Sensation and Perception

Question 1

What is attention?

Answer 1

ability to preferentially process certain parts of a stimuli at the expense of other stimuli

-processed stimuli will be more clear than others

Question 2

Why is attention needed?

Answer 2

• our perceptual system capacity is limited
• can’t process everything in visual scene simultaneously
• therefore, attention helps us from being overwhelmed with stimuli

Question 3

Types of attention

Answer 3

Overt attention - directly looking at an object

Covert attention - looking at one object but focusing attention on another (e.g. looking one way in basketball but passing in another direction)

Question 4

Monitoring Attention

Answer 4

-generally can tell one’s attention by tracking their eye movements
attention is when one fixates on an object

Saccades - very rapid eye movements between fixations
Fixation - rests between jumps where eyes look directly at one object
-fixations are directed by goals and expectations

Question 5

Direction of Attraction

Answer 5

Initial Involuntary Process (attentional capture)
-initial attention fixates on noticeable/important parts (dependent on salience)
Salience - quality of being noticeable
-contrast captures our attention (colour contrast, shape contrast, motion contrast, size, orientation)
Theeuwes (1992) - asked participants to report the orientation of line inside the square. There was a circle of shapes, all green besides one red circle. Although participants were aware of goal, initial attention was was directed at red circle.

Subsequent Voluntary Process (guided by goals/expectations)
-after few fixations, we can direct our fixations depending on goals/expectations
-Unexpected objects can also cause fixations (related to expectations)
SEMANTICALLY consistent and inconsistent objects are objects that do/do not belong to scene
SYNTACTICALLY inconsistent objects are objects that belong but behaving unexpectedly

Question 6

Effects of Attention

Answer 6

Attention increases rate of response
-Posner (1978)
3 groups: valid, invalid and neutral
valid - saw arrow above fixation point pointing in direction of where X will appear
invalid - arrow was pointing in opposite direction of X
neutral - no arrow
Participants had to indicate when X appeared
Results showed valid group responded fastest and invalid group was slowest (when fixated in a spot, participants observed faster)

Attention can influence appearance
-Carrasco (2004) demonstrated attention changes apparent contrast of an object
Shown grating sheet with two sides
Was asked to report which side had higher grating
Fixation point was given either a neutral cue (middle of sheet) or peripheral cue (on the left side of image)
In trials where grating was same contrast, those shown the peripheral cue reported left side to have higher grating
(attention can cause objects to appear bigger, faster or more richly coloured)

Attention can affect physiological responding
-neurons in brain respond more to attended stimuli rather than unattended stimuli

Question 7

What is the Binding Problem?

Answer 7

How an object’s individual features are combined to form a coherent perception (harder with lots of object)

• different parts of a stimuli is processed by different parts of the brain (processed independently)
  e. g. motion is processed by dorsal stream and form is processed by ventral stream

Question 8

Feature Integration Theory (FIT)

Answer 8

• one solution for binding problem suggesting that binding problem is solved by attending to only one location at at time
• features that are present at a given location are processed so those features are bound together
• this avoids binding features from other objects

Illusory conjunctions = due to lack of attention, features of different objects will be incorrectly bound together

Tresiman and Schmidt (1982) - showed participants character string very briefly followed by a noise mask
Participants were asked to report the two numbers at the end of string, and colour of letters inbetween
Results show that participants tend to associate the wrong colours to wrong letters

Question 9

What is Balint’s Syndrome?

Answer 9

Difficulty to focus attention on one object (prone to illusory conjunctions)

RM is a patient with parietal lobe damage where RM can’t focus on a single object (focuses on multiple objects at once)
When shown two letters with different colours, RM gave wrong colour combinations even when looking at them for up to 10 seconds (25% wrong)
-proves feature integration theory

Question 10

Visual Search

Answer 10

perceptual tasks where requirements for binding takes place
e.g. if target contains same features of distractor, binding is required (red horizontal bar is target, but distractor includes green and vertical features too on top of red horizontal bar)

CONJUNCTION search = target differs from distractors only by its specific conjunction features (looking for object that is red AND horizontal)
-FIT predicts conjunction search is very slow, takes time to process each individual object

