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Cortical Pathways for Visual Perception

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Cortical Pathways for Visual Perception. Output from occipital ... Superior longitudinal fasciculus ... on neuronal specificity to faces in the macaque ... – PowerPoint PPT presentation

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Title: Cortical Pathways for Visual Perception


1
Cortical Pathways for Visual Perception
  • Output from occipital lobe follows two major
    fiber tracts
  • Superior longitudinal fasciculus to parietal lobe
  • Inferior longitudinal fasciculus to temporal lobe
  • Ungerleider Mishkin propose that these pathways
    form functionally distinct processing systems
  • Dorsal (occipito-parietal) is the where system
    specialized for spatial analysis
  • Ventral (occipito-temporal) is the what system
    specialized for object perception and recognition

2
Dorsal and Ventral Functional Pathways
  • Pohl experiments reveal double dissociation
  • Landmark task monkeys with bilateral parietal
    lesion have deficit, but monkeys with bilateral
    temporal lesion can learn task
  • Object discrimination task monkeys with
    bilateral temporal lesion have deficit learning
    task, but monkeys with bilateral parietal lesion
    do not

3
Dorsal and Ventral Functional Pathways
  • Pohl experiments reveal double dissociation
  • Other bilateral lesion experiments show
    dissociation within temporal lobe
  • anterior temporal lesions disrupt visual memory
  • posterior temporal lesions disrupt visual
    discrimination

4
Dorsal and Ventral Functional Pathways
  • Pohl experiments reveal double dissociation
  • Other bilateral lesion experiments show
    dissociation within temporal lobe
  • Must lesions be bilateral to cause deficits?
  • Are dorsal and ventral pathways bilateral?

5
Dorsal and Ventral Functional Pathways
  • Ungerleiter and Mishkin combination lesion
    experiments
  • Ventral pathway is bilateral
  • Right striate left inferior temporal lesions
  • No deficit in object discrimination
  • Severing corpus callosum creates deficit
  • Dorsal pathway is primarily unilateral
  • Right striate left parietal lesions
  • Deficit in landmark task
  • Severing corpus callosum increases deficit

6
Dorsal and Ventral Functional Pathways
  • Neuron receptive field differences
  • Parietal lobe neurons
  • Large receptive fields
  • Specific to hemifield
  • More neurons have receptive fields outside the
    fovea than inside the fovea

7
Dorsal and Ventral Functional Pathways
  • Neuron receptive field differences
  • Parietal lobe neurons
  • Temporal lobe neurons
  • Large receptive fields
  • Not specific to hemifield
  • More neurons have receptive fields inside the
    fovea than outside the fovea
  • Majority of neurons respond selectively to
    complex stimuli

8
Dorsal and Ventral Functional Pathways
  • Kohler et al. PET study in humans supports
    "what/where" distinction
  • Position task greater rCBF in right parietal
    lobe
  • Object task greater rCBF biaterally at
    occipito-temporal areas

9
Dorsal and Ventral Functional Pathways
  • Kanwisher et al. PET study in humans fails to
    isolate cognitive functions during passive
    viewing of shapes

10
Computational Problems in Object Recognition
  • How to account for shape-based encoding?
  • Objects are more than the sum of their parts
  • Properties of object constancy
  • Viewing position
  • Illumination
  • Occlusion

11
Computational Problems in Object Recognition
  • Theoretical issues in object recognition
  • Frame of reference object constancy across
    orientation
  • View-dependent
  • Separate representation of an object for each
    viewpoint
  • View-invariant
  • Critical properties used for object recognition
  • Major/minor axes, etc.

12
Computational Problems in Object Recognition
  • Theoretical issues in object recognition
  • Frame of reference
  • Shape encoding hierarchical representations of
    increasing complexity
  • Salient features
  • Invariants parallelism, symmetry, T-junctions,
    occlusion, etc

13
Computational Problems in Object Recognition
  • Theoretical issues in object recognition
  • Frame of reference
  • Shape encoding hierarchical representations of
    increasing complexity
  • Salient features
  • Recognition by parts
  • Beiderman's geons 24 fundamental 3-D shapes

14
Computational Problems in Object Recognition
  • Theoretical issues in object recognition
  • Frame of reference
  • Shape encoding
  • Neurophysiological representations
  • Hierarchical coding hypothesis
  • Object defined by Gnostic (or grandmother) cell
    single neuron that represents"granny" activated
    by outputs from increasingly more complex
    detectors

15
Computational Problems in Object Recognition
  • Theoretical issues in object recognition
  • Frame of reference
  • Shape encoding
  • Neurophysiological representations
  • Hierarchical coding hypothesis
  • Ensemble coding hypothesis
  • Object defined by co-occurrence of complex
    feature detectors

16
Failures of Object Recognition
  • Visual Agnosia Failure to recognize visual
    objects
  • Limited to visual modality
  • Not a sensory deficit
  • Not a memory deficit (anomia)
  • But deficits can co-occur
  • What can disorders of perception tell us about
    perceptual function?

