Topic 2 - Visual Processing

Question 1

Pathway from Retina to Cortex

Answer 1

• from retina through optic nerve to:
• Lateral geniculate nucleus (LGN)
• Primary visual receiving area in the occipital lobe (striate cortex)
• To temporal and parietal lobe before arriving at frontal lobe

Question 2

Lateral Geniculate Nucleus (LGN)

Answer 2

• relay centre in the thalamus for the visual pathway
• has centre-surround receptive field
• Regulates neural information from retina to visual cortex

Question 3

LGN Layers

Answer 3

• six layers
• 2,3,5 receive signals from ipsilateral eye
• 1,4,6 receive signals from contralateral eye

Question 4

Retinotopic map

Answer 4

• each place on the retina corresponds to a place on the LGN

- colour coordinated sections - see notes

Question 5

Cortical magnification

Cortical magnification factor

Answer 5

apportioning of a large area on the cortex to the small fovea

• fovea takes 0.01% of retinal area but 8-10% of cortical maps area

Factor - the size of this magnification

Question 6

Optic Nerve fibre (Ganglion Cell)

Answer 6

• centre-surround receptive field, responds best to small spots

Question 7

Simple Cortical Cells

Answer 7

• side-by-side receptive fields
• responds to spots of light
• responds best to vertical bars

Question 8

Orientation tuning curve

Answer 8

shows response of simple cortical cells for orientations of stimuli

Question 9

Complex cortical cells

Answer 9

Like simple cells, they respond to bars of light of a particular orientation. However, they respond to movement of bars of light in a specific direction

Question 10

End-stopped cells

Answer 10

respond to lines of a specific length or to moving corners of angles
- do not respond to stimuli that is too long

Question 11

Feature detectors

Answer 11

Neurons that fire to specific features of a stimulus

- includes simple cortical cells, complex cortical cells and end-stopped cells

Question 12

Selective adaptation

Answer 12

Firing causes neurons tuned to specific stimuli to eventually become fatigued, or adapt

It causes a decrease in the neuron’s firing rate, and causes the neuron to fire less when that stimulus is immediately presented again

Question 13

Measuring selective adaptation

Answer 13

• measure contrast threshold (sensitivity) to range of one stimulus characteristic
• Adapt to one characteristic by extended exposure of high contrast
• Remeasure the contrast threshold of all stimuli from first step

Question 14

Contrast Threshold

Answer 14

the minimum intensity difference between two adjacent bars that can just be detected

Question 15

Measuring contrast threshold

Answer 15

• measure contrast threshold by decreasing intensity of grating until person can just see it
• calculate contrast sensitivity by taking 1/threshold
• if threshold is low, person has high contrast sensitivity

Question 16

Measuring orientation sensitivity

Answer 16

• measure contrast sensitivity to different orientations
• adapt person to one orientation, using high contrast grating
• re-measure sensitivity to all gratings
• selective adaptation for specific orientation if neurons are tuned to this characteristic

Question 17

Selective rearing

Answer 17

if an animal is reared in an environment that contains only certain types of stimuli, then neurons that respond to these stimuli will become more prevalent

• Due to neural plasticity
• Blackmore and Cooper kitten in a tube experiment

Question 18

Sensory coding

Answer 18

refers to how neurons represent various characteristics of the environment

Question 19

Specificity coding

Answer 19

the idea that an object could be represented by the firing of a specialised neuron that responds only to that object
- unlikely to be correct due to too many objects and faces in the world

Question 20

Population coding

Answer 20

the representation of a particular object by the pattern of firing a large number of neurons

Question 21

Sparse coding

Answer 21

occurs when a particular object is represented by a pattern of firing of only a small group of neurons, with majority remaining silent

