W2.1 and 3.1: Object Recognition Systems

Question 1

What two pathways can be included in the modularity of the visual system?

Answer 1

Dorsal and ventral stream

Question 2

How is visual information processed?

Answer 2

Visual information -> processed in the occipital lobe -> starts to travel forward through the brain -> complexity of neurons changes as it travels and info splits into either the dorsal or ventral stream

Question 3

What is the dorsal stream and where is it located?

Answer 3

The ‘where’ stream- involved in localising, understanding space, ‘vision for perception’. Covers the parietal lobe.

Question 4

What is the ventral stream and where is it located?

Answer 4

The ‘what’ stream, involved in the temporal/occipital pathway, ‘vision for action’. It is located in the occipital lobe and temporal cortex.

Question 5

How did Pohl (1973) study double dissociation in early monkey studies?

Answer 5

Task A- specific pairs of objects predict food reward. Lesions to ventral stream impaired object recognition (what)

Task B- the proximity of the cylinder to the foodwell predicted reward- lesions to dorsal stream impaired spatial recognition (where)

Question 6

What neuroimaging evidence did Kohler et al (1995) find in relation to the dorsal and ventral streams?

Answer 6

Spatial locations tended to activate the dorsal stream and object identities tended to activate the ventral cortex

Question 7

How did Karnath et al (2009) measure the effects of occipitotemporal lesions on vision for action and vision for perception and what did they find?

Answer 7

Task 1- ppts asked to rotate a disk until letters matched the researchers- patients with lesions performed poorly and made much more errors

Task 2- ppts had to post a rectangular object through the slot and no errors were found compared to control, suggesting it did not impair action but did impair perception

Question 8

What can lesions to the ventral visual stream result in?

Answer 8

Agnosia- a selective deficit in recognising objects

Question 9

What are the two types of agnosia?

Answer 9

Visual form agnosia
Associative (higher level) agnosia

Question 10

What is visual form agnosia?

Answer 10

An impairment in visual perception but above the level of a visual field defect
The patient cannot recognise, copy, match or discriminate simple visual stimuli and cannot recognise even simple shapes such as triangles and circles
Inability to group and integrate objects into a whole due to deficit in shape processing (see figure 5)- read this as 7415

Question 11

What is associative (higher level) agnosia?

Answer 11

Where basic perception is fine but recognition does not take place
Can see and copy objects (contrasted to visual form) but cannot recognise them, say what it is or what it does
see figure 6- ppts able to copy pictures but could not do anything else e.g. what they were or what sound they made if it was an animal- they could not even say if it was an animate or inaminate object
Ppts could also not match two objects most closely related to function e.g. an open and closed umbrella, they instead chose a closed umbrella and walking stick as they looked the most similar

Question 12

What three things do patterns from agnosia patients tell us about object recognition?

Answer 12

1. Object recognition is modular i.e. happens in distinct modules of the brain- highlights distinctions between perceptual processing which is impaired in visual agnosia and semantic processing which is impaired in associative agnosia
2. Object recognition is a constructive process- the brain constructs representations of objects based on many different sources of contextual info- these representations are what we are consciously aware of e.g. visual illusions
3. Object recognition is a semantic process- info about the meaning of an object is automatically processed when we see it e.g. its function

Question 13

What can agnosia NOT tell us about object recognition?

Answer 13

Specifically where in the ventral visual cortex this happens

Lesions can be large and very variable and often affect multiple regions across lobes, so it can be difficult to establish causality

It is quite rare to find ‘pure’ cases of agnosia as it is often unclear and takes a lot of neuropsychological work

Question 14

What structures lay inbetween the left and right visual fields (front) and the primary visual cortex (back)?

Answer 14

From front to back:
- Nasal retina
- Optical lens
- Temporal retina
- Optic nerve
- Chiasma
- LGN

Question 15

How is the primary visual cortex structured?

Answer 15

Retinotopically- different regions of VF are perceived in different regions of primary VC, and there is a correspondence between the spatial structure of the primary VC and of the real world

Question 16

What is cortical magnification?

Answer 16

Disproportionately large area of the VC is dedicated to the centre of the visual field, corresponding to the eye’s fovea

Question 17

How does the processing complexity change across the cortex?

Answer 17

It increases as it moves from the v1 to the extra striate cortex

Question 18

What are neurons in the V1 area sensitive to?

Answer 18

Visual features e.g. line orientation, spatial frequency and colour

Question 19

What is the role of the v5 area?

Answer 19

Plays a key role in motion processing

Question 20

What are the features of the LO area?

Answer 20

Begins to see a sensitivity to more complex features such as geometric shape

Question 21

What role does the lateral occipital cortex (LOC) play in object recognition?

Answer 21

Shape perception- not simply sensitive to retinal input but encodes higher level representations of shape and is linked to visual illusions

Question 22

How did Kourtzi and Kanwisher (2001) test the representation of perceived object shape by the LOC?

Answer 22

Ppts shown familiar objects, novel objects and scrambled objects
fMRI paradigm- response to pairs of successively presented stimuli is lower when they are identical than when they were different- data indicates that LOC represents not simple image features but rather high level shape information
Mapping different component processes of object recognition onto different regions within the ventral pathway

Question 23

What region has been shown by fMRI to represent objects by their function?

