Sensation and Perception - Semester 2 Flashcards
(246 cards)
1
Q
What is often perceived as effortless but involves complex processes behind the scenes?
A
Activities such as cooking a meal by a chef
This highlights the difference between surface perception and underlying complexity.
2
Q
What are the basic building blocks of our sensory experiences?
A
External stimuli that are constructed internally through labelling and inference
This refers to how we interpret and understand sensory information.
3
Q
What is the role of the brain in our sensory perception?
A
Everything we sense is a product of the biological machinery inside our brain
This emphasizes the brain’s role in processing sensory information.
4
Q
What range of experiences do we have through our senses?
A
From eating to pain, to listening to music
These experiences illustrate the vast capabilities of human perception.
5
Q
What are the four basic things we sense?
A
- Light
- Chemicals
- Mechanical forces
- Temperature
These elements form the foundation of our sensory experiences.
6
Q
What is psychophysics?
A
The branch of psychology that deals with the relations between physical stimuli and mental phenomena
It explores how physical stimuli relate to our perceptions.
7
Q
What are the two contrasting views on the source of knowledge?
A
- Empiricism
- Rationalism
Empiricism states knowledge comes from outside the mind, whereas rationalism posits that knowledge is shaped by fundamental principles.
8
Q
What does the ‘Blank Slate’ concept refer to in terms of knowledge acquisition?
A
Nurture influences the development of knowledge
This is contrasted with ‘Innate tendencies’ which suggests that nature plays a role.
9
Q
How does exposure to different environments shape perception?
A
Through neural plasticity, development, and effects of stimulus exposure
This indicates that our experiences and environments can alter brain structure and function.
10
Q
What are some basic substrates and laws that drive perception?
A
- Illusions
- Psychophysical laws
- Functional brain anatomy
These factors help explain how we perceive and interpret sensory information.
11
Q
True or False: We often accurately fill in information about things that are not actually present.
A
False
We often make inferences that may not be true, leading to misperceptions.
12
Q
What are the three steps to perceiving something?
A
- Sample physical information
- Integrate and encode it in the brain
- Interpret and use it
13
Q
What is sensory transduction?
A
Transforming physical properties into neural signals
14
Q
What are the four types of sensory receptors?
A
- Light Photoreceptors sense light
- Chemicals Chemoreceptors sense chemicals
- Mechanical forces Mechanoreceptors sense mechanical forces
- Temperature Thermoreceptors sense temperature
15
Q
What is light?
A
- Visible light is electromagnetic radiation of 380-760 nm, emitted by the sun, lightbulbs, etc.
- We have preceptors in our eyes that can perceive them.
16
Q
What is the relation between light and colour?
A
- Colour is the way we process and put labels on light
17
Q
What does light tell us?
A
- Light energy is reflected and absorbed by surfaces around us
- This changes the properties of the light
- Light waves contain information about surfaces
- The brain extracts surface information from light
18
Q
What do photoreceptors do in terms of physical stimulus?
A
Light waves reflected from the image pass through the cornea and enter the eye through the pupil. The lens focuses the light on the retina
19
Q
What is sensation in terms of photoreceptors?
A
Sensory receptors in the retina called roots and cones detect the light waves
20
Q
What is transduction?
A
Rods and cones convert light waves into signals. Those signals are processed by ganglion cells, which generate action potentials that are sent to the brain by the optic nerve
21
Q
How do photoreceptors work?
A
- When light hits a photopigment molecule, it splits
- The split activates the photoreceptor cell – this is the moment of transduction from light wave to neural impulse
22
Q
What are the 5 steps of how photoreceptors work?
A
- Photon strikes photopigment
- Photopigments splits activates cell
- Signal transmitted to bipolar cell
- Signal transmitted to ganglion cell
- Signal transmitted to brain
23
Q
What is the response of rods and cones?
A
Rods = slow
Cones = fast
24
Q
What is the recovery of rods and cones?
A
Rods = slow
Cones = fast
25
What is the acuity of rods and cones?
Rods = low
Cones = high
26
What is the sensitivity of rods and cones?
Rods = high
Cones = low
27
What is the location of rods and cones?
Rods = peripheral retina
Cones = Central retina
28
How many types of rods and cones?
Rods = one
Cones = Three (L, M and S)
29
How many types of rods and cones?
Rods = 120 million
Cones = 6 million
30
What is the function of rods and cones?
Rods = peripheral and low-light achromatic vision
Cones = Detailed, central, chromatic vision
31
What are the three cone types?
- Short (‘blue’) peak at 440nm
- Medium (‘green’) peak at 540
- Long (‘red’) peak at 570nm
32
What is the most common and least common colour blindness?
-- Most commonly: lose L/M differentiation (red/green colourblind)
- Less commonly: lose S cones; ocular albinism; brain injury
33
Where are cones concentrated on the retina?
- Cones are concentrated at the fovea
34
Where are rods on the retina?
- Rods are fewer in the periphery, and increase towards the fovea, but there are no rods at the fovea
35
What does higher receptor density cause?
Higher perceptual acuity
36
What do rods and cones work together to give?
