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Cognitive Psychology (30009) > Visual Perception > Flashcards

Visual Perception Flashcards

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1
Q

What happens after the retina - Parvocellular (P) Pathway

A
  • Sensitive to colour and fine detail
  • Most input comes from cones
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2
Q

What happens after the retina - Magnocellular (M) Pathway

A
  • Most sensitive to motion
  • Most input comes from rods
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3
Q

Pathway from eye to the brain

A

Retina –> Optic nerve –> Optic chiasm –>Lateral Geniculate Nucleus (LGN) –>Cortical area

  • Left visual cortex comes from the
    left sides of the two retinas, and signals reaching the right
    visual cortex comes from the right sides of the two retinas
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4
Q

Property of Visual Neurons - Receptive fields

A

The region of the sensory space (i.e. retina) within which light will cause the neuron to fire.

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5
Q

Property of Visual Neurons - Retinotopy

A

Things that are near to each
other in space are processed
in cells that are physically
near to one another

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6
Q

Property of Visual Neurons - Lateral inhibition

A

A reduction of activity
(inhibition) in one
neuron that is caused by
a neighbouring neuron
* Useful for enhancing
contrast at edges of
objects

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7
Q

1st Stop - Lateral Geniculate Nucleus

A

Part of the thalamus – a subcortical relay for most of the brain’s sensory input and motor output
- Cells have a centre-surround receptive field
- Responds to differences in light across their receptive field (e.g. light in centre, dark in surround)
- Maintains a retinotopic map
- Correlates signals from the retina in space and time
- Provides the early 3D representation of space for action

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8
Q

Primary Visual Cortex (V1)

A

Extracts basic information from the visual scene (e.g. edges, orientations, wavelength of light)
- Sends this information for later stages of processing of shape, colour, movement, etc.
- Maintains retinotopy

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9
Q

Single-cell recordings by Hubel and Wiesel (1979)

A
  • Indicate that some cells respond to simple features (e.g. points of light)
  • Others combine those features into more complex ones (e.g. adjacent points of light may
    combine into a line)
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10
Q

What is the result of damage to V1?

A
  • Leads to cortical blindness - patient cannot consciously report
    objects presented in region of
    space
  • Patient can still make visual discriminations in ‘blind’ area - Blindsight (Weiskrantz, 1974)
  • This is due to other routes between eye and brain
  • Geniculostraite route may be specialised for conscious vision + others act unconsciously
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11
Q

Blindsight

A

Filling-in of ‘blind’ regions similar to filling-in of normal blind spot

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12
Q

Functional Specialisation Theory (Zeki, 1992-93)

A

Different parts of the visual cortex are specialised for different visual
functions

  • V1 + V2: Early stage of visual perception like shapes
  • V3 + V3a: Responsive to form (especially of moving objects)
  • V4: Responsive to colour
  • V5/MT: Responsive to visual motion
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13
Q

Central Assumption of FST

A

Colour, form, and motion are
processed in anatomically
separate parts of the visual
cortex

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14
Q

Brain Imaging (PET) of Human V4 and V5 - Zeki et al, 1991

A

V4 more active for coloured than
greyscale images –>specialised for
colour
* V5 more active for moving dots compared with static dots –>
specialised for motion

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15
Q

V4: The colour centre of the brain + Cortical achromatopsia

A

Patients with cortical
achromatopsia can’t see
colours because of damage to V4,
but often also due to damage to
V2 and V3 (despite a fully functioning retina)
* Case studies indicate intact implicit colour processing in patients with achromatopsia.
* Conclusion: V4 is involved in colour processing but the link between colour processing and V4 is not perfect

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16
Q

V5/MT: The motion centre of the brain + case study of LM

A
  • Damage to V5/MT leads to akinetopsia

Patient LM:
- Bilateral damage to V5/MT
- Was good at locating stationary
objects
- Had good colour vision
- Motion perception was grossly
deficient

17
Q

A Challenge for Functional Specialization– The Binding Problem

A
  • Sighted people don’t perceive colour of things separately so how are different features bound to create coherent object processing?

