Object Recognition Flashcards
THE 2 VISUAL SYSTEM PATHWAYS
- VENTRAL
- what aka. vision for perception
- occipital/temporal cortex - DORSAL
- where aka. vision for action
- parietal lobe
POHL (1973)
- 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
WHAT VS WHERE: HUMAN NEUROPSYCHOLOGICAL EVIDENCE
OCCIPITOTEMPORAL/VENTRAL CORTEX LESIONS
- visual agnosia
- object recognition deficit
PARIETAL/DORSAL CORTEX LESIONS
- hemispatial neglect
- spatial awareness deficits
WHAT VS WHERE: KOHLER ET AL. (1995) PROCEDURE
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)
WHAT VS WHERE: KOHLER ET AL. (1995) RESULTS
- object > spatial = ventral activation (primarily fusiform gyrus)
- spatial > object = dorsal activation (inferior parietal cortex)
KARNATH ET AL. (2009): PROCEDURE
- 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
KARNATH ET AL. (2009): RESULTS
- 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
VISUAL AGNOSIA
- 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
ASSOCIATIVE AGNOSIA
- 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”
ASSOCIATIVE AGNOSIA: MATCHING BY FUNCTIONS TASK
- 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
PROSOPAGNOSIA
- selective deficit in facial recognition
AGNOSIA & OBJECT RECOGNITION: MODULAR APPROACH
- 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))
AGNOSIA & OBJECT RECOGNITON: CONSTRUCTIVE APPROACH
- 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
AGNOSIA & OBJECT RECOGNITON: SEMANTIC APPROACH
- object recognition = semantic process
- info about object meaning = automatically processed when we see it (ie. its function)
VISUAL PATHWAYS: RETINA -> PRIMARY VISUAL CORTEX (V1)
1) nasal retina
2) temporal retina
3) optic nerve
4) optic chiasma
5) lateral geniculate nucleus (LGN)
6) primary visual cortex (V1)
PRIMARY VISUAL CORTEX (V1)
- 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)
PROCESSING COMPLEXITY: V1 -> EXTRASTRIATE CORTEX
- 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
KOURTZI & KANWISHER (2001): PROCEDURE
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
KOURTZI & KANWISHER (2001): RESULTS
- 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
LATERL OCCIPITAL COMPLEX (LOC): PROPERTIES
- 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
FMRI ADAPTATION
- 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
VUILLEUMIER ET AL. (2002): PROCEDURE
- 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
VUILLEUMIER ET AL. (2002): RESULTS
- 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)
YEE ET AL. (2010): PROCEDURE
- 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)