- The rodes and the cones work together to give you accurate and quality vision
37
What do eye movements do?
- Bring new objects of interest to the fovea
- Keep the eyes fixed when head/body move
- Prevent images from fading by shifting their position on the retina
38
What is the blind spot of our vision?
- The blind spot corresponds to the place where the axons of 1.2 million retinal ganglion cells form the optic nerve
39
Why are edges important?
- Signal the presence of an object or boundary (usually)
- Blank spaces are unimportant (usually)
- The visual system exaggerates edges, starting in the retina
40
What is edge enhancement via lateral inhibition?
- Each cell inhibits its neighbours
41
What are retinal ganglion cells?
There are many more photoreceptor cells than there are retinal ganglion cells. This means that retinal ganglion cells receive signals from a constituency of photoreceptor cells
42
What are the two important types of retinal ganglion cells?
Midget cells
Parasol cells
43
What are midget cells?
Type of retinal ganglion cells
1. Midget Cells receive input from cones
- The number of cells they summarize is small
- They project to the parvocellular pathway: the pathway into the brain that carries high-acuity details
44
What are parasol cells?
Type of retinal ganglion cells
2. Parasol cells receive input from the rods
- The number of cells they summarize is large
- The project to the magnocellular pathway: the pathway into the brain that carries low-light peripheral vision, motion and contrast
45
What is the receptive field?
- The place/type of stimulus that elicits a response in a given neuron
- Neurons ‘respond’ selectively to specific regions/stimuli, from sensory receptors all the way through to cortical brain areas
- ‘Respond’ = change their firing rate (increasing OR decreasing)
- Easier to map RFs at early stages (vison/touch) – becomes increasingly difficult the further into the system you go
46
What is mechanical pressure?
Ear, skin and body
47
What does physically deforming mechanoreceptors cause?
- Physically deforming a mechanorecptor causes ion channels to open, which causes the cell to fire
48
What information can mechanical forces provide?
1. Pressure and stretch receptors in the skin
2. Stretch receptors in muscles, tendons and internal organs
3. Movement of hair cells on the inner ear
49
What are examples of pressure and stretch receptors in the skin?
Light touch
Texture
Stretch
Pain
50
What are examples of stretch receptors in muscles, tendons, and internal organs?
Body position
Body movement
Interoception
51
What are examples of movement of hair cells in the inner ear?
Inertia
Gravity
Hearing
52
What are cutaneous mechanoreceptors?
Sense of touch
53
Describe cutaneous mechanoreceptors (the sense of touch)?
- Multiple systems: light touch, firm pressure, vibration, pain and skin stretch
- All types respond to physical deformation
- Receptors shapes are specialised for different types of pressure
54
What is the two-point discrimination threshold?
- Touch the skin with one or two points
- Gradually move the points closer together
- At some point two will feel like one
- This distance is the two-point discrimination threshold
- If two points stimulate two different receptors, you will feel two points. If two points stimulate only one receptor, you will feel only one
- Density of receptors in the skin is highest on the hands and face, lowest on the upper arms, calf etc
55
What is haptic touch?
- Haptic touch: exploring objects with your subcutaneous mechanoreceptors
- Vibrations = roughness/texture
- Position of fingers around object = shape
- Skin stretch, tendon stretch = weight
56
What is proprioception, kinesthesis and interception ?
2 – Proprioception (body position), kinesthesis (body movements) and interoception (body state)
- Strech receptors in muscles and tendons: low-level (spinal/brain stem) control + perceptual input
- Also stretch receptors in smooth muscle (e.g. lungs, bladder, stomach, bowels): low level (spinal/brain stem) control _perceptual input
57
What are the three functions of hair cells in the inner ear?
- Head motion perception (semicircular canals)
- Gravity perception (inner ear)
- Sound perception (cochlea)
58
What do semicircular canals contain?
Endolymph
59
What happens with the acceleration and deceleration of head movements?
- Acceleration and deceleration of head movement – endolymph movement lags behind the hair cells, causes them to bend
- Changes in viscosity of endolymph can interfere with perception
60
What do the hair cells in the inner ear (Otolith organs) do in terms of gravity?
- Inner ear contains the otolith organs
- Gravity shifts the otolith (small crystals) against hair cells
- Provides sense of head position relative to upright
61
What are the three functions of hair cells in the inner ear?
- Head motion perception (semicircular canals)
- Gravity perception (inner ear)
- Sound perception (cochlea)
62
What is the range of human hearing?
The range of human hearing: variable, but 12Hz to 20KHz
63
What is the function of the ear?
The function of the ear is to channel and amplify sound waves
64
What are ossicles?
Ossicles malleus, incus, stapes (three smallest bones in the body)
65
What are auditory hair cells?
- Ion channels on adjacent hairs are connected by a ‘tip link’. Movement of the hair cells pulls the ion channels open, depolarizing (activating) the cell
66
What do mechanoreceptors in the cochlea provide?
- Loudness – amplitude of sound wave increases firing rate
- Pitch – which part of the cochlea is activated
- Timbre – composite frequencies – simultaneous activation of multiple locations on the cochlea
67
What are the 4 minimum types of thermoreceptors?
