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cognitive psychology > perception > Flashcards

perception Flashcards

1
Q

what is perception

A

process of acquiring knowledge about environmental objects or events via the senses

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2
Q

what 2 stages is perception broken down into?

A
  • sensation - process of transforming physical stimuli into electrical signals
  • perception - process of interpreting these signals for conscious awareness and for action
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3
Q

what is the starting point in perception?

A
  • a stimulus
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4
Q

what is a distal stimulus?

A

distant - exists out in the world

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5
Q

proximal stimuli

A

close proximity - enters our senses

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6
Q

what is sensation?

A

conversion to neural signals which are sent to the brain

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7
Q

what does perception involve

A

signal processing and interpretation

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8
Q

what is the perceptual process

A

distal stimuli –> proximal stimuli –> sensation –> perception

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9
Q

what did Aristotle say about perception?

A

animals must have some sort of perception to be able to live

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10
Q

why are our senses here?

A

helped ancestors seek out desirable objects whilst avoiding dangerous things

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11
Q

what are the 5 main senses?

A

somatosensory(touch), visual, gustatory(taste), auditory, olfactory(smell)

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12
Q

what can animals perceive that we can’t

A

caribou - sense UV
elephants - sensitive to low frequency sounds
snakes - detect infrared radiation, generating a thermal image

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13
Q

is perception veridical?

A

our senses do provide accurate information however perception is not necessarily a clear window into reality

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14
Q

what are some examples of illusions

A
  • the lilac chaser
  • the herman grid
  • muller lyer illusion
  • ponzo illusion
  • zolner illusion
  • ebbinghaus illusion
  • cafe wall illusion
  • shepard’s table illusion
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15
Q

what are ambiguous figures?

A

images that can give rise to two or more distinct perceptions e.g. the ‘necker cube’

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16
Q

what are impossible objects

A

sensory input is interpreted by the brain as representing objects or scenarios that are physically impossible e.g. penrose triangle, shepard scale illusion

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17
Q

what do illusions illustrate about perception?

A

it’s not a clear window into reality, objects are not perceived directly

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18
Q

what is bottom up processing

A

take information from the senses and make judgements about the nature of the world solely based on this information, can be referred to as data driven

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19
Q

top down process

A

using knowledge about the structure of the world to influence perception, can be referred to as a ‘conceptually driven’ process

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20
Q

what do constructivist theories of perception emphasise

A

the importance of top down processing

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21
Q

what did hemholtz say (constructivist)

A

inadequate information provided by the senses is augmented by unconscious inference

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22
Q

what did gregory (1923-2010) say (constructivist)

A

perception is not determined by stimulus patterns, rather its dynamic searching for the best interpretation of the available data, going beyond the immediate evidence

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23
Q

what do constructivist theories describe illusions as

A

rational inferences rather than perceptual errors

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24
Q

what do direct theories emphasise

A

importance of bottom up processing

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25
Q

what did James Gibson (1904-1974) say (direct theorist)

A

constructivist approach may underestimate the richness of the sensory evidence we receive

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26
Q

criticisms of perception

A
  • failure to perceive objects
  • perception of objects in the absence of a stimulus
  • multiple perceptions of the same stimulus
  • perceptions that are physically impossible
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27
Q

what is the stimulus for vision

A

light

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28
Q

what is light

A

a band of energy within the electromagnetic spectrum and is defined by wavelengths
- light can also be described as consisting of small packets of energy called photons

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29
Q

what is light intensity

A

the number of photons per unit space which is associated with brightness

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30
Q

how do we see light

A
  • absorption of photons collide with particles of matter
  • reflection as light strikes opaque surfaces
  • transmission as light passes through transparent matter
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31
Q

what are single-chamber eyes

A

uses convex cornea and lens to project an image onto the retina, it enables directional sensitivity - can represent spatial structure rather than sum of total light

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32
Q

what are photoreceptors

A

they transduce light into an electrical potential - they receive light and respond
- they are on the back surface of the eye

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33
Q

what are retinal ganglion cells

A

the last stage - they send info down the optic nerve at the back of the eye

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34
Q

what are rods

A
  • really sensitive to light, in dim conditions
  • located primarily in peripheral retina - not in the middle
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35
Q

what are cones

A
  • in the centre of the retina
  • less sensitive to light - require 100s of photons, daylight conditions
  • 3 different photopigments that allow the cones to respond differently to different wave lengths
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36
Q

what happens after the information leaves the back of the eye

A

it passes through via the optic chiasm where parts of the scene are distributed to different parts of the brain, to the primary visual cortex

