Sensation & Perception Part B Flashcards
How do we perceive depth?
by using different cues, divided into 3 groups:
oculomotor cues
monocular cues
binocular cues
example of binocular disparity
If you hold your finger out at arm’s length and then look at it alternately with your left eye only and then your right eye only, the image of your finger relative to the world behind it will shift somewhat. This is binocular disparity, which helps provide the basis for the determination of depth.
RELATIVE DISPARITY DOES NOT CHANGE BUT ABSOLUTE DISPARITY DOES
What is the correspondence image?
- retinal images can be ambiguous
- if there are multiple identical objects in the scene it can be hard to figure out which images in the left retinal image should be associated with which images in the right retinal image
how can the correspondence problem be resolved?
if the objects in the visual scene are made distinct from one another by colour e.g. the associations become unambiguous
what is the horopter?
the plane containing all points that will fall on corresponding parts of the 2 retinas
size constancy equation
S= K x (R x D)
S = apparent size of object
K is constant
R = size of retinal image
D = perceived distance to object
Size illusions - how do they work?
if an object appears closer than it really is, it will appear SMALLER than it really is and vice versa
e.g. Ames Room
Holway & Boring (1941)
- investigated how observers estimate size of objects –> how DEPTH cues influence size judgments
- observer sat at intersection of 2 corridors & could view a test circle in 1 corridor & comparison circle in another corridor
- their task was to adjust the size of the comparison circle to match the size of the test circle
- test circles were of dif sizes by were presented at dif. distances so that their angular size was always the same
REVIEW HOLWAY & BORING (1941)
condition 1: observers could determine the depth of the test patch using binocular disparity, motion parallax, & shadows
condition 2: observes viewed the test circle with one eye to remove binocular disparity cues
condition 3: observers viewed the test circle through a peephole to remove motion parallax cues
condition 4: in addition viewing the circle through a peephole, drapes were used to remove shadows
How are depth & size related?
how big an object appears can affect how far away it appears & how far away an object appears can affect how big it appears
how can the correspondence problem be resolved?
if the objects in the visual scene are made distinct from one another by colour e.g. the associations become unambiguous
What determines the perceived size of an object?
its angular size
its perceived depth
angular size
the visual angle an object subtends
the closer an object is to person, the larger its angular size
what is size constancy?
the phenomenon where an object’s apparent size does not depend on its physical distance
When an object is far away it appears to
be the same size as when is it closer…
…even though its visual angle is much
larger in the latter case
how to achieve size constancy?
consider both the size of the retinal image AND the distance of the object
if someone misestimates the distance of an object. . .
they will probably misestimate the SIZE of the object
What did holway & boring (1941) conclude?
- concluded that when there are sufficient depth cues, the size of the test patch can be accurately estimated
- when there are not sufficient depth cues, the apparent size of the test patch is BIASED towards the VISUAL ANGLE
further away test patches are PERCEIVED AS SMALLER THAN THEY REALLY ARE
Accurate size estimates can occur only
when distance to the object can be
estimated accurately
Ames room illusion
When a person moves to the left-hand side of the room, they are actually further away and the ceiling is higher. They appear as a smaller image on your retina and you therefore perceive them as small. The opposite effect occurs on the right-hand side of the room
physical definition of sound
sound is PRESSURE CHANGES in the air or other medium (e.g. sound waves in water)
perceptual definition of sound
sound is the EXPERIENCE (i.e. sensation) we have when we hear
pressure waves (sound waves) move through air & water at. . .
air: 340 m/s
water: 1,500 m/s
each air molecule is just moving back & forth to create regions of high + low pressure
when does a PURE tone occur?
occurs when the change in air pressure occurs in a pattern described by a mathematical function called a sine wave (w/ amplitude)
time on x axis, air pressure on y axis
the higher the frequency, the ___ the pitch
higher
1 Hz = ?
1 oscillation per second
humans can hear tones ranging from about 20 Hz to about 20,000 Hz
the greater the amplitude, the ____ a sound seems
louder
amplitude in measured in. . .
decibels
dB = 20 x log(p/po)
where p is the pressure (amplitude) of the sound (measured in micropascals)
po is the reference pressure, usually set to 20 micropascals
the 200 Hz is known as ?
the fundamental frequency & it is also known as the 1st harmonic
400 Hz = 2nd harmonic
600 Hz = 3rd harmonic
800 Hz = 4th harmonic
because the 1st harmonic is 200 Hz, this means that the wave repeats every 5 ms
Perceptually, how is loudness measured?
it is measured in phons (units of loudness for pure tones)
For a pure tone, pitch is determined by. . .