Fast cold
Fast hot
Slow cold
Slow hot
68
Where are thermoreceptors found?
The skin
In the cornea (to trigger blinking)
In the brainstem (to regulate core temperature)
69
What does the slow system of sensing skin temperature come from?
- Slow system comes from unmyelinated C-fibres
70
What is the difference between myelinated and unmyelinated nerves?
- Myelin speeds up neural transmission, so unmyelinated nerves are slow (signals take perceptible amount of time to get to the brain)
- Adapt quickly
71
Where does the fast system come from?
- Fast system comes from A -delta fibres
Fast, extreme hear/cold
No adaptation
72
How do chemoreceptors function?
- Function like a ‘lock and key’: specific classes of receptors are sensitive to specific molecule types.
73
Where are chemoreceptors found?
(a) Tongue (gustation)
(b) Nasal epithelium (olfaction)
(c) Other locations in the body (heart, stomach)
74
How many chemoreceptors does the tongue have?
- Each of the papillae on the tongue contains multiple taste buds
- Each taste bud contains multiple chemoreceptors
75
What are the five tongue receptor types?
sweet, salty, bitter, sour, and savoury (AKA umami)
76
What signals does the sweet receptor take?
Sugars (Calorie-dense foods)
77
What signals does the umami receptor take?
Glutamate (protein-rich food)
78
What signals do the salty receptors take?
NaCL (Electrolytes)
79
What signals do the sour receptors take?
Acid (fermented/unripe foods?)
80
What signals do bitter receptors take?
Toxins, inedible substances
81
What are taste preferences caused by?
- Innate preferences (e.g. sweet over bitter)
- Exposure to amniotic fluid and breast milk (flavour determined by maternal diet)
- Exposure to flavours over lifespan
- Genetic variability in taste bud types and numbers (‘supertasters’, ‘nontasters’, e.g. Barthoshuk et al., 1994)
- Perception of flavour is more than gustation alone
82
What is ageusia?
The inability to taste
- Temporary loss of taste is common
- Permanent ageusia is rare
- Usually caused by nerve damage or deformity
83
What is nasal epithelium?
- Inhaling brings odorants to the nasal epithelium
- Odorants bind to proteins in the cilia of the receptor cells and activate the cell
- Each cell has only a single receptor type
84
What is anosmia?
- Loss of sense of smell
- Temporary loss due to inflammation/blockage is routine
- Permanent loss due to range of causes (congenital, head trauma, disease, aging) common (1-2% in young 12% in elderly)
85
What are examples of chemoreceptors in the body?
- CO2 and O2 sensitive chemoreceptors that sample blood leaving the heart and communicate with brain areas that control breathing rate
- Chemoreceptors in the gastric system cause nausea and vomiting
86
What are the 5 senses?
- Vision: photoreceptors in the retina
- Audition: mechanoreceptors in the cochlea
- Smell: chemoreceptors in the nasal cavity
- Taste: chemoreceptors in the tongue, nasal cavity, digestive tract; plus, mechanoreceptors and thermoreceptors on the tongue
- Touch/somatosensation:
87
What are cutaneous mechanoreceptors for?
light touch, vibration, pain, stretch
88
What are cutaneous thermoreceptors for ?
Skin temperature
89
What does haptic touch involve?
Haptic touch also involves mechanoreceptors in the muscles and tendons, input from the motor system
90
Where does perception come from and how does it work?
- Receptors are distributed and send input to the brain
- If they did not transmit to the brain, there would be no perception
- Does your foot feel warmth? No – it comes from the brain!
91
How do we get sensory input to the brain?
- Vision, audition, and somatosensation all have similar general architecture
- Input goes through the thalamus first, and then to specialised areas in the cerebral cortex
92
What are the five key components of the primary visual pathway?
1. Optic Nerve
2. Optic Chiasm
3. Lateral Geniculate Nucleus (LGN), in the Thalamus
4. Optic radiations
5. Primary visual cortex (AKA striate cortex, V1)
93
Where does sensory input go first?
- Input goes through the thalamus first, and then to specialized areas in the cerebral cortex
94
What are the five key components of the primary visual pathway?
1. The retina
2. The optic nerve, optic chiasm, and optic tract
3. Lateral Geniculate Nucleus (LGN), in the Thalamus
4. The optic radiations
5. Primary visual cortex (AKA striate cortex, V1)
95
Where do the long axons of the retinal ganglion cells end up?
The LGN of the thalamus
96
Where do axons coming from the retinal ganglion cells in the nasal part of the retina cross over at?
Optic chiasm
97
What axons do not cross?
- Axons coming from cells in the temporal (outer) part of the retina do not cross
98
Where does information from the right visual field and left visual field go?
- Information in the left visual filed goes to the right hemisphere
- Information in the right visual field goes to the left hemisphere
99
What is the lateral geniculate nucleus?
- Geniculate = ‘Knee-like’
- LGN has layers with different cell types, primarily
100
What do Parvocellur (P cells) do?
