Perception Flashcards
What is sensation
This describes the processing of the raw senses (i.e. raw data gathereed from outside world, which is sent to brain for further processing. Describes a physiological process)
It describes how our senses transform physical properties of the environment and body into electrical signals relayed to the brain (through transduction)
What is perception
This describes the actual interpretation of the sensory input we are receiving, into meaningful experiences (more of a psychological process)
What is the difference between sensation and perception
Basically sensation is a physiological response which is just the pure sense i.e. the feeling of touch but nothing else. The perception is the process of organising and selecting and interpreting these signals
Give an example to demonstrate the difference between the two
I.e. a camera can sense, but it can’t perceive (gets the sensation of visual fields, but it doesn’t have perception to interpret it)
What are the 6 senses of perception
Vision
Hearing
Taste
Smell
Vestibular
Somatosensation
What process is common to all of the different senses
Process of transduction which is the transformation of the sense into electrical signals for the brain to understand/perceive/interpret it
What is transduction
This is the process of allowing a sense to perceive, and give us a sense of perception. It is ultimately the process of transforming senses into electrical signals for brain to understand it
What is the problem of qualia
It is the idea that if all our senses are a result of our neurons firing (electrical impulses), how does our brain differentiate which set of neurons firing result in sound or what neurons result in vision if they are all the same thing ultimately
In other words:
How does the brain know what is causing the stimulation it receives? How do some neurons allow for sight or sound if they are all the same?
In other words:
Why do we experience one set of electrical impulses as sight, and others as sounds, flavours, smells touch pain or sense etc.
What is synesthesia
This is the perceptual phenomenon where some people who receives stimulation of one sensory or cognitive pathway involuntarily triggers an additional sensory experience from a different pathway
I.e. someone who might hear colours - associate certain musical notes to different colours
What are common forms of synesthesia
Grapheme-colour synesthesia
Chromesthesia
What is grapheme-colour synesthesia
This is where certain letters/numbers are associated with a certain colour
What is chromesthesia
This is where sounds such as musical notes or spoken words evoke a perception of colour
How does synesthesia affect our understanding/ideas about qualia
It impacts us by suggesting that maybe our senses are even closer than expected, and highlights its variability. Also demonstrates how subjective experiences can differ from person to person
What problems do illusions create for our understanding of the perception of the world
Ultimately the main problem is that we rely on our senses to perceive the world, but if illusions can show that our senses can be tricked, how can we rely on our senses for an accurate presentation of the world?
Illusions such as cafe wall illusion, visual thing moving illusion, checker shadow illusion, thatcher iillusion, troxler fading illusion all trick our senses into thinking different thigns
What is the importance of illusions
Demonstrate the active processes the brain deploys to interpret images
They provide insight into contexts where the visual system goes beyond the information in the input
Reveals the general rules the visual system uses to make inferences about the physical world
What is segmentation and grouping
Occurs as our brain can select key features to recover complex info about objects –> our brain does its best to make sense of sensory info it receives by grouping similar sensory info?
What is the dimensionality reduction problem in taste
The problem here is that there are so many different possible tastes out there, but it all gets reduced into only 5 main tastes
(There are a large number of different chemicals. It isn’t possible to have receptors to detect all of them with a finite sized organ, so we must collapse these into few biologically relevant dimensions –> 5 for taste and 400 for smell)
What are papillae
These are the little bumps on our tongue which contain tastebuds (!?)
What are the 4 main types of papillae
Filiform
Foliate
Fungiform
Circumvallate
What is fungiform papillaae
Contains tastebuds. It is located at the front of the tongue, and shaped like small mushrooms.
Variations in fungiform indicate different preferenes in taste
What is foliate papillae
Focused on the side of our tongue, and has tastebuds burried in the folds. They contain taste buds and are sensitive in younger people
What is filiform papillae
There is the most of this papillae on our tongue, but they don’t contribute to taste (no tastebuds). Instead, they contribute to our perception of texture and touch
What is circumvallate papillae
Larger papillae and they are located at the back of the tongue, in a V shaped arrangement, looking like islands surrounded by moats. Also contains tastebuds
What are the 5 dimensions of taste? Explain why we need them
Sweet - allows identification of potential sources of energy rich, nutritional foods
Salty - maintains electrolyte balance
Sour - acidity (dangerous at high levels)
Bitter - potential poison (huge class)
Umami (savoury taste): detection of amino acids (MSG and asparate)
Do we have a preference for sweetness?
Yes, when we are born we have an innate preference for sweetness, however our preferences change as we get older
What is the detection threshold for sweetness, saltiness, sourness, bitterness
Sweetness: Glucose 1/200
Saltiness: NaCl 1/400
Sourness: HCl 1 / 130 000
Bitterness: quinine 1/ 2000000
What is the urban legend about taste about? What does it suggest? Is it true?
