Central Visual Processing

Question 1

Why is layer IV (neocortex) of the primary visual cortex especially thick?

Answer 1

The large amount of visual input coming from the lateral geniculate nucleus

Question 2

How is layer IV organized in the primary visual cortex?

Answer 2

Ocular dominance columns

LGN axons relay information specifically from either the left or right eye to the cortical neurons in one column

Question 3

What is the difference between monocular and binocular neurons?

Answer 3

Monocular neurons receive input from only one eye - e.g. cells in ocular dominance columns

Binocular neurons receive input from both eyes - e.g. some neurons in higher layers of striate cortex receiving converging input from layer IV cells

Question 4

What are blobs?

Answer 4

Defined histologically by a high concentration of cytochrome oxidase

Neurons in the blob of primary visual cortex have wavelength sensitive responses to visual stimuli - i.e. important in color discrimination

Question 5

What are Magnocellular LGN neurons?

Answer 5

Have circular center-surround receptive fields

Monocular

Respond transiently, and are wavelength insensitive

Question 6

What are Simple cells?

Answer 6

Have elongated receptive fields thought to result from converging input from several LGN cells

Orientation selective - respond best to stimuli presented in a specific orientation aligned with their “on” zone

Question 7

How are orientation selective cells arranged in the cortex?

Answer 7

Columns

Question 8

What are directionally selective cells?

Answer 8

In addition to being orientation selective, many of these cells have the additional response property of direction selectivity

Allows for the analysis of motion

Question 9

What are parvocellular, interblob (P-IB) channel neurons?

Answer 9

Located in the PVC, in between cytochrome oxidase blobs - also called complex cells

Highly orientation selective

Fire in response to stimuli anywhere in their receptive field

Small, elongated receptive fields

Analyze object shape/form

Question 10

What are blob channel neurons?

Answer 10

Function to analyze object color

Located within the blob

Wavelength sensitive

Circular receptive fields

Not orientation or direction selective

Question 11

What is retinotopic organization?

Answer 11

Each point in the visual field is represented by neuronal activity within a specific location of striate cortex

Some degree of retinotopic organization is maintained in extrastriate cortical areas

Question 12

What is a hypercolumn?

Answer 12

Small cube of cortex that contains:

1) a complete set of orientation columns (all possible orientations represented)
2) Input from both eyes (complete set of ocular dominance columns)
3) All three information processing channels (M, P-IB, and Blob)

Question 13

How are neurons within the medial temporal (MT) area specialized?

Answer 13

Specialized for analysis of motion

Directionally selective

Large receptive fields

Directional tuning - respond to movement in a narrow range of directions

Allows this are to analyze movement better than V1

Question 14

What types of motion are neurons in the medial superior temporal (MST) area specialized for?

Answer 14

Complex motions such as:

Linear

Radial

Circular

Question 15

What is the result of lesions in the dorsal stream?

Answer 15

Impaired perception of motion

Question 16

What areas are a part of the dorsal stream?

Answer 16

MT - medial temporal

MST - medial superior temporal

Question 17

What areas are a part of the ventral stream?

Answer 17

V4

IT - inferior temporal

Question 18

How are neurons in V4 specialized?

Answer 18

Large receptive fields

Orientation and color selective

Question 19

What can occur from lesions in V4?

Answer 19

Achromatopisa

Complete loss of color vision

Question 20

How are neurons in the IT area specialized?

Answer 20

Respond to colors and highly specific shapes

thought to have a particularly important role in face recognition (fusiform gyrus is located here)

Question 21

What is the parallel activation theory?

Answer 21

Visual information is prcoessed simultaneously, in multpile, parallel areas of the visual system

Perception results from the binding of information from all of these areas

Question 22

What occurs as a result of strabismus in children?

Answer 22

The visual system suppresses input from one eye causing permanent low acuity and poor depth perception in the suppressed eye if untreated

Indicates a critical period of neuron development in which vision must be intact

Can be corrected with patching of the strong eye

Question 23

What is retinal disparity?

Answer 23

Mechanism for near-field depth perception

Objects produce slightly different images on each retina

Neurons which are sensitive to retinal disparity receive binocular input

Question 24

What depth cues are used for far-field depth perception?

Answer 24

Size

Interposition

Linear perspective

Ligh and shadow

Motion parallax