object recognition

Question 1

what are the features of object recognition?

Answer 1

1. Modular – the object recognition system is built of specialised functional modules
2. Constructive – it builds representations from sensory input and contextual information
3. Semantic – higher level information about e.g. objects’ functions are built into the representation

Question 2

What was it hypothesised that the visual pathway could be split into?

Answer 2

It was originally hypothesised that the visual system could broadly be divided into a dorsal ‘where’ system for locating objects in space and a ventral ‘what’ system for identifying objects

Question 3

what is V1

Answer 3

low level visual procesing. This information is transmitted forward through the brain

Question 4

what happens when you present an object within a neuron’s receptive field?

Answer 4

it will fire

Question 5

what happens when you present an object outside a neuron’s receptive field?

Answer 5

it wont fire

Question 6

ventral neurons always encompass where?

Answer 6

the fovea

Question 7

majority of neurons in parietal cortex have receptive fields that don’t encompass where

Answer 7

the fovea

Question 8

what did Pohl 1973 research?

Answer 8

In A, animals must learn that certain objects predict a food reward when paired with other objects.

In B, animals must choose the covered foodwell closest to the landmark cylinder testing the ability to locate items in space.

Found that animals with inferotemporal lesions were impaired on the object identification task but fine on the spatial task whereas the opposite pattern was observed in monkeys with parietal lesions

Question 9

What happens when there are temporal cortex lesions (ventral)

Answer 9

• visual agnosia

- Deficit in recognizing objects

Question 10

What happens when there are parietal cortex lesions (dorsal)

Answer 10

• Deficits of spatial awareness
• hemispatial neglect
  o tends to be on opposite side of lesion
• Optic ataxia

Question 11

What did Kohler et al 1995 find

Answer 11

subjects had to perform two tasks

• In task 1, subjects were presented with two displays and had to judge whether the locations of the objects were the same in both displays.
• In task 2, subjects were again presented with two displays and this time had to judge whether all the pictures were the same objects in the two displays.

They found that contrasting the two tasks produced different patterns of activation
Activation was greater for the object task than the spatial task in ventral temporal cortex – primarily fusiform gyrus
Activation was greater for the spatial task than the object task in dorsal cortex, primarily inferior parietal cortex.

Question 12

What did Karnath et al 2009 find

Answer 12

Effects of occipitotemporal (ventral visual cortex) lesion on vision for action and vision for perception

Task 1 – Perception
- Patient must rotate the disc until the orientation of the two ‘slots’ matches

Task 2 – Action
- Patient must ‘post’ a rectangular object through the slot

They tested a patients (JS) with a circumscribed lesion to ventral occipitotemporal cortex on two tasks, one requiring a perceptual judgement (task 1) and the other requiring a motor action (task 2).
Performance was compared against non lesion controls
They found that the patient was impaired on the perception task but performed normally on the motor task. Table in top right shows results.
This shows that ventral lesions impair vision for perception but not vision for action, suggesting the ventral/dorsal distinction may be more along these lines.

Question 13

What is modularity

Answer 13

more fine-grained than dorsal vs ventral visual streams

Question 14

What are some types of agnosia?

Answer 14

apperceptive agnosia,
integrative agnosia,
associative agnosia,

Question 15

what is apperceptive agnosia

Answer 15

• Little difficulty recognising common objects under normal conditions
• Problems occur when stimulus information is limited or when objects presented from unusual viewpoints

Apperceptive agnosia can be seen to be a deficit in object constancy

Question 16

What is integrative agnosia

Answer 16

• Impairment in the ability to integrate features of objects into a coherent whole
• Another type of agnosia is integrative agnosia, involving an inability to integrate features of objects into a coherent whole.
• So a patient with intergrative agnosia would have no trouble recognising the letters and shapes on the left but would really struggle with the overlapping ones on the right

Question 17

what is associative agnosia

Answer 17

Matching by functions task

• Patients required to match the two objects most closely related by function
• This would be the top two but someone with associative agnosia wouldn’t think this but would instead pick the cane and shut umbrella as thye look similar
• In associative agnosia, patients are unable to associate items with their functions.
• In the matching by functions task, patients are asked to match the two items that are most closely related by function.
• Patients with associative agnosia will choose the two most visually similar items indicating that they are unable to retrieve the functions associated with the objects

Question 18

what is prosopagnosia

Answer 18

• Selective deficit in face recognition
• No problem recognising common objects
• Can recognise people from their voices
• Prosopagnosia can be acquired or developmental
• Evidence that there is something special about faces comes from prosopagnosia in which patients lose the ability to recognise faces but are able to recognise common objects

Question 19

how are faces processed?

