Lecture 13- Reading and object recognition II

Question 1

How does visualisation of hypercolumns work?

Answer 1

-can visualize whole column response by changes in blood flow on surface of cortex -stimuli: different views of same object -columns responding to different views of same object (hypercolumns) overlap -multiple views of same object brought together in one area and treated as equivalent for identification? -hypoercolumn provides invariant view? -always get and invariant response -Neighbouring regions of monkey ventral occipito-temporal cortex respond to different views of same object

Question 2

What did the imaging of columns when shown complex objects?

Answer 2

-complex object may stimulate many columns at once -each column part of a hypercolumn responding to different aspect of object -response may be to very subtle aspect of object -object identified by constellation of simpler elements (no single tiger column)

Question 3

What is the column activation when looking at a fire extinguisher?

Answer 3

• multiple columns define the objects -the redness activates something
• black and white= a different combination lights up
• so spot 1 excited by protrubances (things sticking out of objects)
• spot 2= curved lines
• spot 3= rectangualar bottom =again have multicolumn response that gives us the understanding of the object

Question 4

What are the more complex responses in a monkey ventral occipito-temporal cortex?

Answer 4

-some neurons in monkey ventro-occipito-temporal cortex respond to different versions of multiple objects -cell located high up in object recognition hierarchy -not clear what common elements stimulate this cell -uncertainty due to incomplete testing of cell?

Question 5

What is the neuropsychology of object recognition?

Answer 5

-have looked at some of the neural circuitry underlying object recognition, a lot remains to be understood -now look at at object recognition in a more general way to understand what problems must be overcome -understand what the neural apparatus is trying to do

Question 6

How does understanding of the visual world work?

Answer 6

-need to rapidly analyse scenes into individual elements (objects) and determine identity, distance and movement -can’t rely on having previous experience of object -object recognition modules parse any scene into elements (objects) -the visual system is very interested in intersection (to identify overlap and distance)

Question 7

What are intersections important for?

Answer 7

-object recognition is very hard if intersections are not included -it becomes much easier when intersections are included -the concentration on intersections is the basis for some classic visual illusions

Question 8

What is the visual problem when looking at a whole image?

Answer 8

-1. image clutter: overlapping and partial views of objects (sheer number of objects) -2. object variety: so many different things to handle -3. variable views: similar objects seen from different angles

Question 9

What are the steps in recognising images?

Answer 9

1. Identify edges
2. Identify uniform regions bounded by edges
3. Identify object and ground
4. Assign border ownership
5. Group together things with similar properties (single objects?)
6. Fill in missing bits (interpolate)
7. Identify object (link to name, previous experience, use etc.) -this is not a complex image -first must identify the edges= give you the boundaries

Question 10

What is the object recognition and invariance?

Answer 10

-invariance strongest feature of object recognition -infinite number of views of infinite number of objects, can’t have all possible views stored in memory -how are models of complex objects stored in the brain to allow comparison with stimuli? -Two theories: a)object based=view independent recognition by components b)image based- view dependant, depends on some prototypical views of object in memory

Question 11

What is theory 1- object-based object recognition?

Answer 11

• brain is hard wired for approx 30 shapes
• all objects made up of these shapes
• each shape varies along five axes (curvature, co-linearity, symmetry, parallelism and co-termination)
• the brain can recognise 30 shapes, you break down the things you see are made up of the combination of the 30 objects

Question 12

What is theory 2: Image-based object recognition?

Answer 12

-all possible views of object calculated from handful of different views (side view, head on view, back view) -neither of theories seems compelling evidence is mixed -first couple of times you see an image= you store elemental views, then when see a different view can reconstruct it

Question 13

What is object agnosia?

Answer 13

-when cannot recognise objects

Question 14

What is the connection of strokes and object recognition?

Answer 14

-if inferior occipito-temporal lobe is important for object recognition, then strokes and fMRI should affect object recognition tasks -strokes give two extreme types of problems with object recognition -both lead to agnosia (ignorance or absence of knowledge)

Question 15

What are the two types of agnosia?

