Perception Flashcards
-Evolution -Audition -Vision (203 cards)
1
Q
What is evolutionary anachronism?
A
• Evolutionary anachronism- attribute of living species best explained as a result of having been favourably selected in the past due to coevolution with other biological species that have since become extinct
2
Q
Who should we compare ourselves to when looking at human cognition and why?
A
• When looking at cognition, we shouldn’t compare ourselves to computers or gods, but to animals because we are animals
o We have the same ancestors as animals
o Understanding ourselves means looking at the antecedents of our parts and processes in our ancestors
o Our ancestors evolved to win competitions
o Darwin suggests that we are no different from animals, as any cognitive ability we have is in some shape of form also in lower animals
3
Q
Have we evolved from modern monkeys?
A
o We have common ancestors with modern monkeys, we haven’t evolved from modern monkeys
4
Q
What is the problem of studying animals for human cognition?
A
Can’t look at animals today as we haven’t evolved from them, and ancestral monkeys we have evolved from are dead
5
Q
What is a primary adaptation?
A
• Primary adaptation- original adaptations
6
Q
What is a vestigial adaptation?
A
• Vestigial- Was an adaptation for the organism’s ancestor, but evolved to be non-functional because the organism’s environment changed
7
Q
What is an exaptation?
A
• Exaptation-Trait that has been co-opted for a use other than the original adaptational use due to a difference in environment
8
Q
What is a secondary adaptation?
A
• Secondary adaptation-enhances the exaptation function
9
Q
Describe the adaptation and vestiges of the human spine
A
o For example, the spine
Coccyx and tailbone- tail useful in trees to grasp branches
Curved spine- shock absorber for walking
Spine exapted to hold us up
Secondary adaption to improve shock absorbance
10
Q
What type of adaptation is piloerection for humans?
A
o For example, piloerection
Good for animals with spines, but vestigial for us
11
Q
What is the blink reflex (reactions and purpose)
A
o For example, the blink reflex
A bright light suddenly shone into the eyes, a puff of air upon the sensitive cornea or a sudden loudnoise will produce immediate blinking of the eyes
Purpose- to protect the eyes from foreign bodies and bright light
May be associated tensing of the neck muscles, turning of the head away from the stimulus, frowning and crying
12
Q
Is our brain made for modern uses?
A
• Most (99%) of our brain was made to suit the needs of our animal ancestors, not what we’re trying to do with it now- evolution is slow
13
Q
In what ways is animal psychology and human psychology percieved differently?
A
o Animal psychology Foraging and food choice Predator avoidance Mate choice and courting Communication o Human psychology Perception Cognition Intelligence Language
14
Q
Describe the bag of tricks metaphor for our brains and why it is useful
A
• Bag of tricks metaphor-
o Computer metaphors are used a lot for cognition, but we should not be looking at computer metaphors as computers can do a lot of general things- we can only do specific ones
o We have a specific collection of tools/cognitive faculties
o Bag of tricks has more animal perspective
o Big concepts are not a useful unit for analysis
• Question of what cognition evolved for may be too general
15
Q
What are the 4 types of explanation for a phenomenon?
A
- Proximate explanation-closest explanation to the event that is to be explained
- Developmental explanation
- Neuroscientific explanation
- Functional evolutionary explanation
16
Q
What is the central interest of evolutionary psychology?
A
o Evolutionary psychology is interested in which, and how many, behaviours and mental processes, evolved as the result of specific issues that our ancestors faced
17
Q
What are barriers to people accepting functional evolutionary explanations?
A
o Barriers to the functional evolutionary explanation
People think they are more like gods than animals
Lack of understanding of evolution
Belief that human qualities are not qualities animals have -> tend to identify with higher cognitive abilities that we believe animals don’t have
18
Q
In modern times, is the mentality that we are far away from animals cognitively increasing or decreasing?
A
• However, this mentality is decreasing in some instances and increasing in others
o There is greater acceptance of similarity of animals to ourselves- when people are vegan or vegetarian for ethical reasons
o Feminism is not animalistic-due to our history and culture, we want to close the gap between man and woman whilst in terms of the animal kingdom, there is a large difference between the two sexes
19
Q
How can we find if something is innate rather than learned?
