Sense and Perception

Question 1

What is attention?

Answer 1

Attention is the ability to preferentially process some parts of a stimulus at the expense of processing of other parts of the stimulus.
Your perceptual system has a limited capacity.
You can’t process everything in the visual scene simultaneously
Attention therefore helps us avoid becoming overwhelmed.

Question 2

What directs our attention?

Answer 2

• Initially, when a scene is first presented, your fixations are captured by salient parts of the scene
• This phenomenon is known as “attentional capture” and is involuntary
• After the first few fixations, you can then direct your fixations according to your goals or your expectation
• This process is voluntary

Question 3

What Captures Our Attention

Answer 3

Contrast in size, colour, movement and orientation

Question 4

What Are the Effects of Attention?

Answer 4

Attention speeds up responses
Attention can influence appearance
Attention can influence physiological responding

Question 5

The Binding Problem

Answer 5

different aspects of a stimulus are processed independently, often in separate brain areas.
The problem becomes more difficult when there are multiple objects

Question 6

Feature Integration Theory

Answer 6

Feature Integration Theory (FIT) suggests that the binding problem is solved by attending to only one location at at time.
Crucially, only features associated with that location are processed, so only those features are bound together.
This avoids binding features from different objects.

Question 7

Change Blindness

Answer 7

You can remember only a few parts of a scene at one time.
If one of those parts change, you notice the change
If some other part of the scene changes, chances are
you won’t notice the change – change blindness

Question 8

Problem with perception

Answer 8

A number of factors, but the three most important ones are

• The stimulus on the retina is ambiguous
• Objects can be hidden or blurred
• Objects look different from different viewpoints and in different poses

Question 9

How Do Humans Succeed in perception

Answer 9

• Structuralism claims that sensations combine to form perceptions
• Gestaltism: humans are able to perceive objects and scenes because of perceptual organisation

Question 10

Evidence for Gestaltism

Answer 10

-Apparent motion
In apparent motion an observer sees two stationary dots flashed in succession.
Although each of the dots is stationary, the observer perceives motion
-Illusionary contour
The conscious awareness of the illusory contour is constructed – there is no physical contour at these locations.

Question 11

Gestalt Principles of Grouping

Answer 11

Original Gestalt principles

• Good continuation(Aligned (or nearly aligned) contours are grouped together to form a single object)
• Pragnaz(groupings occur to make the resultant figure as simple as possible.)
• Similarity (grouping of similar object)
• Proximity (grouping due to close distance)
• Common fate (grouping based on movement)
• Common region (grouping by same area)
• Uniform connectedness (grouping by connection of similar characteristic)

Question 12

Principle of segregation

Answer 12

• They are in front of the rest of the image
• They are at the bottom of the image
• They are convex
• They are recognisable.

Question 13

Gist perception

Answer 13

Although observers can extract the gist of a scene very rapidly, the gist they extract is not very detailed.
The longer observers view a scene, the more detailed the gist they extract.
27 ms is enough time to extract some gist, and very accurate perception can be achieved in just 250 ms

Question 14

Function of Motion Perception

Answer 14

• Help break camouflage
• Help attract attention
• Help segregate objects from the background.
• Help us interpret events.
• Help us determine the structure of objects (kinetic depth effect)
• Help us determine what actions people are performing (Point-Light “Walkers”)

Question 15

Life Without Motion Perception

Answer 15


-Sometime due to either disease or trauma, a patient will suffer damage to a part of the brain responsible for motion perception.
-Consequently, the person may no longer be able to
perceive motion.
-This condition is known as akinetopsia.
-could see that things had moved but couldn’t see them moving

Question 16

When Do We Perceive Motion?

Answer 16


-Real motion (something actually moving)
-Illusory motion (nothing actually moving)
-Static image (e.g. rotating snakes illusion - Kitaoka &
Ashida, 2003)
-Apparent motion
-Motion aftereffects
-Induced motion: Moving background (or a moving object) causes a stationary object to appear to move

Question 17

Motion Induced Blindness

Answer 17

Although motion can make things more visible (e.g.
breaking camouflage), it can also cause things to
disappear, as in motion-induced blindness (Bonneh,
Cooperman & Sagi, 2001)

Question 18

Motion Induced Change Blindness

Answer 18



Motion can also make it harder to notice changes

Question 19

Motion Illusions

Answer 19

• Illusion created by the movement of an object
  For example, the Footsteps Illusion shows us that contrast affects motion perception.
  -When the contrast is high, they appear to move faster.
  -When the contrast is low, it appears to move slower.
• This show that contrast affect motion perception
  Aperture problem:
  -If you can’t see the ends of a line, the movement of a
  line is ambiguous.
  -Consequently, the motion of the line viewed through
  an aperture is ambiguous and is “captured” by the
  movement of the terminators (the points where the
  line joins the aperture)

Question 20

Function of Colour Perception

Answer 20

Colour perception can help:

• Find things (like berries)
• Determine if fruit is ripe
• Spot (and identify) poisonous animals
• Identify a potential mate

Question 21

Physics of Colour

Answer 21

• Visible light is electromagnetic radiation with wavelengths varying from about 400 nm to about 700 nm
• White light is a mixture of all these wavelengths
• An opaque object is an object that light cannot pass through. It is not at all transparent.
• The colour of an opaque object is determined by the light that it reflects
• The colour of a transparent object is determined by the colour it transmits.

