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Sensation and Perception > Final > Flashcards

Flashcards in Final Deck (92):
1

Overt attention

Directing the eyes and attention to a stimulus

2

Covert attention

Directing attention to a stimulus, while the eyes are fixated elsewhere

3

selective attention

selecting one stimulus to attend to out of many

4

Attention is like a

spotlight; zoom lens

5

Why attention?

Limited capacity in information processing - only so much can be processed at the same time

6

attentional "bottleneck"

individuals have a limited amount of attentional resources that they can use at one time.

Therefore, information and stimuli are 'filtered' somehow so that only the most salient and important information is perceived - a subset is selected for further processing

7

visual search

a type of perceptual task requiring attention that typically involves an active scan of the visual environment for a particular object or feature (the target) among other objects or features (the distractors)

8

response time

the time that elapses between a person being presented with a stimulus and the person initiating a motor response to the stimulus

9

parallel search

A search in which multiple stimuli are processed at the same time.

10

binding problem

The challenge of tying different attributes of visual stimuli (e.g., color, orientation, motion), which are handled by different brain circuits, to the appropriate object so that we perceive a unified object (e.g., red, vertical, moving right).

11

change blindness

The failure to notice a change between two scenes. If the gist, or meaning, of the scene is not altered, quite large changes can pass unnoticed.

12

feature search

feature computed over the entire image in parallel; does not require attention

13

serial search

Each item needs to be scanned, RT increases with # of distractors, sequential, self-terminating search

14

Motion parallax

Images of objects have different velocities on the retina depending on their depths

15

Iso-luminant

same luminance, different colors

16

White light is not “pure” but a

composite

17

Complementary colors

Don’t need all wavelengths to obtain white light
Just two can be sufficient
Blue + Yellow = White
Red + Green = White

18

The yellow paint/filter absorbs

short wavelengths

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the blue paint/filter absorbs

long wavelengths

20

Trichromacy =

retina

21

Opponecy =

Lgn

22

The “red-green” channel

Take the difference between L and M cone responses

23

The “blue-yellow” channel

Take the difference between the (L+M) response and the S response

24

two possible mechanisms for color constancy

Discounting the illuminant
If the entire scene is purplish, it tells you that the illuminant itself is purplish, and our brain suggests we should try to discount the purple we see in the apple
The brain tries to undo the effect of the illuminant

Color contrast
To compare the color of the apple with surrounding regions
If there’s a lot of blue around a patch, the percept is biased away from blue

25

Horopter

all points at the same perceived depth as fixation

26

Motion parallax

Objects near fixation move slowly across the retina

Objects far from fixation move quickly

Fixation point has no speed on the retina

27

Geons

Defined by three properties:
Shape of cross section
Size of cross section
Axis: straight or curved

28

Why geons?

Recognizable from almost any viewpoint (cylinder, wedge, soap, noodle)

29

Conjunction search

Real life searches not defined by a single feature
Example: find red peppers in photo of produce section

30

Object-based attention

If you have to disengage your attention from one object and attending to a different one, that takes more effort than attending to one for longer

31

Change blindness

Importance of intervening blank screen - grey blank in between photos blocks the brain from seeing the changes as apparent motion

32

Gist

: quick summary

33

Spatial layout

: layout of objects in 3-d space

34

motion agnosia

Had difficulty pouring water because it looks frozen - no sense of motion
Could not see facial movements, mouth of a speaker

35

Motion helps to

Draw attention - especially important because we have small fovea
Segment objects from background
Relative depth (motion parallax)
3d shape
object recognition in impoverished displays

36

Based on point-light motion,
observers can tell:

– sex of walker / dancer
– action / kind of dance
– identity of a friend
– kind of animal

37

motion has two components:

• Direction
• Speed ( = distance / time)

38

Recall: complex cells in v1 are

direction selective

39

Reichardt model

Retinal surface, time delay, directionally-selective cell

T1: light at position a (signal delayed for delta t)

T2: light at position b (no delay)

Cells only fire when it receive inputs from both simultaneously

40

Greater separation between and b in a reichardt detectors,

responds to faster motion

41

Different cells are selective for

different directions of motion

different speeds

42

decrease delta t

responds to faster motion

43

threshold for seeing coherent motion

~3% correlated motion

44

with damage to mt, adults need >___% correlated motion to see coherent motion

30

45

monkeys' responses can be predicted by

seeing which mt neurons are responding

46

monkey's responses can be modified by

electrically stimulating specific MT neurons

47

When we adapt to downward motion

neurons selective for downward motion get fatigued - subsequently, a stationary object will appear to move in the upward direction

