Lecture 4-Vision

Question 1

What is the primary function of vision described by Yantis (2001)

Answer 1

To allow organisms to obtain knowledge of
their surroundings by sensing light from
reflected surfaces

Question 2

What is the primary function described by Goodale and Milner, 1996?

Answer 2

To provide distal sensory control of
movement to ensure survival and reproduction. All visual processing systems
ultimately serve to guide behaviour

Question 3

What are the two fundamental principles that characterize visual processing?

Answer 3

1. Visual processing is characterized by functional specialization within various visual pathways (within retina, subcortical and cortical pathways)
2. And by distributed coding in the visual cortex, indicating that there are no “grandmother cells” but but rather a distributed spatial and temporal coding system.

Question 4

What are the four ways in which primary visual pathways differ according to Livingstone and Hubel?

Answer 4

1. Differ in color perception,
2. Acuity (size of visual field centers, spatial sensitivity)
3. Speedof processing (temporal sensitivity)
4. Contrast (sensitivity to changes in brightness).

Question 5

What is the role of the Lateral Geniculate Nucleus (LGN) in the visual system?

Answer 5

The Lateral Geniculate Nucleus is an importnat part of the retinogeniculate pathway in the visual system, receiving 90% of retinal axons and being integral for vision, with dysfunction leading to vision loss.

Question 6

What proportion of the LGN’s neural mass is dedicated to representing the fovea and its immediate surroundings?

Answer 6

50% of the LGN’s neural mass represents the fovea and its immediate surroundings, highlighting its importance in high-resolution vision.

Question 7

How does the LGN ensure high-fidelity signal transmission from the retina?

Answer 7

The LGN ensures high-precision/accurate signal transmission by having each geniculate neuron receive only a few inputs from retinal ganglion cells.

Question 8

What evidence suggests that there might be top-down control in visual processing within the LGN?

Answer 8

The fact that only 10-20% of the LGN’s presynaptic connections are from the retina suggests there could be top-down control in visual processing (which is when your prior knowledge or expectations influence what you see)

Question 9

How many layers does the LGN have?

Answer 9

1. 2 ventral magnocellular layers
2. 4 dorsal parvocellular layers

Question 10

What is the role of the Parvocellular (P) pathway?

Answer 10

The Parvocellular pathway is responsible for color and feature sensitivity.

Question 11

What is the role of the Magnocellular (M) pathway?

Answer 11

The Magnocellular pathway is responsible for motion sensitivity.

Question 12

What are the characteristics of the Magnocellular (M) pathway? (4) (recieve which kind of cells, what type of recpetive fields, what kind of response, what type of input)

Answer 12

1. Receives A (P-alpha or parasol) retinal ganglion cell projections.
2. Features large receptive fields.
3. Shows transient response.
4. Has rapidly conducting axons.

Question 13

What are the characteristics of the Parvocellular (P) pathway? (recieve which kind of cells, what type of recpetive fields, what kind of response, what type of input)

Answer 13

1. Receives B (P-beta or midget) retinal ganglion cell projections.
2. Features small receptive fields.
3. Shows sustained response.
4. Receives input from 1-2 cone types.

Question 15

What is the Dorsal Stream specialized for in the brain?

Answer 15

The Dorsal Stream is specialized for processing motion and depth.

Question 16

What are MT cells in dorsal stream sensitive to?

Answer 16

Primarily sensitive to direction and have receptive fields that are 10 times wider than in the striate cortex.

Question 17

How do cells in the dorsal stream respond to motion?

Answer 17

Cells in the dorsal stream respond to motion detected by contrasts in luminance, texture, or color, which indicates a crossover from parvocellular specialization.

Question 18

What is MST specialized for in the dorsal stream?

Answer 18

MST (Medial Superior Temporal) is specialized for processing optic flow, particularly regarding movement through space.

Question 19

What happens if there are lesions in the dorsal stream?

Answer 19

Lesions in the dorsal stream can produce scotomas, which are areas of reduced or lost vision, particularly for percieving motion

Question 20

What is the ventral stream specialized for?

Answer 20

The ventral stream is specialized for processing color and form perception.

Question 21

What stimuli do cells in the IT area respond to in ventral stream?

Answer 21

Cells in the IT area are responsive to specific stimulus categories such as faces, hands, and other objects.

Question 22

How are cells in the IT area organized in the ventral stream?

Answer 22

Cells in the IT (Inferior Temporal) area do not have tight retinotopic organization like previous visual areas, and their large receptive fields may include the entire visual field, possibly related to ‘object permanence’.

Question 23

What is evidence of category specificity in the ventral stream?

Answer 23

Evidence for category specificity in the ventral stream is evident in neuropsychological disorders such as visual object agnosias and category-specific agnosias.