perception Flashcards
1
Q
what is perception
A
process of acquiring knowledge about environmental objects or events via the senses
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
3
Q
what is the starting point in perception?
A
- a stimulus
4
Q
what is a distal stimulus?
A
distant - exists out in the world
5
Q
proximal stimuli
A
close proximity - enters our senses
6
Q
what is sensation?
A
conversion to neural signals which are sent to the brain
7
Q
what does perception involve
A
signal processing and interpretation
8
Q
what is the perceptual process
A
distal stimuli –> proximal stimuli –> sensation –> perception
9
Q
what did Aristotle say about perception?
A
animals must have some sort of perception to be able to live
10
Q
why are our senses here?
A
helped ancestors seek out desirable objects whilst avoiding dangerous things
11
Q
what are the 5 main senses?
A
somatosensory(touch), visual, gustatory(taste), auditory, olfactory(smell)
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
13
Q
is perception veridical?
A
our senses do provide accurate information however perception is not necessarily a clear window into reality
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
15
Q
what are ambiguous figures?
A
images that can give rise to two or more distinct perceptions e.g. the ‘necker cube’
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
17
Q
what do illusions illustrate about perception?
A
it’s not a clear window into reality, objects are not perceived directly
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
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
20
Q
what do constructivist theories of perception emphasise
A
the importance of top down processing
21
Q
what did hemholtz say (constructivist)
A
inadequate information provided by the senses is augmented by unconscious inference
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
23
Q
what do constructivist theories describe illusions as
A
rational inferences rather than perceptual errors
24
Q
what do direct theories emphasise
A
importance of bottom up processing
25
what did James Gibson (1904-1974) say (direct theorist)
constructivist approach may underestimate the richness of the sensory evidence we receive
26
criticisms of perception
- failure to perceive objects
- perception of objects in the absence of a stimulus
- multiple perceptions of the same stimulus
- perceptions that are physically impossible
27
what is the stimulus for vision
light
28
what is light
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
29
what is light intensity
the number of photons per unit space which is associated with brightness
30
how do we see light
- absorption of photons collide with particles of matter
- reflection as light strikes opaque surfaces
- transmission as light passes through transparent matter
31
what are single-chamber eyes
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
32
what are photoreceptors
they transduce light into an electrical potential - they receive light and respond
- they are on the back surface of the eye
33
what are retinal ganglion cells
the last stage - they send info down the optic nerve at the back of the eye
34
what are rods
- really sensitive to light, in dim conditions
- located primarily in peripheral retina - not in the middle
35
what are cones
- 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
36
what happens after the information leaves the back of the eye
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
37
bottom up brightness perception
- 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
38
top down brightness perception
brain uses knowledge about how light interacts with objects when determining perceived brightness
39
what is brightness constancy
don't want perception massively changing as we turn lights up and down or move indoor or outdoors
40
light/dark adaptation - what happens if it's light outside?
- turns down the sensitivity of the retina, needs more light to give the same response
41
light/dark adaption- what happens if it's dark
- increase sensitivity
42
what is light/dark adaptation
sensitivity of the retina is constantly adjusted to compensate for changes in luminance
43
what is a negative afterimage
- changes in sensitivity in the retina
44
what is lateral inhibition
- early form of information processing in the retina
- retina ganglion cell receive both excitatory and inhibitory input from neighbouring photoreceptors
45
what is the influence of lateral inhibition
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
46
bottom up influences on brightness
- light/dark adaptations - negative afterimages
- lateral inhibition
47
top down influences on brightness
- 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
48
why does the world appear devoid of colour under low-light conditions
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
49
what are the three types of cone photoreceptors
s-cones - sensitive to short wavelengths
m-cones - sensitive to middle wavelengths
l-cones - sensitive to long wavelengths
50
what is monochromacy
- colour blindness
- only 1 or 0 functioning cone types
- extremely rare - 1 person in 100,000
51
what is dichromacy
- only 2 functioning cone types
- more common in males
- protanopia - missing l-cones
- deuteranopia - missing m-cones
- tritanopia - missing s-cones
52
what is anomalous trichromacy
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
what is colour opponency - bottom up influences on colour
- retinal ganglion cells receive excitatory and inhibitory input from different cone types
- results in distinct red/green and blue/yellow pathways
54
how can colour opponency be demonstrated with negative afterimages
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
top down influences of colour perception - colour constancy
- account for the intensity and composition of light hitting different surfaces
- perceived colour of objects remains the same even if the lighting changes
56
why is it difficult to design a perceiving machine
- 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
how do we perceive depth
- monocular cues - with one eye
- binocular cues - require both eyes
58
monocular cues - relative height and size
- 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
monocular cues - occlusion
- closer objects will occlude further away ones
60
monocular cues - linear perspective and texture gradient
- 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
monocular cues - motion parallax
- as we move, more distant objects will glide past us more slowly than nearer objects
62
monocular cues - shadows and shading
- 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
binocular disparity - what is stereoscopic vision
- our two eyes receive a slightly different image of the world
64
binocular disparity - what is disparity?