FEATURE search = focusing on features that the distractors do not have
type of visual search without solving binding problem
-FIT predicts binding does not need to occur as attention does not need to be applied to every object (faster)

Question 11

Change Blindness

Answer 11

Changes that are obvious with attention but missed with no attention
(attention can determine what we remember)
-this occurs due to our limited capacity of perception (only few parts of scene can be remembered)

Simons and Levin (1998) - demonstrated change blindness in real life situation
Experimenter asked pedestrians on street for directions whilst people carrying a door walk in between them. People swapped behind door but continued to act as if asking for directions.
Results show approximately 50% did not notice person changed

-change blindness is only when changes are large and obvious, missed due to lack of attention

Question 12

Problem of object and scene perception

Answer 12

Perception is harder than it seems due to:
-Stimulus on retina can be ambiguous (if shown different types of lines in 1D, it will all look the same, curved, zigzag, straight liens) (can also occur in 2D)

• Objects can be hidden or blurred (e.g part of glasses are hidden under a book)
• Objects look different at different angles/viewpoints/poses (machines cant detect when in unexpected angles/poses)

To demonstrate how difficult it is, even computers are worse at recognising objects compared to humans
-Computer object recognition systems use artificial neural networks
purposely created images to trick system: showed an image of a turtle but misidentified it as a rifle

Misclassifications of natural objects can happen if presented in unexpected orientations
Alcon (2019) - presented natural objects in different orientations to object recognition systems
School bus, motor scooter and fire truck were all recognisable unless in different orientation (viewed from above, object was rotated or sideways)

Question 13

Solving Perceptual Problem - Structuralism

Answer 13

Arose from Edward Titchner studying Wilhelm Wundt
-distinguishes between sensations and perceptions
Perception = conscious awareness of objects and environment
Sensation = natural reflexes/behaviour in response to stimulation

Structuralism is the combination of sensations to form perception

Conscious awareness is made up of the elementary sensations (nothing is made up in conscious awareness, everything is already present and all from individual sensations

Question 14

Solving Perceptual Problem - Geraltism

Answer 14

• Claims that conscious awareness if MORE than just the sum of elementary sensations
• conscious awareness can have characteristics not present in sensations

Evidence: APPARENT MOTION AND ILLUSORY CONTOURS
-observers see two stationary points flashing in succession. even though they are stationary, observer sees motion. shows that conscious awareness has a character (motion) thats not present in elementary sensations
(conscious perception of motion was created)

-illusory contours are seen in scenes where there is no physical contour
conscious awareness of illusory contour is created

Question 15

Perceptual Organisation

Answer 15

Perceptual organisation grants humans ability to perceive objects and scenes
Perceptual organisation of images to form an object

There is Grouping and Segregation
With grouping and segregation, we can perceptually organise a scene into its individual objects to understand the scene

Question 16

Grouping (perceptual organisation)

Answer 16

-Gestalt principle of grouping
process of which individual parts of an image is perceptually bounded together to form perceptual whole

6 principles (more principles increases likelihood of grouping to occur):

• good continuation = aligned (nearly aligned) contours are grouped together to form an object
• Pragnaz = ‘good figure’, grouping of images to make an image as simple as possible (e.g. WWF panda is made up of black splotches)
• similarity = similar objects group together
• Proximity = closer objects are more likely to be grouped together
• Common fate = objects moving in the same direction/way are grouped together
• Common region = objects in same area tend to be grouped together
• Uniformed connectedness = connected regions with similar characteristics tend to be grouped together (e.g. colour)

Question 17

Segregation (perceptual organisation)

Answer 17

-Parts of a scene that is separated to form ‘wholes’ (perception of individual objects)

Figure-ground perception = objects are considered ‘figures’ and background is ‘ground’
Figural properties: objects are in front of image/scene, bottom of image, convex (curved) images, more recognizableimages

e.g. Rubin vase (where you see either faces or a vase; if silhouette was placed differently, you would see face/vase more easily)

Bottom of image - Vecera et al (2002)

