TOPIC PAGE NUMBER
VISION - CAN YOU BELIEVE WHAT YOU SEE 1
MEMORY – CAN YOU TRUST YOUR MEMORIES 4
EMOTION – DOES EMOTION DISTORT COGNITION 12
SOCIAL – THE DISTORTED SOCIAL WORLD 19
SELF – THE DISTORTED SELF 26
COGNITIVE CONTROL – DISORDERS IN CONTROL 30
LANGUAGE – DISTORTIONS IN LANGUAGE 33
CONSCIOUSNESS – WHAT DISTORTS CONSCIOUSNESS 43
CONVERSION DISORDER 51
PSYCHOSIS 61
Distorted Worlds: Variability in
Memory and Perception Notes
KING’S COLLEGE LONDON
, TOPIC 1- VISION
Understand the Charles Bonnet Syndrome
reasons behind
our perception of • Central visual filed degenerated
visual illusions • Start seeing rich visual hallucinations – faces, bright colours
• Not reported much – may don’t tell medical team as they don’t believe in their hallucinations –
if they tell people they think they will be given different medical care and people will think they
are having psychosis
• Activity in parts of the brain when they see these faces, and activity in the colour part of the
brain when they see these rich colours
• Spontaneous firing related to colour and face
processing interpreted consciously
• Without a loss of reality – how powerful the visual
system is
Misconceptions about vision
• Being able to see is an automatic and effortless process
e.g. babies don’t need to learn how to see
• Vision sends an exact copy of what is in front of you to your brain
• We perceive a rich and continuous visual environment
• We see in detail only those things that we can fixate
• We see in colour only those things we fixate
Light receptors
• RODS
➢ One of the receptor cells of the retina, sensitive to light of low intensity
➢ Work when we have little light
➢ Vision in the dark is black and white
• CONES
➢ One of the receptor cells of the retina; maximally sensitive to one of three different wave
lengths of light and hence encodes colour vision
➢ Sensitive to colour
➢ Work only when we have lots of light enable powerful acuity
➢ Found primarily in FOVEA
➢ Fovea – the region of the retina that mediates the most acute vision of birds and higher
mammals. Colour sensitive cones constitute the only type of photoreceptor found in the
fovea
• We only get rich detailed information, coloured information from the parts we are fixated on, not
anywhere else
• Why is there no acuity in the blind spot?
➢ No cones or rods
• We see in colour and detail only items falling onto the fovea
➢ How do we construct fuller picture of the world around us
➢ Saccades – trans-saccadic memory – allows us to take forward some information from
one saccade to another
➢ Trans-saccadic memory buffer is not every good and cannot take on much information –
exists but in low level forms
• Change blindness
➢ We need to pay attention to something to be able to see it consciously
➢ Eyes fixate parts of interest (people, sphinx)
➢ If distracted by flicker miss change
1
, ➢ Makes it clear that our eyes are not building up a vertical image of the scene
How does vision work
• The eyes are complex sensory organs that
focus on an image of the environment of the
retina. The retina consists of three layers; the
photoreceptor layer (rods and cones), the
bipolar cell layer, and the ganglion cell layer
• Information from the eye is sent to the
parvocellular, koniocellular, and magnocellular
layers of the dorsal lateral geniculate nucleus
and then to the primary visual cortex (striate
cortex)
Visual cortex – the occipital lobes
• Vision is hierarchical – very low level or simple aspects of the visual input are dealt with differently
than more difficult aspects
• Vision is modular – have some modules for visual processing
• But processing is in parallel and projections feedback as well as feedforward
• Happens at the same time, from the back forward but also the other way round too
V1 – Primary Visual Cortex / Striate Cortex
• Most input from LGN directed here (Lateral Geniculate Nuclei)
• Loss of V1 = cortical blindness
• Damage to part of V1 = blindness for the corresponding part of
the visual field (hemianopia)
Beyond V1
• V4 – colour information
➢ Damage to both V4’s can lead to loss of colour vision
➢ Inability to identify or discriminate colour
➢ Preserved processing of form and motion
➢ V4 and fMRI of synaesthetes – Rich et al 2006
➢ Task – detect offset
➢ Coloured letter, grey letters
➢ Synaesthetes and non-synaesthetes activated V4 (blue) for coloured letters
➢ Synaesthetes also for grey letters (red)
• V5 – motion blindness
➢ V5 deals with motion information
➢ Damage to both V5’s = motion blindness
➢ TMS studies on V5 also reveal its role (e.g.