Receive input primarily from cones/midget cells
Pathway for high-acuity vision and colour
101
What do magnocellular (M cells) do?
Receive input primarily from rods/parasol cells
Pathway for detecting contrast and motion, low-light vision
102
If you add pigment together what happens?
- If you add pigment together (e.g. paint), the bigger mix of colours the darker it gets
103
If you add light together what happens?
- If you add light together, the more colours of light, the lighter the colour will become
104
What does the primary visual cortex contain multiple of?
- Contains multiple detailed maps of visual space organised into layers
- The left hemisphere contains maps of right visual field, and vice versa
- The upper half contains maps of lower visual field and vice-versa
105
What information does V1 contain?
- Receptive fields:
- Each cell responds selectively to a region of the visual field
- Cells in V1 are also selective for:
The orientation of edges in their RFs
Colour in that region (‘blobs’)
The left or right eye
106
What happens when V 1 is damaged?
- Patient reports complete blindness in the part of spece associated with the area that has been damaged
- But many of these patients can ‘guess’ accurately about stimuli presented in their blind field
- This visual capacity in ‘blind’ space is called blindsight
107
How do patients guess accurately about stimuli presented in their blind field?
- There are other visual pathways: For example, the retinotectal pathway to the superior colliculus (SC)
108
What does the retinotectal pathway control?
- The retinotectal pathway controls fast, reflexive eye movements
109
What are the four components of the primary auditory pathway?
1. Superior Olive (pons)
2. Inferior colliculus (midbrain)
3. Medial geniculate nucleus (MGN) in the thalamus
4. Auditory cortex
110
What is the role of the superior olive?
- Receives input from BOTH ears
- Critical for detecting interaural time and volume differences
- This gives us information about the location of sounds
111
What is the role of the inferior colliculus?
- Primarily receives auditory input
- Also receives somatosensory and visual input
- Multisensory integration occurs here
- Visual information constrains auditory localization (ventriloquist effect)
- We think that the sound is coming from where are vision tells us it is even if this is not the case (speakers and headphones)
112
What is the medial geniculate nucleus?
- Right next to the lateral geniculate nucleus
- Like the LGN, acts as a relay station on the way to primary auditory cortex
- Auditory input is heavily influenced by other modalities before it reaches the cortex
113
What is the role of the primary auditory cortex?
- Contains a tonotopic map of all frequencies (tones), and selectively for location, timing and amplitude
114
What does damage to the primary auditory cortex lead to?
- Damage leads to an analogous condition to blindsight: inability to consciously identify certain tones, but guessing is above chance
115
What are the three components of the primary somatosensory pathway?
- Three key components
1. Dorsal root ganglion
2. Ventral posterolateral Nucleus in the thalamus (VPL)
3. Primary somatosensory cortex
116
What is the dorsal root ganglion?
Skin receptors are just one part of the nerve cell. The cells body is in the dorsal root ganglion, next to the spinal cord
117
What can damage to the primary somatosensory cortex cause?
- Damage leads to lowered sensitivity to touch and an inability to identify objects by touch
- Damage can also lead to a sense of disownership of body parts
118
What is perception based on?
- Perception is based on sensory input
119
Can perception occur without sensation? If so give examples?
- Perception can occur without sensation
Hallucinations
Elaboration (e.g. illusory contours)
120
Can sensation occur without perception? If so give examples?
- Sensation can occur without perception
Sensorimotor control mediated by spinal cord and brainstem
Selective attention – you select some input and supress/ignore the rest
121
How can we tell that objects are different?
- Movement: moving around means we can perceive from multiple viewpoints and resolve issues
- Knowledge: We can also use our prior knowledge and experience of perceiving objects to resolve problems
122
How easy is it to recognize objects from different view points?
- Familiar objects: recognisable from multiple angles
- Novel objects: require more time
- This is the principle of viewpoint invariance
123
What is important to perceive a scene correctly?
* Disambiguate the stimulus on the receptors
* Recognize objects across changes in size or scale
* Recognize hidden objects
* Recognize blurred objects
* Recognize objects from different viewpoints
124
How do we achieve perceiving a scene correctly?
* Looking at objects/scenes from different viewpoints
* Using experience, context and previous knowledge we have about objects and scenes
125
What is perceptual organisation?
grouping the incoming stimulation into coherent units (i.e. objects)
126
How do we recognize an object?
- Group visual information (put things together)
- Segregate visual information (determine areas are separate from each other)
127
What causes us to group some elements into one object?
- Structuralism (Wilhelm Wundt, Edward Titchner)
- Gestalt perception (M. Wertheimer, K. Koffka, W. Köhler)
- Recognition by components (Irving Biederman)
- Viewpoint-dependent theories (HH Bülthoff, M Tarr etc.)
128
What is structuralism?
Perceptions are created by combining elements called sensations.
129
What are perceptions created by?
- Perceptions are created by combining elements called sensations.
- Perception = ‘adding up’ sensations
130
What is apparent motion?
Apparent motion’: an illusion of motion
131
What can structuralism not account for?
