Midterm 3 Flashcards
do objects have colour
no they have reflectance profiles
is light coloured
no it only has wavelength
you construct the colour and many people experience colour differently
explain the electromagnetic spectrum
energy is described as by a wavelength
spectrum ranges from short gamma (10^-3) to long radio waves (10^15)
visible light = 400-750 nanometres
frequency = speed/ wavelength so wavelength = distace between two peaks
define monochroatic light
one wavelenght
eg laser
physical parametres of monochromatic light
wavelenght
intensity
define heterochromatic light
many wavelengths
what is spectral composition
for heterochromatic light
gives the intensity at each wavelenght
graphically what is the differences between mono and hetero chromatic light
mono = vertical bar down at specific wavelenght
hetero = horizontal line across then white light at all wavlengths present
or steep up and acorss = none of some wavelenghts but the other wavelengths are there
explain the spectral composition of tungsten vs sunlight
tungsten = from light bulb, steady increase as wavefunction increases sunlight = increases at the lower end of the spectrum then decreases
the spectral components of light entering the eye is the product of what two things
the illuminant and the surface reflectance of objects
so illuminant = light type, mono or hetero and if hetero which wavelenghts
surface reflectance = what is reflected is what we see
so purple, blue, green, yellow, orange, red = (low to high wavelength)
what are the three psychological dimensions of colour
hue
saturation
brightness
explain hue
perceived colour of the object
organised around a circle (circumference)
explain saturation
as colour wheel becomes whiter and whiter
is the diametre of the circle`
explain brightness
maps onto energy
how dark or bright
3D HSV colour space
circle top surface = circumference of hue, diameter of saturation and then 3D depth of value or brightness = starts bright and descends into black
for unimodal distributions, how do we go from physical properties of light to pscyhological dimensions of colour
hue =
saturation =
value / brightness =
hue = peak, centre, of spectral distribution so where peak is saturation = spread (variance) of spectral distribution so narrow vs fat peak brightness = height of spectral distirbution so stumpy is dark and tall is bright
additive vs subtractive light
additive = white lights add to make white light, so how monitors (RGB work)
subtractive = add to give black so paint
for pigments so subtractive - in the mixture, the only wavelengths reflected by the mixture are those that are reflected by all the components in the mixture
how do monitors work eg stadium or computer screen
RGB
only three colours - phosphors
almost any colour can be generated by adding different amounts of the three primary colours (red, green, blue)
works because we have three types of photoreceptor (S,M,L cones) (short is vaguely blue, medium is green and long is red)
physiology of colour vision
the normal retina contains three kinds of cones (S,M and L) each maximally sensitive to a different part of the spectrum
trichromatic theory of colour vision
young-helmholtz
our ability to distinguish between different wavelengths depends on the operation of three different kinds of cone receptors, each with a unique spectral sensitivity
each wavelenght of light produces a unique pattern of activation in the three cone mechanisms
No blue, red, green cones!
perceived colour = the relative amount of activity - the pattern of activity - in the three cone mechanism
the principle of univariance
the absorption of a photon of light by a cone produces the same effect no matter what wavelength of light generates the response
so m cones for example will respond equally to a dim green light as a bright red light - as far as just M cones alone, these are exactly the same
so we need 3 cones to tell the difference
so
so how do we see colour
L,M and S responses
will get some output ration of three different cone types
works with mono and hetero chromatic distributions
how do iphone and computer monitors etc work
so slide showed heterochromatic light source activating s,m and l to specific extents
as long as the monochromatic light source acts on the three cones in excatly the same way = then see the same colour
=metamers
metamers
two diff lights
some arbitrary distribution of light you can mix 3 monochromatic light sources in a way to produce the same outputs across the cone types = same perceived colour
on any arbitrary disribution
how iphones etc work
relies on our 3 cones
based on trichromatic theory of colour
so can mix the three primary colours to make amy colour at all (worked this out before discovered the three photoreceptors match onto this
herring’s argument against trichromacy
never see a yellowish blue or greenish red
base on colour after effects
red and green are fundamentlaly opposite and so are yellows and blues so dont see these together
= opponent processing
opponent process theory
colour vision is influences by the activity of two opponent processing mechanisms
= a yellow / blue opponent process
so see loads of yellow, M and L isomerise so calm down, then white light shown = perceived as blue as no yellow opponent process on
= a red / green opponent provess
stare at red, part of retina looking at red drives long wave cones maximally, isomerise and turn off. then white light shown and will perceive as green as no opponent red
complete how we see colour combining two theories
trichromacy = metameric matching