Answer 15

-apperceptive and associative

Question 16

What is the apperceptive agnosia?

Answer 16

-can describe objects and their function from memory -can identify by touch -can’t copy drawing of object -can’t see objects, see assemblage of parts -can’t even see the object, cannot distinguish it from background etc. -because the visual system is damaged in the posterior temporal lobe

Question 17

What is associative agnosia?

Answer 17

-can describe objects and their functions from memory -can identify by touch -can copy drawing of object -can see object as object but can’t name it -can see the object but the connection to the naming etc is damaged

Question 18

Where is the damage to when have apperceptive agnosia?

Answer 18

-damage to first stage of object recognition (visualising the object- in posterior temporal lobe)

Question 19

Where is the damage to when have associative agnosia?

Answer 19

-damage to second stage of object recognition (identifying the object- in anterior temporal lobe)

Question 20

What is alexia?

Answer 20

-alexia is a form of associative agnosia -the same part of the brain is damaged as the part damaged in alexia

Question 21

What is face recognition?

Answer 21

-a special case of object recognition

Question 22

What are the characteristics of face recognition?

Answer 22

-face often used as stimulus for vision tasks -powerful stimulus= faces very important to primates, identify individuals, convey emotion and other information -selectively affected by strokes (prosopagnosia) -can recognise that it is a face, but not who it belongs to, can recognise voice

Question 23

What is prosopagnosia?

Answer 23

-strokes producing prosopagnosia involve fusiform and lingual gyrus in inferior temporal lobe -often damage bilateral but some cases with right damage only -can also involve other forms of agnosia (alexia, some other object classes reported) -much more likely to occur with right side damaged, cases where only right lobe is damaged, both lobes can recognise faces, but right lobe probably better

Question 24

What is developmental prosopagnosia?

Answer 24

-some people born with prosopagnosia (genetic lesion that disturbs wiring in the brain) -have completely normal vision -often face recognition only deficit, normal object recognition -a specific type of object recognition with dedicates neural circuitry -both developmental and induced prospagnosia can include general object recognition deficits -prosopagnosia is often correlated with alexia etc, but can have associated object recognition problems= as the parts of the brain that do this are close to one another

Question 25

Are faces recognised in a different place to letters?

Answer 25

-yes -alternating testing with faces versus words always activates neighbouring areas -faces ventromedial to letters -it’s the same in all 5 subjects -in temporal medial lobe

Question 26

What do faces activate?

Answer 26

-multiple regions in ventral stream -macaques have five other areas in addition to FFA that respond to faces (humans similar) -damage to any one can cause prosopagnosia -not known if non-faces have multiple areas -multiple places in the ventral visual pathway which react to faces, 5 or 6 places -fusiform face area= this is the one where all the information comes together

Question 27

What are the role of multiple face areas?

Answer 27

• each face responsive region does a different thing
• brought together the invariant view of a face and face recognition
• why not have just one face area?
• responses are different depending on the view of the face
• 1. identifies “faces” from one direction
• 2. generalises across mirror images (cf “b” and “d”)
• 3. unites various views of individual face (invariance?)

Question 28

What is the role of hierarchy in object recognition?

Answer 28

-invariance may be sum of activity in sites 1 to 4 -area 5 key to identifying face as individual person -connects to higher centres for naming emotional impact, past history -the substations of going to the fusiform face area that contribite to the ability to identify the face

Question 29

What is face recognition like with a split brain?

Answer 29

-Joe tested with images JW (self) morphed together with MG (other) -compared left and right hemisphere for ability to identify self and not-self -split brain= -right= better at face recognition -the right hemisphere at 80% joe can tell that it is

Question 30

What does the right hemisphere do in a split brain in terms of object recognition?

Answer 30

-much better than left at recognising not self faces -right could recognise self but needed a complete image

Question 31

What does the left hemisphere do in a split brain in terms of object recognition?

Answer 31

• much better than right at recognising self faces
• maybe that left better at working with few clues for self

Question 32

Do faces share the temporal lobe with other object recognition?