FREQUENCY
For a complex tone, pitch is USUALLY determined by. . .
the fundamental frequency
pitch is described in
in terms of musical notes (A, B, C)
all notes corresponding to the same letter are multiples of the same frequency
what is a complex tone?
the summation of 2 or more pure tones
neighbouring letters of the same type (C1 & C2 e.g.) are separated by. . .
an octave
notes with the same letter. . .
sound similar - they are said to have the same chroma
as one moves from left to right on the piano keyboard, the . . .
tone height increases
pitch is a psychology variable with 2 attributes:
- tone height (increases from left to right in continuous matter on piano keyboard)
- chroma
chroma
it is cyclic in that neighbouring letters of the same type sound similar
Explain the concept of missing fundamental
- complex tones can be decomposed into their constituent frequency components
- for MANY SOUNDS, the frequency components are multiples of a particular frequency called the FUNDAMENTAL FREQUENCY
- e.g. 200 is the fundamental frequency of 400, 600, 800 etc.
- the complex tone will continue to repeat at the fundamental frequency even when the it is absent
- humans will perceive this “missing fundamental”
The missing fundamental will determine. . .
the PITCH of the complex tone (even though it is absent)
timbre
as harmonics are removed, the pitch does not change but the tone still sounds different
when 2 dif instruments play the same note, they don’t sound the same. Why? (due to dif timbres)
because in addition to playing the fundamental frequency, each instrument plays many of the harmonics (i.e. multiples) of the fundamental frequency
the amplitudes of these harmonics will be dif so the resultant waveform is dif so the sounds are dif so the timbres are dif
periodic vs aperiodic
periodic - regular
aperiodic - irregular e.g. loud crash
auditory localisation is based on
binaural & monoaural cues
binaural cues include:
- interaural time differences
- interaural level differences
interaural level difference
for high frequency sounds, there can be LARGE INTERAURAL LEVEL DIFFERENCE b/w the 2 ears due to the sound shadow caused by the head
for low frequency sounds, the interaural level difference is much less
cone of confusion
binaural cues cannot be used to distinguish b/w 2 points connected by circumference line on one side of head
monoaural cue for elevation
- sound coming from dif elevations bounces off dif parts of the pinna before entering the ear canal
- so sound acquired characteristic frequency notches that depend on its elevation
precedence effect
- if you hear the same sound twice with a temporal separation of 5-20 ms, you will not register the 2nd sound
- won’t hear an echo
- if temporal separation bw 2 sounds is more than about 10th of a second you will hear an echo
architectural acoustics
indirect sounds affect perceived quality of sound
4 factors
- reverberation time
- intimacy time
- bass ratio
- spaciousness factor
reverberation time
- time it takes for sound to decrease by 60 dB
- for concert hall should be about 2 seconds
intimacy time
- the temporal difference b/w when the direct sound arrives and the first indirect sound arrives
- concert halls w good acoustics usually have about 20 ms of intimacy time
base ratio
- measured for indirect sound
- it is the ratio of low frequencies to middle frequencies for the indirect sound
- ideally, you want a high base ratio
spaciousness factor
- ratio of indirect sound to total sound
- the greater the proportion of indirect sound, the greater the spaciousness factor
- ideally, you want a high spaciousness factor
why is it a good idea to place pillows in concert hall?
so the pillows absorbs the same amount of sound as the average person - so acoustics of hall will be same whether it is full or empty
5 cues people use to separate sound sources
- location
- onset time
- timbre and pitch
- auditory continuity
- experience
location
Because the three musicians will not be playing
exactly the same notes at exactly the same time,
you will be able to hear that they occupy separate
locations using the mechanisms that we discussed
earlier.
you are using INTERAURAL TIME DIFFERENCES + INTERAURAL LEVEL DIFFERENCES
it is a strong cue but not a necessary one
onset time
if 2 sounds start at dif times, chances are they originate from dif sources
timbre & pitch
it is easy to segregate musical instruments that have dif timbres
- even instruments w the same timbre can be separated on the basis of pitch
auditory continuity
tones interrupted by silence are heard as distinct
tones interrupted by noise are heard as continuous (continuing through the noise)