see all colours with 3 cone types
can predict on hue, saturation and brightness
second layer of opponent processing
second order wiring
certain combinations of colours are not perceived based on neuron wiring
name and explain types of colour blindness
monochromat- person who needs only one wavelength to match any colour - pure colour blindness = rods only = rare
dichromat - person needs only two wavelengths to match any colour
anomalous trichromat - needs three wavelenghts in different proportions in different proportions than normal trichromat
unilateral dichromat - trichromat vision in one eye and dichromat in other eye
pure colour blindness = rods only = rare
colour experience of monochromats
very rare, heridatary only rods and no functioning cones ability to perceive only in white, gray and black cones true colour blindness poor visual acuity very sensitive to bright light only output of one colour receptor, touches on principle of univariance no concept of colour
colour experience of dichromats
are missing one of the three cone systems
3 types
protanopes - no L
see in blues to yellows (red - green colour)
dueteranopes - no m
see in blues to yellows (red - green colour)
tritanopes - no S
see in red to green (so blue yellow colour blind)
not true colour blindness, just see colour differently as onl output from two cones
how audition differs from vision
vision - space for free (map created in periheral receptors in retina)
audition - no spatial map, must compute space centrally
-some acoustic information about sound location, but no spatial information at the cochlear
sound (and thus the process of hearing) is inherently temporal in how it physically occurs / provides information - unfolds over time
physical sound is…
compression of air molecules in space
how do loud speakers produce sound
the diaphragm of the speaker moves out, pushing air moecules together
the diaphragm also moves in pulling air molecules apart
the cycle of this process creates alternating high and low pressure regions that ravel through the air
= sound waves
sound waves
pure tone created by a sine wave
period = whole wave = tone
amplitude of a sound wave
height above atmospheric pressure
difference in pressure of high and low peaks
frequency of a sound wave
how may waves are packed in over time
number of repeating cycles in a given second
where wave returns to the same spot
physical properties of a sound wave frequency amplitude timbre result in what perceptual elements of sound
frequency (period)- pitch
amplitude - loudness
complexity - timbre (how we tell between a clarinet and a flute), relative to harmonics. dependent largely on relative energy in different frequency bands of sound’s spectrum. relative power accross the harmonics
reflectance
multiple paths / path lenghts of an acoustic signal; same sound will be variabley decayed / decay thus same sound arrives at ear at different times with different acoustic properties
clarinet demo
the harmonic structure caused timbre to change
pitch and loudness otherwise the same
how we measure / depict sound
waveform - frequency by amplitude
decibels
spectogram
decibels
measure amplitude / sound pressure - perceptual correlate = loudness
10dB increase = perceived doubling of loudness
doubling distance = 6 dB loss in perceived loudness
50-65 dB =average amplitude of human speech
but loudness is not based purely on sound pressure / amplitude
-duration
-frequency
takes a higher decibel to yield the same perceived loudness level in a person for a different frequency
spectrogram
most useful way of visually depicting sound
plots relative power of a given sound across time and its frequency spectrum
fundamental frequency
lowest frequency / base frequency at which there is distinct power for a sound
harmonic structure of a sound is necessary based on what the fundamental is
each harmonic above it is a mutliple of the fundamental
the base frequency band at which a sound has power
determines the structure of the harmomics which will determine the timbre / harmonic structure (bands are multiples of the fundamental frequency)
ear converts
sound waves in the air into electrical impulses
this is interpreted by the brain
track route of sound entering the ear
enters through external auditory canal
timpanic membrane
this vibrates in response to the sound
three bones - auditory osciles (malius, incus, stapes in that order)
movements of timbanic membrane vibrate the osicles passing on the information of frequency and amplitude
three bones pivot togther on amplitude = series of ligaments holding middle ear in place (anterior malial, posterior incutal ligament = important)
footplate of stapes
stapes moves with piston like structure into labrinth
filled with paralimbth
round window flexibility - allows for pressure change
so vibrations enter the labrinth
cochlear - vibration from stapes into cochlear then out to round window
asecending (scala vestibuli) and descending paths (scala tympani)
cochlear duct between the two - filled with endolympth
resner membrane separates and so does basal
organ of corti on basal membrane - this sends impulses to the brain by the cochlear nerve - hair cells do the trandsuction
tactorial membrane covers hair cells
basal membrane moves variabley
specific areas along the basal membrane move specifically for different frequencies
-low frequencies = at apex
-high frequencies = base
=tonatopic orientation
vibrations on timpanic membrane
low pitch / frequency = slower vibrations
lower volume / amp = less dramatic
shape of timbanic membrane
cone shaped
