Sensory Systems: Vision + Touch

Question 1

What do all sensory systems follow

Answer 1

Hierarchical organisation (HR)

Question 2

Sensory Hierarchy order

Answer 2

1. Association cortex
2. Secondary sensory cortex
3. Primary sensory cortex
4. Thalamic Nuclei
5. Receptors

Question 3

Sensory hierarchy- how it works

Answer 3

• each levels of sensory hierarchy receives input from level below
• adds another layer of analysis
• as level increases, neurons respond optimally to stimuli of greater complexity

Question 4

Differentiation between sensation and perception

Answer 4

Sensation: process of detecting presence of stimuli
Perception: higher-order process of integrating, recognising, and interpreting sensations

Question 5

What’s involved in the visual system,

Answer 5

-pupil
-iris
-retina
-fovea
-blind spot
-Optic nerve

Question 6

How visual system works - light

Answer 6

1. Light enters through pupil
2. Size of pupil regulated by iris— high illumination = small pupil
3. Light then goes through lens — focuses incoming light on Retina + turns everything upside down

Question 7

Axons of Retinal ganglion cells

Answer 7

• axons leave eye in one bundle (optic nerve)
• makes gap in receptor layer (blind spot)
  -blind sot filled by visual system from receptors that surround it

Question 8

What it the Fovea and what is it specialised for ?

Answer 8

• small area in centre of retina
• specialised for high-activity vision

Question 9

What receptors does the retina contain

Answer 9

1. Rods
2. Cones

Question 10

Rods:

Answer 10

• abundent in periphery of retina
• respond best to FAINT LIGHT
• outnumber cones (20x)
• many converge to 1 ganglion cells

Question 11

Cones:

Answer 11

• found in + around fovea
• respond best to BRIGHT LIGHT
• essential for colour vision
• each cone associated with 1 ganglion cell
• low convergence

Question 12

Photopigemnetations

Answer 12

-rods + cones contain photopigmentations
- when struck by light, photopigmentations release energy
- energy release activates 2nd messenger — initiating signal transduction across other neurons of brian

Question 13

Retina to Primary Visual Cortex

Answer 13

• 90% of ganglion cells axons = part of retina-geniculate-situate pathway
• signals from left visual fields reach right visual cortex (same vice versa)
• axons from nasal part of retinas cross (optic chiasm)
• axons from temporal part of retinas do not cross
• after optic chiasm, signals go through thalamus
• then goes to primary visual context

Question 14

What are the majority of ganglion cell axons apart of ?

Answer 14

Retina-geniculate-sitrate pathway (90%)

Question 15

What is an edge ?

Answer 15

• most informative feature
• area whee different areas of visual field meet

Question 16

What is edge perception ?

Answer 16

Contrast perception

Question 17

What is lateral inhibition ?

Answer 17

Mechanism where visual system lightens contrast

• we get excitation + inhibition in same area of light = high activity
• info leaving retina = heightened

Question 18

Why do we move our eyes (saccades) ?

Answer 18

Critical for high-acuity, wide-angled, coloured perception
Without eye movement, retinal images disappear after few seconds

Question 19

Why would retinal images disappear in seconds without eye movement?

Answer 19

Neurons in visual system respond to change, rather than stead input

Question 20

Why do we perceive our environment as stable?

Answer 20

• visual syste temporarily integrates info collected in each saccade
• temporal integration: visual system fills gap of incoming info
• means we cam rely on high-quality perception

Question 21

How does colour vision work?

Answer 21

• perception of objects colour depends on mix of 4 wavelengths of light that reflect it
• 2 principles contribute: component + opponent processing

Question 22

Component processing

Answer 22

• 3 different types of cones
• photopigmentations in each type of cone makes it responsive to short/medium long wavelengths
• perceived colour depends on relative activity of 3 types of cones

Question 23

Opponent processing

Answer 23

• neurons respond in opposite directions to complementary colours
• at all levels of visual pathway, except for receptors
• explains why complementary colour cant exist togetehr

Question 24

What is colour blindness?

Answer 24

• certain coupons cant be distinguished
• results from deficiency/ absence of phostopgemnetation responce
• most deficiency = red/ green
• gene for colour-blindness carried on X chromosome
• mainly men affected

Question 25

Colour constancy

Answer 25

We use context to interpret what we think colour should be —- top-down processing

Question 26

What does the primary visual cortex (V1) do ?

Answer 26

- 1st stage of visual processing - receives input from thalamus

Question 27

What does secondary and association visual cortex do?

Answer 27

- composed of different areas - areas specialised for particular type of visual analysis

Question 28

What are the major streams in the visual system ?

Answer 28

Dorsal stream + ventral stream

Question 29

Dorsal stream

Answer 29

- “where” stream : involved in perception of where things are - If damaged: still possible to describe object, hard to reach out and grab it - hard to imagine location or recall from memory

Question 30

Ventral stream

Answer 30

- “what” stream: involved inn perception of what things are - If damaged: hard to describe + imagine objet, no issue reaching and grabbing for it

Question 31

The binding problem — how do visual areas produce perception of a single object?

Answer 31

- sensory info converges areas sensitive for complex stimulus characteristics

Question 32

Problem with Binding Problem theory

Answer 32

- at end of such hierarchy would be neurons that code for whole object - environment = too complex to have neuron for each object