Vision

Question 1

How do we come to make sense of jumbled patterns?

Answer 1

Through scattered input from photons and quantum of light, we extract meaning by identifying the positions of objects, their identity and characteristics.

Question 2

What is object constancy?

Answer 2

As things are moving at a constant rate; If an object is constant in its position we can identify the characteristics of that object.

Question 3

What are a couple of principles of visual perception?

Answer 3

We perceive change and we orient to this.

Anything that doesn’t change becomes background noise.

We perceive constancies in a changing environment.

Question 4

What is the general physics of light?

Answer 4

What we perceive as light is a small part of the electromagnetic radiation spectrum. EMR is generated when an atom emits a “particle” called a photon. Their energy determines their wavelength. We detect light within a narrow range of wavelengths. Different wavelengths give rise to the perception of different colours. Colour is determined by the frequency of their wavelength beginning with violet up to red.

Question 5

Where is the largest amount of light emited in the retina?

Answer 5

It focuses in a straight line, the thing you are looking at will be perceived best, and the largest amount of focus is in the fovea.

Question 6

What are saccades and what happens to photoreceptors when they are fixed on an object?

Answer 6

Saccades are the process of the eye constantly moving. Once the image is stable on the retina all photoreceptors responsible for detecting the object stop working as they have fired to their maximum potential, they essential become bored. The eye fills in missing information that is absent in the blind spot.

Question 7

What is accommodation and how does the ciliary muscle relate to this process?

Answer 7

The lens of the eye is able to stretch and compress through the ciliary muscle. Accommodation is stretching or applying tension on the lens in order to focus on an object that is either near or far.

The lens is round when focusing on an object near in focus, and flat when something is far.

Question 8

What are vergence and stereopsis and how do they work?

Answer 8

Vergence: Two eyes converge to produce different but aligned images of the same target, creating an overlay.

Stereopsis: The perception of depth produced by visual stimulus from both eyes in combination.

Objects in the visual field will be slightly different due to the angles of the eyes. The further away something is the less discrepancy between the eyes, the closer, more discrepancy.

Question 9

What is motion parallax?

Answer 9

Moving the head to perceive which object is closer to you. Whatever object moves the most is closest to you, thus giving an idea of where things are located.

Question 10

What is the role of the choroid?

Answer 10

It is the jet-black part of the eye that captures all the light entering from the visual field. It sits underneath all other cells and protects photoreceptors from too much light.

Question 11

What are cones?

Answer 11

6 million high acuity colour receptors. They are in the fovea and periphery visual systems and have fast dark adaptation and low dark sensitivity. “Yellow sensitive”

Question 12

What are rods?

Answer 12

120 million disparately placed receptors in peripheral vision, you need to look off-centre for them to work. Low acuity, slow dark adaption and high dark sensitivity and “Green” sensitivity.

Question 13

What is the Duplex Retina theory?

Answer 13

Proposes that rods and cones come from two separate visual systems.

Photopic: Bright light vision via cones

Scotopic: Dim light vision via rods.

Question 14

What is the structure of the retina?

Answer 14

Each particle of light comes in from the environment and bounces off the back of the choroid where photoreceptors begin to unscramble information. They converge onto bipolar cells which further work to understand that information, they then converge onto ganglion cells. Ganglion cells ask for information, such as what colour and object the light bounced off.

Question 15

Retinal physiology overview.

Answer 15

Receptor cells synapse with bipolar cells

Bipolar cells synapse with ganglion cells

Horizontal cells connect with different receptors or different bipolar cells

Amacrine cells connect different bipolar or different bipolar cells

Amacrine cells connect different bipolar or different ganglion cells

Connecting cells allow events at one location to influence events at another

Massive convergence as we move deeper into the retina: on average 126 receptors connect to 1 ganglion cell

Process of information reduction

Question 16

What is the role of ganglion cells?

Answer 16

It acts as a lens, capturing an image over an area of the retina called the receptive field. They work as edge detectors in order to enhance an object and reinforce the discontinuities that exist between it.

Question 17

How does Lateral inhibition work?

Answer 17

A ganglion cell’s excitation is relative to the amount of information it is receiving from the visual field. Lateral inhibition is the process of communicating between cells which part of visual information a cell is receiving, meaning cells receiving a larger portion of visual information will inhibit neighbouring cells’ excitation.

If your neighbour is receiving a very bright light your firing of a neuron is being suppressed, if your neighbour is receiving a relatively small light compared to yours your firing is going to be suppressed less than if it was receiving an equivalent amount of light.

Question 18

What are some qualities of ganglion cells that relate to processing the receptive field?

Answer 18

They have both excitatory and inhibitory connections. They work relative to the portion of the environment in which your retina is orientated. They have a centre and a surround. They work as edge detectors.

Question 19

What is on centre off surround?

