Perception Midterm Flashcards
Absolute Threshold
the smallest detectable unit of a physical quality
Difference Threshold
the smallest detectable difference between two physical qualities
so if it says something has a weber fraction of 25% then that means a stimulus must be 25% higher or lower in order to find JND
Two types of threshold seeking methods
classical and adaptive
Three types of classical methods? Describe what they are and their pros and cons.
Method of Adjustment: stimuli is adjusted until they can just detect it, fast but not always accurate
Method of Limits: stimuli goes in ascending and descending order and person says whether they can see it or not, easy on observer and fairly fast and accurate
Method of Constant Stimuli: 5 to 9 stimuli of different intensities are presented many times each, in random order, accurate but takes very long
what is the relationship between the difference threshold and magnitude of stimulus
when magnitude of stimulus increases so does difference threshold
response compression
(b<1)
as intensity increases, the perceived magnitude increases slower than the intensity
response expansion
(b>1)
as intensity increases, the perceived magnitude increases faster than the intensity
Three main categories of mechanoreceptors
encapsulated
accessory-structure-associated
free nerve endings
encapsulated types
meissner
pacinian
ruffini
accessory-structure-associated typed
merkel disk
tactile hair
what is a receptive field
the area of a sense organ affecting the firing of a given neuron
spatial resolution
how many mechnoreceptors are across an area of a sense organ can determine how precisely one can know where a stimulus occurred
temporal resolution
how off does a receptor respond to a given stimulus can determine how precisely one can know when a stimulus occurred
Two pathways from skin to brain
dorsal column-medial lemnisical pathway
anterolateral pathway
serial processing
neurones connect to one another in a sequences
parallel processing
several streams or channels bring information to the brain simultaneously and the brain is able to process it
contralateral processing
sensations from left side of the body cross over to right side of the brain and vice versa
topographic organization
adjacent neurones carry signals from adjacent parts of the body
what determines the size of a brain area?
the number of receptors in the area, not the size of the area
focal dystonia
cortical areas fuse together from neural plasticity
tactile acuity
the ability to locate touch on your body with precision
What area of the body has greatest tactile acuity? Why?
the fingers because they have the highest density of SA-1 Merkel mechanoreceptors in them
what type of fibres and mechanoreceptors are responsible for perceiving vibration?
FA fibres, meissner and pacinian corpuscles
sensory channels
overall subsystems working together to create sensory behaviour (meissner and pacinian corpuscles creating vibration)
envelope function
the psychophysical functions associated with sensory channels (the curves of meissner and pacinian working together)
what is the perceptual correlate or sensory quality for hearing and touch
pitch
Which mechanoreceptor is primarily responsible for fine texture discrimination via vibration sense?
pacinian corpuscles
what are the type of thermoreceptors and what fibres are they linked to fibres
cold (AS fibres)
warm (C fibres)
does thermal sensation have response expansion or compression
expansion, thermoreceptors respond to reduction of thermal energy, unlike other senses
opponent process
warm and cold receptors compete in an opponent process, adapting one causes the other to become more sensitive
what pathway for thermal sensations?
anterolateral pathway
what is proprioception? how is it sensed?
the sense of ones own body position and motion. through proprioceptors, responsible for weight discrimination
what is kinesthesia?
it is part of proprioception, it is the sense of muscle and joint positions in your body
what type of fibres for proprioception?
Aa fibres
type of proprioceptors?
muscle spindle receptors
golgi tendon organs
both have to do with Aa fibres entangling around something since they are accessory structure mechanoreceptors
what are corollary discharge signals (CDS’s)?
an additional way that body position is signalled, when a motor signal is sent from brain to muscle, a copy of that signal (a CDS) is sent to somatosensory cortex, it is like error checking
what is haptic exploration
the active exploration of a 3-D object with the hand
how is shape of an object signaled?
through the firing pattern of groups of mechanoreceptors
what type of RF’s are in the thalamus, what other sensation is this parallel to?
centre-surround RF’s, vision
What are the two major modalities of pain?
a sensory component
an emotional component
what’s the name of the receptors that transduce pain?
nocioceptors
what tare the three types of pain?
nocioceptive
inflammatory
neuropathic
describe nocioceptive pain
healthy and protective
usually a result of high intensity stimuli like heat, chemicals, pressure, or cold
it is the response to tissue damage or the threat of tissue damage
describe inflammatory pain
healthy and protective but can be pathological (arthritis)
caused by damage to tissue or joints the releases chemicals that activate nocioceptors
describe neuropathic pain
generally pathological failure of pain systems
caused by damage to the PNS or CNS
carpel tunnel, spinal cord injury, thalamic stroke
what are some cognitive effects on pain?
expectation
shifting attention
what is gate control theory (GCT)
suggests that inputs from nocioceptors can be gated off at the spinal level
What two general influences can modulate pain according to GCT
afferent tactile inputs (touching the area)
top-down inputs (shifting attention)
What does Melzack’s “Pain is in the brain” idea mean?
pain is not as simple as a reaction to stimuli, pain multimodal and many areas of the brain are involved in it
opioids
exogenous opioids aka painkillers block pain
endorphines
endogenous opioids
released by painful experiences or pleasure/relaxation
naloxone
a chemical that blocks opioid receptors
what are the 4 types of papillae? what do they look like? where are the located?
filiform: cone shaped, entire surface
fungiform: mushroom shaped, on tip
foliate: series of folds, back and side
circumvallate: flat mounds, tenches in back
what are the different ways of transduction for different tastes
salty & sour: ionic channels
bitter & sweet & unami: G protein coupled receptor (GPCR) mechanisms
how do salty & sour ionic channels work
positive ions from salt (Na+) and positive ions from sour(H+) travel through ionic channels in the taste cells that depolarize them and lead to neurotransmitter release
how do sweet GPCR mechanisms work?
