Psychophysical property

Property that depends on our psychological interpretation of it

Spectrum of light wavelengths we can see

400-700

3 steps to color perception

Detection: our S, M, and L cones seeing color

Discrimination: tell the difference between one wavelength and another

• (L-M) and (M-L) for red vs. green

• (L+M)-s and S-(L+M) for blue vs. yellow

Appearance: assign perceived colors to lights and surfaces that are stable in different lighting conditions

3 types of cone photoreceptors

S blue, M green, and L red

L cone peak sensitivity

565 nm - corresponds to yellow

Why do we call cones S, M, L and not B, G, R

Because there is a range of wavelengths that are B, G and R

Photopic

High light, bright enough to saturate rods and stimulate cones

Scotopic

Low light, bright enough to stimulate rods but not enough for cones

Rhodopsin

Rods, 100x more sensitive to light than cones

All rods have same sensitivity to different wavelengths of light

Principle of univariance

Multiple wavelength and intensity combinations can produce the same color

How to solve univariance

Have 3 cones

Trichromatic theory of color vision

Color is defined with three numbers

Metamers

Two different wavelength combinations that result in the same color

Why is it called Young-Helmholtz theory?

They both discovered it independently

James Maxwell color matching technique

Still used today

Additive color mixing

When colors are put together and their effects enhance each other. ex: how we see white

Subtractive color mixing

When colors are put together and their effects subtract from each other. ex: combine blue and yellow to make green

LGN

Has cells stimulated by spots of light

Center-surround organization

Cone-opponent cell

Neuron whose output is based on a difference between sets of cones

Color space

3D space that describes all colors

RGB color space

Amount of R, G, B

HSB color space

Hue: color

Saturation: how intense color is

Brightness: how much light 

Nonspectral colors

Colors that we can only see as a combination of multiple wavelengths

How do we perceive purple?

Activation of S and L cones 

Opponent color theory

Perception of color depends on the output of three mechanisms, each based on opponency between two colors

LGN color activation

Some LGN cells activated by L in center, inhibited by M in surround (red vs. green)

Some LGN cells activated by S in center, inhibited by (L+M) in surround (blue vs. yellow)

…& vice versa

Hering "illegal" color combinations

Red and green, blue and yellow, black and white

Opposite colors on the color wheel

Hue cancellation experiments

Start with a color, the goal is to end with a pure version of that color by shining different lights

Unique hues

Red, blue, green, yellow. Colors that can be described with just one term

Achromatopsia

Fully color blind from brain damage. Can find boundaries between color regions

Cultural relativism

Different cultures describe colors differently, perception determined by cultural environment

Basic color terms

The common color terms that people use

Color category boundaries

if something crosses the color category boundary, it’s easy for us to determine which color is different from others

Why is color blindness more common in men?

M and L cones on X chromosome

Color anomalous

Color blindness. Can still make discriminations from wavelength

Deuteranope

Missing M, yellow-green-red messed up

Protanope

Missing L, yellow-green-red messed up

Tritanope

Missing S

Cone monochromat

Having one cone type

Rod monochromat

Having no cone types

Anomia

Inability to name objects or colors even though you can recognize them. Due to brain damage

Synesthesia

One stimulus automatically activates experience of another stimulus that isn’t present

Color contrast

Two colors next to each other enhance one another, color opponency

Color assimilation

Two colors next to each other dullen one another

Unrelated color

Color that can be experience in isolation

Related color

Color that is only seen in relation to other colors (ex: brown or grey)

Negative afterimages

When you stare at an image and look away, you will see an image with the opposite colors

Illuminant - broadband

Contains many different wavelengths

Surface - broadband

Reflects many different wavelengths

Why is color good for survival?

Determining if food is ripe and finding mates

How does flavor of food get affected by color?

Ex: white wine dyed pink tastes more like rose than undyed wine

Dogs color vision

Dichromatic

Chickens color vision

Tetrachromatic

Mantis shrimp color vision

12 cones

Silver spiny fin fish color vision

38 rods

Bird/reptile color vision

Colored oil on photoreceptors tunes them to different wavelengths

Dots vary in hue

Can distinguish

Dots vary in saturation

Can’t distinguish

How does attention select a group of items, color-wise?

Based on hue

Realism

The world exists

Positivist

The world depends on evidence of senses

Euclidean Geometry

Parallel lines that extend in space don’t cross, all angles of a triangle add to 180

Are images presented onto the retina euclidean?

