Vison (4)

Question 1

What are the three classes of visual cortex?

Answer 1

1. Primary visual cortex (V1) – receives input from the lateral geniculate nuclei.
2. Secondary visual cortex (V2, V3, etc.) – receives input mainly from primary visual cortex.
3. Visual association cortex – receives input from secondary visual areas and other sensory modalities.

Question 2

Where is the primary visual cortex located?

Answer 2

In the posterior occipital lobes, largely hidden in the longitudinal fissure.

Question 3

Where are secondary visual cortex areas located?

Answer 3

In the prestriate cortex (occipital lobe band surrounding V1) and inferotemporal cortex (inferior temporal lobe).

Question 4

Where is visual association cortex located?

Answer 4

Several cortical regions, largest area in the posterior parietal cortex.

Question 5

How does the flow of visual information progress through the cortex?

Answer 5

From primary visual cortex → secondary visual cortex → association cortex. As you move up, neurons have larger receptive fields and respond to more specific and complex stimuli.

Question 6

What is a scotoma?

Answer 6

An area of blindness in the corresponding area of the contralateral visual field caused by damage to primary visual cortex.

Question 7

How is a scotoma detected?

Answer 7

Using a perimetry test, where a patient fixates on a point while dots of light are flashed; the patient indicates when they see the dots, mapping blind spots.

Question 8

What is completion in visual perception?

Answer 8

The phenomenon where a patient perceives a complete image despite part of it lying in a scotoma. Often occurs without conscious awareness of the missing area.

Question 9

What is blindsight?

Answer 9

The ability to respond to visual stimuli in a scotoma without conscious awareness. Most commonly, perception of motion survives.

Question 10

What are two proposed mechanisms for blindsight?

Answer 10

1. Residual islands of functional striate cortex mediate some visual abilities.
2. Alternate visual pathways from subcortical structures to secondary visual cortex bypass V1. Both may contribute.

Question 11

How many functional visual areas have been identified in macaque monkeys?

Answer 11

32 areas: 1 primary, 24 secondary, and 7 association visual cortex areas.

Question 12

How do neurons differ across these visual areas?

Answer 12

Neurons respond to different visual aspects (e.g., color, movement, shape), and selective lesions produce specific visual deficits.

Question 13

How are secondary and association visual areas interconnected?

Answer 13

They are highly interconnected (over 300 pathways in macaques), and connections are mostly reciprocal.

Question 14

How have human visual areas been mapped?

Answer 14

Using PET, fMRI, and evoked potentials while volunteers view visual stimuli. About 12 functional areas have been delineated in humans.

Question 15

What are the two major visual streams, and where do they flow?

Answer 15

1. Dorsal stream (“where”) – V1 → dorsal prestriate → posterior parietal cortex
2. Ventral stream (“what”) – V1 → ventral prestriate → inferotemporal cortex

Question 16

What is the primary function of the dorsal stream?

Answer 16

Processes spatial information: object location, motion, and direction of movement; guides behavioral interactions with objects.

Question 17

What is the primary function of the ventral stream?

Answer 17

Processes object characteristics: color, shape, faces, animals; mediates conscious perception of objects.

Question 18

What is the “where vs. what” theory?

Answer 18

The “where vs. what” theory says the brain has two visual pathways:

The dorsal stream tells us where things are (location and movement).

The ventral stream tells us what things are (object recognition)

Question 19

What is the “control of behavior vs. conscious perception” theory?

Answer 19

Dorsal stream → directs actions on objects (even without conscious awareness)
Ventral stream → mediates conscious perception of objects (even without guiding action)

Question 20

How do these theories explain cortical damage?

Answer 20

• Dorsal stream damage → can see objects but cannot interact accurately

Ventral stream damage → can interact with objects without conscious perception

Question 21

What is prosopagnosia?

Answer 21

A visual agnosia for faces—difficulty recognizing whose face it is, though faces are seen as faces. It can be developmental or acquired.