wide variety of sweet tastants trigger GPCR to release a cAMP mechanism in sweetness-detecting cells
how do bitter GPCR mechanisms work?
wide variety of bitter tastants trigger GPCR to release calcium (Ca++) in bitter-detecting cells
taste pathway
VII, IX,X>NST>VPMN>PGC>SGC of OFC>hypothalamus and amygdala
physical definition of sound
sound is pressure changed in the air or other medium
perceptual definition of sound
sound is the experience of we have when we hear
what are sound waves
they are what make up sounds, they are longitudinal waves which means variations in intensity (air density) are the parallel to the direction the wave is travelling in
transverse waves
water or light
What moves through the air in a sound wave?
air PRESSURE, not the actual air, so it is like wave at sports stadium
What is a pure tone? what qualities define it?
a pure tone is the simplest form of a sound wave, the pressure variations are sinusoidal
amplitude (uPa) = subjective loudness
frequency (Hz) = subjective pitch
all other sounds are made up of many pure tones
Discuss taste quality and methods to assess it
no simple relationship between molecular structure and taste quality so it is hard to measure
Henning’s taste pyramid thing
MDS
Star Charts
what is hedonics
the study of of the pleasurable or unpleasurable aspects of taste
what is PTC how many people can taste it?
a chemical put in toxic products to make it taste bad
75% can taste
6% of them are supertasters
route of odour stimuli affecting taste
odour stimuli>retronasal route>olfactory mucosa
pheromones
messenger chemicals that are released to control the 4 F’s
possible existence of CN0 involved in human pheromonal control of sexual arousal
What are olfactory stimuli
odourants that are found in the air, the concentration of them decides the subjective intensity of the smell
what is the relationship between chemical structures and odour qualities?
it is complex, the same looking chemicals could produce different smells, or vice versa
amplitude
the difference in sound pressure between high and low peaks of a wave (Ps)
db=20 x log10 (Pr/Ps)
decibels formula
what is frequency? how is it measured?
number of amplitude cycles within a given period of time
measured in Hertz (Hz)
1 Hz=1 cycle per second
what are complex sounds?
a combination of pure tones, each with its own amplitude and frequency
what is a fundamental frequency?
the lowest frequency element of a set of tones
overtone
the higher frequency elements of a tone
harmonic/harmonic overtone
a frequency that is a whole integer multiple of the fundamental frequency
what is attack/decay?
attack: the buildup of sound at the beginning of a tone
decay: the decrease in sound at the end of a tone
what are periodic sounds? examples?
sounds that have patterns that repeat across time
musical notes, vowels
what are aperiodic sounds? examples?
sounds that have no repeating patterns
hissing, thumps
What is the basic idea behind Fourier Analysis?
That any function can be broken down into a series of sine waves
Fourier Synthesis?
that any function can be built up from a series of sine waves
relationship between tones, frequencies, and amplitudes
multiple amplitudes make up one frequency
multiple frequencies make up one tone
fourier spectrum
shows the the amplitude for each frequency that make up a tone
how are oldfactory signals coded?
through cross-fibre coding
each odourant has a number of molecular components (different shapes of different colours creates molecule)
each shape can activate a different receptor
(receptors with different shapes indented in them)
this creates a pattern of activated receptors that signal a specific scent
what are enatiomers?
molecules that are exactly the same except they are mirror images of each other
challenges malnic’s olfactory coding theory because they have the same molecular components but they create different scents
what are two methods to measure the quality of smells? pros and cons?
2AFC vial sniffing: given two options, one has stimulus in it one does not, must say which one has the stimulus
it is simple but noisy due to difference in sniff volumes and rates
Olfactometer: a machine that gives controlled bursts of air into nose with smells in them
stimuli is well-controlled but it is very complex machine
odourants experience response compression or expansion?
compression (b<1)
Odour Primaries
Henning’s created odour prism with the odour primaries
flowery, spicy, putrid, burning, burnt, resinous
what is easy and what is difficult in odour identification?
detecting that an odour is there is easy, but naming them is difficult
What is sensitivity?
one’s ability to detect a signal (the simulus)
d’ (dee-prime)
How do you measure sensitivity?
You make the four possible result squares
the stimulus is either present (test trials) or not (catch trials)
and the person either says they hear it or not
What do we call it when the stimulus is present and the person says they do detect it? How is this used in measuring sensitivity
a hit
we look proportions of hits (Ph)
What do we call it when the stimulus is not present and and the person says they do detect it? How is this used in measuring sensitivity
a false alarm
we look at proportions of false alarms (Pfa)
What is criterion?
a person’s tendency to say yes a lot or no a lot
What is it called when someone tends to say yes more? Why would they do this?
A Lax Criterion
If the cost (punishment) of a miss is raised
If the reward (benefit) of a hit is raised
You will say yes more because you do not want to miss it and you want to get them right when they are there
What is it called when someone tends to say no more? Why would they do this?
A Balanced Criterion
If the cost of a false alarm is raised
If the reward for a correct rejection is raised
You will say no more
When c<0, yes __ no
When c>0, yes__no
When c<0, yes>no
When c>0, yes<0
The lower the criterion value, the more of a chance that someone will say yes
What happens when you increase d’ in SDT?
Increasing d’ means that the two sounds sound nothing alike (increases distance between probability distributions) so you are more likely to hear the signal even with the noise with a neutral c (no tendency to say yes or no)
What happens when you decrease d’ in SDT?