- Structuralism cannot account for the illusion
- No real movement involved
- No sensation between lines
- Adding two sensations wouldn’t lead to perception of motion
132
What issues can illusory contours cause?
- Perception of an object where there is none
- Perception by adding sensations cannot explain this
133
Who were the Gestalists?
- Max Wertheimer (1880-1943)
- Kurt Koffka (1886 – 1941)
- Wolfgang Kohler (1887 – 1967)
134
What does the gestalt approach suggest?
- The Gestalt approach suggests several rules or principles of perceptual organisation
- These set out how different components in an image should be organised:
- I.e. what causes some of the black spots in the picture below to be bound together into a Dalmation?
- Pragnanz
- Similarity
- Good continuation
- Proximity
- Common region
- Uniform correctness
- Synchrony
- Closure
- Common fate
- Meaningfulness/Familiarity
135
What is the law pragnanz or law of simplicity?
- Reality is organised to the simplest for possible
136
What is the law of similarity?
Similar things appear to be grouped together
137
What is the law of good continuation?
- Points that, when connected, result in straight or smoothly curving lines are seen as belonging together
- The lines tend to be seen in a way that follows the smoothest path
138
What is the law of proximity?
Things that are near each other are grouped together
139
What is the law of common region?
things within the same region of space are grouped together
140
What is the law of uniform connectedness?
a connected region is perceived as a single unit
141
What is the law of synchrony?
Visual events that occur at the same time are seen as belonging together
142
What is the law of common fate?
things that are moving in the same direction appear to be grouped together
143
What is the law of closure?
Incomplete or fragmented visual elements are perceived as a single object. Missing sections are ‘filled in’, so that we have the perception of a single coherent form
144
What is the law of familiarity ?
Things that form patterns which are familiar or meaningful are likely to be grouped together
145
What is perceptual segregation?
- Figure-ground segregation
- The figure has a form or shape
- The background lacks form
- The figure is perceived as being in front of the ground
- Edges belong to the figure (border ownership
146
What are objects broken down into?
- All objects can be broken down into basic units
- These units are known as ‘geons’ – geometric ions
- As ions are the base unit of molecules, geons are the base unit of objects
147
What is object identify?
- Which geons are involved
- The spatial relations between them
148
How can we identify which geons make up an object?
- Geons have non-accidental properties
- Which are viewpoint-invariant
- Which makes the geons discriminable
- And allows for componential recovery
149
What are Non-accidental properties (NAPS)?
- Most of the time, when we see an object such as a book, we will perceive its three edges
150
How do NAPS give geons discriminability?
- Each geon has its own set of NAPs, which are unique to it
- This means geons have discriminability- they can be distinguished from other geons
151
What is meant by NAPS are viewpoint invariant?
- Because the NAPs are visible from most viewpoints, we can identify the geon from most viewpoints
- This is the property of viewpoint invariance
152
What is the viewpoint dependent recognition theory?
- Viewpoint dependent recognition (Tarr, 1995; Tarr and Bulthoff, 1995;1998)
- Opposes the key aspect of RBC: that of viewpoint invariance (objects can be recognised easily from nearly all viewpoints)
- VDR assumes that recognition is affected by the viewpoint
- Our representations of objects are encoded based on the angle we see them from
- Objects seen in novel or less familiar viewpoints are less well recognised
- If we see an object from a viewpoint we already have stored, recognition is easier
- Hence familiar objects can be recognised more easily, as we have more chances to experience different viewpoints of the items (Tarr and Bulthoff, 1995)
153
What is pareidolia?
seeing a face alongside a form
154
What salient information do faces provide?
Identification
Emotions
Communications
155
How do we process familiar faces?
- Recognition is a holistic or configural process:
Internal features: (nose, eyes, mouth)
External features (hair, ears)
Feature relations (distance between the features)
Face shape
156
What is the inverted face illusion?
- When inverted, the face appears normal
- Inverted face: Piecemeal processing
- Upright face: Configural processing
157
What is the composite face effect?
- The composite face effect: matching bottom and top half of faces
- Accuracy is lower for aligned faces
- Higher for misaligned
- Dominance of holistic processing
158
How do you recognize someone you don't know?
- Research:
- Recognition = have seen this face before (earlier in study)
- Real world:
- Recognition = match photos of the same person/photo and person
159
What factors influence face recognition?
- Pose: Changing viewpoint worsens recognition
- Expression: emotional expressions help familiar face recognition only (Kaufmann and Schweignberger, 2004)
- Context: No effect on familiar faces, impairs unfamiliar faces (Davies and Milne, 1982)
160
What is face adaptation?
- Face adaptation: view a face with a distortion in one direction then perceive an opposite distortion for unmanipulated face
161
What do we adapt to when looking at faces?
Basic facial features (width of a face)
Identity
Gender
Expressions
- We adapt to common facial features, allowing neuronal resources to be left to identify uncommon characteristics
- Face adaptation indicates that we have neurons or neuronal networks that are specifically tuned to above properties
162
What areas of the brain is important in facial recognition?
The area in the brain that seems to be particularly important is the fusiform face area, or fusiform gyrus
fMRI scans show high activity in this area when participants are studying faces
163
What are the two main disorders of facial recognition?