A
• To find if something has evolved or is learned, need to examine something important in our ancestral environments, but not so important in the environment of kids and adults today, so that a special response to it is unlikely to be learned
20
Q
Describe New, Cosmides and Tooby 2007 study, as well as potential confounds
A
o Animals were very important for almost all humans and their ancestors, until very recently (when we started living in species)
o Animals are especially important to keep track of (prey and predators), so arguably should be attended to more
o If evolutionary demands shaped specific aspects of attention, then attention should be spontaneously directed to animals more
o New, Cosmides and Tooby 2007 study
Change blindness study
If evolutionary history dictates what we turn our attention to, then images with changes involving subjects should be detected in this hierarchy
• People
• Animals
• Plants
• Moveable/manipulable artifacts designed for interaction with human hands/body
o Brain is responsive to tools
• Fixed artifacts construable as topographical landmarks
o Important for navigation but don’t expect these things to move
Results of upright condition-
• People and animals had a significant detection advantage- attention was drawn towards them when they changed
Confounds-
• Backgrounds, locations, visual features, color differences, texture differences, spatial frequency differences of the target are changed between pictures
To address confounds, did inverted conditions
• Found that people and animal advantage was removed
Hence can conclude that confounds not reason that people and animals drew increased attention from subjects
21
Q
Describe the New and German 2015 study as well as potential problems with it
A
o New, German 2015 study-
In an evolutionary psychology view, should be less susceptible to things that are real threats now if it was learned rather that evolved
Claimed that spiders can surmount inattentional blindness by using different spider shapes and comparing them to needles
Inattentional blindness model
Found that only the certain spider shapes had a detection advantage over non-spider shapes, except for the flower shape which puts in question the results
There is a problem with these results as we don’t know what visual features the brain responds to the most
This experiment was also done on adults, so the innateness of spider detection is questionable-do we learn to be afraid of spiders due to our cultural education or is it innate
22
Q
Describe which part of the brain is extremely responsive to faces
A
• Part of temporal lobe (fusiform gyrus) extremely responsive to faces
23
Q
Describe the Kanwisher, Chun and McDermott (1997) experiment on facial recognition
A
• Experiment- Kanwisher, Chun, McDermott (1997)
o Showed faces to people and would look at responsiveness in the brain compared to other objects such as hands or other visually similar objects (to control for visual features)
o Scrambled stimuli as a control condition with the intention of preserving the visual features
So stimuli were arranged as a face vs not face but using the exact same shapes
But maybe manner in which stimulus was broken up disrupted visual feature that the brain area cared about
o Larger responses to faces in all conditions
24
Q
Describe why inversion is a better design than scrambling to eliminate visual feature bias
A
• Inversions of something makes it harder to recognise them as an object (although visual features are maintained and no disruption occurs)-less confounds than scrambling features
• Inverting photos perfectly preserves their lower- level stimulus properties but makes identifying the semantic category to which a target belongs more difficult
o The low level stimulus properties (colours, textures, shapes) are still processed very similarly but the system no longer easily recognises what is a person and what is an animal
o With the system not recognising the people and animals as people and animals in the inverted case, it is therefore no longer predicted that the people and animals should have an advantage
• If lower level properties are causing the animate attention advantage, then it should appear even when photos are inverted. In contrast, if the attentional bias is category-driven, then manipulations that interfere with categorization but preserves lower-level perceptual features should eliminate the animate change-detection advantage
25
Describe how the brain evolved and how it is currently used
• There is no general problem-solving system because we did not have general problems. We had foraging and food choice problems, mating problems and social problems
o Hence the bag of tricks metaphor
• But, at some point, we developed fairly general problems solving
o Most human organs have specific function, but the brain can multipurpose
Primary adaptation of brain-foraging, mate choice…
• Brain started out as a bag of tricks
Secondary adaptation of brain- gaining more neurons allowed us to do a wider range of things
• Brain didn’t originally evolve to have such general abilities
26
Describe how we should look at the brain if the brain is like a bag of tricks
o If the brain is a bag of tricks, it makes sense to look at specific things it’s adapted to do
27
Describe how we should look at the brain if the brain is like a general purpose device. What are the disadvantages of this metaphor?
o If the brain is a general purpose device, it makes sense to look at its building blocks to understand its particular character
But easy to fall too hard for this metaphor, and think that we are a general purpose computer with few constraints on thinking, planning or language
Instead we have many limitations, and don’t do things like a conventional computer
28
How should we determine ancestral adaptation and what a function originally evolved for/how it has evolved?
o Fossil record
o Organisms that have adaptation in one stage of life but not another stage of life
o Organisms that have adaptation versus those that don’t have adaptation
o Exaptations- features with functions for which they were not originally selected
Look at what organisms seem to use it for
29
What is thought to be the first organism who evolved neurons?
Think that organisms that would have had the first neurons were jelly-fish like systems
• Contraction for movement requires a fast and coordinated neuron system
30
Why are neurons needed for the peristaltic wave and what is it?
• This need for a fast and coordinated neuron system can also be seen in other organisms such as humans
o Need a fast system for the peristaltic wave
The muscular action of the digestive tract moves food continuously in an action known as a peristaltic wave
31
Describe the life cycle of the tunicate and what it demonstrates about neurons
E.g. Tunicate
• Will swim around for most of their life
• Beginning of lifetime-
o Has only got 100 neurons
• Then have another stage of life where they set up on a nice rock and go through metamorphosis
o During metamorphosis, they eat their own brain
o Neurons become deconstructed
• The now immobile form of the tunicate becomes filter feeder and waits for plankton
• When it has neurons, a lot of them are stimulating muscles so tunicate can swim around, but when it has eaten them, it can no longer move
32
Describe the difference between plant and animal signalling systems
Plants don’t have neurons but can still move-they still have a signalling system but it’s extremely slow
Animals with neurons-neuron signalling system is very fast
33
Compare chemical diffusion to neuronal action potentials and justify why neuronal action potentials evolved in comparison
• Neurons allow for rapid transmission around the body, allows repeated rhythmic signalling
o Faster than hormonal communication/chemical diffusion, which is what plants and some organisms exclusively have. Chemical diffusion has
Slow propagation
Little specificity
Variability in how much signal reaches destination
Sluggish on and off
o Neuronal action potentials allow for
Fast speed up to 50m/s
Point-to-point specificity
Precise amount of signal reaches destination
Can stop quickly
• Rapid inhibition means that signalling can stop quickly: no straggler signals
34
Why did neurons evolve?
