Week 3 - Visual Perception

Question 1

How is electromagnetic radiation (EMR) generated

Answer 1

EMR is generated when an atom emits a particle called a photon.

Question 2

Principles of perception

Answer 2

• perception is dynamic, we perceive change
• we perceive constancies in a a changing environment

Question 3

For an object to be visible is must emit or reflect_

Answer 3

Light

Question 4

What determines the wavelength of a photon?

Answer 4

The energy of the photon.

Question 5

What does the variation in wavelengths within the visible spectrum determine?

Answer 5

Different wavelengths give rise to the perception of different colours

Question 6

eye movements (saccades)

Answer 6

• constantly moving
• if an image stays stabilised on the retina it disappears (photoreceptors stop firing) and brain fills in space
• blind spot at the optic nerve

Question 7

Accomodation

Answer 7

ligaments (ciliary muscles) that attach the lens to the eye control the shape of the lens to accomodate near of far targets.
- stops working once you turn 40 years old so struggle to focus on middle distance

Question 8

Vergence and stereopsis

Answer 8

two eyes converge on the information to produce two different but aligned images of the same target. Helps to tell how far away something is

Question 9

Physiology of the retina

Answer 9

• densely packed with photoreceptors that point towards the back of the eye (light kills photoreceptors)
• structure of retina is upside down:
  Ganglion Cells
  Bipolar Cells
  Photoreceptors
  Choroid

Question 10

Rods (photoreceptor)

Answer 10

• black and white vision
• low acuity (widely spaced throughout retina, in peripheral field)
• work well at night (scotopic vision)

Question 11

Cones (photoreceptor)

Answer 11

• colour vision
• high acuity (can see fine detail bc densely packed in fovea)
• work in bright light (photopic vision)

Question 12

Lateral Inhibition

Answer 12

every adjacent unit within the photoreceptor cell or ganglion cell slightly changes the output of the unit next to it

Question 13

Passage of the visual signal

Answer 13

both eyes have a left and right visual field that send information to the left or right side of the brain.
- right visual field is on the left side of each eye and sends info the left side of the brain - vice versa
- Optic chiasm is where the nerves cross

Question 14

Lateral Geniculate Nucleus (LGN)

Answer 14

• six layers all replicated
• same properties as ganglion cells
• ganglion and LGN cells respond to the present of a spot of light on the retina
• LGN cells receive input from visual cortex

Question 15

Tectopulvinar System

Answer 15

• optic tract fibres that react to information that are fast moving (periphery)
• serves several functions:
  1. localisation of objects in space
  2. guidance of eye movements
  3. gross pattern perception

Question 16

Tectopulvinar System Physiology

Answer 16

• located in thalamic region called tectum
• cells in superior colliculi have receptive field on the retina and receive input from retinal genglion cells
• tectopulvinar system reveives back projects from the cortex
• calls organised in topographic maps

Question 17

Schneider (1969) study

Answer 17

• removed LGN from hamsters and superior colliculi from others
  no LGN = unable to recognise patterns
  no superior colliculi = recognise patterns but not accurately approach them

Focal system: recognition
Ambient system: localisation

Blindsight: damage to focal system can react to visual stimuli but claim they cannot see them

Question 18

The visual cortex

Answer 18

• LGN projects to primary visual cortex and occipital lobe at rear of brain
• LGN fibres enter layer IV, where the neurons center-surround receptive fields
• other layers have neurons with more complex behaviour