Answer 32

• yes -face, word, everyday object and place
• recognition areas are all present in neighbouring regions of inferior temporal lobe

Question 33

What is the organisation of object recognition areas visualised with fMRI?

Answer 33

• organisation not necessarily sequential or neat
• multiple areas for each object class can exist
• the same pattern in monkey and a human
• multiple regions that are specialised for obejcts of a particular nature

Question 34

What are other object recognition areas?

Answer 34

• tend to be in reproducible places
• body parts: extrastriate body area (lateral occipito temporal cortex and fusiform body area)
• places/landmarks
• parahippocampal place area (loss leads to landmark agnosia)
• words: visual words form area, left inferior temporal lobe (loss leads to alexia)

Question 35

What is the inferior occipito-temporal cortex and object recognition for?

Answer 35

-does the inferior-temporal lobe really have regions specialised for identifying specific classes of objects? -what about train spotters and dog breeders? -could we identify parts of human inferior temporal cortex for train or dog identification? -if we can what is the significance of this (cf the letterbox)? -is the brain plastic to give you what you need?

Question 36

Does the inferior temporal cortex have a gradient of capability?

Answer 36

• inferior temporal lobe may have rostro-caudal and medio-lateral gradients representing a range of object features
• specific classes of objects ay be best detected by a particular location where cortex sensitivity match object parameters
• results in reproducible locations on cortical surface for best detecting specific classes of objects
• if you treat trains as a special class of object then you will have a train spotting region
• other people will recognise trains using their normal object recognition area

Question 37

What is the letter box and the visual pathways?

Answer 37

-the letter box lies in the what visual pathway -down to the temporal lobe, ventral pathway -we are pre-adapted to recognise letters and words by the existence of an object recognition system

Question 38

How are letters objects?

Answer 38

-letters are just objects -analysed by part of the object recognition circuitry in the ventral occipital-temporal cortex -shares this region with other specialised object recognition regions -have written symbols been optimised to match the underlying object detectors of the inferior occipito-temporal cortex -writing systems share many features : high contrast characters, average three strokes per characters, a reduced lexicon of shapes that recur across cultures

Question 39

What is the hypothetical scheme of word recognition?

Answer 39

-

Question 40

How is reading object recognition?

Answer 40

-letters as objects are new (approx. 6000 years old) -left ventro-occipital area is object recognition area -now contains letter-box for processing written language -what did this area do more than 6000 years ago -what was recycles to provide space for letters

Question 41

Who are the studies done on mostly?

Answer 41

-virtually all fMRI studies are done on literate university students -not the condition during our evolution -literacy changes anatomy of the brain

Question 42

What does literacy change?

Answer 42

-changes corpus callosum -compared corpus callosum size in literates versus non-literates -small change in region where parietal fibres cross -compared corpus callosum size in literates versus non-literates -small change in region where parietal fibres cross -compared corpus callosum size in literates vs non-literates -small change in region where parietal fibres cross

Question 43

Does literacy changes grey and white matter throughout the brain?

Answer 43

-yes -grey and white matters regions also larger in literates (mainly parietal and occipital) -explains corpus callsoum differences

Question 44

What is the cortical functions in literates vs illiterates?

Answer 44

-reading tasks in literates activates standard “reading/language” network -silent in illiterates -literacy meant VWFA became highly selective for words

Question 45

What is lost from VWFA?

Answer 45

-compared images of faces, houses, tools, words, or checkerboards at location of VWFA -in illiterates, similar responses from all -in literates strongest response to words and greater loss (left side) is in response to faces and checkerboards -face response now dominant on right side in literates, but equal bilaterally in illiterates -incidentally showed house response varied with birth location (rural vs city) -so face recognition is lost in left hemisphere, replaced with the letter recognition

Question 46

Summary:

Answer 46

-1. we have evolved verbal language skills -2. the existence of these circuits has preadapted us to manipulate language using other, non-verbal, learned symbol systems -3.Letter and word recognition depends on existing object recognition areas that are pre-adapted to recognise objects no matter how they are presented -4.The letter box is in left hemisphere, close to language circuits, partially in place of strong left hemisphere face recognition