Possible solution: Coherent perception depends on synchronised neural activity between brain regions, which my depend on attention

17
Q

Beyond visual cortex: Parietal processing pathway

A

Also known as dorsal
Concerned with movement processing - vision for action

17
Q

Beyond Visual Cortex - Temporal processing pathway

A

Also known as ventral
- Concerned with colour + form processing

17
Q

Case study of DF - Vision for perception vs action

A

-Had a lesion on lateral occipital cortex - trouble locating and identifying objects
- But, conscious perception was different from information available to her motor system - had where but not what

17
Q

Model of Object Recognition - Step by Step

A
  1. Early visual processing (colour,
    motion, edges etc.)
  2. Perceptual segregation: grouping of visual elements (Gestalt principles, figure–ground segmentation)
  3. Matching grouped visual description onto a representation of the object stored in the brain (called structural descriptions)
  4. Attaching meaning to object based on prior semantic knowledge
17
Q

Perceptual Segregation

A
  • Separating visual input into individual objects
  • Thought to occur before object
    recognition
17
Q

Gestalt Psychology

A

Fundamental principle: the “Law of
Prägnanz”:
- “Of several geometrically possible
organisations, that one will actually
occur which possesses the best,
simplest, and most stable shape”
(Koffka, 1935, p. 138)
– Assumes a set of rules that operate early in visual processing

17
Q

Gestalt Psychology: Problems

A
  • Segmentation processes aren’t always bottom-up and following the laws of perceptual organisation
  • Most evidence is only descriptive not explanatory
  • Relies on introspection + evidence from 2D drawings
  • Some segmentation clearly occurs via top-down prior knowledge
17
Q

Object recognition deficits - Agnosia

A
  • Impairment in object recognition
    (without primary visual deficits)
  • Different kinds of impairments should arise depending on the
    stage at which object
    recognition is damaged
17
Q

Apperceptive agnosia

A

– Impairment in constructing a perceptual representation from vision (e.g. grouping)
– Seeing the parts but not the whole
– Associated with lateral occipital lobe damage

17
Q

Associative agnosia

A
  • Impairment in the process which maps a perceptual representation onto knowledge of the object’s functions and associations
    – Seeing the whole but not its meaning
    – Associated with occipitotemporal damage
17
Q

Case study of Apperceptive agnosia - HJA (Riddoch & Humphreys,1987)

A

Bilateral ventral-medial occipital damage
- HJA could recognise objects from touch but had a marked impairment in visual object recognition, particularly for line drawings over silhouettes.
- HJA had problems grouping or
organising information (e.g., recognising any objects presented together with other objects)

17
Q

Case Study of Associative Agnosia - LH

A
  • Had visual object agnosia + damage to occipitotemporal regions
  • Preserved ability to copy drawings of objects, but unable to
    name them or show what they are for- i.e. no access of semantics
18
Q

Object perception: Caveats

A
  • Most research comes from white male researchers + pps
  • Westerners prioritise processing/categorising objects while East Asians prioritise relationships between objects + context
  • Less activation of object perception regions in EAs during scene viewing
  • Generalisable?
18
Q

Different categories of objects

A
  • Some evidence that
    patients with damage to the
    ventral visual stream (“what
    stream”) have impairments in
    only one particular category of
    objects
  • Lesions to different areas of the
    what stream can be associated
    with agnosia for different types
    of objects, like naming faces,
    animals and tools
19
Q

The Problem with Faces

A

Face recognition is a within-category discrimination – all faces look very similar
- Other object recognition is between categories – e.g. distinguishing a pen from a cup
- Faces require different types of
processing to other objects?
- Faces are Important from a
social/evolutionary perspective that they may have its own mechanism

19
Q

Are Faces Special? - Neuropsychological Evidence

A
  • Prosopagnosia - impairment of face processing that doesn’t come from damage to early visual processing
  • De Renzi (1986): Patient failed to recognize his own family but
    could do so by voice or clothes
  • Could match different views of faces and name other objects
  • Impairment at the stage of matching to stored information
20
Q

Are Faces Special - Neuroscience Evidence

A

Fusiform Face Area
- Part of the ventral (what) stream
- Responds to faces more than
other types of objects in
functional imaging experiments

21
Q

Holistic Processing

A
  • Features (parts) of faces are processed (and subsequently
    remembered) less than for other types of objects, like houses
22
Q

Holistic Processing in Face Recognition - Inverted Faces

A
  • Sighted ppl identify inverted faces slower + less accurately
  • Interpreted as evidence of processing
  • Qualitative differences in processing of upright + inverted faces
  • Spatial-relational information is
    disproportionately affected by
    inversion, and therefore face
    recognition suffers
23
Q

Faces are special due to Visual Expertise - Gauthier et al, 1999

A
  • Suggest that faces are special as we are now experts at within-category discriminations
  • Claims it involves fusiform face area
24
Q

Criticism that we are Visual Expertise - Case Studies

A

Not all prosopagnosic patients are impaired on within-category discrimination

  • WJ - had sheep and could distinguish between them
  • RM - could distinguish between 5000 mini cars but couldn’t identify famous/his own/his wife’s face

Cognitive Psychology (30009) (11 decks)

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