Answer 23

Regions in left temporal cortex within medial temporal lobe

Question 24

What are there separate modules in the ventral visual pathway for during object recognition?

Answer 24

Integration of features into shapes (LOC)

Viewpoint invariant representation of objects (left fusiform cortex)

Representation of objects’ functions (left medial temporal cortex)

Question 25

How did Tanaka and Farah (1993) investigate and find in object and face processing?

Answer 25

Face task- learn to associate faces with names House task- learned to associate houses in names Ppts were then asked to identify individual features or whole faces/houses We are able to recognise individual faces as whole parts rather than pieces of faces e.g. a nose, but this is not the same for houses- we recognise and process whole faces differently - percent of correctly identified individual features was much lower for parts of faces

Question 26

What is the composite face illusion (Rossion) and how does it link to our understanding of visual face processing?

Answer 26

Two identical top halves of a face are perceived as being different when their bottom halves belong to different faces, showing that parts of a face cannot be perceived independently- suggesting we process faces holistically

Question 27

What is prosopagnosia?

Answer 27

Acquired deficit in face recognition after brain damage, including ability to recognise friends/family or learn new faces. Patients can still recognise people by their voices and cognitive skills often remain intact alongside other visual abilities.

Question 28

What side of the brain is propopragnosia associated with?

Answer 28

The right side- it is a denominately right sided disorder and dominates the right hemisphere- it can result from a lesion in any area of the right ventral occipitotemporal cortex, however the majority have language damage in left hemispshere which takes up a lot of neuronal space and so face processing may be pushed towards the right hemipshere

Question 29

How did Kanwisher et al (1997) use a region of interest approach to measure face processing?

Answer 29

Presented faces, objects, hands and houses Functional localiser scan used to identify face-selective voxels and subsequent scans to test the selectivity of voxels to other stimuli and rule out confounds Contrasts produced activation in the same brain region- concluded this area seems to activate and is associated with facial recognition

Question 30

What region in the ventral visual cortex activates selectively to pictures of human bodies?

Answer 30

The extrastriate body area (EBA) No other category of objects shows a selective pattern of activation in a cortical region

Question 31

What are the key points in favour of the FFA hypothesis as discussed?

Answer 31

- Evidence for anatomically distinct modules for processing different categories of objects in the VVP - Holistic processing of faces as behavioural evidence - Neuropsychological evidence- prosopagnosia - fMRI - TMS

Question 32

What are the main points of evidence against the FFA module hypothesis?

Answer 32

- Expertise related activation in FFA - Activation in other brain regions to faces - Developmental prosopagnosia - Distributed patterns of activation to different object categories in ventral visual cortex

Question 33

Explain how expertise related activation in FFA goes against the FFA module hypothesis

Answer 33

Evolved patch of visual cortex that takes on the processing things we have been good at recognising, enabling us to recognise things we have become experts at- idea we just happen to be experts in recognising faces as we have become trained to

Question 34

How did Gauthier et al (1999) investigate expertise related activation in the FFA?

Answer 34

Found activation in people who had been trained to recognise novel objects (greebles)- found an activation in FFA to greeble experts but not novices. This was also seen for bird experts- stronger FFA reaction to birds in bird experts

Question 35

How has the expertise hypothesis been criticised?

Answer 35

Evidence is weak and inconsistent- increases are small and several studies have failed to replicate findings Greeble experiment has been confounded by similarity of stimuli to faces Prosopagnosics can become experts as identifying other objects Part/whole behavioural effects are observed for faces but not for other expertise objects

Question 36

What is the multiple face selective cortical regions challenge to the FFA module hypothesis?

Answer 36

Separation of regions does not argue against the idea that the FFA has evolved superficially to mediate the recognition of faces, but an interesting emerging field of how these regions interact to process face recognition

Question 37

What is the developmental prosopagnosia challenge to the FFA module hypothesis?

Answer 37

There is no hole in the FFA of people with developmental prosopagnosia but it is difficult to study this as not many people have this condition- there is no clear pathology e.g. a lesion in the FFA, functional imaging evidence is inconclusive

Question 38

How did Haxby et al (2001) investigate multi voxel pattern analysis when challenging the modularity of the ventral visual object recognition system?

Answer 38

Presented ppts with pictures of different categories e.g. faces, cats, houses, shoes, in the scanner Preprocessing of fMRI data included no spatial smoothing For each run and for each category, activation was measured in each voxel in the ventral visual cortex to each category For each pair of categories, the within category correlation and between category correlation was measured

Question 39

What did Haxby et al (2001) find when investigating multi voxel pattern analysis when challenging the modularity of the ventral visual object recognition system?

Answer 39

They found that within category correlations were consistently higher than between category correlations for all voxels across the ventral visual cortex Pattern of results remained even when they removed voxels that showed higher activation to each category, e.g. FFA Suggests patterns of activation across the ventral visual cortex contain info about the category of an object someone is looking at

Question 40

What cortical regions did Pitcher et al identify when investigating what cortical regions respond selectively to faces, objects and bodies?

Answer 40

Occipital face area- rOFA for face discrimination Extrastriate body area (EBA) for body discrimination Lateral occipital area (LO) for object discrimination

Question 41

What is a facephene and what does it imply?

Answer 41

An illusory experience of seeing a face due to electrical stimulation in a region of the FFA, provides evidence that the FFA is involved in face perception