Convex images - Peterson & Salvagio (2008)
when shown images with single border, observers tend to perceive border that is convex to be the ‘object’

Question 18

Gist Perception

Answer 18

Gist perception occurs when an overall impression of a scene can be determined just by scene being rapidly flashing in front of us

-Potter (1976)
Observer was cued (1-2 words) of a particular scene than flash 16 random scenes. When asked whether one of the scenes matched the description, observers were close to 100% accuracy
Rapidly can get a gist percetion

-Fei-Fei (2007)
Investigated the minimum amount of time required to get a gist perception
Showed the scene then a mask and asked to describe the scene
27ms is minimum amount of time required to perceive gist (although not accurate)
Accurate gist can be achieved in just 250ms

Question 19

Motion Perception

Answer 19

• Motion perception helps us break camouflage, bring attention to items, segregating objects from its background
  e. g. a camouflaged animal can be invisible, but when its moving its camouflage is broken and attention is drawn to the animal + motion helps us break this object from the environment

-Interpret events
we can see how objects interact (casuality relationship and even social relationships)
e.g. a large triangle gets into an argument with small circle + triangle and eventually chases them off away from his home (we can tell a story just through motion of objects)

-Determine structure of objects
helps us determine a shape of a moving object
-Kinetic Depth Effect
motion can help us detect a 3D object

-What actions (and why) people are performing
static poses can be unclear (vague) where motion can help us make one’s behaviour clear
POINT-LIGHT WALKERS EXPERIMENT
=circle points on joints on a human is shown on a black screen where they perform an action and observers guess the action
results show that humans are very good at processing motion stimuli, they can guess the action

Question 20

Akinetopsia

Answer 20

Akinetopsia is the inability to perceive motion due to either disease or brain trauma (suffer damage to brain part responsible to motion perception)

L.M. - patient who had difficulty in pouring tea, crossing the street, following speech (hard to read lips)
can see objects
(real life example = seeing a ship from very far away but it doesn’t appear to be moving, however after a while, it has been moved)

Question 21

When do we perceive motion?

Answer 21

-Real motion (actually moving)

-Illusory motion (nothing moving)
e.g. static image (kiatoka & ashida - 2003; rotating snake illusion)
unsure of why it causes illusory motion, however, perception of motion occurs due to contrast of colour

-Apparent motion
e.g. displaying two separated dots that flash consequently, appearing as if dot was moving side to side
RULES: dots must be sufficiently close enough
-if its too far + rate is too fast, dots will not appear as moving
AS SEPARATION INCREASES, ALTERNATION RATE MUST DECREASE (Korte’s Third law of Apparent Motion)
(apparent motion can be insensitive to colour but can also disambiguate ambiguous apparent motion)

-Motion aftereffects
occurs when fixation on a moving visual stimulus for a while, with stationary eyes, then fixing on a stationary stimulus (stationary stimulus will appear to be moving, but in opposite direction of moving stimulus)

-Induced motion
moving background can cause a stationary object to appear as moving
nearby objects (usually large) affects motion of second object (smaller objects) or causes second object to move

Question 22

Motion Induced Blindness

Answer 22

Motion can also make things disappear (which we have no explanation for)
If we focus on a stationary point (that is flashing), with a moving background, the moving objects behind will disappear

Question 23

Motion Induced Changed Blindness

Answer 23

Motion can make it harder to notice changes in a scene
e.g. with a ring of circles that change colour, if the ring begins moving, it is harder to distinguish the colour change of circles

Colour changes attract attention (transient signals) associated with changes. However, when the objects are moving, transient signals are associated with all the objects
Attention is no longer drawn to preferentially changing objects, thus colour changes are not perceived (we perceive that far fewer objects are changing colours, but all are)

Question 24

Motion Illusions

Answer 24

Motion illusions can inform us of the underlying motion perception (e.g. footsteps illusion - how contrast affects motion perception; yellow and blue rectangle go up and down the striped background where they appear to be moving at different rates (appear to be they are out of sync but they are actually moving at the same rate)

When the yellow rectangle box has low contrast (edges are on white background), blue rectangle box has high contrast (edges on black background)
Higher contrast = moves faster, Low contrast = moves slower
(e.g. real life example = cars in fog)