Answer 19

Retina ganglion cells which depolarise as a result of light being in the centre of their visual field.

Question 20

What is off-centre on surround?

Answer 20

Retina ganglion cells which depolarise when light is outside of their receptive field.

Question 21

There are different ganglion cells that react to light either on or off its centre, why is the helpful?

Answer 21

They help to integrate patterns of lightness over an area and indicate whether patterns of lightness within an area is different to that in an adjacent area (an edge)

Question 22

There are both on- and off-centre surround ganglion cells, what is the third type?

Answer 22

Ganglion cells that depolarise regardless of which area of their receptive field is illuminated. Cells that exhibit centre-surround antagonism are called X- or Y-cells, while these third types of cells are called W-cells.

Question 23

What are the two different visual channels that X- and Y-cells are associated with?

Answer 23

The transient and sustained systems. These are visual systems that have evolved through our history and have become redundant maps of the visual system, they are now called the parvo and magnocellular systems.

Question 24

What are the parvo and magno cellular systems?

Answer 24

They are two systems of cell types that exist retinotopically in the lateral geniculate nuclei. The parvo (meaning small) ganglion cells detect shapes and objects whereas the magno (meaning large) cells detect movement. Magno cells are in the first two layers of the LGN and parvo cells are in the 3rd, 4th, 5th and 6th layers.

Question 25

What is the main quality of the Parvo cellular systems?

Answer 25

They are small dense layers of the LGN that help process detail in the visual field. They register high-fidelity within the centre of the visual field which comes from the fovea.

Question 26

What is the main quality of the magnocellular system?

Answer 26

It is a very fast transient system that is able to detect your periphery and all the information around the centre of the visual field.

Question 27

What is the structure inside of the thalamus responsible for transmitting information to the left and right occipital lobes?

Answer 27

Lateral Geniculate Nucleus.

Question 28

What happens to visual information once it’s moved through the retinotopic map of the lateral geniculate nucleus?

Answer 28

It goes through a process of decussation, some information is sent to the occipital lobes and other information is sent to the superior colliculi. Information is also relayed back into the LGN from the occipital lobe. We can only act on information sent to our occipital lobes as information stored in the superior colliculi is out of our awareness.

Question 29

What is the tectopulvinar system?

Answer 29

An evolutionary system that allows us to act on visual information straight away. Optic fibres project to the superior colliculi and then to the pulvinar and lateral posterior nuclei. Responsible for the localisation of objects in space, the guidance of eye movements and gross pattern perception.

Question 30

What does the tectopulvinar allow us to do?

Answer 30

Allows us to automatically respond to visual information in the environment, whereas higher levels of visual reception give us the ability to think about what we are seeing.

Question 31

What happens when the LGN and superior colliculi are removed?

Answer 31

no LGN = inability to recognise patterns
no superior colliculi = able to recognise patterns but unable to accurately approach them

Question 32

What are the two separate pathways of the tectopulvinar system?

Answer 32

The focal system for recognition
The ambient system for localisation

Question 33

What is blindsight and how can this help explain the tectopulvinar system?

Answer 33

Some people with damage to the focal system can still react to visual information although they claim they cannot see it. The visual system is functioning but there is no awareness of what they are seeing. When they point to objects, this is a function of the ambient tectopulvinar system.

Question 34

What happens to visual information in the V1 visual cortex?

Answer 34

Information is passed from the eye to the thalamus to the visual cortex. Higher-order cells receive input from higher-order ganglion cells and create a map of a local order of space and compare the input according to orientation. Lines are formed and sorted by order and orientation.

Question 35

Feature detectors in primary visual cortex: Simple cortical cells.

Answer 35

These respond to bars of a particular orientation.

Question 36

Feature detectors in primary visual cortex: Complex cortical cells.

Answer 36

Often respond best to a correctly orientated bar moving across the entire receptive field. Some cells are direction sensitive.

Question 37

Feature detectors in primary visual cortex: Hypercomplex cortical cells.

Answer 37

They fire to moving lines of a particular length or moving corners or angles.

Question 38

What is the ‘where’ pathway beyond V1?

Answer 38

The dorsal stream of information in the visual cortex that moves up to the parietal lobe is concerned with motion perception and spatial awareness.

Question 39

What is the ‘what’ pathway beyond V1?

Answer 39

The ventral stream of information travels from the visual cortex to the temporal lobe concerned with object recognition.

Question 40

In visual research, visual illusion phenomena test the plasticity of the visual system, what are they and the explanations?

Answer 40

Adaption and constancy experiments/illusions.

The system slowly reduces responding to constant stimulation; stopping a stimulus slowly reduces responding to constant stimulation; stopping a stimulus can result in an aftereffect.

Testing: How constant effects of stimulation effect what is normal at any given time demonstrating the plasticity of the system.