Cognitive Science 126 Perception Midterm

Wavelength of visual light

400-700 mm

blue light has shorter wavelength, higher frequency

red light has longer wavelength, lower frequency

Particle properties of light

Tubes

One direction of light can be absorbed by each point

Lens

refracts/converges light

focal point

where an image will be reconstructed after being refracted through a lens

Pinhole optics

tiny hole only allows one point of light from each point on the actual object

image is projected upside down

smaller hole -> better resolution, lower brightness

Camera obscura

large pinhole camera in SF

Refraction

changing the angle of light by slowing it down

light moves at different speed through different substances

Refractive index

how much light bends towards a surface

proportional to the ratio of the speeds

power of lenses are measured in dioptecs = 1/f,

where f = focal length

more powerful lenses focus closer/have smaller focal length

Converging prism

a prism that converges light by refracting it inward

Photoreceptors

Rod cells and Cone cells

In the retina

Humans have 260 million receptors

Convert visible light into signals that can stimulate biological processes -> transduction

Rods

Rod shaped, smaller, used to see in the dark and perceive shapes, all one type, higher ration of rods to cones at the periphery

Cones

blue/green/red sensitive cones used to see colors

only cones at the fovea, less towards periphery

diurnal animals have more cones than nocturnal mammals

don't work well in low light situations

Compound eye

found in basic animals

early eye, 500 million years old

multiple lenses each with one photoreceptor, tubes

e.g. most insects, mantis shrimp

Simple eye

one lens focuses light on many photoreceptors

e.g. squids, humans, scallops (and most vertebrates?)

giant squid's eyes are like human eyes but bigger/better

Sensitive to transparent things, polarized light, broader parts of the EM spectrum

Limpet

100 receptors, no lens

Pinhole camera eye

Chambered Nautilus

Can let in a lot of light

Mirror eye

uses reflective material on the back of the eye to focus

very rare

e.g. brownsnout spookfish

Amoebe/paramecium

1 receptor, no lens

Copilia

2 lenses, 2 receptors

back lens scans over the image plane of front lens, used to focus

Extromission

the early idea that light shoots from our eyes

Scotopic vision

low light vision

rods only

only periphery sees

only in black and white

poor resolution

Photopic vision

bright light vision

only fovea/cones

good resolution

in color

Squid eyes

giant simple eyes, like human eyes but bigger/better

Sensitive to transparent things, polarized light, broader parts of the EM spectrum

Pupil

the pinhole, lets light in

Cornea

focuses light

lens

fine tunes focus

Iris

muscle that controls the size of the pupil

Retina

photoreceptors, where transduction from light to biological signals happens

Converging light

light rays that are parallel to each other are bent towards each other, focused

Optic function of an eye

form an image of an object on retina: cornea and lens work together to converge light to it

Optic nerve

Where nerves come together and exit the eye towards the brain

no photoreceptors where the optic nerve connects to the retina --> creates the blind spot

Fovea

the central focal point in the retina, around which the eye's cones cluster

periphery

optic disk

Area of the retina without rods or cones, where the optic nerve exits the back of the eye.

Types of cones/rods

1 type of rod

3 types of cones (correspond to R, G, B)

Are cones or rods larger?

cones

How many types of cones vs how many types of rods?

3 cones, 1 rod

Where are cones located?

mostly in the fovea

blood vessels in eye

cover retina, pushed away at fovea avascular zone (.5mm in diameter)

Adaptation

Our vision is most sensitive to change, no change in stimulation causes fatigue or adaptation in photoreceptors

This is why we don't see our blood vessels even though they are in front of the retina

Troxler fading

weak stimuli with no change--> brain ignores it

Receptive field of skin

area on skin that causes certain neurons to fire would be those neuron's RF

Photoreceptor RF

the area of the visual field that corresponds to single photoreceptor

receptive field of vision

area of your visual field that corresponds to an area on the retina

Neuron

a nerve cell

communicates using action potentials

can be very long

signals are very brief and fast

signals propagate to the end of the axon without decrement

what triggers an action potential?

a neuron will fire an action potential once the sum of it's IPSP's and EPSP's hit a certain threshhold

can be triggered with a strong input or lots of weak inputs

Action potential

the change in electrical potential associated with the passage of an impulse along the membrane of a nerve cell.

