Vision

Question 1

In reference to depth perception, what is occlusion?

Answer 1

Occlusion is the perception that when something is covering something else, it is closer.

Question 2

How does retinal size translate to depth perception?

Answer 2

The image projected onto our retina shrinks the further away an object gets. Therefore, larger image = closer object.

Question 3

What does the Ames window show in relation to depth perception?

Answer 3

The Ames window demonstrates that longer lines on what are typically rectangualr objects, such as windows, are percieved as closer than shorter lines.

Question 4

What is the linear effect in depth perception?

Answer 4

Parallel lines appear to converge in the distance.

Question 5

What does texture indicate in relation to depth perception?

Answer 5

A rougher texture indicates that an object is closer, whereas a smoother texture indicates that an object is further away.

Question 6

What does the shading effect indicate about the shape of objects?

Answer 6

Shading from the top (light at the bottom) indicates that an object is concave, whereas shading from the bottom (light from the top) indicates that it is convex.

Question 7

What is the light scatter effect in relation to depth perception?

Answer 7

The light scatter effect makes objects in the distance appear hazier and blueer.

Question 8

What is the motion parallax effect?

Answer 8

Motion parallax means that objects that are closer appear to move faster when we turn our head than objects that are further away.

Question 9

What is the name of the primary vision pathway, what are the three main aspects and where do these take place?

Answer 9

Retino-geniculate-striate pathway
Image formation - takes place in the eye
Transduction - takes place in the retina
Visual processing - takes place in the thalamus, primary visual cortex (occipital lobe), extrastriate cortex, extended cortex (temporal and parietal lobes)

Question 10

Where did we get vision before we developed the lobes, and how much information is taken there?

Answer 10

Superior colliculus on the tectum - 10% of information.

Question 11

What does the Superior colliculus do? What is the extrastriate pathway from the Superior colliculus?

Answer 11

SC deals with orienting of gaze, it plays a role in unconscious perception, and is exogenous (stimulus driven).
SC -> pulvinar -> amygdala

Question 12

What are the other three (beside geniculo-striate and extrastriate) visual pathways?

Answer 12

Pretetcum (pupillary reflex)
Accessory optic pathway
Retino-hypothalamic pathway

Question 13

Define retinotopic

Answer 13

Adjacent points in the visual field map onto adjacent points on the retina.

Question 14

Define cortical magnification

Answer 14

More cortex is dedicated to processing the central visual field than the periphery

Question 15

What is the role of the eye?

Answer 15

To form an image and generate a neural signal (transduction).

Question 16

Describe the cornea and it’s function.

Answer 16

The cornea is the transparent outer layer. Light bending occurs here due to the refractory index of the eye being different to the refractory index of the air.

Question 17

What is the lens’ function, and how does it adjust?

Answer 17

The lens fine tunes image information altering the degree in which the light entering the eye is bending. When objects are further away, the muscles contract, the lens pulls out and light will bend less. When objects are closer, the muscles relax, the lens goes rounder and the light will bend more.

Question 18

What is the function if the iris and pupil?

Answer 18

The pupil is the opening into the eye, which is regulated by the contractile tissue around it (iris). This varies light and focal length.

Question 19

What is the function of the retina?

Answer 19

The retina transduces light signals to neural signals.

Question 20

What is the fovea, what is it’s function, and what are the main type of receptors that make up this area?

Answer 20

The fovea is a dent in the retinal ganglion cells that allows for high acuity vision. The majority of the receptors in the fovea are cones.

Question 21

What is the optic disc, and what does this create in the field of vision?

Answer 21

The optic disc is the point where the RCG axons become the optic nerve. This creates a blindspot in vision.

Question 22

How does the brain respond to the blindspot in vision?

Answer 22

The receptors around the blindspot fill in the gaps, excluding it from our perception of the world. Edges are continued, surfaces are interpolated.

Question 23

What are the five types of cells in the retina?

Answer 23

Retinal ganglion cells, amacrine cells, bipolar cells, horizontal cells, cone and rod receptors.

Question 24

What are the functions of cones, what are the three types of cones?

Answer 24

Cones provide phototopic vision and colour perception. 3 types - short, medium and long wavelength.

Question 25

Describe the difference between rods and cones in terms of sensitivity, convergence and positional acuity.