APERTURE PROBLEM = if you can’t see the ends of a line, the movement of that line is ambiguous
motion of line can be viewed through the aperture (image in front of the line), motion is ‘captured’ by the movement of terminators (where line meets apertures)

When terminators move horizontally, the line appears to move horizontally, when terminators move vertically , the line appears to move vertically
(when we can see the ends of the line, we can actually see motion of line)
real life example = barber pole illusion (line curves around a cylinder which appears to be continuously moving up; line is just moving vertically)

Question 25

Function of colour vision

Answer 25

• it was suggested that colour vision was evolved to help humans to search for items (e.g. foraging berries)
• colour vision helps us to make judgement (e.g. whether a banana is ripe or not or if an animal if poisonous)
• animals use colour to attract mates

Question 26

Physics of colour

Answer 26

Visible light is electromagnetic radiation with wavelengths ranging from from 380nm to 700nm

white light is the mixture of all these wavelengths

opaque objects = an object which light cannot pass through, it is not transparent (colour of an opaque object depends on which light is reflects)

transparent objects = an object where colour is determined by which colour it transmits (goes through)

Question 27

Mixing colours

Answer 27

Blue paint - absorbs red light but reflects blue and green light
Yellow paint - absorbs blue light but reflects red and green light

if we mix blue and yellow paint, new colour will absorb both blue and red light, will reflect green light

Question 28

Munsell Colour System

Answer 28

Colours are categorized into 3 groups:

• Value (lightness of colour: dark to light)
• Hue (colour)
• Chroma (saturation)

Question 29

Trichromatic Theory of Vision

Answer 29

Photoreceptors (found in retina) = rods and cones

Rods = cannot distinguish between colour, mainly for black/white shades
only active in low light

Cones = 3 types of cones that respond to different wavelengths
active in bright light
S CONES = 419 nm (blue, short wavelengths)
M CONES = 531 nm (green, medium wavelengths)
L CONES = 558 nm (red, long wavelengths)
(depending on relative activity of cones, we can distinguish colour)

Question 30

Colour matching (cones)

Answer 30

As there’s only 3 cones, any colour can be matched by combining the 3 ‘lights’

Preferentially stimulating specific cones to match the colour (based on relative activity of cones) which makes the colour same as copied colour
Two patches of colour may not have same spectral composition, but it will appear the same

METAMERS = physically different stimuli that appear to be the same

Question 31

Colour Deficiency

Answer 31

MONOCHROMATISM

• affects 1/100,000 people
• cones are non functioning
• are truly colour blind, only see shades of grey
• since rods are very sensitive to light, they must wear sunglasses during the day

DICHROMATISM
-lacks 1 of the 3 cones
PROTANOPIA - lacks L cones (red wavelengths, male dominant)
can’t distinguish between red and green (unable to distinguish as relative activity between L and M cones must be made to determine red or green colour)

DEUTERANOPIA - lack of M cones (green wavelengths, male dominant)
can’t distinguish between red and green

TRITANOPIA - lack of S cones (blue wavelengths, small cases in both genders)
can’t distinguish between blue and green

Question 32

Unilateral Dichromats

Answer 32

dichromatic vision in one eye and normal trichromatic in other eye
-unilateral dichromats allow us to see how dichromats see the world

Protanopes and deuteranopes = see world in shades of blue, yellowish-green
Tritanopes = sees world in shades of blue and red

Question 33

Opponent-process theory of colour vision

Answer 33

Supplementary theory to trichromatic theory

• colour is not only determined by cones in retina, but also the CORTEX where they are combined into three colour opponent channels
• red-green channel
• blue-yellow channel
• white-black channel

AFTERIMAGES
-visual illusion where retinal impressions are still present even when visual stimulus is taken away
(after fixating on a box for a while (divided into 4 different coloured boxes), NEGATIVE AFTERIMAGE occurs where opposite colours are seen in a blank, white background)
-looking at red stimulus would tire the red processing channel, which is why green would show up in afterimage
-shows proof of red-green and blue-yellow channel

