Object Recognition

Question 1

THE 2 VISUAL SYSTEM PATHWAYS

Answer 1

1. VENTRAL
   - what aka. vision for perception
   - occipital/temporal cortex
2. DORSAL
   - where aka. vision for action
   - parietal lobe

Question 2

POHL (1973)

Answer 2

• what VS where in monkey visual cortex
  A
• specific pairs of objects predict food award
• lesions to inferotemporal/ventral cortex impair object recognition aka. WHAT
  B
• proximity of cylinder to foodwell predicts reward
• lesions to parietal/dorsal cortex impair spatial recognition aka. WHERE

Question 3

WHAT VS WHERE: HUMAN NEUROPSYCHOLOGICAL EVIDENCE

Answer 3

OCCIPITOTEMPORAL/VENTRAL CORTEX LESIONS
- visual agnosia
- object recognition deficit
PARIETAL/DORSAL CORTEX LESIONS
- hemispatial neglect
- spatial awareness deficits

Question 4

WHAT VS WHERE: KOHLER ET AL. (1995) PROCEDURE

Answer 4

TASK 1
- pps presented w/2 displays; judged if object locations were the same in both (aka. spatial locations)
TASK 2
- pps were again presented w/2 displays; had to judge if all pics = same objects in both (aka. object identities)

Question 5

WHAT VS WHERE: KOHLER ET AL. (1995) RESULTS

Answer 5

• object > spatial = ventral activation (primarily fusiform gyrus)
• spatial > object = dorsal activation (inferior parietal cortex)

Question 6

KARNATH ET AL. (2009): PROCEDURE

Answer 6

• effects of occipitotemporal/ventral visual cortex lesion on vision for action/perception
• tested a patient (JS) w/circumscribed lesion to ventral occipitotemporal cortex on 2 tasks:
  1) required perceptual judgement
  2) required motor action
• performance compared against non-lesion controls

Question 7

KARNATH ET AL. (2009): RESULTS

Answer 7

• perception task = impaired; BUT motor task = normal performance
• aka. ventral lesions impair vision for perception BUT not vision for action; suggests ventral/dorsal distinction may be more along such lines
• patient DF (dif study) = similar pattern w/lesser circumscribed lesion

Question 8

VISUAL AGNOSIA

Answer 8

• impairment in visual perception BUT above lvl of basic sensory deficit (ie. visual field defect)
• patient cannot recognise/copy/match/discriminate simple visual stimuli OR recognise simple shapes (ie. triangles/circles)
• inability to group/integrate objects into whole
• shape processing deficit

Question 9

ASSOCIATIVE AGNOSIA

Answer 9

• basic perception = fine BUT recognition cannot take place
• patient can make good object copies BUT cannot recognise them
• not due to language deficit (ie. anomia)
• anomia = describe dog pic; say it barks/is a pet
• associative agnosia = would not know if the dog is animate/inanimate object
• inability to associate items w/functions
  TEUBER (1968)
• “a normal perception stripped of its meaning”

Question 10

ASSOCIATIVE AGNOSIA: MATCHING BY FUNCTIONS TASK

Answer 10

• patients asked to match 2 items most closely related by functions
• patients w/associative agnosia will choose 2 most visually similar items indicating that they’re unable to retrieve functions associated w/the objects

Question 11

PROSOPAGNOSIA

Answer 11

• selective deficit in facial recognition

Question 12

AGNOSIA & OBJECT RECOGNITION: MODULAR APPROACH

Answer 12

• object recognition = modular
• separate brain systems for dif processes
• dif agnosia types broadly highlight distinction between:
  1) perceptual processing (shape analysis); impaired in visual form agnosia
  2) semantic processing (associated knowledge activation (ie. function))

Question 13

AGNOSIA & OBJECT RECOGNITON: CONSTRUCTIVE APPROACH

Answer 13

• object recognition = constructive process
• brain constructs representations of objects based on many dif sources of contextual info
• these representations (not simply retinal input) are what we’re consciously aware of

Question 14

AGNOSIA & OBJECT RECOGNITON: SEMANTIC APPROACH

Answer 14

• object recognition = semantic process
• info about object meaning = automatically processed when we see it (ie. its function)

Question 15

VISUAL PATHWAYS: RETINA -> PRIMARY VISUAL CORTEX (V1)

Answer 15

1) nasal retina
2) temporal retina
3) optic nerve
4) optic chiasma
5) lateral geniculate nucleus (LGN)
6) primary visual cortex (V1)

