4 Visual Cortex

Question 1

Q: What is the pathway of ganglion cell fibers from the retina?

Answer 1

A: Ganglion cell fibers leave the retina along the optic nerve.

Question 2

Q: What is the optic chiasm?

Answer 2

A: The optic chiasm is the crossover point where some fibers of the optic nerve cross over to the opposite side of the brain.

Question 3

Q: What happens to the optic nerve beyond the optic chiasm?

Answer 3

A: Beyond the optic chiasm, the optic nerve becomes the optic tract.

Question 4

Q: How is information organized in the optic tract?

Answer 4

A: Information in the optic tract is separated by visual field rather than by eye.

Question 5

Q: How is information from the right visual field represented in the brain?

Answer 5

A: Information from the right visual field is represented by the left hemisphere of the brain.

Question 6

Q: What is the LGN?

Answer 6

A: The LGN (Lateral Geniculate Nucleus) is a bilateral structure that receives input from the optic tract.

Question 7

Q: How does the LGN receive input from the eyes?

Answer 7

A: Each LGN receives input from both the left and right eyes but keeps the inputs separate.

Question 8

Q: What receptive field organization do cells in the LGN have?

Answer 8

A: LGN cells have the same receptive field organization as retinal ganglion cells, exhibiting center-surround antagonism.

Question 9

Q: What is the function of the receptive field organization in LGN cells?

Answer 9

A: The receptive field organization is ideal for detecting spots of light and edges but not the orientation of visual stimuli.

Question 10

Q: Where is the primary visual cortex located in the brain?

Answer 10

A: The primary visual cortex is located at the back of the brain at the bottom.
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Question 11

Q: What is retinotopic mapping in V1?

Answer 11

A: Retinotopic mapping in V1 means that objects close together in the visual scene are analyzed by neighboring parts of V1.

Question 12

Q: What is cortical magnification in V1?

Answer 12

A: Cortical magnification in V1 refers to the distortion in the amount of cortex devoted to representing each part of the retinal field.

Question 13

Q: How is the fovea represented in V1?

Answer 13

A: The fovea, though accounting for only 0.01% of the retina, is represented by a large area of cortex in V1, approximately 8-10%.

Question 14

Q: What is the method used for studying receptive fields in V1?

Answer 14

A: Single-cell recording is used in V1, where a visual stimulus is presented to an animal, and an electrode is inserted into a V1 neuron to measure its electrical activity.

Question 15

Q: What was the response observed in V1 cells during initial studies?

Answer 15

A: V1 cells exhibited baseline activity when no stimulus was presented, and researchers initially struggled to find a stimulus that excited them.

Question 16

Q: What did Hubel and Wiesel discover about V1 cells’ response?

Answer 16

A: They found that V1 cells responded strongly when the edge of a slide moved across their receptive field, indicating that they respond to lines rather than spots.

Question 17

Q: What is orientation selectivity in V1 cells?

Answer 17

A: Orientation selectivity refers to V1 cells’ preference for lines of a particular orientation.

Question 18

Q: What are the three different types of cells in V1 with distinct receptive field organization?

Answer 18

A: The three types are simple, complex, and hypercomplex cells.

Question 19

Q: What stimuli do simple cells respond to?

Answer 19

A: Simple cells respond to oriented lines and edges.

Question 20

Q: What is the structure of the receptive field in simple cells?

Answer 20

A: The receptive field of simple cells has both excitatory and inhibitory regions, but they are elongated.

Question 21

Q: Do simple cells have orientation selectivity?

Answer 21

A: Yes, simple cells exhibit orientation selectivity.

Question 22

Q: What does it mean for a simple cell to be orientation tuned?

Answer 22

A: Orientation-tuned neurons respond best to their preferred orientation but also respond to similar orientations.

Question 23

Q: What are the characteristics of complex cells?

Answer 23

A: Complex cells respond to oriented lines but do not have discrete on/off regions.

Question 24

Q: What types of stimuli do complex cells respond best to?

Answer 24

A: Complex cells respond best to moving oriented lines and edges.

Question 25

Q: What are hypercomplex cells also known as?

Answer 25

A: Hypercomplex cells are also known as end-stopped cells.

Question 26

Q: What types of stimuli do hypercomplex cells respond to?

Answer 26

A: Hypercomplex cells respond to lines of a particular orientation, direction, and length.

Question 27

Q: How do receptive fields change in complexity from simple to hypercomplex cells?

Answer 27

A: Receptive fields increase in complexity from simple to hypercomplex cells, with hypercomplex cells having more specific response characteristics.

Question 28

Q: How many visual areas are there beyond V1?

Answer 28

A: There are over 30 visual areas beyond V1.

Question 29

Q: How are visual areas beyond V1 interconnected?

Answer 29

A: All visual areas beyond V1 are interconnected, and there is no simple separation of function.

Question 30

Q: What are some examples of specialized visual areas?

Answer 30

A: Examples include V4, which is specialized for color processing.

Question 31

Q: What are the two processing streams in visual processing?

Answer 31

A: The “what” stream travels ventrally to the inferotemporal cortex, while the “where” stream travels dorsally to the posterior parietal cortex.

Question 32

Q: What is the function of the “what” stream?

Answer 32

A: The “what” stream is important for recognizing and discriminating objects.

Question 33

Q: What is the function of the “where” stream?

Answer 33

A: The “where” stream is important for determining where an object is located and how to act upon it.

Question 34

Q: What is another name for the “where” stream?

Answer 34

A: The “where” stream is sometimes referred to as the “how” stream.

Question 35

Q: Are the pathways of the processing streams totally separate?

Answer 35

A: No, there are many connections between the “what” and “where” streams, and signals flow both upwards and backwards between them.

Question 36

Q: What evidence supports the distinction between the “what” and “where” streams?

Answer 36

A: Lesion studies in monkeys and neuropsychological studies in humans provide evidence for the functional distinction between the streams.

Question 37

Q: What is visual form agnosia?

Answer 37

A: Visual form agnosia is a condition where damage to the ventral pathway results in an inability to identify objects despite knowing their features.

Question 38

Q: What is optic ataxia?

Answer 38

A: Optic ataxia is a condition where damage to the dorsal pathway results in difficulties reaching to grasp objects, while object recognition and description remain intact.

Question 39

Q: How do the deficits in visual form agnosia and optic ataxia differ?

Answer 39

A: Patients with visual form agnosia have deficits in object recognition despite intact reaching abilities, whereas patients with optic ataxia have deficits in reaching and grasping despite intact object recognition.