where)

Question 29

What evidence do we have for separate what and where pathways?

Answer 29

Ablation monkeys

Temporal ablation = lose what
Parietal ablation = lose where/how

Question 30

What are typical characteristics/symptoms of someone with damage to their ventral pathway?

Answer 30

Can’t tell you what they’re picking up

If the injury is exclusively to the ventral pathway, they will still be able to reach out appropriately for the object

Understand “how” to use the structural features of an object

Question 31

What are typical characteristics/symptoms of someone with damage to their dorsal pathway?

Answer 31

If the injury is exclusively to the dorsal pathway, they will still be able to recognize objects

No longer understand “how” or “where” to use the structural features of an object

Question 32

What are three characteristic symptoms of Balint syndrome?

Answer 32

Optic ataxia: Loss of visual guidance of hand and arm

Oculomotor apraxia: Difficulty performing voluntary eye movements

Simultagnosia: Inability to perceive more than one object at a time

Question 33

Located at the apex of the ventral/”What?” pathway

Answer 33

Inferotemporal (IT) cortex

Question 34

Why can neurons in the inferotemporal cortex respond to much more complex stimuli?

Answer 34

By the time we get here, the size of neuron’s receptive fields no longer correspond to just simple features; They are large enough now to encompass whole objects

Question 35

Describe Charles Gross’ (1972) discovery of the function of the inferotemporal cortex

Answer 35

Was recording the firing of neurons in a monkey’s temporal lobe but was troubled when they found a neuron that didn’t respond to any simple stimuli

Put hand in front of the projector:
In response, the neuron fired with a burst of activity, so they determined that this neuron fired maximally to complex stimuli, and barely at all for simple ones

Further testing of the IT region found neurons in our temporal lobes that respond almost exclusively to faces, and not to non-face stimuli.

Question 36

Provide three examples of regions towards the end of the temporal pathway that respond to incredibly specific complex stimuli

Answer 36

FFA: Fusiform face area

EBA: Extrastriate body area

PPA: Parahippocampal place area

Question 37

Damage to which area causes prosopagnosia?

Answer 37

Fusiform face area (FFA)

Question 38

Inability to recognize faces

Answer 38

Prosopagnosia