IMPOSSIBLE COLOUR COMBINATIONS
-we are unable to perceive bluish-yellow or reddish-green
these colours are OPPONENT COLOURS (are at opposite ends of colour opponent channels)
if we mix the colours:
blue + yellow = eventually green (not bluish yellow)
red + green = yellow (not reddish green)

Question 34

Colour Constancy

Answer 34

Colour can also be determined by the colour of light shined on it (not just the colour it reflects)
e.g. if white light was shined on a green sweater, green sweater will reflect green light
if red light was shined on a green sweater, it will reflect red (even though green objects absorb red light, if you shine enough red light, it will reflect some)

Light reflected by an object is determined by the product of its reflectance and illumination
Reflectance x Illumination = reflected light

why do we see green sweater even though it reflects red light?
-HABITUATION (part of explanation) = becoming less sensitive to that colour
(if entire scene was red, we habituate to red, viewing the scene greener than it would actually be)

-DISCOUNTING THE ILLUMINANT = in situations where habituation cannot occur as there is equal amount of both colours, humans can discount the blue and yellow illuminants

Question 35

How do we perceive depth?

Answer 35

Oculomotor cues - cues based on our ability to sense the position of our eyes (whether eyes are focused or not)
BINOCULAR CONVERGENCE = when an item is close by, our eyes converge. when item is far away, our eyes diverge (brain can estimate distance of item depending on binocular convergence)
ACCOMODATION = lens changing shape depending on distance of item (moving finger closer or further from eyes leads to eye lens changing shape to keep focus on finger)

Monocular cues - cues based on available information with one eye (cues that can be picked up with one eye)
ACCOMODATION
PICTORIAL CUES - consists of 7 pictorial cues
-occlusion (covering of items)
-relative height
-familiar and relative size (familiar with size of cars)
-perspective convergence (road lines that get smaller the further they are)
-atmospheric perspective (clouds cover objects that are distant)
-texture gradient (texture of grass is more obvious up close)
-shadow (relative depth + depth perception)
MOVEMENT-BASED CUES -
Motion parallax = objects that are closer appear to be moving faster compared to objects further away; we can estimate distance of object depending on natural speed
(objects closer cover a longer distance in retinal image compared to further objects; closer objects change retinal position more)
Deletion and Accretion = parts of scenes that get ‘deleted’ and ‘accreted’ (coming in and out of view) (rate of deletion and accretion can give us an estimate of distance/depth of object)

Binocular cues - cues that depend on visual information from both eyes (cues required to be picked up by both eyes) (if we place finger in front of nose and close 1 eye simultaneously, position of finger shifts slightly)
BINOCULAR DISPARITY = closer object can appear to have different allignment with both eye views
(Retinal image being directly looked at does not move as eyes are converged on object)
HOROPTER = plane containing all the points that will fall on corresponding parts of both retina (same place)
If object is in FRONT OF horopter, object will appear on opposite side of retinal image (e.g. right eye open, views front object on left of fixated point)
If object is BEHIND horopter, object will appear same side of retinal image
(Relative disparity = relative separation of objects in real life
= Difference in absolute disparity of both objects
separation between retinal images between two objects does not depend on point of fixation)
(Absolute disparity = point of fixation affects where fixated point/object has ZERO ABSOLUTE DISPARITY
=Difference in angular distance of retinal image from fovea in both eyes (right eye angular distance - left eye angular distance)
Points IN FRONT OF HOROPTER have negative absolute disparity
points BEHIND HOROPTER have positive absolute disparity

Question 36

Cues that Indicate Relative Depth

Answer 36

relative depth = relative height of object

Occlusion - objects that are close and greater than 20m far
Deletion and Accretion - objects from 2m to greater than 20m far (hard for very close objects)
Relative height and Atmospheric perspective - objects further than 20m only (only for very far objects)

Question 37

Cues that Indicate Absolute Depth

Answer 37

absolute depth = relative size of object

Familiar/Relative size = 0 - greater than 20m (good for very close and far objects)
Texture Gradients = from 2m and above (hard with very upclose objects)
Motion Parallax = 0 - greater than 20m (good for very close and far objects)
Accomodation and Convergence = 0-2m (only for very close objects)

Question 38

Correspondence Problem

Answer 38

• Retinal images can be ambiguous (multiple identical objects in a scene, it can be hard to associate which images in left retinal image should be associated with images in right retinal image)
• If objects are distinct from each other, the associations become unambiguous (e.g. colour)

Question 39

How do we perceive size?