• Neurons allow for rapid transmission around the body, allows repeated rhythmic signalling
• Neurons provide synchronisation needed for movements-coordinated movements
o Can be done with weak connections that excite each other: central command not needed
Combination of neurons following own rules and hubs sending rules to neurons
• Intricate patterns required
o Partly innate, partly learned
35
Describe what allows organisms to walk in terms of evolution and learning
E.g. walking has to be coordinated-only able to walk easily due to large ancestral lineage working on locomotion
• Million years of evolution allow for walking in organisms but still requires a slight learning process and hence some period of interacting with the world
o Needs interaction with the world for brain to adapt to length of muscles and other features needed for walking as adaptation can’t predict exact measurements of organism. Also need learning to work out muscle coordination based on feedback
Walking is much the same as it was a million years ago: perceptual demands are not too different but what we have to do cognitively is very different
o Animals need to perform intricate complex patterns of synchronisation and oscillations so that they don’t fall over
36
What nerve system generates patterns of oscillating units with complex relationships- some in synchrony, others not
Spinal cord
37
What is the advantage and disadvantage of humans evolving to being born at a particular immature stage?
o Humans evolved to be born at a particularly immature stage
Disadvantage is that not much is pre-programmed
• Many animals have to function independently almost immediately, but young humans can’t do much: rely on learning to achieve perception, cognition and intelligence by developing a network
Advantage- our neurons experience plasticity at longer amount of time and hence we can learn a lot of information that is arbitrary
38
Why is programming robots to walk extremely hard?
• Programming robots to walk using computer-type information processing is really hard
o Computer programs traditionally are expected to work perfectly even the first time they run, which is not true of humans
39
Why is hearing important?
• Allows us to locate stimulus events in the environment and represent the world internally
• Inform us about our environmental surroundings
• Auditory perception is omnidirectional and constant
o Cf vision: we can hear behind us, and with eyes closed
• Vital to human communication
40
What is the definition of sound?
• Sound is a repetitive change in air pressure over time -series of compressions and rarefactions
41
What kind of wave is sound?
• Sound is a longitudinal wave (oscillates along its axis)
| o Expands from a source in 3D (spherical wave)
42
How is sound represented?
o Often represented as a sine wave, but this is an oversimplication
43
How does sound travel?
• Sound travels through space as waves (acoustic vibrations) with long sound waves
o Surrounded by particles in the atmosphere
44
What are the wavelengths of audible sound waves?
• Audible sound waves have wavelengths from 0.0172m to 17.2 m
45
Can sound bend around corners?
Yes
46
Is sound reflected or produced by its source
• Sound is usually produced by its source rather than reflected
47
Describe the inverse square law
• Sound waves expand over distance and lose intensity
| o Inverse square law- sound intensity decreases with the square of distance
48
Describe what sound is absorbed by and what is this affected by
• Sound energy is absorbed by the air, more for higher frequencies and hence higher frequencies are more easily muffled
o Attenuation of pressure over distance varies as a function of frequency
49
Describe the 3 perceptual attributes of sound and what they are affected by
* Frequency-perception of frequency is pitch
* Amplitude- perception of amplitude is loudness
* Complexity- perception of complexity is timbre
50
Describe the human hearing range
o Human hearing range is approximately 20-20000Hz
51
Describe the little brown bat hearing range
little brown bat can hear 10.3kHz-11.5 kHz
52
Do we hear all the frequencies in the world?
We don’t hear all frequencies- organisms only select a small narrow band
53
Are pitch and frequency identical?
No, but they are related
54
What is the Mel scale? Describe the relationship between the Mel and Hertz
The Mel scale: a scale of pitch (perceived frequency) rather than Hz. Equal Mel steps are perceived as equal intervals.
• Mel plot is a scale of pitch, not frequency
• Below 1000Hz, the Mel and Hertz scales coincide (linear relation)
• Above 1500Hz, bigger frequency steps are needed to maintain equal perceived interval -relationship becomes non-linear
55
What produces loudness and what is it measured by?
o Loud sounds are produced by larger oscillations
o Intensity of compression is loudness
o Loudness is measured in decibels
56
What do decibels measure? How do you work out decibels?
o Decibels measure changes in sound pressure
Number of decibels= 20* log(P/Pref)
• How many times louder is a sound than the minimum sound that could be heart
• +6dB is a doubling of sound pressure level
• -6dB is halving of sound pressure level
57
How can sound pressure be measured?
Sound pressure is measured on a relative scale: relative to detection threshold (Pref: the minimum sound a healthy human ear could hear)
58
What is the minimum sound threshold?
• In a quiet environment, 20 micropascals is minimum sound threshold
59
What does loudness required to detect a tone vary with?
o Loudness is frequency dependent- sound pressure level (loudness) required to detect a tone varies with frequency
o Equal loudness requires different intensities over frequency
Contour is flattest at moderate sound levels
60
What is the most sensitive frequency range and why?
Sensitivity is best from 500-4000Hz as need small sound pressure to detect these frequencies (coincides with speech frequency range)
61
How many hertz are vowels and fundamental frequencies?
• Smaller than 1000Hz: vowels and fundamental frequencies
62
How many hertz are consonants?
• Higher than 1000Hz: consonants
63
At what loudness are all frequencies uniformly sensitive?
80 dB
64
What is complexity?
o Complexity- a fundamental frequency (lowest frequency) gives a complex sound its pitch, but higher harmonics in various proportions give it timbre (or colour)
65
What defines pitch?
Lowest harmonic defines pitch as it’s the lowest common divisor of the harmonics- even if lowest harmonic is filtered out, the brain derives it and you still perceive it (periodicity pitch)
66
Why do different instruments have a different timber
o Different instruments have a different timber because their higher harmonics differ (i.e. number, amplitude phase of harmonics varies between instruments and human voices)
67
What is timber and what is it determined by?
o Temporal components also determine timbre
| o Timber- complex patterns added to the lowest, or fundamental, frequency of a sound, referred to as spectrum envelope
68
What is the use of a spectral envelope?
o Spectrum envelopes enable us to distinguish multiple instruments
69
What do multiples of fundamental frequency give?
o Multiples of fundamental frequency give music
70
What do multiples of unrelated frequencies give?
o Multiples of unrelated frequencies give noise
71
What is the outer ear composed of?