17
Failures of Object Recognition
  • Patient GS
  • Normal visual acuity
  • Normal verbal memory

18
Failures of Object Recognition
  • Patient studies of visual perception deficits
    that support "what/where" distinction
  • Patient DF bilateral occipital lobe lesions
  • Differentiates "perception for identification"
    from "perception for action"

19
Failures of Object Recognition
  • Subtypes of agnosia
  • Apperceptive agnosia deficit in perceptual
    processing
  • Associative agnosia "normal" perceptual
    processing, but deficit in linking percept to
    name

20
Failures of Object Recognition
  • Apperceptive agnosia
  • Deficits in perceptual processing may be subtle
    and may not be apparent in standard clinical
    tests

21
Failures of Object Recognition
  • Apperceptive agnosia
  • Warrington
  • RH patients had greater deficits in the Gollin
    Picture Test and Incomplete Letters Test than LH
    patients
  • RH patients with posterior damage have difficulty
    with object constancy
  • Unusual Views Test can't recognize objects from
    unusual view
  • Shadows Test can't recognize objects when
    illumination changes

22
Failures of Object Recognition
  • Associative agnosia
  • Warrington Deficits are not at a perceptual
    level but at a semantic level
  • Patient FRA
  • LH occipito-temporal lesion
  • Could normally parse complex drawing into
    constituent objects, but could not name objects

23
Failures of Object Recognition
  • LH and RH patients both fail Matching-by-Function
    Test but for different reasons

24
Failures of Object Recognition
  • LH and RH patients both fail Matching-by-Function
    Test but for different reasons
  • Warrington's two-stage model of object
    recognition
  • Perceptual categorization occurs in the RH
  • Semantic categorization occurs in the LH
  • Perceptual categorization precedes semantic
    categorization
  • But, unilateral LH patients don't always have
    associative agnosia, usually requires bilateral
    lesions

25
Failures of Object Recognition
  • Integrative agnosia some elements of
    apperceptive and associative agnosias
  • Patient HJA
  • Bilateral occipito-temporal lesion
  • Could recognize individual objects, but not line
    drawing of objects
  • Could perform Unusual Views Test
  • Could not recognize overlapping objects
  • Deficit in integrating and grouping features

26
Failures of Object Recognition
  • Integrative agnosia
  • May common problem in most agnosics
  • Other Integration failures
  • Patient CK
  • Closed head injury
  • Patient JR

27
Failures of Object Recognition
  • Category-specific agnosia associative agnosia
    where deficit is specific to a semantic category
  • Patient JBR
  • Herpes simplex produced severe associative
    agnosia that was worse for living things than for
    inanimate objects

28
Failures of Object Recognition
  • Category-specific agnosia associative agnosia
    where deficit is specific to a semantic category
  • Semantic knowledge is structured
  • Object categories
  • Tools, vehicles, etc.
  • Living vs nonliving

29
Failures of Object Recognition
  • Category-specific agnosia
  • Damasio suggests that nonliving activate
    kinesthetic associations that living things do
    not

30
Failures of Object Recognition
  • Category-specific agnosia
  • Gaffan and Heywood showed that normals made more
    errors to short latency exposures of living
    things than of nonliving things
  • Living things are more similar and share more
    features than nonliving things and are inherently
    more difficult to discriminate

31
Failures of Object Recognition
  • Farah and McClellands computational explanation
    for category-specific agnosia
  • Property-based organization of semantic system
  • Two main layers semantic and input
  • Semantic has 31 ratio of visual and functional
    properties
  • Input is verbal and visual
  • Objects have visual and functional property codes
  • 7.71 for living things
  • 1.41 for nonliving things
  • Train model to discrimination 20 living and
    nonliving things
  • "Lesion" model and evaluate recognition accuracy

32
Prosopagnosia
  • Inability to recognize faces
  • Is there a separate face recognition system?
  • Evolutionary support
  • Phylogeny of face recognition
  • Primates show similar activation to faces
  • Development of face recognition
  • Neonates track faces longer than other stimuli
  • Cross-cultural interpretation of facial
    expression
  • Universal recognition of facial expressions

33
Prosopagnosia
  • Is there a separate face recognition system?
  • Evolutionary support
  • Neurophysiological support in primates
  • Baylis et al study on neuronal specificity to
    faces in the macaque
  • Farah's taxonomy of lesion foci

34
Prosopagnosia
Majority of lesions in occipito-temporal area
35
Prosopagnosia
  • Is there a separate face recognition system?
  • Evolutionary support
  • Neurophysiological support in primates
  • Farah's taxonomy of lesion foci
  • Function neuroimaging in humans
  • Kanwisher et al. fusiform face area

36
Prosopagnosia
  • Can face and object perception be dissociated?
  • Dissociations between object and face perception
  • Right side up faces vs upside down faces
  • Patient CK
  • Could not identify objects in Arcimbaldo painting
    when right side up, but could identify face when
    painting was upside down
  • Patient WJ
  • Sheep farmer who had prosopagnosia for human
    faces but could still recognize sheep

37
Prosopagnosia
  • Can face and object perception be dissociated?
  • Dissociations between object and face perception
  • Tanaka and Farah face recognition is more than
    the sum of parts

38
Prosopagnosia
  • Two systems for object recognition
  • Farah study of patterns of co-occurrence of
    prosopagnosia, visual agnosia, and alexia
    (acquired dyslexia)
  • Analytic processing
  • Holistic processing

39
Co-occurence of Prosopagnosia, Visual Agnosia,
and Alexia
Number of patients possibly
40
Visual Imagery and Perception
  • Does visual imagery use the same neural
    mechanisms as visual perception?

41
Synesthesia
  • Involuntary experience of cross-modal association
  • 0.05 occurrence in population
  • More common in artists, novelists, poets, etc.
  • May be related to variation of fusiform area of
    temporal lobe
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