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37
Q

bottom up brightness perception

A
  • the retina does not simply record light intensities
  • responses are shaped by processes occurring within the retina, most notably light/dark adaptation and lateral inhibition
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38
Q

top down brightness perception

A

brain uses knowledge about how light interacts with objects when determining perceived brightness

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39
Q

what is brightness constancy

A

don’t want perception massively changing as we turn lights up and down or move indoor or outdoors

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40
Q

light/dark adaptation - what happens if it’s light outside?

A
  • turns down the sensitivity of the retina, needs more light to give the same response
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41
Q

light/dark adaption- what happens if it’s dark

A
  • increase sensitivity
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42
Q

what is light/dark adaptation

A

sensitivity of the retina is constantly adjusted to compensate for changes in luminance

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43
Q

what is a negative afterimage

A
  • changes in sensitivity in the retina
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44
Q

what is lateral inhibition

A
  • early form of information processing in the retina
  • retina ganglion cell receive both excitatory and inhibitory input from neighbouring photoreceptors
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45
Q

what is the influence of lateral inhibition

A

makes the visual system sensitive to changes in luminance and can have dramatic effects on perceived brightness e.g. herman grid illusion is a consequence of lateral inhibition

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46
Q

bottom up influences on brightness

A
  • light/dark adaptations - negative afterimages
  • lateral inhibition
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47
Q

top down influences on brightness

A
  • shadows - visual system uses knowledge of how light interacts with 3D objects in the world when determining brightness e.g. tries to maintain brightness constancy when the amount of light falling on a surface is affected by shadows
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48
Q

why does the world appear devoid of colour under low-light conditions

A

only rod photoreceptors are sensitive enough to operate - they only contain a single type of photopigment so we can’t see colour - don’t respond differently to different wavelengths

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49
Q

what are the three types of cone photoreceptors

A

s-cones - sensitive to short wavelengths
m-cones - sensitive to middle wavelengths
l-cones - sensitive to long wavelengths

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50
Q

what is monochromacy

A
  • colour blindness
  • only 1 or 0 functioning cone types
  • extremely rare - 1 person in 100,000
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51
Q

what is dichromacy

A
  • only 2 functioning cone types
  • more common in males
  • protanopia - missing l-cones
  • deuteranopia - missing m-cones
  • tritanopia - missing s-cones
52
Q

what is anomalous trichromacy

A

all 3 cones but one or more responds to wavelengths of light in a slightly different way
- more common in males
- protanomaly - l-cone defect
- deuteranomaly - m-cone defect
- tritanomaly - s-cone defect

53
Q

what is colour opponency - bottom up influences on colour

A
  • retinal ganglion cells receive excitatory and inhibitory input from different cone types
  • results in distinct red/green and blue/yellow pathways
54
Q

how can colour opponency be demonstrated with negative afterimages

A

staring at a red object will result in a green afterimage, adaptation to the red causes a reduction of long wavelength cones, creating an imbalance in the inputs to red/green opponent retinal ganglion cells

55
Q

top down influences of colour perception - colour constancy

A
  • account for the intensity and composition of light hitting different surfaces
  • perceived colour of objects remains the same even if the lighting changes
56
Q

why is it difficult to design a perceiving machine

A
  • visual input provides ambiguous info about the 3D structure of the world, the same 2D retinal image could be produced by an infinite number of 3D objects
  • image complexity makes it increasingly tricky for computers to organise the visual scene into distinct objects
57
Q

how do we perceive depth

A
  • monocular cues - with one eye
  • binocular cues - require both eyes
58
Q

monocular cues - relative height and size

A
  • when objects are below the horizon, where the base is tells us how far away the object in the image is - higher bases are perceived is more distant
  • more distance means one takes up less of your field view so is perceived as smaller
  • we need prior knowledge about relative sizes to judge distance
59
Q

monocular cues - occlusion

A
  • closer objects will occlude further away ones
60
Q

monocular cues - linear perspective and texture gradient

A
  • parallel lines extending away from observer converge in the distance - linear perspective
  • texture elements get smaller and more dense with distance and foreshortening occurs when surface is tilted away
61
Q

monocular cues - motion parallax

A
  • as we move, more distant objects will glide past us more slowly than nearer objects
62
Q

monocular cues - shadows and shading

A
  • cast shadows can create a strong perception of depth
  • brightness of a surface depends on it’s orientation with respect to the light source
63
Q

binocular disparity - what is stereoscopic vision

A
  • our two eyes receive a slightly different image of the world
64
Q

binocular disparity - what is disparity?

