Processing the Environment

P/S

Visual cues

Depth, Form, Motion, Constancy

depth

how far or close an object is

motion

our ability to sense and interpret movement, encompassing both the movement of objects around us and our own body's movement

form

visually perceive objects in the world in response to the patterns of light that they caste on our retinas

Binocular Cues

retinal disparity

convergence

convergence

looking far way→ eyes are relaxed

looking closer to us → eyes contract

monocular cues

relative size

interposition

relative height

shading and contour

motion parallax

relative size

one object percieved to be bigger → think of it being closer to us

interposition

object in front is closer to us

relative height

higher object → further away

shading and contour

using light and shadow to interpret form

constancy

our perception of object doesn’t change even if it looks different on retina

size, shape, color

sensory adaptation

change in the sensitivity of your perception of a sensation

hearing

adapt to loud noises → inner ear muscles contract to protect ear drum

touch

sensory nerves saturated → temperature receptors densensitized

smell

can detect chemicals in air

over time desensitized to molecules

proprioception

sense that tells your brain where your body parts are in space and how they are moving, without needing to look

just noticeable difference

threshold where you notice a change in sensation

𝚫I

Weber’s law

𝚫I/I = k

ratio of the just noticeable difference over intensity is constant

𝚫I/I = k

the just noticeable distance and the intensity are directly proportional

absolute threshold

minimum intensity of stimulus that a person can detect half the time

• more likely to detect it right when the intensity is higher

subliminal

stimuli we can’t detect 50% of the time

what influences detecting stimulus?

-expectations

-experiences

-motivation

-alertness

vestibular system

balance and spatial orientation

semicircular canals

posterior, lateral, and anterior canals are at 90 degrees to each other

filled with fluid called endolymph

cochlea

specialized auditory receptors that process sound and send info the brain

endolymph

shifts and allows us to detect what direction our head is moving in and strength of rotation

otolithic organs

utricle and saccule

information related to balance and spatial recognition

helps detect linear acceleration and head positions

how do otolithic organs help with detecting head position?

structures contain calcium carbonate crystals attached to hair cells with gel

if we move fast→ crystals move→pull on hair cells → action potential

what causes dizziness?

endolymph doesn’t stop spinning after stopping

signal detection theory

how we make decisions under conditions of uncertainty

how we discern between important stimuli and unimportant noise

at what point can a signal be detected

hit

stimulus present, guessed yes

miss

stimulus present, guessed no

false alarm

stimulus absent, guessed yes

correct rejection

stimulus absent, guessed no

d’ strategy

hit>miss → strong signal

hit<miss → weak signal

c strategy

conservative v.s liberal

conservative strategy

always no unless 100% sure

all correct rejections but some misses

liberal strategy

yes all the time

all hits but some false alarms

the signal distribution

the difference between the means of the two is d’

if signal shifts right → d’ is big and easy to detect

if signal shifts left → d’ is small and hard to detect

If strategy B choses a threshold 2

anything more than 2 is yes

less than 2 is no

strategy C

expressed via choice of threshold → threshold individual deems necessary for them to say yes

ideal observer, minimizes miss and false alarm

C = B-d’/2

When C = 0

participant is ideal observer

If <1 liberal

if >1 conservative

beta

beta = d’ x C

Bottom up processing

stimulus influences our perception

Top down

background knowledge influences perception

Gestalt principles

why we percejve things the way we do

Gestalt principle of similarity

items similar to one another are grouped together

Gestalt principle of pragnanz

reality is often organized reduced to simplest form as possible

ex: olympic rings perceived as five circles

Gestalt principle of proximity

objects that are close are grouped together

Gestalt principle of continuity

lines are seen as following the smoothest path

Gestalt principle of closure

objects grouped together are seen as a whole

Gestalt principle of common Fate

Elements that move in the same speed/direction are perceived as a group

conjunctiva

first layer that light hits

protects the cornea

cornea

transparent thick sheet of tissue

anterior 1/6th

anterior chamber

space filled with aqueous humor which provides pressure to maintain the shape of eye ball

what forms the ciliary body?

suspensory ligaments, attached to a ciliary muscle secretes the aqueous humor

posterior chamber

area behind the ciliary muscle

filled with aqueous humor 

vitreous chamber

filled with vitreous humor, jelly-like substance to provide pressure to eyeball

retina

filled with photoreceptors

macula — special part of the retina rich in cones 

fovea — completely covered in cones, no rods

choroid 

pigmented black in humans, a network of blood vessels

it’s black because all the light is reflected  

sclera

whites of the eye,

thick fibrous tissue that covers posterior 5/6th of the eyeball

attachment point of muscles 

visual sensory information

sensation requires light to turn into a neural impulse by a photoreceptor

light 

electromagnetic wave part of a large spectrum 

Violet (400 nm) —  Red (700 nm)

rods

for night vision

when light comes in → pupil → hits rod → rod is turned off → turns on bipolar cell → turns on a retinal ganglion cell → optic nerve → brain 

cones

3 types: red (60%), green (30%), blue (10%)

all centered in fovea

rhodopsin 

inside the rod there are a lot of disks stalked on top of one another with a lot of proteins on them

rhodopsin is a multimeric protein with 7 discs

contains a molecule called retinal which undergos a change conformation from bent to straight when light hits it

when retinal changes shape, rhodopsin changes shape 

Phototransduction cascade 

transducin (has 3 parts: alpha, beta, gamma) breaks from rhodopsin → alpha part comes to disk and binds to phosphodiesterase → phosphodiesterase takes cGMP and converts it to GMP → Na+ channels allow Na+ ions to come in → channels close as cGMP decreases as they need cGMP to bind to open → less Na+ enters the cell → cells hyperpolarize → turn off → glutamate is not released → doesn’t inhibit ON bipolar cells → bipolar cells turn on → activates retinal ganglion cell → sends signal to optic nerve 

photoreceptors

specialized nerve that can take light and convert it to neural impulse

in rods there are optic discs (large membrane bound structures ) → proteins in membanes that fire APs to the brains

rods have rhodopsin while cones have photopsin

Differences between rods and cones

120 million rods v 6 million cones

cones are concentrated in the fovea

rods are 1000x more sensitive to light than cones (better at telling us whether light is present) (night vision)

cones are less sensitive but detect color 

rods have slow recovery time compared to cones and takes a while to adjust to dark. 

photoreceptor distribution in retina

where optic nerve connects to retina is a blind spot

rods found in periphery, cones found in foveo

If light hits peripher → goes through bundle of axons → energy lost

fovea light hits cones directly 

Visual field processing

right side of body controlled by left side

all right visual fiels goes to the left side of the brain and vice versa 

parvocellular pathway 

form\shape of a stationary object  

good at spatial resolution — able to capture fine details and boundaries of an object 

poor temporal resoulution — can’t track motion

magno pathway

encode motion

high temporal resolution - can track motion

poor spatial resolution - can’t capture the boundaries of the object 

no color

parallel processing

see all pathways at the same time

sound needs

pressurized sound wave

hair cell

sound waves

air molecules are pressurized and try