Composed of skin and ear canal
72
What is the purpose of the outer ear?
Gathers and directs sound into ear canal: amplification of mid-frequencies through canal resonance: vertical direction coding
Coarse amplification
73
What is the purpose of the middle ear?
Amplifies signal for inner ear (impedance matching)
Much less than 1% of sound energy passes from air into water
Middle ear amplifies sound in 2 ways better to drive the fluid-filled inner ear
• It drives a small plate on the inner ear with sound energy collected from a large area
• The malleus is 2x longer than the stapes, boosting the signal using mechanical leverage
74
What is the middle ear composed of?
Composed of malleus, incus and stapes
| Filled with air
75
Describe the role of the inner ear
Location of auditory receptors: frequency analysis: transduction of physical signal to neural impulses
76
Describe the composition of the inner ear
Cochlea is fluid-filled and contains primary receptors
| Composed of cochlea
77
Describe the basilar membrane and its role in encoding frequency
o Basilar membrane has differing thickness and width, which is why only some parts of it will start vibrating depending on the frequency
If oscillation at the base, it is a high frequency
If oscillation at the tip, it is a low frequency
o Depending on which nerve fibres which are attached to basilar membrane are activated, brain knows the frequency
78
Describe what range the cochlea works best
But not a perfect code- works best between 500-3500Hz
| • Within a range of 500-3500Hz, pitch is determined by the location of the standing oscillation on the basilar membrane
79
Describe the pathway of the ear
• Ear pathway
o Sound goes through ear canal and hits the tympanic membrane (ear drum) and makes it oscillate
o Anvil, hammer and stirrup are moved by ear drums vibrating and stirrup (which is attached to the cochlea) and sets up standing wave and oscillation in cochlea
o Cochlea is full of fluid- bones are levers that crank energy up enough to get fluid filled cochleal membrane vibrating, and where it vibrates is the frequency that will be heard
80
What sits on the basilar membrane and what does it attach the basilar membrane to?
• Hair cells sit in rows on the basilar membrane
o Inner hair cells- 1 row
o Outer hair cells- 3 rows
• Fine hairs known as cilia protrude from the hair cells and attach to a roof called the tectorial membrane
81
What dorms the auditory nerve?
Axons from inner hair cells bundle together to form the auditory nerve
• Only sparsely do the outer hair cells go up to auditory nerve
82
What is the function of inner hair cells?
Inner hair cells signal the basilar membrane oscillations to the central nervous system (like ganglion cells in the eye)
83
How many inner hair cells are there?
About 3,500 inner hair cells
84
What is the role of outer hair cells?
These add to the mechanical movement
A process called electromotility helps amplify basilar membrane
Outer hair cells actually change shape to help push/pull the roof, boosting the shear driving inner hair cells (and the signal they send to the brain)
• Not passive basilar membrane oscillation
85
How many outer hair cells are there?
About 12,000 outer hair cells
86
Can hair cells be damage? What can damage them?
o Hair cells damage easily and some antibiotic drugs- once the hair cells are damaged, they cannot be regenerated
High amplitude oscillations on the basilar membrane cause the cilia to break from too much shearing force
87
What is the impact and cause of outer hair cell damage?
Outer hair cell damage- raises threshold, and broader bandwidth
• Increased bandwidth means less selectivity: sounds are blurred and less distinct
• Common cause- loud music
88
What is the impact and cause of inner hair cell damage?
Inner hair cells- raised thresholds, normal bandwidth
| • Common cause- disease or infection
89
What is sensorineural deafness and what are the symptoms of it/how can they be treated?
Sensorineural deafness- damaged outer hair cells (mostly) also inner hair cell damage may be associated
• Inner hair cells
o Thresholds increased and filter bandwidths normal
• Outer hair cells
o Thresholds increased and filter bandwidths increased
• Symptoms
o Raised thresholds
Can be helped by amplification
o Wider bandwidths
No help possible
o Recruitment (restricted dynamic range)
Partly helped by automatic gain controls in modern digital aids
o Often accompanied by tinnitus
90
How do cochlear implants work?
• Cochlear implants
o When hair cells are dysfunctional
o Stimulates nerve fibres on basilar membrane
A long fibre with 20 spaced electrodes is wound into the cochlear
External microphone records acoustic signal
Signal is filtered into 20 passbands and sent to the electrode
Electrical acitivity from electrode activates adjacent inner hair cells
Latest devise uses 28 channels
91
What is the disadvantage of cochlear implants?
o Cochlear implants are very poor at conveying musical pitch and melody (bandwidths are quite broad: poor pitch and timber)
o Also hard to localise the sound source with cochlear implants
92
What is conductive deafness and its symptoms?
Conductive deafness- middle earbones not working, little signal transfer to inner ear
• Increased thresholds and normal filter bandwidths
• Can be caused by ear infection
93
Does hearing loss have to be present in all frequencies?
o Hearing loss can be specific to certain frequencies
94
What is the roof of the cochlea?
Tectorial membrane
95
How does the cochlea transmit signals to the auditory nerve?
o Acoustic signal drives ear drum, middle-ear bones and makes the basilar membrane oscillate
The oscillating basilar membrane creates a shearing force
The shear flexes the cilia, causing a mechanical gate to open and close ion channels, generating neural impulses
o This oscillation makes the cilia push up and pull down on the roof, flexing the cilia
o The moving roof triggers inner hair cells to send signals along the auditory
96
How is frequency encoded?
