Sensation and Perception Exam 2

Orientation Tuning

tendency of neurons in straite cortex to respond more to cars of light at certain orientations and less to others at diff oriention

• Organizes V1 nuerons

Edge detector

What V1 functions as

The 3 types of cones

Short (s), medium (m), and long (l)

What is problem of univariance

two input variables combine to produce a single output

Is it true that for any cone type a membrane voltage can result from an infinite number of combinations of intensity and wavelength?

yes

What does the ratio for multiple cone type of wavelengths of ligth look like

(S:M:L)

Metamers

ligth sources that are physically diff from each other but result in same ratio of cone response (same perceoved color)

Most perceived colors are perceived by

single wavelemgths rather than pure

“Color blindness”

typically results from absent cone type

Why do some individuals perceive color but can’t distinguish as many

they have more metamer pairs that makes them say that multiple diff colors are just one

why are there not more cone types?

there are no adaptive selective pressures

Categorization

Judgement and label you apply to things

Categorical Perception

how things actually look or what the expression actually looks like

What is color perception’s problem?

the environment

How do objects change spectrum of light even when the objects are unchanged

Different light sources do that

Illuminant

Cone ratios produced by an object that change w a spectrum

What is the solution to recognizing an obejct regardless of the illumination changes

color constancy

• as lighting spectrum changes, perceived color varies much less than cone outputs would predict

• it draws on context and seeing what essence is presented

What does color constancy have the ablity to do?

discount the illuminant

• subtracting out the spectrum of light source from spectrum of light entering eye

• which can be accomplished by all areas under the same illuminant

Color contrast

items producing identical cone ratios and produced diff perceived colors based on illumination differences

Color Oppency

noted relationship bt blue/yellow and red/green

• ex: color aftereffects; exposure to blue makes gray look yellow; exposure to red make gray look green

Single Opponenet

• one red one green

• one yellow, one blue

Double opponent

• two reds, two greens

• two yellows, two blues

How does R/G channels provide “fine” info abt wavelength?

by comparing M to L

Gelb effect

demonstrates that “white” (brightness in general” is contextually defined

What’s the problem of depth perception

• Photons carry no info abt how far they’ve traveled

• 2D tells us what;s up/down, left/right but we need to know near/far

What are monocular depth cues dependent upon?

lots of assumptions

Monocular

information abt depth that you’d have access to if you had only one eye

Binocular

information about depth that you have only with 2 eyes

take a look at cues from 2/27

Convergence of the eye

them coming closer together

Divergence of the eye

then becoming more distant

The most important binocular cue: stereopsis

• aks “depth perception”

• the direct perception of depth

Horopter

• an imaginary circlethat includes both eyes and the object you are focused on (foveas of both eyes)

• all points exactly on this circle project corresponding retinal locations

Diplopia

really far off the horopter — so a large # of degrees of disparity

Crossed disparity

created by objects in front of the plane of the horopter

Uncrossed disparity

type of objects created by objects behind the plane of the horopter (in the eye, they are in the direction opposite of the eye)

How can you tell the difference bt light source w crossed and uncrossed disparity?

• determine average position of the images of source in the two retinas

• if actual images in two diff eyes are positioned temporally (temporal edge of the retina) relative to average position, it’s crossed dispaority

  • if positioned nasally, they’re uncrossed disparity

Stereopsis only works for

• objects a little inside or outside horopter

• when horopter apx 30 ft or less in diameter

Detection of disparity is basis of stereopsis

Any stimulus that produces non-zero retinal dispairty — as a result of depth or not — will produce perception of depth

Free fusion

stereograms require you yo cross your eyes to get diff images onto corresponding retinal points

How is disparity detected in the human brain

Requires neurons that receive input from both eyes

Disparity tuning

neurons with RFs at corresponding locations in each eye are tuned for zero disparity

• this means they respond best to a stimulus that casts images to corresponding retinal locations

Can neurons respond best to a stimulus that casts images to non-corresponding locations?

yes

Strabismus

when two eyes are not aligned

Stereopsis is

fragile

Sound is

periodic changes in air pressire — “waves” of high/low pressure

How is frequency measured

cycles/second (Hertz)

How is wavelength measured

meters per cycle

Speed of sound

(m/s) = frequency (cycle/sec) X wavelength (meters/cyc)

if you know frequency, you know…

wavelength

what’s a physical feature that we don’t have in light

amplitude

Harmonics

pressure waves at integer multiples of frequency of the fundamental

A fundamental frequency

the lowest frequency pressure wave present (usually named pitch)

Pinna

the outer ear

• shape matters — not only reflects sound into ear canal, but alters it slightly depending upon direction of source

Middle ear:

convert pressure waves in air to pressure waves in liquid ear (inner ear)

One of smallest bones in the body

ossicles

• malleus, incus, stapes — collectively acts as leverage

Inner ear

aka cochlea

• transduces physical energy into nueral energy

Base of basilar

• thick/rigid

• only tends to vibrate in high frequency

Tip of basilar

• thin/floppy

• tends to vibrate in low frequency

Primary sesnory neurons in OofC are

hair cells

Organ of corti

basilar membrane and tectorial membrane move relative to each other

Pure tones

waves composed of single frequency

Compelx tones

mixture of frequencies