Question 16

PRIMARY VISUAL CORTEX (V1)

Answer 16

• structured retinotopically
  -dif visual field regions (IRL) = perceived in dif V1 regions
• correspondence (mapping) between spatial structure of primary visual cortex/spatial structure of IRL
• cortical magnification: disproportionately large V1 area is dedicated to visual field centre (corresponding to eye’s fovea)

Question 17

PROCESSING COMPLEXITY: V1 -> EXTRASTRIATE CORTEX

Answer 17

• processing complexity ^ V1 -> extrastriate cortex:
  V1) neurons sensitive to simple visual features (ie. line orientation/spatial frequency/colour)
  LO) begin to see sensitivity of more complex features (ie. geometric shape)
  V5) plays key role in motion processing

Question 18

KOURTZI & KANWISHER (2001): PROCEDURE

Answer 18

LATERAL OCCIPITAL COMPLEX (LOC)
- specialised brain region; integrates features into shapes according to fMRI
- subjects viewed 3 dif types of object (familiar/novel/non-objects)
- 2/3 required feature integration into shapes
- other objects = just disjointed features collection

Question 19

KOURTZI & KANWISHER (2001): RESULTS

Answer 19

• lateral occipital complex activation (part of ventral processing stream) = ^ for familiar/novel objects > scrambled non-objects
• aka. lateral occipital complex plays role in integrating feature into whole shapes

Question 20

LATERL OCCIPITAL COMPLEX (LOC): PROPERTIES

Answer 20

• largely non-retinotopic area activated by both contralateral/ipsilateral visual fields
• LOC = not simply sensitive to retinal input
• seems to encode higher-lvl shape representations even when not defined purely by retinal input
  MENDOLA ET AL. (1999)
• fMRI evidence that LOC responds to shapes defined by illusory contours

Question 21

FMRI ADAPTATION

Answer 21

• used to map dif component processes of object recognition onto dif regions in ventral visual pathway
• can investigate sensitivity of neuron groups to dif object properties
• ie. a neuron sensitive to object identity “knows” pics of car from dif angles = all same object as it reduces its response w/repeated presentations
• reduction occurs even when repetition occurs from dif POVs aka. neuron = insensitive to POV

Question 22

VUILLEUMIER ET AL. (2002): PROCEDURE

Answer 22

• fMRI adaptation; extent to which activation decreases w/repetitions
• when you present same object/word x2 -> activation tends to decrease as neurons “adapt” responses to object via varying dif stimuli properties you can access extent to which brain region processes the property
• eg. dif frequency tones; you may present via dif lengths/frequencies; neurons that process frequency will adapt response to tones of same frequency even if length = dif

Question 23

VUILLEUMIER ET AL. (2002): RESULTS

Answer 23

• found reduced activation in left fusiform cortex to same object from dif POV relative to when dif objects were presented
• aka. region treats top 2 pics as the same even if presented from dif angles; indicates region may play role in object constancy (enabling us to recognise object under multiple dif contexts/POVs)

Question 24

YEE ET AL. (2010): PROCEDURE

Answer 24

• presented pairs of words that had similar:
  1) function (flashlight-lantern)
  2) shape (marble-grape)
  3) function & shape (pencil-pen)
  4) unrelated (saucer-needle)
  5) identical (drill-drill)
  6) manipulation (defined as type of movement you make when manipulating it)

Question 25

YEE ET AL. (2010): RESULTS

Answer 25

- several brain areas showed adaptation to function esp. in medial temporal lobe (ventral stream) - suggests that these neurons actually represent object function aka. objects can be represented in these regions via their functions explaining how neuron loss can result in associative agnosia

Question 26

VENTRAL VISUAL PATHWAY: SEPARATE MODULES

Answer 26

LATERAL OCCIPITAL CORTEX - for integrating features into shapes LEFT FUSIFORM CORTEX - for viewpoint invariant representation of objects LEFT MEDIAL TEMPORAL CORTEX - for representation of objects' functions

Question 27

SUMMARY

Answer 27

- 2 visual systems (distinction supported by evidence): 1) ventral (what/perception) 2) dorsal (where/action) - agnosia: 1) visual form VS associative agnosia 2) implications for object recognition system - mapping function -> structure in ventral visual pathway; anatomically separate brain regions mediate dif object recognition aspects: 1) lateral occipital cortex (shape) 2) left fusiform cortex (object constancy (POV invariant representation)) 3) left temporal cortex (function)