No

Probability summation

Increased probability of seeing stimulus when you have two or more samples

Binocular summation

Combination of information from both eyes that makes you better at something that if you had only one eye

Binocular disparity

The two eyes see slightly different things

Stereopsis

Perception of depth by using both eyes

Monocular depth cue

A depth cue you can see with one eye

Binocular depth cue

A depth cue you can see with two eyes

Occlusion

Something in front of something else

Metrical depth cue

A cue where you know exact sizes

Cells code precise distance of feature from the plane of fixation

Nonmetrical depth cue

A cue that gives you information about relative depth (ex: occlusion)

Cells code whether feature is in front of or behind plane of fixation

Relative size

Knowing the size of something compared to something else without knowing their actual sizes

Relative height

When objects touch the ground, those higher in the visual field appear to be farther away

Texture gradient

When things are bigger and get smaller in a photo, we assume the bigger things are closer to us

Familiar size

Knowing approximate size of something familiar

Relative metrical cue

A cue that can specify that object A is 2x further away than B without knowing absolute distance to A or B

Absolute metrical depth cue

Provides quantifiable information about distance in the third dimension

Aerial perspective

Depth cue based on implicit understanding that light is scattered by atmosphere

Linear perspective

Lines in 3d appear to converge into 2d as they extend in the distance

Vanishing point

The point where parallel lines converge

Pictorial depth cue

Depth cues artists use to make photos look 3D

Anamorphosis

Create a 2D image so distorted it only looks correct from a special angle

Motion parallax

When something is closer to us we see it as moving faster

Accommodation

Lens changing shape to let more or less light in

Convergence

Eyes going inward, ex: crossing

Divergence

Eyes going outward

Corresponding retinal points

Points on the two different retinas that allow someone to see one thing

Horopter

Location of objects whose images lie on corresponding points

Vieth-Muller circle

Location of objects whose images lie on corresponding points

We can consider horopters and Vieth-Mullers to be...

The same

Panum's fusional area

Region of space in front of and behind horopter where binocular single vision is possible

Diplopia

Seeing two things because they’re not on corresponding points

Crossed disparity

Objects in front of plane of horopter. Image is to the left in the right eye and to the right in the left eye

Uncrossed disparity

Objects behind plane of horopter. Image is to the left in the left eye and to the right in the right eye

Stereoscope

Device that shows a different photo to each eye

Free fusion

Converging or diverging eyes to view a stereogram without a stereoscope

Stereoblindness

Unable to use binocular disparity as a depth cue

Does binocular vision develop during critical period?

No

Brock string

Hold one end of a string to a wall and the other to someone’s nose. It has beads on it and they have to focus on the beads to practice their stereoacuity

Random dot stereogram

Stereogram made of random dots, has no depth cues

Cyclopean

Stimuli defined by binocular disparity alone

How do 3D movies work?

Have two slightly different images in each eye

Correspondence problem

Figuring out which bit in image in left eye should be matched with which bit in image in right eye

Correspondence problem solution

Blurring the image, uniqueness constraint, continuity constraint

Uniqueness constraint

Observation that feature in the world is represented once in each retinal image

Continuity constraint

neighboring points in the world lie at similar distances from viewer

Are binocular neurons tuned to binocular disparity?

Yes

Binocular rivalry and when do we get it?

Competition between two eyes for control of visual perception, get it when two different stimuli are presented to the two eyes

Stereoacuity

Smallest binocular disparity that can generate a sensation of depth

Dichoptic

Presentation of two stimuli, one to each eye

Onset of stereopsis

3-5 months

Development of stereoacuity

6-7 months

Strabismus

Misalignment of eyes

Esotropia

One eye turns inward

Exotropia

One eye turns outward

Esotropia during critical period

If it’s during the critical period, it leads to stereoblindness

Selective attention

Attention involved when processing is restricted to a subset of the possible stimuli

Internal attention

Paying attention to something internally. Ex: repeating a sentence in your head

Overt attention

Turning an organ to something Ex: moving head to look at something

Covert attention

Paying attention to something without an outward sign that you’re doing so

Invalid vs. valid cues

Invalid: doesn’t cue to right direction

Valid: does cue to right direction

Posner cueing paradigm

Showed symbolic and peripheral cues

Peripheral vs. symbolic cue

Peripheral: cue directly shows where something will be.

Symbolic: cue indirectly shows where something will be. Takes longer. Ex: if this dot turns green, the image is on the left. 

Inhibition of return

Once we pay attention to something, our brain prevents us from going back to the area immediately after, good for visual searches

Spotlight model

We have a certain point of fixation that moves as we move around

Zoom lens model

Our point of fixation gets bigger or smaller depending on the size of the area we’re scanning

Visual search target, distractor, set size

Target: what we’re looking for

Distractor: everything in the set that isn’t the target

Set size: the amount of things in the set

Search slope

Time/object; ms/object

Large search slope implications

Inefficient search

Feature search

Looking for something that is defined by one feature

Salience

Vividness of stimulus relative to its neighbors

Parallel

Processing multiple things at once

Serial self-terminating search

Looking from item to item and when we find it, we stop looking

Archerfish study

Archerfish spray their prey. They were trained to spray a screen if they thought a fish was on the screen, and their searching skills are similar to humans.

Guided search

Restricted to a subset of possible items based on information about its basic features

Conjunction search

Looking for something that differs based on multiple features.