Answer 39

ANGULAR SIZE = visual angle an object subtends (angle viewed from our point)
the closer an object is, the larger its visual angle is, causing retinal image to be bigger

Perceived Depth = how far object is from us (ability to see in 3D)

SIZE CONSTANCY = where an object’s apparent size does not depend on the physical distance (object appears to look same size far and close, even though angular size is larger up close)
Observers must take into account the physical distance AND size of retinal image to achieve size constancy
S = K * (R*D)
s (apparent size)
k (constant)
r (size of retinal image)
d (perceived physical distance to object)

Size Illusions = when people mistake the distance to an object (object appears smaller/larger than it really is) (if an object appears closer than it actually is, it will appear smaller than it actually is;
if an object appears further than it actually is, it will appear larger than it actually is)

Question 40

Holway and Boring (1941)

Answer 40

Investigation in how observers inaccurately estimate the size of objects (how depth cues influence size judgements)

Observers sat at an intersection of two corridors and could view a test circle in one corridor and a comparison circle in other corridor
-Task was to compare the size of comparison circle to test circle (test circles were different sizes for each trial but presented at different distances, so perceived angular size appeared the same always)

Condition 1 = observers can determine depth of test circle using binocular disparity, motion parallax and shadows
Condition 2 = observers viewed with one eye to remove binocular disparity cues
Condition 3 = observers viewed test circle through a peep hole to remove cues of motion parallax (only shadows)
Condition 4 = peephole + drapes (no cues)

RESULTS
condition 1 and 2 accurately matched size of test circle (condition 1 was slightly larger than actual)
condition 3 and 4 was not accurate

(if we can estimate depth/distance of an object, we can accurately estimate the size of object)
with no depth cues, we only estimate based on visual angle

Question 41

Physical Aspect of Sound

Answer 41

Sound - often used to refer to both the physical phenomenon (sound waves) and the perceptual phenomenon (experience of hearing with the presence of a person)

SOUND AS PRESSURE CHANGES
-e.g. when a speaker moves in and out, it compresses air and forms high pressure waves (condensation) and moves out
rarefraction - low pressure areas

Waves have the frequency which is determined by the speaker cone
Pressure waves move through air at 340 m/s and water at 1500 m/s
(only pressure waves moves, individual air molecules are moving forwards and backwards to create regions of high/low pressure)

Question 42

Pure tones

Answer 42

Occurs when the change in air pressure changes in a pattern (like a sin wave, beginning at 0 otherwise it is atmospheric pressure)

FREQUENCY:
Higher the frequency, the higher the pitch
1 Hz (hertz) = 1 oscillation per second
(humans can hear from 20 Hz to 20,000 hz)

AMPLITUDE:
Greater the amplitude, the louder the sound seems
Measured in decibels (db)
dB = 20 x log(p/p(0)
p = pressure (micropascals)
p(0) = reference pressure (usually 20 micropascals), 1 amplitude, 0 dB

Question 43

Complex tones

Answer 43

Complex tones are the combination of sin waves
(e.g. 200Hz tone + 400Hz wave)

200Hz tone = fundamental frequency, first harmonic
(wave repeats every 5ms, can be as much as 200 times a second)

400Hz tone = second harmonic (2 full waves compared to 1 in 200Hz)

600Hz = third harmonic

600 Hz = fourth harmonic

Question 44

Perceptual aspects of sound

Answer 44

Perceptual loudness = measured in PHONS (units of loudness for pure tones)
ACTUAL LOUDNESS DEPENDS ON FREQUENCY
no qualitative measure, it is how humans perceive how loud it is

Complex tone = pitch is usually determined by the fundamental frequency (e.g. first harmonic)
(pitch is a psychological quantity, not physical, and depends on a number of factors)