Question 22

Is prosopagnosia specific only to faces?

Answer 22

Not necessarily. Some patients also struggle to recognize specific objects in complex classes (e.g., particular cows, cars, or houses). Prosopagnosia may not be a unitary disorder.

Question 23

Which brain areas are most associated with prosopagnosia?

Answer 23

• Fusiform Face Area (FFA): ventral surface between occipital and temporal lobes; critical for face identification.
• Occipital Face Area (OFA): ventral surface of occipital lobe; helps discriminate faces.
• Lateral prefrontal cortex may also contribute to face identification.

Question 24

How do we know prosopagnosics can sometimes recognize faces unconsciously?

Answer 24

Skin conductance studies show physiological responses to familiar faces even when patients claim not to recognize them (Tranel & Damasio, 1985).

Question 25

What is akinetopsia?

Answer 25

The inability to perceive smooth motion; the world appears as a series of snapshots. Can be acquired via brain damage or transient from high-dose antidepressants.

Question 26

Which brain area is critical for motion perception and associated with akinetopsia?

Answer 26

Area MT (middle temporal area): near the junction of temporal, parietal, and occipital lobes.

Question 27

What is special about neurons in MT?

Answer 27

- 95% respond specifically to direction of movement, not color or shape. - Large binocular receptive fields track movement over a wide range.

Question 28

What evidence links MT to motion perception?

Answer 28

1. Damage to MT → akinetopsia 2. fMRI: MT activates with motion perception 3. TMS: blocking MT → motion blindness 4. Electrical stimulation of MT → induces perception of motion

Question 29

How does recent research challenge the dorsal/ventral stream dichotomy?

Answer 29

Both streams carry information about what an object is and how to interact with it, opposing the strict “dorsal = behavior / ventral = perception” view.

Question 30

What structures in the eye does light pass through to reach the retina?

Answer 30

Cornea → Aqueous humor → Pupil (controlled by iris) → Lens → Vitreous humor → Retina

Question 31

What type of vision is mediated by rods and cones?

Answer 31

Rods: low-light (scotopic) vision, no color, high sensitivity, low acuity Cones: bright-light (photopic) vision, color vision, low sensitivity, high acuity

Question 32

What happens to a photoreceptor’s electrical activity when it is activated by light?

Answer 32

It hyperpolarizes, reducing glutamate release at synapses with bipolar cells

Question 33

Describe the retinal pathways and their path to the primary visual cortex.

Answer 33

Retina: Photoreceptors → Bipolar cells → Ganglion cells → Optic nerve → Optic chiasm (nasal fibers cross) → Optic tract → LGN → Optic radiations → Primary visual cortex (V1) | Pretty Boys Get Outta Class To Learn Real Vision

Question 34

What is cortical magnification?

Answer 34

Cortical magnification means that the fovea (center of vision) gets more space in the visual cortex than areas in the peripheral vision.

Question 35

Differences in receptive fields: retinal ganglion cell vs. simple V1 cell

Answer 35

Retinal ganglion: center-surround, responds to spots of light, small receptive field Simple V1: elongated/edge-shaped, responds to bars or edges at specific orientation, larger receptive field

Question 36

Differences between parvocellular and magnocellular LGN neurons

Answer 36

Parvocellular: small cells, color/detail, cones, slow, “what” pathway Magnocellular: large cells, motion/contrast, rods, fast, “where” pathway

Question 37

Advantages and disadvantages of intracellular vs. extracellular recording

Answer 37

Intracellular: measures membrane potential, captures subthreshold, technically hard, cell may die Extracellular: measures action potentials, easier, multiple neurons, cannot see subthreshold

Question 38

What is a hypercolumn in V1 and its components?

Answer 38

Functional unit representing all orientations and ocular dominance for a retinal patch: Ocular dominance columns (left/right eye) Orientation columns (specific edge angles) Blob regions (color-sensitive neurons)