- difference in image location of an object seen by left and right eyes
- the size of the disparity depends on an objects depth
65
binocular disparity - what is a horopter
- set of points in space that project to corresponding positions in the two retinas (zero disparity)
- includes the fixation point
66
binocular disparity - what are crossed disparities
- objects closer than the horopter - you would have to cross eyes to fixate on it
67
binocular disparity - what is stereopsis
- detect disparities and extracting depth information, developing a sense of 3 dimensional depth
68
what is structuralism in perceiving objects?
- Wilhelm Wundt
- proposed that perceptions are simply the sum of 'atoms' of sensation
69
what is the gesalt school - perceiving objects
- 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
what is illusory contours - perceiving objects
- 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
what are the Gesalt principles of perceptual organisation
- 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
positives of Gestalt principles
- 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
criticisms of Gestalt principles
- 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
what is the perceptual definition of sound
- sound is the experience we have when we hear
75
what is the physical definition of sound
- pressure changes in the air or other medium caused by the vibration of an object
76
what is the pure tone in sound
- occurs when changes in air pressure form a perfect sinusoidal wave
77
how do we visualise sound
- 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
what is the amplitude of a sound wave - pure tones
- 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
what is the frequency of sound waves - the pure tone
- number of cycles per second - measured in hertz
- higher frequency is a shorter wavelength
- higher the frequency, the higher the pitch
80
what are complex sounds
- 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
what are the 3 subdivisions of the ear
- outer ear
- middle ear
- inner ear
82
what is the pinnae in the outer ear
- visible external parts of the ear
- act to capture sound waves and direct them down auditory canals
83
what are the auditory canals in the outer ear
- 3cm tube-like structure
- protects middle ear
84
what is the tympanic membrane - outer ear
- 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
what is the middle ear
- 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
what is the main structure of the inner ear
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
what is auditory transduction in the ear
- 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
how we perceive loudness
- related to amplitude of soundwaves
- the range of amplitudes we encounter is extremely large
89
how are sounds measured to describe differences in amplitude
- a logarithmic scale in units called decibels
- a change of 20dB corresponds to a ten-fold increase in amplitude
90
what is rate code - perceiving loudness
- 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
what needs to happen for a sound to be perceived twice as loud
amplitude needs to be increased by a factor of approximately 3.16 (10dB)
92
how is loudness perception effected by frequency
- auditory systems are not equally sensitive to all sound frequencies
93
what 2 main factors are loudness perception affected by
- amplitude
- frequency
94
how do we perceive pitch - what is the lowest and highest frequencies humans can hear
- 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
what is place code when perceiving pitch
- some frequencies cause vibration in specific area along the basilar membrane
- low frequencies - near apex
- high frequencies - near base
96
what is timing code - perceiving pitch
- 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
why does the same note sound different when played on different instruments - perceiving pitch
- 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
what is the missing fundamental illusion - perceiving pitch
- 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
comparing location information in vision and audition
- 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
what are binaural cues - localising sound
- require comparison of signals in left and right ears and are vital for signalling location of a sound in azimuth
101
what are the 2 types of binaural cues - localising sound
- interaural time differences
- interaural level differences
102
what are monaural cues - localising sound
- work with one ear can help localise the elevation and distance of a sound
- filter properties of the pinna
- intensity and reverberation
103
localisation - binaural cues - what is interaural time differences
- 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
what does the range of interaural time differences depend on - binaural cues - localisation
- 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
what are interaural level differences
- 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
what is the basic physiology of binaural processing
- 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
what are the 2 classes of neurons in the superior olive - binaural processing
- lateral superior olive - neurons are sensitive to ILDs
- medial superior olive - neurons are sensitive to ITDs
108
what are strengths of binaural cues
- 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
weaknesses of binaural cues
- 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
monaural localisation cues - how does sound interact with the pinnae to explain elevation
- 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
monaural localisation cues - distance - what is relative intensity
- sound intensity decreases with distance, so closer object will tend to have greater amplitudes than farther ones
112
monaural cues - distance - reverberation
- 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
why is localising sounds within rooms difficult
- 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
what is the precedence effect when localising sound within rooms
- 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
what is auditory scene analysis
- 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
what are the strategies for auditory grouping in auditory scene analysis
- follows principles such as common fate, proximity, similarity and continuity
- we need to consider spectral grouping and sequential grouping
117
what is spectral grouping in auditory scene analysis
- 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
what is harmonicity in spectral grouping - auditory scene analysis
- if a component is mistuned to other components, it will be heard as a separate sound
119
what is common frequency change in spectral grouping - auditory scene analysis
- analogue to the principle of common fate
- frequency components that change together tend to group together
120
what is sequential grouping
- combining sequences of sounds over time
121
what is auditory stream segregation in sequential grouping - auditory scene analysis
- the process of organising sounds over time into separate perceptual events
122
what is similarity of pitch in sequential grouping - auditory scene analysis
- sounds with similar pitch are often produced by the same source
- increasing frequency difference promotes stream segregation
123
what is temporal proximity in sequential grouping - auditory scene analysis
- sounds that occur in rapid progression tend to be produced by the same source
- increasing presentation rate also promotes stream segregation
124
what is similarity of timbre in sequential grouping - auditory scene analysis
- sound sources often have distinct timbre, providing a good cue for stream segregation
125
what is continuity in sequential grouping - auditory scene analysis
- 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