The two sounds sound very similar (the probability distributions will be very close together)
so you are more likely to have false alarms or misses regardless of where c is
physical definition of sound
pressure changes in the air or medium
perceptual definition of sound
the experience we have when we hear
what are sound waves? what kind of waves are they? how do they work?
objects make sounds by moving back and forth through a medium (air)
longitudinal waves
compression and rarefaction cycle creates high and low pressure regions that travel through air
variations in intensity (air density) are parallel to the wave’s direction of travel
what moves through the air in a sound wave?
sound pressure
pure tones
the simplest form of a sound wave
pressure variations are sinusoidal
all other sounds are
2 defining qualities of pure tones and what are they
1) amplitude (uPa): subjective loudness
2) frequency (Hz): subjective pitch
what is amplitude and how do we measure it?
difference in sound pressure between high and low peaks of a wave
sound pressure (P) is measured in (uPa)
sound intensity, related to subjective loudness, is a square of P (I=P squared)
ratio of squared pressures (Ps squared/ Pr squared)
Pr=reference pressure typically 20 uPa
sound pressure level (SPL)
20 uPa is the lowest pressure variation amplitude detectable by an average human at 1000 Hz frequency
decibels
The range of pressure ratios that humans can hear covers 7 orders of magnitude (i.e., from 1 to 10000000)
how do we measure decibels?
dB = 20 × log10(Ps/Pr)
Ps: difference between mac and min pressure
Pr: is SPL usually 20 uPa
what is frequency? how do we measure it?
number of amplitude cycles within a given time period
measured in Hz
1 Hz= 1 cycle/minute
complex sounds
natural sounds do not have a single freq and/or amplitude
made up of complex sets of combined pure tones
each of these pure tones has its own freq and amp
the doppler effect
When a sound source approaches at high speed, its sound
seems to increase in frequency, then decrease as it passes
due to compression and expansion of sound waves
fundamental frequency
the lowest frequency element of a set of tones
overtone
higher frequency elements of a sound
harmonic
overtones whose frequency is a whole integer multiple of the fundamental frequency
frequency spectrum
the tones that together make up a sound, partly responsible for a sounds timbre
attack of tones
quality of timbre
buildup of sound at the beginning of the tone
decay of tones
quality of timbre
decrease in sound at the end of the tone
periodic sounds
have patterns that repeat across time
ex: musical notes, vowels
aperiodic sounds
have so repeating sounds
ex: thumps, contants, hissing
fourier analysis
any function can be be mathematically broken down into a series of sine wave elemets
fourier synthesis
any function can be built up from a series of sine waves
fourier spectrum
shows lines, the heights of the lines indicate the amplitude
of each of the frequencies that make up the tone
what does the speed of sound transmission depend on?
the density and the elasticity of the medium it is traveling through (air)
More dense = slower transmission
More elastic = faster transmission
what happens with sound and objects
objects will absorb, reflect, transmit, or diffract sound based on their physical properties
when do objects absorb sound?
the larger and denser the object is, the more it will absorb sound
the shape of the object also affects it
when do objects reflect sound?
the more elastic the object is, the more it will reflect sound
the shape of the object also affects it
when do objects diffract sound?
occurs when sound encounters an object, sound waves will re-form on the other side of small objects but not large ones
inverse square law
As sound moves out from a point source, its energy is
spread over a larger and larger area
Area is proportional to square of the relative distance
2×distance = 1/4 intensity
3×distance = 1/9 intensity
If the sound intensity is 180 units at distance
10 m, what will it be at 30 m?
30m/10/=3
3x30=90
180/90=20 sound intensity units
outer ear parts and functions
pinna: helps with sound localization
auditory canal: approx 3 cm long tube,
protects tympanic membrane at the end of the canal
resonance frequency of outer ear
amplifies frequencies between 2000 and 5000 Hz
middle ear function and parts
≈2 cm3 cavity separating inner from outer ear
three ossicles: malleus, incus, stapes
eustachian tube: equalizes pressure
ossicles function
outer and inner ear are filled with air and inner ear is filled with fluid that is denser than air, this causes poor pressure changes from air to fluid
ossicles act in two ways to amplify the vibration for better transmission to the fluid
ossicles condensation effect
force is concentrated down on a smaller area to create higher pressure
larger of the 2 effects, 25 dB
ossicles lever effect
ossicles are set up like a lever arm
allows weaker force of air vibrations to move liquid to cochlea
smaller effect, 2 dB
inner ear parts
cochlea: fluid like structure set into vibration by the stapes
structure of the cochlea
divided into 3 canals by 2 membranes
canals: scala vestibuli, scala media, scala tympani
membranes: reissner’s membrane, cochlear partition
cochlear partition structure
cochlear partition: narrow at the apex and wide at base
basilar membrane: wide at apex and narrow at base
spiral lamina: makes up rest of cochlear partition
other cochlea structure, the organ of corti description and function
has inner and outter hair cells and their supporting structure
rests on basilar membrane which vibrates in response to sound stimuli, activating hair cells
inner hair cells are receptors for hearing
Tectorial membrane extends over the hair cells
Transduction at the hair cells takes place due to
the bending of tectorial and basilar membranes
Two theories of how nerve fibres signal frequency
1) Place theory
2) Frequency Theory
place theory
see which fibres are firing since different hair cells along the OoC fire to different sound frequencies
Hz of sound is coded by the place on the organ of corti that has the greatest vibration, and thus greatest stimulation of neurones
Békésy suggested that sounds produce a travelling wave along the basilar membrane
The peak of this wave occurs at the point where the
membrane’s resonant frequency matches that of the sound’s frequency
the resonant frequency of the base of the basilar membrane is much higher than the apex
frequency theory
how fibres are firing, rate or firing patter of nerve impulses
proposed that all hair cells fire to every sound, and their rate of vibration indicates frequency of sound
action potentials from IHCs are found to be phase locked to the sound signals
phase locking
phase is a characteristic of sine waves describing where the wave starts
IHCs spike when a pure tone is at highest compression
but max firing rate is 500 spikes/sec, so how to code for higher frequencies? volley theory
volley theory
no single neurone can signal each pressure maximum for
tones above about 500 Hz
by aliasing and firing out of phase with one-another,
several neurones can together encode high frequencies.