Question 22

Mixing colour

Answer 22

Paints
-Blue paint absorbs red light but reflects blue and green light.
-Yellow paint absorbs blue light but reflects yellow and green light.
-Mixing blue and yellow paint results in a mixture that absorbs both red and blue light but reflects green light – so looks green.
Light
-Mixing red and green light makes yellow light.
-If you mix blue light with yellow light (i.e. light that contains both green and red), you will get light that contains blue, green and red.
This light will look white….

Question 23

Munsell Colour System

Answer 23

In the Munsell colour system colours are categorized according to:
Value (lightness)
Hue (colour)
Chroma (saturation)

Question 24

Trichromatic Theory of Vision

Answer 24

In the retina, there are photoreceptors known as rods and cones.
Rods can not distinguish between colours and are active only at low light levels.
There are three types of cones. Each type responds maximally to a different wavelength
S cones – 419 nm (blue)
M cones – 531 nm (green)
L cones – 558 nn (red)

Question 25

Colour Deficiency

Answer 25

There are two main types of colour deficiency
Monochromatism
Dichchromatism

Question 26

Monochromatism

Answer 26

Monochromatism affects about 1 in 100,000 people
Monochromats usually have no functioning cones
Only have functioning rods
Thus are truly colour blind and see the world only in shades of gray
Very sensitive to light – need to wear dark glasses during the day.

Question 27

Dichromatism

Answer 27

Dichromats are lacking one of the three types of cones

• -Protanopes lack L cones
• -Deuteranopes lack M cones
• -Tritanopes lack S cones.

Question 28

Opponent-Process Theory of Colour Vision

Answer 28

-What colour we perceived is determined not only by the cones in our retina
-The signals from these cones are processed by the cortex where they are combined into three colour opponent channels
Red-green
Blue-yellow
White-black
-Opponent processing can explain the existence of afterimages and why some colour combinations are impossible

Question 29

Color constancy

Answer 29

• the light reflected by an object is determined by the product of its reflectance and the illumination
• Colour constancy is an example of subjective constancy and a feature of the human colour perception system which ensures that the perceived colour of objects remains relatively constant under varying illumination conditions
• Thus, there are at least two ways the visual system achieves colour constancy
• Habituation (becoming less sensitive to that colour)
• Discounting the illuminant

Question 30

Depth & Size

Answer 30

Depth and size are closely related.
How big an object appears can affect how far away it appears and…
…how far away an object appears can affect how big it appears…
Accurate size estimates can occur only when distance to the object can be estimated accurately.

Question 31

Perceiving Depth

Answer 31

By using a number of different cues, which can be divided into three groups:
Oculomotor cues
- Cues based on our ability to sense the position of our eyes
Monocular cues
- Cues based on the visual information available within on eye
Binocular cues
- Cues that depend on visual information within both eyes

Question 32

Oculomotor Cues

Answer 32

There are two main oculomotor cues

• Binocular convergence( two eyes moving closer when view a nearby object and father when viewing a far object. the divergence is used to estimate the distance)
• Accommodation (size of the lens change base on the distance of an object. this is used by the brain to estimate distance)

Question 33

Monocular cues

Answer 33

There are three main monocular cues

• Accommodation
• Pictorial cues(Occlusion, Relative height, Familiar and relative size, Perspective convergence, Atmospheric perspective, Texture gradient, Shadows)
• Movement-based cues (when moving, far away object take longer to disapear)

Question 34

Binocular Disparity

Answer 34

• Because the left and right eyes are offset relative to each other, they see the world from slightly different viewpoints
• Each eye sees a slightly different view of the scene.
• the point of fixation does not alter relative disparity.
• However, the point of fixation does affect absolute disparity.
• Whichever object is fixated on has zero absolute disparity.
• all objects that lie on the horopter fall on corresponding parts of the retinas.

Question 35

Correspondence Problem

Answer 35

• 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.
• Figuring out these associations is known as the correspondence problem.
• If the object in the visual scene are made distinct from each other the associations become unambiguous

Question 36

Perceiving Size

Answer 36

The perceived size of an object is determined by two factors
Its angular size
Its perceived depth

Question 37

Angular Size

Answer 37

• Angular size is just the visual angle an object subtends.

- The closer an object is to person, the larger its angular size

Question 38

Size Constancy

Answer 38

-Size constancy is the phenomenon where an object’s apparent size does not depend on is 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.
-To achieve size constancy an observer needs to consider both the size of the retinal image and the distance of the object.
-This is why size and apparent depth are so closely linked.
-If someone misestimates the distance of an object, they will probably misestimate the size of the object.