Beckers and Zeki, 1995)
Visual pathways beyond early visual cortex
• Ventral and dorsal streams
• ‘what’ and ‘where’ pathways
• Recognition of forms, shapes and categories of objects
• Human face recognition (fusiform)
• Colour recognition
2
, • ‘association’ cortices
Describe and Visual agnosia
define visual • damage to the human visual association cortex can cause a category of deficits known as visual
agnosia agnosia
• agnosia (failure to know) refers to an inability to perceive or identify a stimulus by means of a
particular sensory modality, even though its details can be detected by means of that modality
and the person retains relatively normal intellectual capacity
Damage to Ventral ‘what’ pathway
• Agnosia ‘failure to know’
• Can no longer identify by sight even simple objects
• No problem with memory for the word
• No problem with language skills needed to produce the word
• Failure to recognise simple shapes
• Recognition possible only by touch
Dorsal ‘where’ pathway
• Movement perception -
• Spatial sense – where something else in comparison to us, and in comparison, to one another
(similar to visual spatial neglect)
• Optic ataxia – can see when people need to reach for an object – can see it and can compare it
to other objects but can’t plan and execute and reach for it
Challenges for visual perception
• Input often insufficient - doesn’t contain all the information we need to understand what we
are seeing
• Input often ambiguous – we get a lot of information but because it is insufficient and which part
belongs to what and the focus
• Input often overwhelming – information coming in but there is so much of it and doesn’t make
much sense to consciously see it all at one time clearly
• Interpretation is vital – constructs perception at any one moment
Insufficient information
• Deficit in our general vision – the blind spot
• Over- interpretation – mind is over interpreting certain
incoming information (illusory contours)
• Automatic computation of occluders
➢ ‘B’ illusion
• Ambiguous information
➢ Binding the correct parts together
➢ Visual system needs to bind together the lines, dots together
➢ Ambiguity shows it is a cognitively demanding task
Gestalt principles – binding the correct parts together
• Wertheimer 1932
• Wanted to look at rules of vision
• Things that we use automatically to help us bid together information coming in at any one time
• Bind together things that are more similar e.g. shape, colour, texture
• Similarity – we tend to groups these dots into rows rather than columns of similar colour
• Proximity – we perceive groups, linking dots that are close together
• Good continuation – we tend to see a continuous green bar rather than two smaller rectangles
• Closure – we tend to perceive an intact triangle, reflecting our bias toward perceiving closed
figures rather than incomplete ones
3
VISION - CAN YOU BELIEVE WHAT YOU SEE 1
MEMORY – CAN YOU TRUST YOUR MEMORIES 4
EMOTION – DOES EMOTION DISTORT COGNITION 12
SOCIAL – THE DISTORTED SOCIAL WORLD 19
SELF – THE DISTORTED SELF 26
COGNITIVE CONTROL – DISORDERS IN CONTROL 30
LANGUAGE – DISTORTIONS IN LANGUAGE 33
CONSCIOUSNESS – WHAT DISTORTS CONSCIOUSNESS 43
CONVERSION DISORDER 51
PSYCHOSIS 61
Distorted Worlds: Variability in
Memory and Perception Notes
KING’S COLLEGE LONDON
, TOPIC 1- VISION
Understand the Charles Bonnet Syndrome
reasons behind
our perception of • Central visual filed degenerated
visual illusions • Start seeing rich visual hallucinations – faces, bright colours
• Not reported much – may don’t tell medical team as they don’t believe in their hallucinations –
if they tell people they think they will be given different medical care and people will think they
are having psychosis
• Activity in parts of the brain when they see these faces, and activity in the colour part of the
brain when they see these rich colours
• Spontaneous firing related to colour and face
processing interpreted consciously
• Without a loss of reality – how powerful the visual
system is
Misconceptions about vision
• Being able to see is an automatic and effortless process
e.g. babies don’t need to learn how to see
• Vision sends an exact copy of what is in front of you to your brain
• We perceive a rich and continuous visual environment
• We see in detail only those things that we can fixate
• We see in colour only those things we fixate
Light receptors
• RODS
➢ One of the receptor cells of the retina, sensitive to light of low intensity
➢ Work when we have little light
➢ Vision in the dark is black and white
• CONES
➢ One of the receptor cells of the retina; maximally sensitive to one of three different wave
lengths of light and hence encodes colour vision
➢ Sensitive to colour
➢ Work only when we have lots of light enable powerful acuity
➢ Found primarily in FOVEA
➢ Fovea – the region of the retina that mediates the most acute vision of birds and higher
mammals. Colour sensitive cones constitute the only type of photoreceptor found in the
fovea
• We only get rich detailed information, coloured information from the parts we are fixated on, not
anywhere else
• Why is there no acuity in the blind spot?