- Prosopagnosia aka face blindness: an inability to recognise faces
- Capgras Delusion or Capgras Syndrome: the perception that close acquaintances have been replaced by identical imposters
164
What is prosopagnosia?
literally: ‘without knowledge of faces’ (Cf. agnosia, which is just ‘without knowledge’, and refers to objects)
- Other visual processing functions are intact (e.g., object discrimination)
- Intellectual functioning intact (e.g., decision making)
165
What is acquired prosopagnosia?
- Lesions in right occipital, temporal or fusiform brain regions.
166
What is developmental prosopagnosia?
- Lifelong deficit that manifests itself in early childhood and cannot be attributed to acquired brain damage
167
What are super recognizers?
- Can memorise and recall thousands of faces
- Typically, after seeing each only once
- Estimate 1-2% of the population
- Russell et al., (2009)
168
What is capgras syndrome?
- Patients think a friend (spouse/close family member) has been replaced by an identical-looking impostor.
- First described by Joseph Capgras in 1923: first known as “l'illusion des sosies”- the illusion of the look-alikes
- Suggested to have some neurological basis, due to brain lesions or degeneration of particular areas
169
What are the differences between prosopagnosia and Capgras syndrome?
- Prosopagnosia
Cannot recognise familiar faces
Show physiological responses
Covert recognition intact
- Capgras Syndrome
Can recognise familiar faces
No physiological response
Overt recognition intact
170
What type of processing is face recognition?
- Face recognition uses configural processing
- Inverting faces disrupts this (Thompson, 1980)
- Inverting objects doesn’t slow recognition as much as it does for faces (Yin, 1969)
- Distinct processing types used
171
What is attention?
- It is the taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought…
- It implies withdrawal from some things in order to deal effectively with others
172
What is selective attention?
- Selective attention: or focused attention; focusing on specific objects and filtering out other.
Studied by presenting multiple stimuli to a participant and asking them to respond to only one
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What is divided attention?
- Divided attention: paying attention to more than one thing at a time
- Studied by presenting multiple stimuli to a participant and asking them to respond to everything
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How can we achieve selective attention?
- Eye movement
- By moving our eyes, we can bring the fovea of the eye onto the regions of the scene/environment
- We fixate on the regions of the scene that are important to us
- We also use information in peripheral vision to guide our next fixations
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What information has high and low resolution?
- Information falling on the fovea – highest resolution
- Information falling on other regions of the retina: lower resolution
- Need to move eyes to achieve clear visual input
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How can we measure selective attention?
- Measuring eye movements lets us measure which regions of the scene are most important/informative
- Done via camera-based eye-trackers
- We make approximately 3 fixations per second
- During saccades, vision is suppressed
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What is the cocktail party effect?
- The ability to follow one conversation while others go on around us
- Selective (auditory) attention by
- Use physical information about the speaker to maintain attention
Gender
Voice intensity
Location
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What determines how we scan a scene?
Stimulus salience
Our knowledge about scenes
Nature of the observer’s task
Learning from past experience
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How does salience affect how we can a scene?
- Salience: areas of the scene that attract attention due to their properties
Colour
Orientation
Contrast
- This is a low level, bottom-up influence
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What is inattentional blindness?
- Inattentional blindness: failure to perceive a stimulus that isn’t attended
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What is change blindness?
- Change blindness – a failure to detect that an object has moved or disappeared
- Occurs often when there has been a visual disruption
- Eye movements/brief occlusion of scene or image
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Does attention enhance perception?
attention to a stimulus makes it ‘more clear and vivid’
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Can perception occur without attention?
- Yes: Important/potentially salient information is processed without focused attention
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Does attention affect perception?
- Yes: Large changes go unnoticed if attention focused elsewhere (inattentional blindness) or viewing is disrupted (change detection)
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What is hemispatial neglect?
- Patients do not recognise that the left-hand side of the world exists (contralesional)
- But their visual fields are intact (no loss of vision on the neglected side)
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What is hemispatial neglect caused by?
damage to right posterior parietal cortex
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What is balint's syndrome caused by?
- Damage to the parietal lobe in both hemispheres
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What is balints syndrome?
- Three different impairments leading to an inability to perceive the visual field as a whole
- Difficulty in fixating the eyes
- Inability to visually guide the hand to a specific object
- Strong tendency to fixate/perceive only one item at a time
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What are treatments of balint's syndrome?
- Visuospatial retraining, e.g.
Training eye movements to improve visual scanning/convergence
Visuokinetic exercises (reading and tracing letters)
Visual search tasks (e.g. word searches)
- Functional adaptation, e.g.
Participation in daily activities i.e. shopping
Use of public transport (escorted and unescorted)
- Note of course that this is one patient- not all patients might be able to follow the same kind of retraining etc.
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What is motion perception?
- Perception of motion
When stationary, and things move around us
When moving ourselves
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Functions of motion perception?