Question 22

Contextual modulation

Answer 22

the effect of stimulating outside the receptive field

Question 23

Location columns

Answer 23

• perpendicular to the surface of the cortex

- receptive fields in the same location on the retina are in the column

Question 24

Tiling

Answer 24

when columns cover the entire visual field

Question 25

Orientation columns

Answer 25

• each column contains cells that respond best to a particular orientation
• adjacent columns change preference in an orderly fashion
• 1mm across cortex represents entire range of orientation

Question 26

Ocular dominance columns

Answer 26

• neurons in the cortex respond preferentially to one eye
• neurons with the same preference are organised into columns
• columns alternate in a left-right pattern every .25 to .50 mm across the cortex

Question 27

Hypercolumn

Answer 27

a location column with all of its orientation columns (0-180 degrees), and left and right dominance columns

Question 28

fMRI

Answer 28

Functional Magnetic Resonance Image

• haemoglobin carries oxygen in the blood and contains ferrous (iron) molecule which is magnetic
• Brain activity takes up oxygen, makes haemoglobin more magnetic as it loses oxygen
• fMRI determines activity of areas of the brain by detecting changes in magnetic response of haemoglobin

Question 29

Lesioning and ablation experiments

Answer 29

Refers to the destruction or removal of tissue in the nervous system

• First animal is trained to indicate perceptual capacities
• Second, specific part of brain is removed
• Third, animal is retrained to determine which perceptual capacities remain

Question 30

Ungerleider and Mishkin ablation experiment

Answer 30

• Object discrimination problem - monkey shown one object, presented with two-choice task
• Landmark discrimination problem - monkey is trained to remove cover of food closest to tall cylinder
• Removal of parietal or temporal lobe from monkeys
• Removal of temporal lobe resulted in issues with object discrimination (ventral)
• Removal of parietal lobe resulted in issues with landmark discrimination (dorsal)

Question 31

Double dissociations

Answer 31

One person has function A but not B, other has B but not A, allows us to conclude the two operate independently of each other

Question 32

Ventral and Dorsal pathways

Answer 32

Ventral pathway - the “what” pathway, responsible for objects identity

Dorsal Pathway - the “where” and “how” pathway, responsible for objects location and how to take action on object

Question 33

Patient D.F.

Rod and Frame illusion

Answer 33

D.F.

• damage to ventral pathway
• not able to match orientation of card with a slot but able to if placing card in the slot

Rod and Frame

• two tasks, length estimation and grasping (ventral and dorsal)
• Frame orientation affected matching but not grasping

Question 34

Modularity

Answer 34

the idea that specific areas of the cortex are specialised to respond to specific types of stimuli

Question 35

Inferotemporal (IT) cortex

Answer 35

• responds best to faces with little response to non-face stimuli
• removal causes monkeys difficulty in telling the difference between objects

Question 36

Prosopagnosia

Answer 36

• difficulty recognising faces of familiar people

- can be caused by damage to temporal lobe

Question 37

Fusiform face area (FFA)
Parahippocampal area (PPA)
Extrastriate body area (EBA)
Lateral occipital complex (LOC)

Answer 37

FFA - responds best to faces
PPA - responds best to spatial layout
EBA - responds to pictures of bodies and parts of bodies (but not faces)
LOC - responds to objects

Question 38

Distributed representation

Answer 38

when a stimulus causes neural activity in a number of areas of the brain, so the activity is distributed across the brain

Question 39

Mind-Body problem

Answer 39

How to physical processes like nerve impulses become transformed into perceptual experience?

Question 40

Expertise hypothesis

Answer 40

Our proficiency in perceiving certain things can be explained by changes in the brain caused by long exposure, practice, or training

Question 41

Evolution and perception

Answer 41

• newborn monkeys respond to direction of movement and depth of objects, babies prefer looking at pictures of assembled parts of faces
• “hardwiring” of neurons plays a part in sensory systems

Question 42

Experience-dependent plasticity

Answer 42

• brain imaging experiments show areas that respond best to letters and words
• fMRI experiments show that training results in areas of the FFS responding best to objects that people are experts on