* Place code: perceived frequency is coded by local location on the basilar membrane
* Frequency theory-encode frequency by counting spike rate
97
Describe the basis of the place code theory
• Place code: perceived frequency is coded by local location on the basilar membrane
o Need to keep track of where inner hair cells are located on the basilar membrane
o Basilar membrane oscillates at different locations, depending on frequency (known as tonotic mapping)
Low frequencies drive the tip (apex), high frequencies the base
o Complex waves decompose into comments, producing several local oscillations
98
At what frequencies does the place code theory work?
o Place code theory explains high frequencies above 800 Hz best
o Works well for high frequencies
99
Describe the basis of the frequency theory
• Frequency theory-encode frequency by counting spike rate
o Spikes from inner hair cells occur at the peak of the modulation
Once per cycle, will get spike from auditor nerve fibre so can get response that is phase-locked to the input and read that off as a code for frequency
This is due to phase locking among groups of inner hair cells to ensure all spikes are signalled
o Frequency (temporal) theory
Periodic stimulation of membrane matches frequency of sound
• One electrical impulse at every peak
• Maps time differences of pulses to pitch
100
At what frequencies does frequency theory work best and why?
o Spike timing has a limit- at higher frequencies, not ideal
Phaselock spike responses can encode frequencies up to 1000 Hz
• Sometimes misses a spike, even at low frequency
• Misses a lot of spikes at high frequency
Frequency theory explains best frequencies below 1000 Hz
Works well for low frequencies
101
What theory is used for middle range frequencies?
Place code and frequency theory
102
Describe the volley theory and what it explains
Humans can hear much higher frequencies than maximum neural firing rate
• Volley theory-groups of neurons fire in well-coordinated sequence. Rate theory with a shared load among several fibres
103
What does the auditory nerve connect?
• Auditory nerve-a bundle of fibres connecting the cochlea to the cochlear nucleus
104
How is each auditory nerve tuned and how can this be shown?
o Auditory nerve fibres narrowly tuned in frequency because each samples a narrow spatial section along basilar membrane
o The filter tuning of each fibre can be shown by frequency masking studies
• The fibres in the auditory nerve are narrow filters, responding to a small range of frequencies
o Auditory nerve fibres have a fixed bandwidth
105
How can frequency masking studies be used to determine filter tuning of each fibre?
o The filter tuning of each fibre can be shown by frequency masking studies
When there is a bandwidth around the noise, the signal can be masked
• Portion where had to turn up intensity of signal for it to be the same
• Zone of masking determines how wide the channel is
106
What is the relationship between too wide bandwidth and signal masking?
When bandwidth widens so much, the signal stops being masked
107
Describe how to calculate bandwidth in terms of frequency
o Full bandwidth is approximately an eighth of the frequency
| f/8=12.5%
108
Are low or high frequencies impaired the most in hearing loss? What is the impact of this?
* Hearing loss, whether noise-induced or due to normal ageing, impairs high frequencies most
* This dramatically degrades speech comprehension. Although speech is composed of low-and high-frequency sounds, the high frequencies contribute more to speech intelligibility
109
What happens at the superior olive in terms of audition pathway
• Pathway becomes binaural at the brain stem (in superior olive)
110
How is sound organised in the primary auditory cortex?
• When get to primary auditory cortex (area 41), sound is organised by frequency and time
o Primary auditory cortex is organised by frequency
111
Is discriminating auditory signal possible without the auditory cortex? How?
* Discriminating auditory signals is possible without auditory cortex
* Process signals such as pitch, direction, melody can be done peripherally
* Auditory cortex only analyses complex aspects of sound
112
Describe the two parallel streams in the cortex for context and location
• As in vision, there are two parallel streams in cortex for context and location
o Dorsal stream (parietal lobe) analyses components to find context
o A ventral stream (temporal lobe) analyses spatial cues to find location
113
How are auditory spatial locations specified and why?
• Auditory spatial locations specified in coordinates of azimuth and elevation due to spherical space
114
What does azimuth mean?
left/right angle
115
What is azimuth encoded by?
Encoded by binaural cues (require both ears)-Interaural time difference and Interaural level difference
• Difference between time it takes for signal to hit far ear vs near ear
o This changes with azimuth
• Interaural time difference and interaural level difference are both binaural cues to azimuthal location
116
How can interaural time differences be calculated?
o ITD=tR-tL
tR-time for sound to travel to right ear
tL-time for sound to travel to left ear
117
What is the maximum time difference between two ears and when does this occur?
0.6ms
| When sound fully 90 degrees to the sound
118
Where are interaural time differences processed in the brain?
o Processed in medial superior olive
119
Describe the Jeffres 1948 model and the evidence for this model
o Jeffres 1948 model
Could easily detect the time lag between each ear with a series of coincidence detectors due to different path lengths
Only in one coincidence detector will the left and right ear signals hit at the same time, which indicates where sound is
• Coincidence detector cells would only respond when simultaneously activated from left and right sides
Clear evidence for this model in birds, but less in mammals
120
Describe the two channel Interaural time difference model
o Two channel ITD model
Suggests a balance of two ITD channels is used
A change in balance between the left and right channels determines lateral position
Two sets of neurons- one neuron has a peak for negative time differences and another for positive time differences
• Then calculate relative contribution of these two neurons
121
What is the basis of interaural level differences?
• Interaural level difference (ILD)
o Near ear gets signal first, it also gets the sound louder
o Far ear gets signal last, sound is softer when it reaches it
Due to absorbance of sound by the ear
122
Where are interaural level differences processed?
o Gets processed in lateral superior olive
123
Describe the effect of dB and frequencies on interaural differences
o For high frequencies, ILD at shadowed ear can drop as much as 20 dB at 90 degrees, and can exceed 20 dB for really high frequencies
High frequencies get absorbed more easily, low frequencies have lower changes in sound levels
124
At what frequencies are interaural time differences and interaural level differences used at?