You would describe pitch in terms of letters (e.g. C, D, E) and not 200 hz tone
-as pitch increases, each octave increases with the pitch doubling
-they have the SAME CHROMA (same sound quality)
-tone height increases as pitch increases
(chroma and tone height are fundamental variables to pitch)

Complex tones are made up of several frequencies (they are just multiples of a specific frequency aka fundamental frequency) e.g. if 200 hz, 400 hz and 600hz are joined, they are all multiples of 200hz thus tone will repeat at 200hz
(even if fundamental frequency is not included in complex tone, it will still repeat at fundamental frequency because they are multiples)

Missing fundamentals = humans perceiving the fundamental frequency even when it is absent (missing fundamental will determine the pitch of the complex tone; even when its absent)
e.g. we hear low pitch (tone height) of male voice over the phone at 100hz frequency even though telephones do not reproduce sounds below 300hz

TIMBRE = when harmonics are removed, it is the difference in tone even though the pitch is same
-when instruments are played, they play the fundamental frequency alongside different multiples of it
(amplitude would be different making waveforms different and sound different; different timbres)

PERIODIC VS APERIODIC
Aperiodic = when wave forms repeat at irregular intervals (e.g. door slamming shut or gun shot)
e.g. transient (pulse), continuous (noise)

Question 45

Auditory localisation

Answer 45

(hearing a sound and instantly turning left/right)

Auditory localisation is based on:
Binaural cues (both ears)
-Interaural time different (the time difference of sound arriving at one ear and the other)
-Interaural level different (amplitude of sound arriving at one ear relative to the other)
(for high frequency sounds, there can be a large interaural level difference between both ears as the head is a SOUND SHADOW)

Cone of confusion - any two points connected by a circumference in the cone will have the same difference in distance to both ears
(same interaural time and level difference)
Binaural cues CANNOT help distinguish between two sounds (we have to use monaural cues)

Monaural cues (1 ear; we use for localisation)

• sound coming from different directions bounces of different sections of pinna of ear before entering ear canal
• sound has characteristic frequency notches that depend on elevation (notches can be used to determine elevation of sound source) (notches occur at higher frequency and higher elevation + lower frequency and lower elevations)

Question 46

Hearing inside rooms

Answer 46

In rooms, sound can travel directly and indirectly (bouncing off walls) to the observers
(why do we not hear echoes all the time then?)

PRECEDENCE EFFECT
-if you hear the same sound twice with the temporal separation of 5-20 ms, you will not register the sound (typically we only hear the direct sound, NOT the echo)

Architectural acoustics = perceived quality of sounds (factors affecting architectural acoustics affect quality)

-Reverberation time = time it takes for sound to decrease by 60 dB (concert hall = 2 seconds, opera hall = 1.5 seconds to make voices more distinguishable)
(walls in halls make sound bounce off thus voice does not immediately disappear causing more indirect waves)

• Intimacy time = temporal difference between the arrival of firsts direct sound and first indirect sound
• Base ratio = measure of indirect sounds, the ratio between low frequencies to medium frequencies (high base ratio (lots of low frequencies) = good)
• Spaciousness factor = ratio of indirect sound to total sound (the greater the proportion of indirect sounds, the greater the spaciousness factor; high spaciousness factor = good quality)
  (e. g. pillows are designed to absorb same amount of sound as humans do so hall sounds just as good when it is full/empty)

Question 47

Auditory Organisation

Answer 47

How we separate sound sources:
-Location = we hear the separate locations that the sound occupies (we use interaural time/level differences to determine; good cue for segregation)

• Onset time = if two different sounds start at different times, high chances they come from different sources
• Timbre and Pitch = easy to segregate instruments due to difference in timbre (if they have the same timbre, we can separate on the basis of pitch)

-Auditory Continuity = tones interrupted by silence are known as DISTINCT
tones interrupted by noise (or another stimulus) are heard as CONTINUOUS
(we perceive tones to be continuous but broken up if interrupted by silence)

-Experience = know what a specific melody/sound is like thus having the ability to segregate it from back noise or another melody