synthesis
For sounds below 1000 Hz, only volley theory
applies
For those between 1000 and 5000 Hz, both place
and volley theory apply
For 5000 Hz and above, only place theory applies
which end of the basilar membrane codes
for low frequency sounds and which for high?
low=apex
high=base
where does transduction occur for hearing and how does it happen?
in the inner hair cells (IHCs)
1) stereocilia in the IHCs are bent
2) tip links (tiny filaments in stereocila) are pulled
3) tip links open ionic channels
4) causing the IHC to alternately hyperpolarize and depolarize
what is active response where does it occur and how?
in the outer hair cells (OHCs)
do not transduce sound by boost IHC response
1) sound stimulates OHCs
2) OHCs rhythmically contract and expand like muscles
3) this amplifies the motion of the basilar ad tectorial membranes
4) this actively stimulates the IHCs
amplitude transduction
a single class of neurones cannot code for the whole range so instead different hair cells code for different limited ranges of amplitude
“A” codes for a low range, starting at ≈10 dB & saturating at ≈50 dB. It has a high resting response rate
“B” responds only to upper range, starting at ≈50 dB and
saturating at ≈100 dB
what does it mean to say that the basilar
membrane performs Fourier analysis?
the basilar membrane shows the highest response in auditory nerve fibers with characteristic frequencies that correspond to the sine wave components of complex tones
In this sense the basilar membrane does a Fourier
Analysis of the incoming sound signal, breaking it down
into component pure tones
what are the subcortical structures in the pathway from the cochlea to cortex
C? SONIC MG is A1!
1) Cochlear nucleus
2) Superior olivary nucleus (in the brain stem)
3) Inferior colliculus (in the midbrain)
4) Medial geniculate nucleus (in the thalamus)
5) Auditory receiving area (A1 in the temporal lobe)
cochlear nucleus
has tonotopic organization: Ventral = low Hz Dorsal = high Hz contains 3 types of cells 1) bushy cells 2) stellate cells 3) octopus cells
cochlear nucleus: bushy cells function
code for different frequencies and inhibit one another to get sharper frequency tuning
cochlear nucleus: stellate cells function
fire for duration of stimulus (slow adapting)
their rate indicates intensity of the sound
cochlear nucleus: octopus cells function
fire at sound onset/offset (fast adapting)
may provide sound timing information
superior olivar nucleus
located in the brain stem tonotopic organization first site of binaural activity integrate signals from both ears first analysis of sound direction (horizontal only) via analysis of time and intensity differences between both ears
inferior colliculus
located in the midbrain
receives inputs from higher areas like AI
may be a “switchboard” for regulating auditory attention
also an integrating area for multi-modal
perceptual responses such as startle reflexes
and reflexive looking
medial geniculate nucleus
nucleus of the thalamus tonotopic organization processes all aspects of sound may be the first site of complex pitch (as opposed to simple frequency) perception
descending pathways function
olivocochlear neurones–going from superior olivary down to cochlea–can turn down the gain on IHCs to allow them to process higher sound volumes
descending connections also cause contractions in small
muscles attached to ossicles, causing them to be less mobile and thus “turning down the volume” on high amplitude sounds
AI primary auditory cortex
located in the temporal lobe
processes relatively simple sound information regarding frequency and location
AI organization
organized in isofrequency sheets which run left to right
neurones within a sheet have the same characteristic frequency (Hz to which the cell is most sensitive; lowest
threshold)
transverse to the sheets are aural dominance
columns and suppression/summation columns
suppression, sum, right, left, binaural for different Hz
“what” stream for hearing
starts in the anterior temporal lobe and extends to the prefrontal cortex
responsible for identifying sounds
“where” stream for hearing
starts in the posterior temporal lobe and extends to the parietal and prefrontal cortex
responsible for locating sounds
what is loudness? what is it most related to?
the subjective perceptual quality of sound
pressure or intensity, also depends on frequency, etc
what is the max sensitivity to loudness?
2-5 kHz (human speech)
psychometric function
function on physical quantity of a behaviour, shows one threshold
psychophysical function
function of 2 physical quantities shows hows threshold on 1 quantity varies as a function of the other
other factors affecting loudness
binaural vs monaural presentation (spatial integration)
duration of sound (temporal integration)
the dynamic range
interval between the softest and loudest sound that the ear can hear (100-500)x10
minimum audibility curve
threshold of hearing vs frequency
spatial and temporal integration
any sensor (biological or artificial) must integrate (add up) signals across a certain range
longer/larger integration=?
higher sensitivity, lower acuity
what are sound masking experiments? what are the two types? what are the two methods used?
psychophysical experiment examining how one sound affects perception of another
types:
1-tonal masking
2-noise masking
methods:
1-constant target Hz with varying masker Hz, mainly used with tonal masking
2-varying target Hz with constant masker Hz, mainly used with noise making
tonal masking
asking how much one pure tone impairs perception of another
test tone of fixed frequency chosen
series of masking tones of different frequencies presented
for each masking tone, observer adjusts its intensity (dB) until it drowns out the the test tone
most effective masking is at the same frequency as the test tone
noise masking
asking how much do aperiodic sounds impair perception of tones
constant mask is used, usually a narrow-band white noise, which is aperiodic sound with frequency in a certain range
subtract the baseline from the masked constant masked audibility curve and you get the get how much the threshold was elevated by the noise mask
noise mask shows asymetry
describe 410 +/- 45Hz
has centre frequency of 410 and a bandwith of 90Hz
why masking asymmetries occur
because of asymmetries in how the basilar membrane responds to pure tones
the travelling wave builds up gradually then collapses suddenly
what will be the response to test and masking tones due to asymmetries?