➢ No cones or rods
• We see in colour and detail only items falling onto the fovea
➢ How do we construct fuller picture of the world around us
➢ Saccades – trans-saccadic memory – allows us to take forward some information from
one saccade to another
➢ Trans-saccadic memory buffer is not every good and cannot take on much information –
exists but in low level forms
• Change blindness
➢ We need to pay attention to something to be able to see it consciously
➢ Eyes fixate parts of interest (people, sphinx)
➢ If distracted by flicker miss change
1
, ➢ Makes it clear that our eyes are not building up a vertical image of the scene
How does vision work
• The eyes are complex sensory organs that
focus on an image of the environment of the
retina. The retina consists of three layers; the
photoreceptor layer (rods and cones), the
bipolar cell layer, and the ganglion cell layer
• Information from the eye is sent to the
parvocellular, koniocellular, and magnocellular
layers of the dorsal lateral geniculate nucleus
and then to the primary visual cortex (striate
cortex)
Visual cortex – the occipital lobes
• Vision is hierarchical – very low level or simple aspects of the visual input are dealt with differently
than more difficult aspects
• Vision is modular – have some modules for visual processing
• But processing is in parallel and projections feedback as well as feedforward
• Happens at the same time, from the back forward but also the other way round too
V1 – Primary Visual Cortex / Striate Cortex
• Most input from LGN directed here (Lateral Geniculate Nuclei)
• Loss of V1 = cortical blindness
• Damage to part of V1 = blindness for the corresponding part of
the visual field (hemianopia)
Beyond V1
• V4 – colour information
➢ Damage to both V4’s can lead to loss of colour vision
➢ Inability to identify or discriminate colour
➢ Preserved processing of form and motion
➢ V4 and fMRI of synaesthetes – Rich et al 2006
➢ Task – detect offset
➢ Coloured letter, grey letters
➢ Synaesthetes and non-synaesthetes activated V4 (blue) for coloured letters
➢ Synaesthetes also for grey letters (red)
• V5 – motion blindness
➢ V5 deals with motion information
➢ Damage to both V5’s = motion blindness
➢ TMS studies on V5 also reveal its role (e.g.
Beckers and Zeki, 1995)
Visual pathways beyond early visual cortex
• Ventral and dorsal streams
• ‘what’ and ‘where’ pathways
• Recognition of forms, shapes and categories of objects
• Human face recognition (fusiform)
• Colour recognition
2
, • ‘association’ cortices
Describe and Visual agnosia
define visual • damage to the human visual association cortex can cause a category of deficits known as visual
agnosia agnosia
• agnosia (failure to know) refers to an inability to perceive or identify a stimulus by means of a
particular sensory modality, even though its details can be detected by means of that modality
and the person retains relatively normal intellectual capacity
Damage to Ventral ‘what’ pathway
• Agnosia ‘failure to know’
• Can no longer identify by sight even simple objects
• No problem with memory for the word
• No problem with language skills needed to produce the word
• Failure to recognise simple shapes
• Recognition possible only by touch
Dorsal ‘where’ pathway
• Movement perception -
• Spatial sense – where something else in comparison to us, and in comparison, to one another
(similar to visual spatial neglect)
• Optic ataxia – can see when people need to reach for an object – can see it and can compare it
to other objects but can’t plan and execute and reach for it
Challenges for visual perception
• Input often insufficient - doesn’t contain all the information we need to understand what we
are seeing
• Input often ambiguous – we get a lot of information but because it is insufficient and which part
belongs to what and the focus
• Input often overwhelming – information coming in but there is so much of it and doesn’t make
much sense to consciously see it all at one time clearly
• Interpretation is vital – constructs perception at any one moment
Insufficient information
• Deficit in our general vision – the blind spot
• Over- interpretation – mind is over interpreting certain
incoming information (illusory contours)
• Automatic computation of occluders
➢ ‘B’ illusion
• Ambiguous information
➢ Binding the correct parts together
➢ Visual system needs to bind together the lines, dots together
➢ Ambiguity shows it is a cognitively demanding task
Gestalt principles – binding the correct parts together
• Wertheimer 1932
• Wanted to look at rules of vision
• Things that we use automatically to help us bid together information coming in at any one time
• Bind together things that are more similar e.g. shape, colour, texture
• Similarity – we tend to groups these dots into rows rather than columns of similar colour
• Proximity – we perceive groups, linking dots that are close together
• Good continuation – we tend to see a continuous green bar rather than two smaller rectangles
• Closure – we tend to perceive an intact triangle, reflecting our bias toward perceiving closed
figures rather than incomplete ones
3