A
  • difference in image location of an object seen by left and right eyes
  • the size of the disparity depends on an objects depth
65
Q

binocular disparity - what is a horopter

A
  • set of points in space that project to corresponding positions in the two retinas (zero disparity)
  • includes the fixation point
66
Q

binocular disparity - what are crossed disparities

A
  • objects closer than the horopter - you would have to cross eyes to fixate on it
67
Q

binocular disparity - what is stereopsis

A
  • detect disparities and extracting depth information, developing a sense of 3 dimensional depth
68
Q

what is structuralism in perceiving objects?

A
  • Wilhelm Wundt
  • proposed that perceptions are simply the sum of ‘atoms’ of sensation
69
Q

what is the gesalt school - perceiving objects

A
  • led by Wertheimer, Kohler and Koffka
  • reaction against structuralism
  • argued that the whole form or configuration is greater than the sum of it’s parts
70
Q

what is illusory contours - perceiving objects

A
  • some images evoke the perception of edges in locations where there is no change in luminance or colour
  • this is difficult to explain via the structuralist approach
71
Q

what are the Gesalt principles of perceptual organisation

A
  • recognised that any given image could be interpreted in many different ways - come up with the simplest interpretation
    1) proximity - things that are closer together group together
    2) similarity - things that are similar group together
    3) common fate - things that move together group together
    4) good continuation - group elements to form smooth continuing lines rather than abrupt or sharp angles, helps preserve occluding objects
    5) closure - group elements to form complete figures, even if incomplete - top down
    6) symmetry - elements more likely to be formed into groups that are balanced or symmetrical
72
Q

positives of Gestalt principles

A
  • seem correct about many things - perceptual objects are not simply the sum of their parts
  • Gestalt principles generally hold across wide range of images
  • led to Kohler’s electrical field theory - lines of flow are created in the brain which match the structure of perception
73
Q

criticisms of Gestalt principles

A
  • some principles seem vague - not always clear what is meant by ‘good’ or ‘simple’ shape
  • no coherent workable account of the underlying neural mechanisms
  • no empirical evidence for Kohler’s electrical field theory
74
Q

what is the perceptual definition of sound

A
  • sound is the experience we have when we hear
75
Q

what is the physical definition of sound

A
  • pressure changes in the air or other medium caused by the vibration of an object
76
Q

what is the pure tone in sound

A
  • occurs when changes in air pressure form a perfect sinusoidal wave
77
Q

how do we visualise sound

A
  • a Ruben’s tube
  • cylinder - block at one end and pump in gas and a long the top create a sequence of holes and block the other end with a membrane - start playing sounds at that end which causes vibration of the membrane - differences in pressure due to vibration allows different amounts of gas to escape causing more flames
78
Q

what is the amplitude of a sound wave - pure tones

A
  • size of the variation in air pressure e.g. difference between peak and trough - more vibration lead to larger changes in pressure and more amplitude
  • related to perception of loudness
79
Q

what is the frequency of sound waves - the pure tone

A
  • number of cycles per second - measured in hertz
  • higher frequency is a shorter wavelength
  • higher the frequency, the higher the pitch
80
Q

what are complex sounds

A
  • made up of lots of different frequencies
  • combination of sine waves
  • naturally produced complex sounds have a fundamental frequency which is the lowest most dominant frequency and harmonics - additional frequencies with higher frequencies
81
Q

what are the 3 subdivisions of the ear

A
  • outer ear
  • middle ear
  • inner ear
82
Q

what is the pinnae in the outer ear

A
  • visible external parts of the ear
  • act to capture sound waves and direct them down auditory canals
83
Q

what are the auditory canals in the outer ear

A
  • 3cm tube-like structure
  • protects middle ear
84
Q

what is the tympanic membrane - outer ear

A
  • eardrum - cone-shaped membrane separating the outer and middle ear
  • sound waves induce a difference in pressure either side of tympanic membrane, causing it to vibrate
85
Q

what is the middle ear

A
  • a small cavity - contains ossicles which are the 3 smallest bones in the human body
    1) malleus (hammer shape)
    2) incus (anvil shape)
    3) stapes (stirrup shape)
  • the bones amplify the vibrations of the tympanic membrane and transmit them to the inner ear
86
Q

what is the main structure of the inner ear

A

the cochlea - filled with liquid
- vibration of the oval window displaces the fluid in the cochlea, resulting in change in pressure which propagates up and down the spiral structure
- cochlea consists of three parallel canals
- auditory transduction is triggered by motion of the basilar membrane, which separates the middle and tympanic canals