A-more similar if mask is < the test in frequency
B- more different if the mask is > test in frequency
If a masking tone is 500 Hz in frequency: What Hz of target tone will it most effectively mask? Which target tone will it mask more: A 400 Hz tone, or a 600 Hz tone?
500 Hz 400 Hz (?)
how are frequency and pitch related?
tone height (aspect of pitch): increases linearly as frequency increases tone chroma (aspect of pitch): increases in a circular fashion as frequency increases
auditory space
surrounds an an observer and exists where there is sound
what are location in auditory space defined by?
1) azimuth coordinates=left and right
2) elevation coordinates=up and down
3) distance coordinates=position from observer
what are the cues for sound localization?
1-Binaural Cues (ITD, IID)
2-Monaural Cues (HRTF)
binaural cues
location cues based on comparison of the signals received by the left and right ears
ITD=difference between the time sounds reach the two ears
IID=difference in sound pressure level reach the two ears
what affects ITD?
when source is to the side, times will differ
when distance to each ear is the same, no difference in time
what affects IID?
head casts an acoustic shadow
reduction in intensity occurs for high frequency sound for the FAR ear
there is no reduction in intensity for low frequency sounds as they diffract around the head
what are cones of confusion?
a given ITD/IID on its own cannot tell you WHERE a sound is coming from
can only tell you it’s coming from somewhere on a particular cone of points
monaural cues
as sounds encounter the head, they are modified by its structures (bones, muscles, etc) especially the pinna
some frequencies are reduced in amplitude, others are increased due to resonance and constructive interference
HRTF=the pattern of increases and decreases of frequencies’ amplitudes
what makes HRTF differ?
the elevation of the sound source
the head and pinna leave a unique “fingerprint” on sounds based on the elevation
this helps to resolve which point on the cone is the source of the sound but doesn’t solve distance
explain Hoffman’s experiment on judging elevation
experiments investigated spectral cues
put moulds in their pinnae
right after moulds were inserted, performance at locating sounds at different elevations was poor
after 19 days, close to original performance
once removed, performance stayed high
what does Hoffman’s experiment suggest?
that there might be two different sets of neurones, one for each set of HRTF cues
what are the distance cues for sound?
1) spectrum
2) loudness
3) movement
3) reflection
spectrum distance cue
for sound with known spectrum like speech, distance can be estimated by degree of muffling
high Hz sounds are more quickly damped by air, so distant sources of sound are muffled
loudness distance cue
self-explanatory
movement distance cue
motion parallax=nearby sound sources pass faster than distant ones
reflection distance cue
in enclosed areas, direct sound arrives at ears without being reflected at the wall
reflected sound arrive later, after bouncing off walls
ratio between direct and reflect arrival time can give an indication about the distance of a sound source
two methods for measuring sound location accuracy
1) free-field presentation
2) headphone presentation
what is free-field presentation? advantages/disadvantages
sounds are presented by speakers located around listeners head in a dark sound-proof room
indicates location by pointing, giving azimuth and elevation coordinates
advantage=high naturalistic
disadvantage=expensive equipment and some lack of control over exact sound contents
headphone presentation advantages/disadvantages
advantage=precise control over sounds and cheaper
disadvantage=cues from pinna (HRTF) are eliminated, results in sound being internalized
sounds can be externalized by measuring each subjects’ HRTF and applying it to presented sounds
physiological representations of auditory space
1) interaural time-difference detectors: panoramic neurones
2) topographic map
panoramic neurones
neurones that respond to specific ITDs, found in the auditory cortex at the first nucleus (superior olivary), in the system that receives input from both ears
signal location by their pattern of firing
topographic maps as psychological representation of auditory space
neural structure that responds to location in space, these neurones have RFs for sound location
barn owls have in the MLD
mammals have in subcortical structures like the inferior collicus
auditory scene
array of all sound sources in a listener’s environment
auditory scene analysis
process by which sound sources in the auditory scene are separated into individual perception
does not happen in the cochlea as simultaneous sounds are combined together in the pattern of vibration of the basilar membrane
segregation of sound signal into those coming from different sources
grouping of separate sounds into those coming from one given source
sound localization
gestalt heuristics
heuristic=rule of thumb used by a system (ex. brain)
gestalt heuristics=a rule of thumb applied to organizing sensory inputs to make determinations
which elements of a scene belong to which objects, which elements represent edges between an object and its background
ex: proximity and similarity principles
auditory grouping
sound stimuli perceptually organized according to certain heuristics
principles of auditory group (3)
1) proximity: sounds from a single source tend to come from one location
2) similarity: sounds from a single source tend to be similar in pitch, loudness, etc
3) smoothness: sounds from a single source change in pitch, loudness, etc, in a smoother and continuous way
auditory streaming as auditory scene analysis
when sound A and B are similar in pitch, they are grouped together in a single “galloping” sound stream based on proximity in time and timbre
when sound A and B are different in pitch, they are grouped into 2 separate streams
changing the speed does the same
Deutch’s melodic channeling experiment method, results, reason for results?
stimuli were 2 sequences alternating between the right left ears
listeners perceive 2 smooth sequences by grouping the sound by similarity in pitch
caused by proximity and smoothness heuristic
what does wessel’s timbre illusion demonstrate?
demonstrates how heuristics can compete with each other
smoothness heuristic: tries to group by smoothly changing pitch, dominates at low speeds
similarity heuristic: tries to group by timbre, dominates at high speeds
Bregman continuation heuristic demonstration
tones were presented interrupted by either gaps of silence or by noise
silence condition= perceived sound stopped during the gaps
noise condition=perceived the sound continues behind the noise
Dowling effects of experience experiment methods, results, meaning
used 2 interleaved melodies (three blind mic and mary had a little lamb)
listeners reported hearing meaningless jumble of notes
once they were to listen for the melodies, they were able to hear them by using a melody schema
this shows how heuristics can be affected by learning and knowledge
interactions between vision and sound
visual capture or the ventriloquist effect: an observer perceives the sound as coming from the seen location rather than the source for the sound
Sekuler experiment on interactions between vision and sound
balls moving without sound appeared to move passed each other
balls with added “click” appeared to collide
what is light
a form of electromagnetic (EM) radiation
how does electromagnetic radiation vary? (3)
1) wavelength
2) intensity
3) polarity
1) wavelength? measured? causes?
measured in lambda
measured in units of distance (nanometers)
variations in wavelength cause colour experience
range of visible light to human? why is there this limit?