Scene-based guidance

When we have previous knowledge of something that helps us search

Binding problem

Issue with tying different attributes of visual stimuli to appropriate object until we see a unified object

Different neurons perceive different things

Feature integration theory

Limited set of basic features can be processed parallely preattentively

Preattentive stage

Processing of a stimulus before selective attention is deployed to stimulus

Illusory conjunction

Erroneously thinking two features are attributed to the same object

Rapid serial visual presentation

Showing a stream of images at once. 8/second

Used to study temporal dynamics of visual attention

Attentional blink

If we see one target and another right after, we will not process the second one

Second target is missed if its within __ of first target

200-500 ms

People who have reduced attentional blink

First shooter video games

Marvin Chun's fishing metaphor

Fishing, as you pick up a fish you are unable to pick up other fish for a few seconds and may miss some

Attention neural activity

When you pay attention to different things, different parts of the brain work

Attention used in fMRI

Attentional neural activity can be used in fMRI

Fusiform face area

In fusiform gyrus that specializes in perceiving faces

Parahippocampal place area

In temporal lobe that specializes in perceiving places

Three ways cell response can be changed by attention

Response enhancement, sharper tuning, altered tuning

Visual-field defect

Portion of visual field with no vision or abnormal vision

Damage to visual nervous system

Damage to parietal lobe: visual field defect where one side of world is ignored

Neglect

When you ignore one side of something

Cotralesional vs. ipsilesional

Visual field on opposite side of brain lesion vs on same side of brain lesion

Neglect task example

Ask someone to draw a house, they will only draw one side

Is neglect on one side of object or visual field?

Can be either

Extinction

Can’t perceive a stimulus to one side of the point of fixation in the presence of another stimulus

Selective attention and ADHD

Attention deficit disorders that don’t affect visual attention

Selective pathway

Analyzes specific objects, small range

Goes through bottleneck

Nonselective pathway

Analyzes scenes, gists

Doesn’t go through bottleneck

Ensemble statistics

Average and distribution of properties over a set of objects or a region in a scene, nonselective

Spatial layout

Layout of something

What pathway analyzes spatial layout?

Nonselective pathway

Brandy memory task

People looked at 2500 objects, then had to choose which objects they had previously seen. Different types > same category > different states

Change blindness

Not noticing a change in a scene

Inattentional blindness

Not noticing the addition of a new stimulus in a scene because you’re focusing on something else

Motion aftereffects

When you look at something in motion for a while and then look at something stationary, it will look like that thing is moving

Interocular transfer

Transfer from one eye to another

MAE must be in neurons that...

Respond to both eyes

Which brain region is MAE in/after?

V1

Describe motion detector neurons

Neuron → D cells (detection) → X cells (multiplication) → M cells (ensure both neurons are responding)

Apparent motion

If photos are flashed rapidly of someone in different positions, it will look like they are moving

What does apparent motion tell us about the motion detector circuit?

We don’t need actual motion for the motion detector circuit to be activated

Correspondence problem

Not being able to tell which movement corresponds to what frame

Aperture problem

If we see something moving through an aperture, we can’t actually tell which direction it’s moving

Global motion of the object

Allows us to tell which direction something is moving. Global motion is the direction the every aperture is moving in

Lesion in magnocellular layers

Problems processing large, quick moving objects

MT role in motion perception

Processing motion

Akinetopsia

Inability to process motion, seeing things in stop-motion

What causes akinetopsia?

Damage to the MT

Newsome and Pare study

Taught monkeys to respond to moving dots. When their MT was lesioned, they needed 10x more dots to respond. However, since lesioning is invasive it’s better to electrically stimulate portions of their brain, which is also better because you can bias it towards brain regions that respond to certain directions.

First-order motion

Motion defined by changes in luminance

Second-order motion

Motion defined by changes in texture. Usually only seen in labs

Optic array

Lights in the world around us

Optic flow

Points in our vision moving as we move

Optic flow field

Flow pattern that happens when we are moving forward rapidly in space

Focus of expansion

If we go straight into the horizon, things on the sides of us will look like they’re expanding

Time to collision

We can tell time to collision using tau

Tau

Ratio of size of object on retina to rate that object is expanding

Troxler fading

When we stare at something stationary, stationary things in our periphery will disappear

Motion induced blindness

When we stare at something in motion, stationary things in our periphery will disappear

Smooth pursuit

When we look at something in motion and follow it with our eyes, our eyes move smoothly

Saccade

When we move our eyes to another point of fixation it is very jerky

Eye muscles

6 muscles, in pairs

Superior colliculus

Part of the midbrain that processes and controls movements

Saccadic suppression

This reduces the sensitivity that happens when we have saccades

Efference copy

When there is movement, the motion system sends a copy to other cortexes

Comparator

Comparator receives efference copy and motor system copy and compare them. if they’re the same, movement is of eyes. If they’re different, movement is physical.

Dynamic remapping

When our mind predicts a saccade, the neurons start remapping towards that area so we start processing that location before our eyes move to it

When do people get reflexive eye movements

Infant at birth

When do people get adult sensitivity to motion

3-4 years

When do people get sensitivity to motion defined form and biological motion

4+ years