87
Q

what is auditory transduction in the ear

A
  • motion of the basilar membrane are translated into neural signals by structures of the organ of corti, which extends along its surface
  • a voltage is generated when specialised hair cells contained within the organ of corti are bent
  • this produces impulses in the auditory nerve cells which are sent to the brain
  • hair cells are extremely sensitive
88
Q

how we perceive loudness

A
  • related to amplitude of soundwaves
  • the range of amplitudes we encounter is extremely large
89
Q

how are sounds measured to describe differences in amplitude

A
  • a logarithmic scale in units called decibels
  • a change of 20dB corresponds to a ten-fold increase in amplitude
90
Q

what is rate code - perceiving loudness

A
  • sound amplitude is coded in the firing rate of auditory nerve fibres
  • response increase with increasing sound intensity which tells us it’s loud
  • some fibres have high spontaneous rates and saturate rapidly, while others have low spontaneous rates and saturate slowly
  • this enables us to discriminate loudness across a range of sound levels
91
Q

what needs to happen for a sound to be perceived twice as loud

A

amplitude needs to be increased by a factor of approximately 3.16 (10dB)

92
Q

how is loudness perception effected by frequency

A
  • auditory systems are not equally sensitive to all sound frequencies
93
Q

what 2 main factors are loudness perception affected by

A
  • amplitude
  • frequency
94
Q

how do we perceive pitch - what is the lowest and highest frequencies humans can hear

A
  • the lowest frequency humans can hear is 20Hz - below that we feel the sound
  • the highest frequency humans can hear is 20,000 Hz
95
Q

what is place code when perceiving pitch

A
  • some frequencies cause vibration in specific area along the basilar membrane
  • low frequencies - near apex
  • high frequencies - near base
96
Q

what is timing code - perceiving pitch

A
  • frequency is not only signalled by which auditory nerve fibres respond, but also when they respond
  • auditory nerve responses are synchronised to changes in pressure
  • this property is called phase-locking and occurs up to frequencies of about 4000Hz
97
Q

why does the same note sound different when played on different instruments - perceiving pitch

A
  • pitch is typically determined by the fundamental frequency of a sound
  • the number, frequency ratios and relative amplitudes of the harmonics dictates the quality or timbre of the sound
98
Q

what is the missing fundamental illusion - perceiving pitch

A
  • if we remove the fundamental frequency when perceiving pitch
  • we continue to perceive a pitch consistent with the fundamental frequency
  • suggests that pitch isn’t simply determined in the cochlea - the brain infers the missing fundamental from the harmonics
99
Q

comparing location information in vision and audition

A
  • visual info for the relative location of objects is contained within the retinal image
  • however, the place activated by a sound on the cochlea does not indicate it’s location
100
Q

what are binaural cues - localising sound

A
  • require comparison of signals in left and right ears and are vital for signalling location of a sound in azimuth
101
Q

what are the 2 types of binaural cues - localising sound

A
  • interaural time differences
  • interaural level differences
102
Q

what are monaural cues - localising sound

A
  • work with one ear can help localise the elevation and distance of a sound
  • filter properties of the pinna
  • intensity and reverberation
103
Q

localisation - binaural cues - what is interaural time differences

A
  • the relative time at which a sound arrives at the two ears depends on its location in azimuth
  • if the sound source is straight ahead, the distance to each ear is the same and there is no difference in time
  • when the source is positioned to one side, the sound will reach the nearer ear first
104
Q

what does the range of interaural time differences depend on - binaural cues - localisation

