W10: Perception 2

Question 1

What percentage of the brain’s cortex is involved in visual processing?

Answer 1

50%

Question 2

The important parts of the human eye

Answer 2

Cornea, iris, lens, retina, photoreceptors, optic nerve, vitreous humour

Question 3

Process which lights turn into visual images

Answer 3

Lights enter the eye, it passes through the cornea and lens, which focus it on the retina

Photoreceptors covert light into electrical signals that travel along the optic nerve to the brain, where lights are processed into visual images

Question 4

What are the 2 types of photoreceptors?

Answer 4

Rods and Cones

Question 5

What is the primary different between the two types of photoreceptors?

Answer 5

Rods:
* Enables vision in low light condition
* Do not provide colour vision

Cones:
* Active when there is enough light stimulation
* Provide colour vision
* 3 types of cones, which are sensitive to diffrent wavelengths and frequencies of length

Question 6

What are the three type of cones? Their wavelengths and what colour are they sensitive to?

Answer 6

Blue cones/ S-cones:
* Sensitive to blue light
* Short wavelenghts

Green cones / M-cones:
* Sensitive to green light
* Medium wavelength

Red cones / L-cones:
* Sensitive to red light
* Long wavelengths

Question 7

How does colour blindness occur?

Answer 7

• Occurs due to genetic mutation
• Affects the funcitoning of on or more types of cone cells
• e.g. red-green colour blindness –> deficiency in red sensitve or green sensitive cones

Question 8

Structure of a retina and how light approach the photoreceptor

Does the incoming light hit the part that is sensitve to that light first?

Answer 8

No.

• The incoming light needs to travel through a bunch of neurons, e.g. ganglion cells, amacrine cells, bipolar cells, horizontal cells, before getting to the photoreceptor cells (the cones and rods)

Question 9

How does the incoming light travel to the brain?

Answer 9

• Incoming light need to travel through a bunch of neurons before getting to the photoreceptor cells
• When there is enough simulation in the receptor cells, action potential occurs and the light get send back again to the ganglion cells
• When light reaches the ganglion cells, the axons are then bunched up into the opitc nerve, which then travel through the retina into the brain

Question 10

Can there be photoreceptor cells there the optic nerves leave for the brain?

Answer 10

No, where the optic nerves leave for the brain, there are no rods or cones cells

Question 11

Where is the blind spot located?

Answer 11

Located toward the nasal retina, so closer to the nose

Question 12

How does the brain compensate for the blind spot?

Answer 12

By filling in what it thinks should be there

Question 13

How does stereopsis help overcome blind spots?

Answer 13

Through crossover of the optic chiasm

• Since the eyes are separated horizontally, each eye perceive a slightly different depth and view
• The right side of space gets processed in the left hemisphere and the left side is processed in the right hemisphere
• The brain combines both view and create a three-dimentsional image with depth

Question 14

What is stereopsis?

Answer 14

Depth perception that enables 3D images by combining the perception of the visual stimuli from both eyes

Question 15

What is the trade off between sensitivity and resolution of photoreceptor cells?

Answer 15

Rods:
* Greater light sensitvity at the reduction in resolution
* Because many rods send nerve impulses or action potentials to the ganglion cells

Cones:
* Less light sensitive but provide high resolution images with better fine details
* One or two cones that send signals to several ganglion cells

Question 16

Visual receptive field

Answer 16

‘Hotspots’ in the vision that, when stimlated by specific visual cues (e.g. lights, patterns), causes certain neurons to become active

Question 17

Can the visual receptive field vary in size and complexity?

Answer 17

Yes, the visual receptive field can vary in size and complexity.

E.g.:
* Retina:
* Individual dangdlion cells have small receptive fields
* resopnds to simple features, e.g. edges
* Primary visual cortex:
* Receptive fields become larger and more sophisticated
* Responding to more complex shapes, colours and movements

Question 18

What are the main types of visual receptive field? What is their use?

Answer 18

On centre receptive field:
* Neurons are most active when the centre is exposed to light

Off centre receptive field:
* Neurons are most active when the centre is in darkness

This enables the visual system to detect contrasts and edges in the environment

Question 19

Centre-surrouding antagonism

Answer 19

Ganglion cells exhibit centre-surround antagonism

Sensory neurons respond differently to stimulation in the central and surround areas

Help detect edges and contrasts in the visual field

Question 20

The neuronal response to centre and surround stimulation

Answer 20

Centre stimulation:
* Neurons are most excited when the central region is stimulated

Surround stimualtion:
* Stimulation in the surrounding areas elads to reduced or inhibit activity

Question 21

The significance of centre-surround antagonsim

Answer 21

The contrast of central and surround stimulation:
* Crucial for detecting boundaries between objects
* Emphases the differences in light intensity accross adjacent areas

Question 22

Lateral geniculate nucleus (LGN)

Answer 22

• In the thalamus
• Serve as a relay station for visual information from the eyes to the visual cortex
• Receptive fields suchas ganglion cells, including the centre-surround antagonism is present in the LGN

Question 23

Primary visual cortex (V1)

Answer 23

• Located in the occipital lobe
• Processes initial visual information
• Detects feature such as edges and orientations, helps brain extract crucial infomation about object and scence structures
• Neuons in V1 act as line detectors, angles detectors and square detectors neurons –> forming the basis for recognising shapes and objects

Question 24

Significance of orientation detection

Answer 24

• V1’s neurons’ specilisation is essential for recognising whole objects
• The specilisation is a result of writing and connections in the visual pathway during development