- Disambiguation of shapes/objects and the image they project on the retina
- We can also take in more information about an object when we move around it
- Motion helps us compute the 3D shape of an object
- Motion allows us to determine heading direction and distance (motion parallax)
- Motion attracts our attention – (highly salient cue)
- Recognise other’s actions
- Motion gives us cues to interpret and understand situations around us
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Give examples of different types of motion?
- Real motion occurs when we perceive something moving across our field of view
- Illusory motion: perceive motion when nothing happens
Implied motion
Apparent motion (mentioned in L6)
Motion aftereffect (compared to facial adaptation, mentioned in L7)
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What is implied motion?
- Implied motion: stationary pictures can depict an action that involves motion
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What is apparent motion?
perception of motion when two static stimuli are played one after the other
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What are the two visual streams?
Ventral and dorsal
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What does the dorsal stem do?
- Dorsal stream for motion processing
To Medial Temporal (MT) region- motion processing, movement direction, overall global motion
To superior temporal sulcus (STS)- involved in biological motion
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What does the ventral stream do?
- Ventral stream for static processing
(faces/objects)
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What are neurons in the Medial Temporal selective for?
Motion directions
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What are neural responses in the medial temporal correlated with?
Perception of motion
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What does damage to the medial temporal cause?
- Damage to MT or temporary inactivation causes deficits in visual motion perception
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What does electrical stimulation in the medial temporal cause?
- Electrical stimulation in MT causes changes in visual motion perception
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What is motion coherence detection?
- Motion coherence detection: at what level can participants detect coherent motion accurately? What is happening in MT at this time?
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What happens when movement coherence increases ?
- Movement coherence increases: MT neuron firing increases (for specific neurons)
- Accuracy motion detection increases
- Specific neurons have a particular preferred direction
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Describe receptive fields?
- Each neuron has its own receptive field
- The region in space which the neuron repsonds to
- I.e. changes in this region will cause the neuron to respond
- Simple and complex cells
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What are simple cells?
- Simple cells: inhibitory and excitatory regions lie side by side
- Bar stimulus only in the excitatory section: high firing
- Bar stimulus that crosses into the inhibitory areas: reduced firing
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What are complex cells?
- Complex cells: Larger receptive field
- Respond when a bar moves over the entire receptive field
- For some, bar must also be moving in the right direction
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What are neural mechanisms?
- Motion selectively studies for both orientation and direction
- Demonstrate neurons are responsive to particular dimensions
- This is reflected in the neuronal arrangement
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What is the aperture problem?
how does the firing of a single neuron indicate the direction that an object is moving? Is a single neuron enough?
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What is distinguishing motion?
- Distinguishing motion: how do we perceive things that are moving when we are also moving
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What does observation of small portion of larger stimulus lead to?
- Observation of small portion of larger stimulus leads to misleading information about the direction of movement.
- Activity of a single complex cell does not provide accurate information about direction of movement
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What do MT neurons initially respond depending on?
- MT neurons initially respond depending on orientation
Bar moving L to R response = Bar moving L to R and Up)
- 140ms MT neurons respond depending on direction
Bar moving L to R response different to Bar moving L to R and Up)
- MT neurons are receiving signals from neurons in V1 that they combine to determine the actual direction of a stimulus’ movement
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What is akinetopsia?
- Akinetopsia, also called motion blindness
- A disorder in which the patient cannot see motion, although they are able to see stationary objects without any problem
- Colour vision and visual acuity, as well as face and object recognition, are all intact
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What happened in the case of Patient LM?
- Patient LM, 43yrs old at time of diagnosis, is the main source of most of our knowledge of akinetopsia
- Following a stroke: damage wide-spread across visual areas
No direct localization of relevant regions for motion perception possible.
- She was impaired at seeing coffee being poured into a cup, or seeing traffic move
- LM felt uncomfortable in a crowded room or on a street.
"People were suddenly here or there, but I have not seen them moving... “
“When I'm looking at the car first it seems far away, but then when I want to
cross the road suddenly the car is very near".
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What systems help us navigate?
- Vision
- The vestibular system
- Proprioception
- These three systems are key in the perception of self-motion
- Information from each must be integrated in other to successfully navigate
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What happens in terms of vision?
- As we move, there are changes in the retinal input
- These are analysed to determine movement direction
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What is alongside vision?
- Without vision, we are still able to know where our body parts are in the world
- And in relation to each other
- This is due to Proprioception
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What is proprioception?
- Proprioception: ability to sense the position of our body/it’s limbs
- And if/how it is moving through space
- A solely internal system – functions without vision
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What does proprioception tell us?
Where things are in relation to each other
If the body part is moving with enough effort
If changes need to be made to the amount of effort
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What are proprioceptors?
: the neurons found in the muscles/joints that send signals to the brain
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Where are proprioceptors found?
- Found in the muscles
Muscle spindles
- In the tendons
Golgi tendon organs
- And in the joints
Joint receptors
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What do muscles spindles inform us?
- Muscles spindles inform us about limb velocity and limb movement
How much the muscle is extended
How quickly this change happens
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What do golgi tendon organs inform us?