Answer 19

holistically

Question 20

What did Tanaka and Farah 1993 show

Answer 20

In this study subjects learned first to associate faces with names and houses with names.
Then they were tested on whether they recognised a) individual parts of faces and houses, e.g. noses and doors and b) whole faces and houses

Results showed subjects were better at processing whole faces than face parts but there was no such difference between whole houses and house parts.
Suggests we encode individual faces by encoding the spatial relations between features whereas other objects may involve simply coding of individual features.

Question 21

what did Gauthier 1999 show

Answer 21

Gauthier et al. (1999) trained subjects to recognise novel objects (‘Greebles’) and found activation in FFA in greeble experts but not in greeble novices
However, these greebles look a bit like faces

Question 22

Evaluate the expertise hypothesis

Answer 22

• Evidence for increased FFA activation for ‘expertise’ is weak and inconsistent – increases are small and several studies have failed to replicate findings
• Studies that have found increased FFA activation for expertise have also found increased activation outside this region
• Prosopagnosics can become experts at identifying other objects – e.g. case of a prosopagnosic sheep farmer who could recognise individual sheep
• Part/whole behavioural effects are observed for faces but not for other ‘expertise’ objects e.g. dog experts

Question 23

What is the parahippocampal place area (PPA)

Answer 23

• A region in ventral visual cortex that activates selectively to scenes
• (Epstein et al., 1999)

Question 24

what is the extrastriate body area (EBA)

Answer 24

• A region in ventral visual cortex that activates selectively to pictures of human bodies
• (Downing et al., 2001)

Question 25

what does univariate fMRI look for?

Answer 25

'peaks’ of activation

Question 26

what does multivariate fMRI look for?

Answer 26

patterns of activation

Question 27

what did Vuilleumier show about apperceptive agnosis

Answer 27

Looked at fMRI adaptation – the extent to which activation decreases with repetitions (when you present the same object or word twice, activation tends to decrease – neurons ‘adapt’ their responses to the object – by varying different properties of stimuli you can assess the extent to which a brain region processes that property). A simple example would be tones of different frequency. You might present tones of different length and different frequency. Neurons that process frequency will adapt their response to tones of the same frequency even if the length of the tone differs. Found reduced activation in left fusiform cortex to the same object from a different viewpoint relative to when different objects were presented. Thus, this region treats the top two pictures the same even though they’re presented from a different angle, indicating this region may play a role in object constancy – enabling us to recognise an object under multiple different contexts, viewpoints etc. Visual adaptation- presenting the same tones to a neuron again and again, it will adapt its response over time.

Question 28

what did Kourtzi, Z., & Kanwisher, N. (2001) show about integrative agnosia

Answer 28

fMRI evidence has revealed a specialised brain region for integrating features into shapes. The lateral occipital complex seems to be responsible for combining visuals into shapes. In this study, subjects viewed three different types of object – famililar objects, novel objects and non-objects. Only two of these types of objects required the integration of features into shapes. The other objects were just collections of disjointed features. Activation in the lateral occipital complex, part of the ventral processing stream, was higher for the familiar and novel objects than the scrambled non-objects. This region plays a role in integrating features into whole shapes. Associative Agnosia

Question 29

what did Yee, E., Drucker, D. M., & Thompson-Schill, S. L. (2010). show about associative agnosia

Answer 29

fMRI reveals a region in the ventral stream that enables functions to be associated with objects. Presented pairs of words that had similar shape, function or manipulation (defined as the type of movement you make when manipulating the object). Here, several brain regions showed adaptation to function (blue regions) especially in the medial temporal lobe (ventral stream) suggesting that these neurons actually represent the function of an object – essentially, objects can be represented in these regions by their functions, explaining how loss of these neurons can result in associative agnosia.