Final Flashcards
Overt attention
Directing the eyes and attention to a stimulus
Covert attention
Directing attention to a stimulus, while the eyes are fixated elsewhere
selective attention
selecting one stimulus to attend to out of many
Attention is like a
spotlight; zoom lens
Why attention?
Limited capacity in information processing - only so much can be processed at the same time
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
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)
response time
the time that elapses between a person being presented with a stimulus and the person initiating a motor response to the stimulus
parallel search
A search in which multiple stimuli are processed at the same time.
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).
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.
feature search
feature computed over the entire image in parallel; does not require attention
serial search
Each item needs to be scanned, RT increases with # of distractors, sequential, self-terminating search
Motion parallax
Images of objects have different velocities on the retina depending on their depths
Iso-luminant
same luminance, different colors
White light is not “pure” but a
composite
Complementary colors
Don’t need all wavelengths to obtain white light
Just two can be sufficient
Blue + Yellow = White
Red + Green = White
The yellow paint/filter absorbs
short wavelengths
the blue paint/filter absorbs
long wavelengths
Trichromacy =
retina
Opponecy =
Lgn
The “red-green” channel
Take the difference between L and M cone responses
The “blue-yellow” channel
Take the difference between the (L+M) response and the S response
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
Horopter
all points at the same perceived depth as fixation
Motion parallax
Objects near fixation move slowly across the retina
Objects far from fixation move quickly
Fixation point has no speed on the retina
Geons
Defined by three properties:
Shape of cross section
Size of cross section
Axis: straight or curved
Why geons?
Recognizable from almost any viewpoint (cylinder, wedge, soap, noodle)
Conjunction search
Real life searches not defined by a single feature
Example: find red peppers in photo of produce section
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
Change blindness
Importance of intervening blank screen - grey blank in between photos blocks the brain from seeing the changes as apparent motion
Gist
: quick summary
Spatial layout
: layout of objects in 3-d space
motion agnosia
Had difficulty pouring water because it looks frozen - no sense of motion
Could not see facial movements, mouth of a speaker
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
Based on point-light motion,
observers can tell:
– sex of walker / dancer
– action / kind of dance
– identity of a friend
– kind of animal
motion has two components:
- Direction
* Speed ( = distance / time)
Recall: complex cells in v1 are
direction selective
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
Greater separation between and b in a reichardt detectors,
responds to faster motion
Different cells are selective for
different directions of motion
different speeds
decrease delta t
responds to faster motion
threshold for seeing coherent motion
~3% correlated motion
with damage to mt, adults need >___% correlated motion to see coherent motion
30
monkeys’ responses can be predicted by
seeing which mt neurons are responding
monkey’s responses can be modified by
electrically stimulating specific MT neurons
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
motion after-effect
After adaption, “downward” neurons respond more weakly than “upward” neurons
MAE also occurs with
radial motion (i.e, expansion or contraction)
motion informs us about
heading direction
whether we are on a collision course with an object
how soon a “collision’ is likely to occur
Optic flow
flow patterns created on the retinas by the relative motions of objects
backward motion
inward flow (contraction)
forward motion
outward flow (expansion)
v1 cells have _____ RFs, hence motion is _________
small, ambiguous (aperture problem)
V1 cells cannot determine
object motion
local motion signals must be integrated to perceive unambiguous motion, this happens in
area MT
Area MT
All cells in MT exhibit directional selectivity
Much larger RFs than v1 cells
An MT cell receives inputs from many V1 cells
what is sound?
A vibrating surface generates compressions and rarefactions in the medium (e.g. air)
compression
increase in air pressure
rarefaction
decrease in air pressure
acoustic energy
waves of compression and rarefaction through the medium
sound
perceptual experience based on acoustic energy
Acoustic waves need
a medium to travel in - can’t hear through a vacuum
Speed (sound) depends on
density of the medium - faster in liquid than air, even faster in solids
amplitude
maximum deviation from baseline pressure - amplitude determines loudness
sound intensity is measured in
decibels
decibel is a ___ scale
log - adding to the db value, amplitude get multiplied
Frequency determines
the pitch of a sound
Frequency is measured in
cycles per second (hertz, hz)
wavelength
separation from one wave peak to the next
normal human range of hearing
50 hz - 20,000 hz
wavelength =
1 / frequency
sinusoidal acoustic waves are known as
pure tones
Fourier’s theorem
Any complex wave can be created by adding sine waves
vision (fourier’s theorem)
any image can be created by adding sine gratings
audition (fourier’s theorem)
any complex sound can be created by adding pure tones
the lowest-frequency component is known as its
fundamental
pinna
shell-like flap of the outer ear - gives sound a unique signature, helps in localizing sounds
eardrum
thin, oval membrane
vibrates in response to the acoustic waves
passes vibrations to the middle ear
ossicles
“tiny bones” Malleus, Incus, Stapes - passes the vibration from the eardrum to the inner ear and amplifies the vibrations from the eardrum
Amplification is needed because
the inner ear (cochlea) is filled with fluid
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
Organ of corti has ~_____ hair cells per ear
20,000, 1/4 inner HCs (1 row), 3/4 outer HCs (3-4 rows)
cilia
bristle-like structures at the top of hair cells
___% of nerve fibers originate from _____ hair cells
95, inner
transduction takes place mostly in
inner hair cells
Outer hair cells _______ the motion of the basilar membrane
amplify - make contact with tectorial membrane
contract/expand - motor-like action
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
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
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
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
tonotopic organization
precise mapping between sound frequency and location
frequency encoded by location along cochlea where nerve fibers are active