A
  • speed of sound - typically constant - 330m/s through air
  • distance between the two ears (larger heads create bigger range of ITDs
  • the maximum ITD in humans is typically around 0.6ms
  • requires precise signalling of timing
105
Q

what are interaural level differences

A
  • the relative sound pressure level reaching the two ears also depends on the location of the source in azimuth
  • a reduction in sound level occurs for the far ear, due to the acoustic shadow created by the head
  • this reduction occurs for high frequency sounds but no low frequency
106
Q

what is the basic physiology of binaural processing

A
  • ear leads to auditory nerve - after auditory nerve leaves the ear it travels through a series of stages through the brain stem - the superior olive where the binaural cues start to be calculated
107
Q

what are the 2 classes of neurons in the superior olive - binaural processing

A
  • lateral superior olive - neurons are sensitive to ILDs
  • medial superior olive - neurons are sensitive to ITDs
108
Q

what are strengths of binaural cues

A
  • ITDs and ILDs provide complementary info about azimuth location
  • ITDs work particularly well for low-frequency sounds
  • ILDs provide information about high frequency sounds
109
Q

weaknesses of binaural cues

A
  • provide ambiguous info about elevation and tell us nothing about distance
  • cone of confusion - set of points from which a sound source will produce identical ITDs and ILDs
110
Q

monaural localisation cues - how does sound interact with the pinnae to explain elevation

A
  • when sound reflects off the nooks and crannies of your external ear, the relative intensity of different frequency sound waves changes
  • this changes with sound elevation and azimuth.
  • individuals have different ear shapes and will filter the frequency content of complex sounds in slightly different ways
  • artificially altering ear shape with plastic moulds impairs the ability to localise sound elevation
111
Q

monaural localisation cues - distance - what is relative intensity

A
  • sound intensity decreases with distance, so closer object will tend to have greater amplitudes than farther ones
112
Q

monaural cues - distance - reverberation

A
  • the way in which sounds reflects off objects also provides cues to distance
  • multiple reflections combine to produce a persistence of sound called reverberation
  • the distance of a source alters the relative intensity and timing of direct and reverberant sounds
113
Q

why is localising sounds within rooms difficult

A
  • reflected sounds poses a potential problem for localisation
  • with multiple sounds reaching the listener from different directions, how can we tell the true number and location of the source.
114
Q

what is the precedence effect when localising sound within rooms

A
  • similar sounds arriving in quick succession from different locations are localised according to the direction of the first sound
  • provided the delay is short, only a single sound is perceived
115
Q

what is auditory scene analysis

A
  • natural environments can often contain multiple sound sources
  • that auditory system needs to make sense of the mixture of component sounds that makes up the auditory scene
  • it needs to segregate the components of the sound that come from different sound sources
  • needs to group the components of the sound that come from the same sound source
116
Q

what are the strategies for auditory grouping in auditory scene analysis

A
  • follows principles such as common fate, proximity, similarity and continuity
  • we need to consider spectral grouping and sequential grouping
117
Q

what is spectral grouping in auditory scene analysis

A
  • combining different frequency sounds components that occur at the same time
  • frequency components of a sound are more likely to be grouped into a single sound if it is likely that they have been caused by the same sound-producing event
118
Q

what is harmonicity in spectral grouping - auditory scene analysis

A
  • if a component is mistuned to other components, it will be heard as a separate sound
119
Q

what is common frequency change in spectral grouping - auditory scene analysis

A
  • analogue to the principle of common fate
  • frequency components that change together tend to group together
120
Q

what is sequential grouping

A
  • combining sequences of sounds over time
121
Q

what is auditory stream segregation in sequential grouping - auditory scene analysis

A
  • the process of organising sounds over time into separate perceptual events
122
Q

what is similarity of pitch in sequential grouping - auditory scene analysis

A
  • sounds with similar pitch are often produced by the same source
  • increasing frequency difference promotes stream segregation
123
Q

what is temporal proximity in sequential grouping - auditory scene analysis

A
  • sounds that occur in rapid progression tend to be produced by the same source
  • increasing presentation rate also promotes stream segregation
124
Q

what is similarity of timbre in sequential grouping - auditory scene analysis

A
  • sound sources often have distinct timbre, providing a good cue for stream segregation
125
Q

what is continuity in sequential grouping - auditory scene analysis

A
  • sounds that stay constant or change smoothly are often produced by the same source
  • perceived as continuous even when interrupted by noise
  • phonemic restoration - this effect is not restricted to tones, but can also occur with speech

cognitive psychology (8 decks)

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