* Interaural time differences are used at low frequencies
| * Interaural level difference are used at higher frequencies
125
Which is more precise/robust- interaural time differences or interaural level differences?
• Interaural time differences are generally more precise/robust than interaural level difference • Interaural time differences are generally more precise/robust than interaural level difference
126
What does elevation mean?
up/down angle
127
How is elevation encoded?
Encoded by monaural cues (special filtering)-from outer ear
128
How does spectral filtering work?
• Outer ear has convolutions which are non-symmetrical: this makes certain sounds focused and defocused on varying amounts
• Pattern of reflections is different for every point in space
o Every ear is unique
• Pinna (outer ear) filters high frequencies
• The pinna is asymmetrical, therefore the filtering pattern of gain and loss of sound is unique for each direction
o Brain associates pattern of sound intensity/spectral pattern with specific location
o Spectral pattern of ears is learned, not innate as ear pattern is unique to each individual
129
Are monoaural cues as reliable as binaural cues?
• Not as reliable as binaural cues: judging location by spectral received at the ear can be misled by the content of the signal
130
How is distance coded through hearing?
o Distance also needs to be coded. Several cues are used:
Absolute level, spectral balance, reverberation
Distance perception is not precise
131
Describe the auditory pathway
• Cochlea-> Cochlear Nucleus-> Decussates and binaural combination at superior olivary nucleus-> inferior colliculus-> Medial geniculate nucleus -> auditory cortex
132
What is the precedence effect and its basis?
• Often, the same sound is heard in quick succession from different directions with delay
o Common cause is reverberation
• Provided delay isn’t very big, the brain ignores reflections as it recognises them as echoes
• The precedence effect- When a sound is followed by another sound separated by a sufficiently short time delay, listeners perceive a single auditory event; its perceived spatial location is dominated by the location of the first-arriving sound
133
What is the precedence effect for clicks?
o For clicks, precedence holds for up to 5 ms delay
134
What is the precendence effect for complex sounds?
o For complex sounds, precedence holds for up to 40ms delay
135
How are successive sounds encoded beyond the precedence limit?
o Beyond the precedence limit, the second sound is heard as an echo
136
Describe background noise in terms of frequency
• Background noise is generally random and low-frequency biased (pink noise-low frequencies)
137
Describe speech background noise in terms of frequency
• Background noise from speech occurs at higher frequencies (speech frequency: 500-4000 Hz)
138
How do noise-cancelling headphones work? What are they useful for and what are they not useful for and why?
o Current active cancelling technology works best for frequencies below 500 Hz
o But noise from human speech is not cancelled
• Noise-cancelling headphones turn down noise but can still hear speech
• A microphone captures external sound, an inverted signal is played through speakers in the headphone enclosure
o Because opposite signals sum to zero, the sound should be cancelled
• Noise-cancelling headphones do not work for high frequencies because need to sample the sound to be cancelled, then play the anti-phase version to cancel the unwanted noise, which takes time. A short latency doesn’t matter for low frequencies (low wavelengths, more margin for error) but prevents cancelling of high frequency.
139
How does colour cohesion occur in the brain and what is the impact of this on colour perception?
• Interpreting colour reaching the eye requires brain to make sense of 2 different properties:
o Illumination properties
Illumination can vary
o Reflective properties
• People who see colours differently are making different estimates of these two properties
• Brain transforms continuous variation of light into qualitatively different experiences of colour
140
What is light?
• Light is an electromagnetic wave
| o Nanometer wavelengths
141
What is the visible light spectrum?
o Photoreceptors absorb light from 400-700nm of light
142
How does light move?
• Light moves in a straight light- acts as a particle
| o Dual wave-particle nature
143
Describe how refraction occurs and why, as well as the effect of wavelength on refraction
• In changes of optical density, light bends (refracts) at that interface, but bends in a specific way-
o Shorter wavelengths bend the most and the longest wavelengths bend the least- creates a rainbow
144
What are two different reflection types and how do they work?
o Specular reflection-
1: 1 mapping between the direction of the incoming light and the outgoing reflection
• Angle of incoming light is same as angle of outgoing reflection
o Diffuse reflection-
Outgoing light is scattered off the matter
Light penetrates object, some light is absorbed and some light is reemitted
Reemitted light is the colour of that object
• The colour of a material is associated with its diffuse reflectance
145
What is non-chromatic material?
Non-chromatic: all wavelengths are reflected equally in equal proportions
146
Describe the geometrical optics definition and assumptions
• If the dimensions of obstacles or apertures are much larger than the wavelength of light, then light can be treated as if they are rays that move in a straight line
• This forms the basis of geometrical optics
• The simplifying assumptions of geometrical optics includes that light rays:
o Propagate in straight-line paths as they travel in a homogeneous medium
o Bend, an in particular circumstances may split in two, at the interface between two dissimilar media
o Follow curved paths in a medium in which the refractive index changes
o May be absorbed, reflected or transmitted
147
Describe important features of the human eye including:
- Layers
- Choroid
- Aqueous humour
- Cornea
- Lens
- Fovea
- Periphery composition
- Optic disk
```
• Three layers-
o Fibrous tunic
o Vascular tunic
o Retina
• Choroid- nourishes photoreceptors
• Aqueous humour is generated by the ciliary body in the anterior chamber. Maintains pressure (failures to do so gives rise to glaucoma)
• Cornea- biggest refraction occurs at the cornea due to differences between air and cornea density
• Lens- fine tuning
• Fovea- has no rods, only cones
• Periphery- has rods
• Blindspot-optic disk
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148
What is sclerosis?