48

motion after-effect

After adaption, "downward" neurons respond more weakly than "upward" neurons

49

MAE also occurs with

radial motion (i.e, expansion or contraction)

50

motion informs us about

heading direction
whether we are on a collision course with an object
how soon a "collision' is likely to occur

51

Optic flow

flow patterns created on the retinas by the relative motions of objects

52

backward motion

inward flow (contraction)

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forward motion

outward flow (expansion)

54

v1 cells have _____ RFs, hence motion is _________

small, ambiguous (aperture problem)

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V1 cells cannot determine

object motion

56

local motion signals must be integrated to perceive unambiguous motion, this happens in

area MT

57

Area MT

All cells in MT exhibit directional selectivity

Much larger RFs than v1 cells

An MT cell receives inputs from many V1 cells

58

what is sound?

A vibrating surface generates compressions and rarefactions in the medium (e.g. air)

59

compression

increase in air pressure

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rarefaction

decrease in air pressure

61

acoustic energy

waves of compression and rarefaction through the medium

62

sound

perceptual experience based on acoustic energy

63

Acoustic waves need

a medium to travel in - can't hear through a vacuum

64

Speed (sound) depends on

density of the medium - faster in liquid than air, even faster in solids

65

amplitude

maximum deviation from baseline pressure - amplitude determines loudness

66

sound intensity is measured in

decibels

67

decibel is a ___ scale

log - adding to the db value, amplitude get multiplied

68

Frequency determines

the pitch of a sound

69

Frequency is measured in

cycles per second (hertz, hz)

70

wavelength

separation from one wave peak to the next

71

normal human range of hearing

50 hz - 20,000 hz

72

wavelength =

1 / frequency

73

sinusoidal acoustic waves are known as

pure tones

74

Fourier's theorem

Any complex wave can be created by adding sine waves

75

vision (fourier's theorem)

any image can be created by adding sine gratings

76

audition (fourier's theorem)

any complex sound can be created by adding pure tones

77

the lowest-frequency component is known as its

fundamental

78

pinna

shell-like flap of the outer ear - gives sound a unique signature, helps in localizing sounds

79

eardrum

thin, oval membrane

vibrates in response to the acoustic waves

passes vibrations to the middle ear

80

ossicles

"tiny bones" Malleus, Incus, Stapes - passes the vibration from the eardrum to the inner ear and amplifies the vibrations from the eardrum

81

Amplification is needed because

the inner ear (cochlea) is filled with fluid

82

cochlea

3 fluid-filled canals

the vibrations from the Stapes set the fluid in motion

Generates a wave motion in the basilar membrane

converted to nerve impulses in the Organ of corti

83

Organ of corti has ~_____ hair cells per ear

20,000, 1/4 inner HCs (1 row), 3/4 outer HCs (3-4 rows)

84

cilia

bristle-like structures at the top of hair cells

85

___% of nerve fibers originate from _____ hair cells

95, inner

86

transduction takes place mostly in

inner hair cells

87

Outer hair cells _______ the motion of the basilar membrane

amplify - make contact with tectorial membrane

contract/expand - motor-like action

88

Temporal theory

Entire basilar membrane vibrates with the same frequency as the sound (like a microphone diaphragm)

Sound frequency 500 hz

BM vibrates at 500hz
nerve fibers fire 500 hz

89

Problems with the temporal theory

Entire BM cannot vibrate uniformly - narrower/stiffer at base; wider/flexible at apex

Neurons cannot fire > 1000 hz; but we can hear frequencies up to ~20,000hz

90

The place theory

Bekesy's traveling wave

Vibration at oval window set fluid in motion

generates a traveling wave along bm

gradually increases in amplitude, attains maximum value; then dies down

91

traveling wave theory

locus of maximal amplitude depends on sound frequency

High-frequency: near base

Low-frequency: near apex

Different groups of hair cells are activated along BM

Nerve signals initiated in different fibers along cochlea

92

tonotopic organization

precise mapping between sound frequency and location

frequency encoded by location along cochlea where nerve fibers are active