400nm-700nm
bc where most of the energy is sunlight is
other ranges can be damaging (UV)
or pass through objects too easily (radio)
natural light
have ranges of lambdas
each with its own intensity
laser lights
single lambda
what is a light’s subjective colour determined (in
part) by
by its intensity spectrum
what are spectral functions
describes some property of a stimulus as a function of wavelength or frequency
This can be wavelengths of light, sound, physical vibration, etc.
Most stimuli have a broad range of wavelengths, each with
its own amplitude.
A spectral function can describe properties of emission, transmission, scatter, etc. but also detection/differentiation
2) intensity
variations of intensity cause the sensation of brightness, but relationship is nonlinear
measured in units of power per area (candela (cd)/m2)
Human vision can handle between about 10-6 and 107 cd/m2 (beyond this, damage occurs)
3) polarity
Polarity refers to the angle (e.g., in degrees) other electric component
emitted light
light is emitted from a s source and travels in all diffraction until it is either absorbed, refracted, or reflected
At a sufficient distance(called optical infinity):
Spherical wave fronts can be treated as flat
Light rays can be treated as parallel
By convention, optical infinity is said to be 6 m
light’s journey to the eye (6)
1-light is emitted by a source
2-transmission through a medium (lightbulb, sun, etc)
3-interaction with surfaces or objects
4- transmission through a medium again (air, water, etc)
5-interactions with outer structure of the eye
6-interactions with structures of the retina
what can happen to light at each stage of its journey to the eye?
1) Transmission: refraction or scatter
2) Absorption
3) Reflection: specular or body
what is the difference between specular and
body (a.k.a. diffuse) reflection?
body: light scattered in all directions
specular: light reflect at opposite angle
what is focus? how do you do it? 2 methods?
an acute image system (camera or eye) form a sharp image on it imaging system (film or retina)
to do so must direct the light from each point in its field of view to a small patch on the imaging system
can accomplish focus by 2 methods
1) pin-hole light gathering
2) lenses
pin-hole light gathering to get focus, problem?
sharpen light by allowing light to reach the imagine surface via only one small opening
problem: only allows a small amount of light in, creating dim images
lenses, how is lens strength measure?
transparent surface that transmits and refracts light to sharpen image
measured in diopters (dp)
different types of lenses (2)
what are their measurements in dp?
convex lens: gathers light to a focal point (magnifying glasses, reading glasses, etc)
positive dp
concave lens: spreads light beams apart, so no real focal point (glasses to correct myopia)
negative dp
calculating focal distance (F) formula
F= 1/dp therefore dp=1F
combining pinholes and lenses
small pinhole: focus is ok, but image is dark due to the small amount of light allowed to enter
large pinhole: focus is poor but image is bright due to the large amount of light allowed to enter
large pinhole with lenses: focus is excellent and image is bright due to the large amount of light allowed to enter
combining lenses
+3dp lens on top of +5dp lens
+3 dp len and -3dp lens
= +dp lens
= 0, cancels each other out
what does the cornea and crystalline lens do?
focus images on the retina
The cornea is (on average) a +43 dp lens
The crystalline lens is also a lens that can vary its shape/power from +15 to +25 dp
Total focussing power is thus 43+15 = 58 dp
when lens is relaxed and 68 dp at maximum accommodation
Eye is about 25 mm in diameter, but distance
from lens to retina is about 18 mm (≈1/58 m).
emmetropic /emmetropia eye
relaxed states of eye
light rays are focus to a point on the retina
light rays parallel from optical infinity
20/20 vision
myopia/myopic eye
light focussed in front of retina
eye has too strong a lens for its length
causes near-sightedness
hyperopia/ hyperopic eye
lens not power enough for length of eye so images are blurred
causes far-sightedness
corrected by convex (+dp) lenses
accomodation
when objects are closer than optical infinity, light rays from points are not parallel
therefore a blue is produced
crystalline lenses can change shape to accommodate this
the near point
the distance at which objects get too close and the crystalline lens cant accommodate so it defocusses
presbyopia
as we age, the lens becomes harder and accommodation becomes limited, so the near point gets further away
a convex (+dp) lens can correct for this
the retinal image
extended objects consists of a large number of point sources
due to the way lenses work ,the imagine on the retina is upside-down and backwards but not pose a problem for analysis of the info
the image on the retina is of higher quality in the centre of the retina
the distribution RFs in the centre is sparser too
Objects at distances other than the depth off focus are blurred
The degree of blur depends on pupil size
Thus, we have greater depth of field under bright conditions than dim ones
anatomy of the retina (4)
1) macula
2) fovea
3) optic disc
4) peripheral retina
layers of the retina back-front (4)
1) pigment of epithelium
2) photoreceptor layer
3) inner nuclear layer
4) ganglion cell layer
photoreceptors (4)
function
size amount of each
1) rods: night vision
2) S-cone: day vision
3) M-cone: day vision
4) L-cone: day vision
rods larger and more numerous than cones
120 million rods, 6 million cones
Distribution of Rods & Cones Across Retina
fovea: rods=none, cone=max density
macula: rods=max density, cones=?