Answer 25

Cones - lower sensitivity, high positional acuity due to low convergence
Rods - higher sensitivity, lower positional acuity due to high convergence

Question 26

What type of early processing occurs in the retina?

Answer 26

Edge detection, motion detection (directional selectivity in the cells) and convergence (reduce the size of the optic nerve).

Question 27

What type of cells are retinal ganglion cells? What do they detect? Where are the smallest inputs?

Answer 27

RCGs are centre-surrounded receptive field cells. This allows them to determine contrast, not just light detection. The smallest inputs are at the fovea, allowing for higher visual sensitivity.

Question 28

Where is the first synapse in the retino-geniculate-striate pathway after the optic nerve leaves the eye?

Answer 28

The lateral geniculate nucleus in the thalamus.

Question 29

How many layers are there in the lateral geniculate nucleus, and what are the different channels?

Answer 29

There are 6 different layers. The P channel and M channels.

Question 30

What is decussation, and what is partial decussation?

Answer 30

Decussation is when pathwyas cross the midline -> the left visual field goes to the right cortex and the right visual field goes to the left cortex. Partial decussation is when only parts of the information cross - in humans, 50% of optic nerve fibres cross at the optic chiasm

Question 31

What stimulation do centre-surround cells respond to? What do they detect?

Answer 31

Light in the middle with dark surroundings, or vice versa. They detect contrast.

Question 32

What stimulation do simple cells respond to? What do they detect? Are they binocular or monocular?

Answer 32

Simple cells respond to a light line in dark surroundings, or vice versa. This is achieved when a row of centre-surround RF cells fire, synapsing onto the simple cell, causing it to fire. This allows them to detect contours and object outlines. They are monocular.

Question 33

What do low spatial frequencies correspond to? What cell subfields do these frequencies activate?

Answer 33

Low spatial frequencies corresponds to textures. Low SF activates cells with wide subfields.

Question 34

What do high spatial frequencies correspond to? What cell subfields do these frequencies activate?

Answer 34

High SF correspond to edges. High SF activates cells with narrow subfields.

Question 35

Are complex cells binocular or monocular? How does this effect firing rate of the cells.

Answer 35

Complex cells are binocular. This means that there will be a more vigorous/ higher firing rate if inputs arrive from both eyes simultaneously.

Question 36

What type of cells underlie stereoscopic depth perception?

Answer 36

Complex cells.

Question 37

Define ocular dominance.

Answer 37

Ocular dominance occurs in complex cells, in which some cells favour and respond more vigorously to one eye over the other.

Question 38

What can occur from damage to the V1.

Answer 38

Scotomas and blindsight

Question 39

What are scotomas, how do they effect vision, and what test can you use to detect one?

Answer 39

Scotomas are an area of blindness in a contralateral field in both eyes. Unless it is very big, it typically does not effect vision as completion occurs (the blind spot is filled in).

Question 40

What characterises blindsight, and what structure is damaged to result in this?

Answer 40

Blindsight occurs when you can see, but you have no conscious awareness of it, ie. they can’t tell if youre holding a ball, but if you threw the ball at them, they would move. The V1 primary cortex is damaged.

Question 41

Where does the dorsal stream run to?

Answer 41

The posterior parietal cortex.

Question 42

Where does the ventral stream run to?

Answer 42

The inferior temporal cortex.

Question 43

What is the main function of the dorsal stream? According to Ungerleider ‘what vs where’ and Goodale ‘action vs perception’?

Answer 43

To enable interaction with the environment. Dorsal specialises in visual spatial recognition and visually guided behaviour.

Question 44

What are the main functions of the ventral stream? According to Ungerleider ‘what vs where’ and Goodale ‘action vs perception’?

Answer 44

Integration of visual features into objects and association of objects with knowledge. Ventral specialises in visual pattern recognition and conscious visual perception.

Question 45

What are the two basic types of agnosia? What structure is damaged to cause this?

Answer 45

Apperceptive agnosia - loss of visual perception, in which a person has trouble drawing or naming objects.
Associative agnosia - loss of visual meaning, in which a person has trouble naming the object but not drawing it. The ventral stream is damaged.

Question 46

What is prosopagnosia, and what structure and area of the brain is damaged to cause this?

Answer 46

Prosopagnosia is face blindness. Damage to the ventral stream and the fusiform face area of the right inferior temporal lobe.