• Sclerosis (stiffening) of lens with age
149
How do we sample images?
• Two different types of photoreceptors- duplicity theory of vision (Kries 1896)
o Use two different classes of photosensitive receptors that operate in different luminance regimes
150
What is scotopic vision?
low-light, rod dominated
151
What is photopic vision?
high light levels, cone dominated
152
What part of the eye do we attentionally point at objects and why?
• When looking, pointing the fovea at object (this is the highest resolution part of the eye)
153
What is eccentricity in terms of vision?
• Eccentricity- Fovea is reference point- how far out from the fovea subject is
154
Are rods or cones more sensitive?
Rods
155
Why are rods more sensitive than cones?
• Rods are more sensitive than cones
o Rods absorb light better
Takes less intense light for them to absorb the light
o Rods are bigger- more surface area and hence better chance that light going through retina will hit photoreceptor and get absorbed
o Rods have higher degree of convergence
Rods take much larger regions of the eye and mapping them onto a single neuron- makes lower resolution image
156
How many rods are there in the eye?
120 million
157
How many cones are there in the eye?
6 million
158
How many ganglion cells are there in the eye?
1 million
159
Describe the pathway light takes to reach photoreceptors and how the signal is transferred to optic nerves
• Light rays go through ganglion cells, amacrine cells, bipolar cells, horizonal cells and finally touch rods and cone receptors
• The signal must then return through the opposite way to ganglion cells
• Hence the formation of a blindspot-optic disk
o Gathering of neuronal axons into one area
160
Describe what happens to vision when go from dark room to sunlight?
o Within minutes, rods stop responding
Bleaching of photoreceptors
o Cones don’t start responding until high levels of light
o Different photoreceptors adapt their levels by changing their sensitivity
As light levels go up above a certain level, firing rate of rods slows and stops and cones take over
161
Describe what happens from sunlight to dark room in terms of vision?
o Cones will be desensitized
| o As cones become more sensitive, start to become a bit better, but at a sudden level will be able to see something
162
How many types of rods do humans have?
1
163
How many types of cones do humans have?
3
164
What wavelength can rods detect?
Can detect 400-600 nm
165
What is the peak absorbance of rods?
Peak absorbance at 498 nm
166
What pigment do rods have?
Rhodopsin pigment
167
What does rhodopsin absorption correspond to?
Rhodopsin absorption corresponds to human scotopic sensitivity
168
How is human scotopic sensitivity measured?
• This is measured by making participant sit in dark room and adjust different wavelengths of light until they are the same sensitivity
o Peak sensitivity is the one that needs to be turned up the least
169
Why can't we differentiate between colours using only rods?
Can’t differentiate different colours with one photoreceptor as can’t tell difference between intensities vs wavelengths as photon count would be the same at a higher intensity but lower wavelength vs lower intensity at higher wavelength
170
Why do we have three types of cones?
```
o Cones-
Three types of cones
• Gives colour experience
• Contain different pigment types
There are individual differences in cone distributions
```
171
What are pigments?
Things that absorb certain wavelengths of light and reflect others
172
What is the use of pigments in photoreceptors?
o Photoreceptors are subtractive colour devices
o Pigments in photoreceptors are absorbing particular wavelengths of light and the wavelengths of light it absorbs are the wavelengths it can turn into an electrical signal
173
Why do most forms of colour blindness occur?
• Most forms of colour blindness arise because some people are effectively missing one of the cone types (or the long and medium cones overlap too much and behave as if they are a single photoreceptor (red-green colourblind))
174
Describe the properties of light
o Light comes in discrete units called photons
| o Photons also have different wavelengths.
175
What happens when we increase amplitude of light?
When we increase the intensity (amplitude) of light we are increasing the number of photons
176
What is the use of photoreceptor curves
o Photoreceptor curves tell you how likely it is that a photon of a particular wavelength will be absorbed
177
Describe the equation for light capture for cone i
```
Light capture for cone i is:
ConeResponsei=∫E(λ) P_(i ) (λ)dλ
Where λ is wavelength (nm)
i= a given cone
E is the light reaching the retina
P is the cone absorption spectrum
```
178
Describe information that can be obtained from a photoreceptor curve
• This means that all wavelengths under its curve (made of nm extremities and peak) can be absorbed
o Peak of curve-how likely it is to absorb that photon
o Extremities of curve- which photons it can absorb
o The peak of the curve corresponds to 100% absorption
179
Describe how photoreceptors use photons to send signals
o Each photoreceptor counts photon number that it absorbs
Firing rate of photoreceptor is proportional to number of photons it absorbs
• Each absorbed photon elicits on unit of response
180
What is the principle of univariance?
If absorb a photon at any wavelength, has exact same effect on the cone than any other wavelength absorbs -exactly the same response
• The principle of univariance states that all absorbed photons generate the same response independently of wavelength (that is, any photon that is absorbed by photopigments generates the same response in the photoreceptor)
181
How many dimensions is human colour perception and why?
• Human colour perception is 3 dimensional as dimensions of that space is determined by number of cones
182
What is the trichromatic theory and who formulated it?
```
Trichromatic theory (Young and Helmholtz)-
• Different colour experiences are due to the differential activation of just 3 receptor types
o Based on observation that could generate all possible colours if mix light of just three different wavelengths
```
183
Describe the three types of cones in human perception and what wavelengths they absorb
```
Long wavelength- red
• Readily absorbs 564nm light
Medium wavelength-green
• Readily absorbs 534nm light
Short wavelength-blue
• Readily absorbs 420nm light
```
184
What is chromatic aberration and the result of this?