optic dic: rodes=none, cones=none
peripheral retina: rods and cones= drops rapidly as we move out towards it
the blind spot
optic disc is where optic nerves leaves eye
no receptors here
create hole in our vision
but one eye covers the blind spot of the other
It is located in the periphery, where acuity is
low anyway
The brain “fills in” the spot
specialization across the retina
fovea= detailed vision
periphery=low-light vision
averted vision
look slightly away from things at night to see them better
phototransduction
the process of transducing light energy into bioelectrical signal in neurones
odd, backwards
transduction of light
photoreceptors (rods and cones) have inner and outer segments
outer segments contain visual pigments:
rods=rhodopsin
cones= 3 types of photopsin
these “opsins” are GPCRs
the dark current (in darkness)
sodium ions (Na+) flow into outer segments of photoreceptors
potassium ions (K+) flow out into the inner segment
sodium-potassium pumps keeps potential at steady -40mV
sodium inflow can only happen with the help of cGMP
the phototransduction cascade
1) light is absorbed by an opsin, isomerizing it into an active form
2) activates cGMP
3) activates an enzyme that converts cGMP to GMP
4) makes for less cGMP, sodium (Na+) channels shut down
Thus more light means lower positive inflow
The end result of all this is greater polarization
Down to -70 mV from -40 mV!
Name two weird things about how the
receptors work
1) More light = less neurotransmitter release from
the photoreceptors
And it’s glutamate, which is normally excitatory
2) This is all rectified by the fact that ON bipolars are weird and fire more when they get less glutamate
only _____ absorbed by an ______ are traduced into neural signals
photons, opsin
what does number of photons absorbed depend on? (2)
1) number of photons hitting retina
more photons present = more photons absorbed
2)wavelength of photons
each photoreceptor has a lamba it absorbs best
how do you get the absorption spectra of photopigments?
shine a laser through a vil of rhodopsin or cones
measure how much is transmitted
do this across the of lambdas (400-700nm)
peak absorption for each photopigment
rhodopsin=400nm
S-cone= 440 nm
M-cone= 530
L-cone=560 nm
absorption spectra and human sensitivity spectra
to see if a.s. relates to variations in human sensitivity across the spectrum
how do we measure absorption spectra and human sensitivity spectra
have to measure 2 human Spectral Sensitivity Functions (SSFs)
compare a.s. of the various photopigments to the SSFs
what is an SSF
a psychophysical function, two physical units
it shows sensitivity as a function of wavelength
sensitivity (S) as the inverse of of the threshold (T)
S=1/T therefore T=1/S
S=1/T therefore T=1/S
what is this for
Spectral Sensitivity Functions
to see if absorption spectra relates to variations in human sensitivity across the spectrum
what are the two types of SSFs and how do you do them
Scotopic=rods, night vision
in low light levels
place stimulus just off fixation
Photopic=cones, day vision
make stimulus small
place stimulus directly at fixation
how do rods and cones a.s. match the SSF
rods a.s. matches well to SSF
the 3 cone functions must be combines to explain the SSF, specifically M and L cones, little input from S
the Purkinje Shift
at twilight/night, blue/grreen things brighter while red/yellow things look darker
rods more sensitive to light around 500 nm (blue/green)
cones more sensitive to light around 550 nm (yellow)
compare cones when it comes to night/day vision, sensitivity, acuity, and colour sense
rods=night vision, more sensitive, no colour sense
cones-day vision, better acuity, provide colour sense
what is photopic? what happens to both cones and rods when this occurs?
when light levels are > 1cd/m squared
rods=bleached (all photopigments are isomerized)
only cones function
what is scotopic? what happens to both cones and rods when this occurs?
when light levels are <0.01/m squared
rods=regenerated and become functional
cones=available but not sensitive enough to detect such low light levels
what is mesopic? what happens to both cones and rods when this occurs?
when light levels are 0.01 to 1 cd/, squared
what is odd about colour vision and photoreceptors
all 3 receptor types work at once
dark adaption
the process of switching from cone vision to rod vision
not due to pupil dilation, retinal phenomenon
time course of dark adaption
takes 20 min or more cone adaption (5 min) rop adaption (20 min)
what are the three experiments to measure time course of dark adaption, what do all three have in common method wise
1) rods and cones: stim placed at side of fixation
2) cones only: stim light right at fixation
3) rods only: test colour-blind person
exposed to bright light so cones and rods are bleached
then lights turned off, measure absolute threshold for light brightness at various time intervals thereafter
light adaption
the process of switching from rod vision to cone vision
not due to pupil dilation, retinal phenomenon
time course of light adaption
takes less than a min
why does dark adaption take longer than light adaption?
LA only require that pigments be bleached (used up)
DA takes takes longer bc pigments must be regenerated after being bleached
neural circuits
a group of neurones connected by excitatory and inhibitory links
what are the three principles of of neural circuits
1) linearity
2) convergence
3) lateral inhibition
why is stim placed on the side of fixation for rods and cones experiment of time course of dark adaption
to stimulate both rods and cones
the peripheral sees things on the sides
the fovea sees thing in the centre but only has cones
what type of neural circuits contain all three principles
centre-surround circuits
what is a linear circuit?
simply a chain of neurones, one stimulating the next
input into each receptor has no effect on the output of neighbouring cells
each circuit can only indicate single spot of stimulus
what is a convergent circuit?
a chain of neurones where input from each receptor summates into the next neurone in the circuit
output varies based on input
increases output as stimulus increases in some characteristics like length and bandwith
what does greater convergence lead to? (3) why?
greater convergence=more receptors feeding into one neurone
1) higher sensitivity to faint signals because high rod to ganglion cell ratio and rods are sensitive to light
2) less specificity/ acuity of signal detail/ reduces detail because foveal cones need more light to respond that rods, they are less sensitive
3) greater spatial summation
what is lateral inhibition in neural circuits? what does this result un?