- Golgi tendon organs inform us about the level of resistance a muscle is experiencing
Indicates the load/weight being carried
- Joint receptors indicate when a joint is at a specific position
Typically, at the extreme position
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What is the Pinocchio illusion?
- Pinocchio illusion: manipulating the proprioceptors to affect experience of bodily shape
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What is the rubber hand illusion?
- The Rubber Hand Illusion: an experience of proprioceptive drift-transferring body ownership
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What are some impairments in proprioception?
- Many amputees continue to report a proprioceptive awareness of their amputated limb, they are aware of it’s position, and may feel they are able to move it voluntarily
- Amputation removes the visual feedback about the limb, but the proprioception remains
- ‘Proprioceptive memory’ (Anderson-Barnes et al., 2009)
- Phantom Limb pain (PLP): experience of pain/unpleasant sensations in the missing limb
- Amputees may also feel that the phantom limb is ‘frozen’ or stuck in position
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What is mirror therapy?
- Treatment of PLP
Patients view a reflection of their intact limb in a mirror, making is appear that the amputated limb is now intact
- The intact limb is moved (flexed, extended, etc)
- Evidence that the therapy reduced PLP
- Relinking of visual feedback and proprioception
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What is the vestibular?
- System for balance – found in the inner ear
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What are inputs of the vestibular?
- Forces produced by body and head movements
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What are outputs of the vestibular?
- Eye movements (compensate for head motion – VOR)
- Movement sensations
- Posture changes (stabilisation)
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What do otolith organs do?
- Perceive linear force
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What do semicircular canals do?
Perceive angular foce
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What are the three types of angular motion?
- Pitch: y-axis, forward/back (e.g. noddling)
- Roll: x-axis, left/right (e.g. doing a cartwheel)
- Yaw: z-axis; around itself (e.g. doing a pirouette
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What are the two types of otolith organs?
- Utricle (horizontal); saccule (Vertical)
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What is the role of otolith organs?
- Give information about displacement and acceleration
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What are the three types of semicircular canals?
- Three types of canals – anterior, posterior and horizontal
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Where are the three different types of semicircular canals positioned from each other?
- Positioned at 30 degrees to each other
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What happens in the semicircular canal at rest?
- At rest: equal signalling from both left and right canals
- Left turn: endolymph flows to left
- In left SCC: increases signals (excitatory)
- In right SCC: decrease signals (inhibitory)
- Integration of signals: interpreted as a leftwards turn
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What are some dysfunctions of the vestibular system?
- Inflammation of the inner ear- affects the equilibrium within the system
Vertigo (dizziness, spinning sensation)
Nystagmus (involuntary eye movements, blurred vision)
Nausea
- Alcohol also affects the density of the endolymph
- Hair cells can be deflected more easily, small movements feel larger
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What is BBPV?
- BBPV (Benign paroxismal positional vertigo)
- Parts broken off the otolith organs which slip into semicircular canal
- Due to head trauma or age
- Exercises to remove the broken stones can be performed to fix the problem when only a few stones are involved
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What are some illusions of the vestibular systems?
- Vestibular illusions can be problematic in aviation – particularly when vision is low (clouds/darkness)
- Examples:
The leans: vestibular illusion
Graveyard Spin: adaptation
Graveyard Spiral: adaptation
Heads Up Illusion: vestibular illusion
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What is the leans illusion?
- Failure to detect a lean leads to overcompensation
- Occurs when a turn is started too slowly- which is not detected by the semicircular canals
(Rotational acceleration of < 2 deg/s is below the detection threshold of the semicircular canals.)
- Pilot perceives that they are still straight and level
- Abrupt correction to level flight- pilot feels they are turning in the other direction
- Pilot compensates, leaning into original turn
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What is the graveyard spins illusion?
- The result of adaptation to motion
- After a spin begins, there will eventually be adaptation by the hair cells
- When the spin stops, the fluid in the canals moves in the opposite direction
- Although the spin has stopped, there is a perception of turning in the opposite direction
- To compensate, pilot re-enters the spin in the original direction
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What is the heads up illusion?
- Problem when pilot is taking off
- Otolithic organs respond similarly to tilting the head or acceleration
- Acceleration can lead to perception of moving upwards
- Pilot corrects downwards to compensate
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What does the integration of our systems do?
- Integrating visual, proprioceptive and vestibular information helps us orient in our environment
- Integration of vision and vestibular: Vestibular Ocular Reflex (VOR)
- Stabilisation of images on the retina during head movements
- Compare moving your hand in front of your face to moving your head back and forth while looking at your hand
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What are steps of VOR?
- Head moves to left
- Excitatory signal from right SCC
- Excitation of nerves moving eyes to the right
- Inhibition of nerves moving eyes to the left
- Vice versa for the right
- A reflex action- no conscious input
- Works in darkness
- Necessary for reading
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What are some disagreements in VOR?
- Disagreements between visual and vestibular information can lead to nausea
- Motion sickness: e.g. seasickness or car-sickness (particularly when trying to read)
- When reading- peripheral visual information indicates movement while you are focusing on a stationary page
- Vestibular system indicates motion: but no strong visual perception of this
- Disagreement= nausea