Question 39

Size Illusions

Answer 39

• Most size illusions are caused by causing people to mistake the distance to an object so that it appears larger or smaller than it really is.
• If an object appears closer than it really is, it will appear smaller than it really is.
• If an object appears further away than it really is, it will appear larger than it really is.

Question 40

Holway and Boring (1941)

Answer 40

• Holway and Boring (1944) investigated how observers accurately estimate the size of objects.
• In particular, they investigated how depth cues influence size judgments.
• Observer sat at an intersection of two corridors and could view a test circle in one corridor and comparison circle in the other corridor.
• Their task was to adjust the size of the comparison circle to match the size of the test circle.
• The test circles were of different sizes but were presented at different distances so that their angular size was always the same.

Question 41

Different condition of the Holway and Boring Expiriment

Answer 41

In condition 1, observers could determine the depth of the test patch using binocular disparity, motion parallax and shadows.
In condition 2, observers viewed the test circle with one eye to remove binocular disparity cues.
In condition 3, observers viewed the test circle through a peephole to remove motion parallax cues.
In condition 4, in addition to viewing the circle through a peephole, drapes were used to remove the shadows

Question 42

Physical Aspects of Sound

Answer 42

-The pressure waves (i.e. the sound waves) move though the air at 340 m/s and water at 1,500 m/s.
-However, only the pressure wave is moving.
Each air molecule is just moving back and forth to create regions of high and low pressure.
-It include pure tone, frequency and amplitude

Question 43

Pure Tones

Answer 43

A pure tone occurs when the change in air pressure occur in a pattern described by a mathematical function called a sine wave.

Question 44

Frequency

Answer 44

• The higher the frequency the higher the pitch (for pure tones)
• 1 Hz (spelt Hertz) = 1 oscillation per second
• Humans can hear tones ranging from about 20 Hz to about 20,000 Hz

Question 45

Amplitude

Answer 45

-The greater the amplitude, the louder a sound seems.
-Amplitude is measured in decibels (db)
dB = 20 x logarithm(p/po)
-Where p is the pressure (i.e. amplitude) of the sound (measured in micropascals)
po is the reference pressure, usually set to 20 micropascals

Question 46

Complex tone

Answer 46

• Combination of many pure tone

- speed of the loop is based on the first tone

Question 47

Loudness

Answer 47

• The greater the amplitude, the louder a sound seems.
• However, the actual loudness of sound depends on the frequency
• Perceptually loudness is measured in phons
• Phons are units of loudness for pure tones.

Question 48

Pitch

Answer 48

-For a pure tone, pitch is determined by the frequency.
-For a complex tone, pitch is usually determined by the fundamental frequency.
Pitch is a psychology variable with two attributes:Tone height and Chroma
Chroma is cyclic in that neighbouring letters of the same type (e.g. C1 and C2) sound similar
Conversely, tone height increase from left to right on the piano keyboard in a continuous manner.
Thus, when talking about pitch you need to be clear whether you are talking about tone height or chroma

Question 49

Missing Fundamental

Answer 49

For many sounds they frequency components are multiples of a particular frequency.
This frequency is called the fundamental frequency
However, the complex tone will continue to repeat at the fundamental frequency, even when the fundamental frequency is absent….

Question 50

Timbre

Question 51

Periodic Vs Aperiodic

Answer 51

• Periodic sound repeat themselves

- aperiodic sound doesn’t repeat themself

Question 52

Auditory Localisation

Answer 52

Auditory localisation is based on both binaural and monaural cues.
Binaural cues include
-Interaural time difference (the closer ear would detect the sound first)
-Interaural level difference (For high frequency sounds, there can be a large interaural level difference between the two ears due to the sound shadow caused by the head.)
Monaural clue is sound acquires characteristic frequency notches that depend on its elevation

Question 53

Cone of Confusion

Answer 53

Any two points connected by a circumference line on the surface of this cone have the same difference in distance to the two ears.
Thus they will have the same interaural time difference and interaural level difference.
So binaural cues cannot be used to distinguish between the two points

Question 54

Precedence Effect

Answer 54

• If you hear the same sound twice with a temporal separation of 5-20ms, you will not register the second sound.
• if the temporal separation between the two sounds is more than about a 10th of a second, you will hear the two sounds as separate

Question 55

Architectural Acoustics

Answer 55

Although you typically don’t hear the indirect sound, it will affect the perceived quality of the sound.
Consequently, the architectural acoustics of a concert hall affect the quality of the sound in the concert hall.
There are four factors that determine the quality of the architectural acoustics
-Reverberation time(This is the time it takes for sound to decreased by 60 dB)
-Intimacy time (This is the temporal difference between when the direct sound arrives and the first indirect sound arrives. a good intimacy time of about 20 ms)
-Bass ratio(It is the ratio of low frequencies to middle frequencies for the indirect sound)
-Spaciousness factor (The ratio of indirect sound to total sound)

Question 56

Separating Sound Sources

Answer 56

There are five cues that people tend to use:
Location
Onset Time
Timbre and Pitch
Auditory Continuity
Experience