adjacent receptors inhibit one another
results in a strong response from stimuli have a given narrow range of a particular characteristic (size, frequency, sweetness, etc)
weaker response from stimulus close to range
no response from stimulus outside of range
retinal ganglion cells (RGCs)
type of neurone throughout the retina
photoreceptors send signals to RGCs via neural circuits
125 million of each convergence 100:1
RFs of RGCs
almost all are centre-surround small near fovea large in peripheral half ON/OFF, half OFF/ON this is why visual acuity so much greater near the centre of visual field
centre-surround RFs firing
fire maximally to stimulus of just the right size
fire less if stimulus is smaller or bigger
types of RGCs (2) what are they and percentage of them
1) midget: small cells with small RFs, 70%
2) parasol: big cells with big RFs, 30%
what are inner nuclear layer cells and what how are they set up
between photoreceptor layer and RGC layer is inner nuclear layer
1) bipolar cells
2) horizontal cell
3) amacrine cells
all set up in such a way that give the RGCs a centre-surround RF
what are bipolar cells in the inner nuclear layer?
carry info vertically from receptors to RGCs
on=light
off=dark
decides whether an RGCs Rf has an on centre or off centre response
horizontal cells in the inner nuclear layer?
obvious
inhibitory=off surround response
excitatory= on surround response
amacrine cells in the inner nucleus layer?
carry info horizontally across ganglion cells
many roles
what is A=2xarctan[(S/2)/D]
visual angle calculation
why is acuity best in the fovea? (3)
1) densest possible receptor mosaic
3) smallest RFs
3) best optical quality image
what is MAR how do you calculate it?
measures acuity
20/20 vision means being able to resolves 1 min of angle (1/60th of a degree)
20/60 means only resolve 3 min of angle (60/20=3)
what is grating acuity
measures the min contrast needed to detect a grating across the spatial frequency spectrum
what do each of these things detect? RGCs VI V4 temporal lobe
dot detectors
line orientation, motion, colour
shapes
objects, faces
who is the brain organized? (4)
1) modules
2) streams
3) columns
4) maps
what are the two streams of vision processing?
1) dorsal: where pathway, motion processing
2) ventral: what pathway, object identification
explain contrlaterality in vision
right nasal visual filed—->temporal retina—–>ipsilateral hemisphere
right temporal visual field—>nasal retina—>contralateral hemisphere
what are the two paths from the eye to cortex?
1) geniculocortical pathway: LGN—>VI (90% of RCGs)
2) testopuvin pathway: superior colliculus—>pulvinar nucleus in visual cortex (10%)
what is the LGN, where is it, how is it organized?
in the thalamus
the nuclei for early sensory processing
a module organized in layers and columns
what are the layers of the LGN?
1&2: magnocellular
3&4&5&6: parvocelular
1&4&6: contralteral
2&3&5: ipsilateral
the LGN’s retinoptic map
adjacent neurones in LGN have adjacent neurone on the retina
how do we know about retinoptic maps and location columns in LGN?
single-cell recording experiments on monkeys
superior colliculus
small branch from optic tract goes to to here
receives descending signals from visual, auditory, and somatosensery cortices
integrates all of them to coordinate eye and body movement towards stimuli
layers of VI
1: no neurones, just fibres from neurones below
2 and 3: communicate horizontally with other visual cortical areas
4A and 4B: received input from LGN
4alpha: receives LGN’s magnocellular inputs
4beta: receives LGN’s parvocellular inputs
5 and 6: sends descending communications back to subcortical areas (LGN and SC)
difference between minocular/bionocular neurones
majority in VI?
mino=respond to stim of only one eye
bino=respond to stim of either eye
mostly bionocular
what is orientation selectivity of VI?
most VI neurones have elongated RFs that are like rectangles
each neurone responds best to a line of light or dark of given orientation
draw the model showing this
M vs. P channels
two channels that start in the retina
M channel—>MT—->dorsal stream
P channel—>V4—>ventral stream
where does the ventral stream mostly engage in vision?
the inferior temporal area (IT)
what are the 3 zone of the the inferior temporal area (IT)
1) PIT: complex form procession tasks
2) CIT: complex form processing tasks
3) AIT
what are some examples of complex form procession tasks done by the PIT/CIT of the IT
inverse projection: determining 3D shape from 2D info
segmentation: differentiating objects from background and each other
viewpoint invariance: objects look different from different viewpoints
what are the two models of viewpoint invariance?
1) structural description models: geons
2) image description models: identify 3D objects from stored 2D viewpoints from different perspectives
prosopagnosia
inability to recognize faces
often due to damage in AIT
five ways to perceive movemnt
1) real movement
2) apparent movement
3) induced movement
4) movement aftereffect
5) movement illusion in static stimuli
motion agnosia
damage to cortex causing inability to perceive movement
two approaches to studying motion
1) ecological
2) physiological
local distubrance
occurs in the optic array, causes other motion
an object moves relative to a static background and vice versa
global optic flow
causes self motion
overall movement of the whole optic ray indicates the observer is moving
corollary discharge theory signals (3)
1) motor signal (MS): signal sent to eyes to move eye muscles
2) corollary discharge signal (CDS): copy of the motor signal
3) image movement signal (IMS): movement of image stimulus receptors across the retina
the aperture problem
complex cortical cells respond to an orientated bar moving in a specific direction
observation of small portion of larger stimulus leads to misleading/incomplete info about the direction of movement
solution to the aperture problem
VI complex cells with different direction sensitivities are pooled
may occur in MT cortex
how is shown that the ventral stream processes motion
the MT is part of it
lesions in monkey’s MT led to motion detection issues
apparent motion
biological plausibility
one object must have occluded the other
shortest-path constraint
implied motion
pics that are stations that depict an action that involves motion
MT/MST fire
representational motion
reed and vinson experiment with rocket and dumbells