Neuron structure

soma (cell body) + dendrites -> axon -> presynamptic terminals-->axon terminal

what type of output does an action potential produce?

all or nothing

EPSP input or connection

Excitatory post synaptic potential

Makes neuron fire/Increases likelihood that neuron will fire

Depolarize a neuron

IPSP input or connection

Inhibitory post synaptic potential

Makes neuron not fire/Decreases likelihood cell with fire

Hyperpolarize a neuron

Depolarization

reduce the amount of negative charge in a neuron

Recording from neurons with an electrode

Sounds like rapid static

a neuron at rest has spontaneous activity

can measure depolarizations/hyperpolarizations to get a sense of when a neuron is firing

Excitation and inhibition counteract each other

summation of EPSPs and IPSPs trigger an action potential if cell hits the proper level of depolarization

Ganglion cells location

located past photoreceptors in retina

Ganglion cell RF

Ganglion cells have center/surround organization, on/off or off/on, measure local contrast

Preferred stimulus of an ON-center ganglion cell

bright light in middle of dark background, sensitive to local contrast

LGN RF

RF identical to ganlgion

Cells with orientation preference (how + which)

Simple cells, arrangement of LGN/ganglion cell RF's arranged with centers aligned

LGN location

thalamus

LGN input

take information from contralateral and a little from ipsilateral

LGN organization

organized topographically

LGN sends information to __ in the __ lobe

V1, occipital

Hermann grid RF explanation

Cells with RF that are near the corners of the grid signal low contrast because the junction of 4 paths impede the off surround

Why don't we see herman grid illusion at the center of our vision?

Fovea has smaller receptive fields

Simple cells: who discovered

Hubel and Wiesel, accident, with cat

Simple cell RF

on center/off surround, with bars not circles

Simple cell stimulus preference

Bars of light

Tuning curve for orientation

closer to orientation preference = higher response

Complex cell input

several simple cells

Complex cell preference

Bars of light that align with the RF, doesn't matter if it's dark or light, only sensitive to motion direction and orientation

Complex cell RF

Every location has an ON response from at least one simple cell and an OFF response from another simple cell

Preferences of complex RF's

position insensitive within the receptive field

contrast insensitive

orientation sensitive

direction of motion

Hypercomplex cells

same as complex cells but with length preference

end-stopped cells

have inhibitory regions surrounding RF

White matter

axons w/ myelin sheaths, show cells communicating with each other

Gray matter

cell bodies (soma)

Soma

cell bodies

Cerebral cortex

high level thinking and processing happens here (the lobes)

V1 location

Occipital lobe

Phineas gage

pole through frontal lobe

became an uninhibited, unreasonable jerk

Broca's area

Controls language expression - an area of the frontal lobe, usually in the left hemisphere, that directs the muscle movements involved in speech.

Phrenology

obsolete (and racist) theory that bumps on skull correspond to certain talents

Four lobes of the brain

frontal, parietal, temporal, occipital

Motor cortex

M1: frontal, precentral gyrus

Somatosensory cortex

S1: parietal

postcentral gyrus

Homunculus

Motor homunculus vs Sensory homunculus

size of body part is proportional to the proportion of the motor or sensory cortex devoted to it

area of cortex that corresponds to different body parts (either for motion or sensation)

Corpus Callosum

Located in the center of the brain: allows for communication between two hemispheres

white matter

Cortical magnification

parts of the body (hands, lips, face) are more represented on the cortex because more detailed sensory information

Tonotopy

areas in temporal

Somatotopy/ Motor topography

spatial mapping of the somatosensory and motor functions: adjacent areas correspond to adjacent body parts

retinotopy

mapping of visual input from retina to neurons, points that area adjacent on the retina are adjacent on cortex

Visual fields crossover

Contralateral organization of vision: 90% contralateral input, 10% ipsilateral

Walter Penfield

Neural surgeon who stimulated exposed brain of alert patients, used a probe to deliver slight electrical stimulation

different locations evoked different memories, sensations, or muscle twitches

mapped cortical homunculus

ventral pathway

What, occipital to inferior temporal lobe, object recognition

dorsal pathway

where, occipital to parietal lobe, location action naviagating and grasping

Medium scale modules

color, motion, facial recognition

note we can have deficits in all of these specifically b/c they are localized

Small scale models

Hypercolumns and columns

Hubel&Wiesel Hypercolumn structure

organized in slabs/ columns (orientation columns)

topographically organized

Hypercolumns

located in v1

each hypercolumns analyzes information from 1 region of the retina

fovea is overrepresented

one hypercolumn measures: light/dark, red/green, blue/yellow, size, orientation, motion, depth