• Chromatic aberration- when light is passed through, eye decides to perfectly focus around 578nm light: short wavelengths are more strongly blurred than other wavelengths
o The failure of refraction to focus all of the wavelengths of light
o Blue is not well focused by the human eye-this is why short wavelength cones are so sparse
Short wavelengths don’t have to be sampled as densely as other wavelengths (because there’s less fine structure in the blue parts of the image)
185
What type of colour mixing is light colour mixing? What are the primary colours used in that type of mixing?
```
• Lights are additive
o Primary colours
Red
Green
Blue
o If add two wavelengths of light, they combine
```
186
What type of colour mixing is pigment colour mixing? How does it work? What are the primary colours used in that type of mixing and how do they work?
• Pigments are subtractive
o Primary colours
Yellow
• If red, green and blue coincide with yellow, yellow will let red and green pass but subtract the blue
Cyan
• If red, green and blue coincide with cyan, cyan will let green and blue pass but subtract the red
Magenta
• If red, green and blue coincide with magenta, magenta will let red and blue pass but subtract the green
o Objects appear colored if they reflect some wavelengths of light better than others- selectively absorb wavelengths of light and reflect a select range of wavelengths according to nm
o Primary colours subtract a wavelength of red, green or blue- acts like a filter: hence by placing several of these yellow, cyan and magenta primary colours together, they act as filters and take out certain colours
Selectively removing particular set of wavelengths
187
What is colour constancy?
• Colour constancy- brain adjusts colour differences in object under different lights to how object is illuminated, not changes in colour
188
What is the goal of colour reproduction and how is it achieved?
• What gets sent to brain is firing rate of different S, M and L cones (which is determined by photon count absorbed)
• Colour reproduction goal- To reproduce the response of the cones to the colors of naturally viewed images using a subset of light sources of pigments
o Need to know how likely it is that each cone will absorb a particular wavelength of light
189
What is colour?
• Colour-capacity to distinguish between different wavelengths of light
190
Why can't we distinguish colour using one type of photoreceptor?
o One type of photoreceptor- means that cannot distinguish between different wavelengths of light as different wavelengths can result in same photon number if they have different intensities
191
How can cones be used to distinguish colour?
o Cones can distinguish between different wavelengths by using different receptor types and using relative response in each of the 3 cones to pinpoint wavelength
All of the different colors you see occur because each color experience begins with a particular pattern of activity in the 3 cone types
192
What are metamers and how are they used in the real world?
• There are a lot of different physical stimuli that will generate the exact same relative activity in the 3 cone types. These are called metamers: physically different spectra that generate the same perception of colour because they generate the exact same response in the cones
o All color devices exploit metamers to generate color: all the brain ever sees is whatever the cones send it. And all each cone does is count the number of photons it absorbed
o All that matters is the cones responses, not the physical spectrum that produced the responses
193
What is the main role of photoreceptors?
• Number of photons caught by photoreceptors= number of signals to the brain
o All photoreceptors do is receive and count photons
194
Describe how to calculate the weighted sum of a photoreceptor response
• Total response to all lights is a weighted sum of response to each individual wavelength
o Photon number*% + Photon number* %+_____= response units
195
What is photoreceptor adaptation?
• When stare at colour, adapt to colour
o Excessive firing of particular receptors makes them reach threshold
• When neutral colour is added, cone that has not been firing fires more than other cones, who have reached their firing threshold and hence don’t fire much anymore
o The excessive firing of the cones used when staring at the colour skews towards opponent colour
196
What are phenomenological problems with the trichromatic theory?
• Color blindness always occur in pairs (always red and green, blue and yellow)
o The phenomenology of primary colors- there appear to be four, not three: red, green, blue and yellow
• Fails to explain the absence of certain colour mixtures
197
How is colour organised in opponent processes?
• Colour is organized in a 3D opponent space
• To get full color space, need three opponent axes
o Blue to yellow
o Red to green
o Black to white
• Opponent structure to colours- some colours don’t add together
198
What is grey?
* Gray is neutral- neither green nor red nor blue nor yellow
| * Mixing colors from any points on the opposite sides of the perimeter takes you though a neutral point (grey)
199
What is chroma?
Saturation
200
What is the CIE? Describe its features
• CIE-international commission on illumination: standardized colour space so that coordinate of space corresponds to particular colour
o Spectral locus-a set of rainbow colours: what happens when you pass white light through spectrum
o Line of purple- created by mixing longest wavelength with shortest wavelength
o Any hues oppositely mapped on CIE combine to form grey and are opponent processes
201
What is lightness constancy and how does it work?
• Lightness constancy refers to our ability to perceive the relative reflectance of objects despite changes in illumination
o Brain is accounting for fact that certain objects which are returning same amount of photons are under different illuminations, and hence tries to match colour with intensity and illumination
202
What is colour constancy and how does it work?
• Color constancy- color of objects remains relatively constant under varying illumination conditions
o For our brains to recover the intrinsic reflectance properties of objects, it has to somehow account for the effects of illumination, so that the color of objects doesn’t change when the illumination changes
203
Why is lightness and colour constancy necessary?
• The light reaching the eye depends on both the illumination and the reflectance properties of objects
o For an achromatic surface, the reflectance of light is just the proportion of the light that surface reflects, which we characterise with a simple percentage. The light reaching your eye depends on both the intensity of the light source and the percentage of light reflected
o The colour of a surface is exactly the same idea, but now we need to characterize the percentage of each wavelength of light that is reflected. This can be done without reference to the illumination