Suggests that taste is localised to different areas of the tongue. THIS IS DEFINITELY NOT TRUE
Instead, all areas of the tongue contribute to overall experience of taste
What is the labelled line model of taste
Proposes that each taste quality (sweet, salty, sour, bitter and umami) is detected by a sepaarate, dedicated type of receptor cell in the taste bud
Each cell sends siggnals along specific pathways to the brain- individual taste receptor cells are tuned to respond to only one type of taste
IT IS BELIEVED THAT THIS ACCURATELY REPRESENTS OUR EXPERIENCE OF TASTE
What is the cross fibre model of taste
The cross-fiber model of taste (also known as the across-fiber pattern model) is a theory that explains how taste perception occurs based on the combined activity of multiple types of taste receptor cells. This model suggests that each taste sensation (such as sweet, salty, sour, bitter, and umami) is not the result of a single receptor’s activity, but rather a pattern of activity across many taste receptor cells.
THIS IS NO LONGER BELIEVED TO BE THE CASE
What are supertasters? What do they have that makes them different?
They have more papillae. This causes some people to have more fungiform taste receptors of their tongue –> enables greater taste
Identified using a chemical called PROP
They are unlikely to enjoy Brussel sprouts and broccoli, and are unlikely to consume coffee and fatty foods
What populations are more likely to be supertasters
In Indonesia, only 1.2% of popualtion were PROP non tasters, whereas France had 73% of population as PROP non taters
More common in Asians and Africans
Most likely to occur in women
Does taste require presence of taste experience?
No, because sometimes theres things like miracle fruits which binds to taste buds, and at low pH they can contribute to activating sweet receptors
Pine nuts –> makes everything taste bitter
What makes something spicy? What receptors signal spicy food to the brain
Spice is not a taste, but its pain and temperature arising from chemosensory irritation signalled by the trigeminal nerve
Spice is just pain, it doesn’t go through the flavour pathway
What is smell caused by
It is caused by molecules of a certain something entering your olfactory nerves/bulb
Olfaction provides info about the chemicals suspended in the air around us
(we can probably only identify 400 smells)
Explain why dogs have a higher ability to smell than humans do
They can pick up smell 1 part per trillion –> good for identification of drugs, cancer etc
They have much bigger olfactory bulbs, much bigger noses etc
They also have up to 300 million nerve cells to detect odours, whilst we only have 5 million
What is the shape pattern theory of olfaction?
Suggests that odour perception is based on shapes of odorant molecules, and the way they fit/bind to specific olfactory receptors
Suggests that each odourant molecule has a unique shape and ultiately, the whole thing functions as a ‘lock and key’ mechanism
Why is the shape pattern theory of olfaction wrong? Proof against it?!
Molecules with very different shapes could smell very similar, whereas those with similar shapes smell very different (inconsistent odour perceptions based on shape), as similar binding patterns should hypothetically produce similar smells
Explain proof for olfactory adaptation or what happens there?
We cannot escape the smell of ourselves - we are in olfactory adaptation
Smokers are usually unaware of the smell of themselves, until they quit smoking
When does sense of smell increase and decrease across lifespan?
Sense of smell increases in childhood and early adulthhood, but decreases starting middle-age
We need increased concentrated odour to detect it as we get older, and once detected, it will be judged as less intense –> also process of odour adaptation occurs
What is flavour
Flavour is a combination of taste, smell and temperature
What are the two major subsystems of the somatosensory system
Detection of external stimuli
Proprioceptors
What info do receptors which detect external stimuli convey
They convey information about the senses from external sources
Typically refers to skin and sub-skin mechanoreceptors on the body surface
What info do proprioceptors convey
Refer to receptors located in muscles, joints and other deep structures of the body
It monitors mechanical forces generated by the musculoskeletal system (also detects things about the body like body position etc)
How do mechanoreceptors work generally
Stimuli applied to the skin deforms or changes the nerve endings, which in turn affect the ionic permeability of the receptor cell membrane. This induces a depolarising current in the nerve ending, which trigers action potentials (sensory transduction)
what is the perceptual quality of a stimulus
What and where it is
what signals the perceptual quality of a stimulus
Depends on the reeptors that respond and where they prject
Quantitity or strength depends on the no. of action potentials generated
What categories can the variety of receptors be split into? WHat do they do?
Mechanoreceptors -detect stimuli like touch
Nociceptors - pain
Thermoreceptors - temperature
What are the two types of touch fibres
Slow adapting and fast adapting touch fibres
What info do rapidly adapting touch fibres convey
These provide information about change or dynamic quality of stimuli –> they respond quick to changes in stimulus, and detect dynamic actions on skin like tapping
What info do slowly adapting touch fibres convey
They provide information about shape, edges, rough texture, persisting features etc
What is adaptation
This refers to desensitisation (in terms of sensory experiences), thus adapting in this case is how quickly the touch fibres stop responding
Explain what tactile afterimages is
Opponent - like after-effects such as texture contrast aafter effects (after touching something rough, a medium rough surface feels smoother); can be observed for temperature as well
Explain what tactile adaptation is
Importance of movement in perceiving spatial patterns in the skin; stabilised (i.e. non moving) objects on skin are less salient when skin is first pertrubed
Does tactile system perceive best with active or passive touch
Active is better for exploration using tactile system
What are the types of mechanoreceptors in the skin
Pacinian corpuscle
Ruffini Organ
Merkel Disks
Meissner corpuscles
What does the pacinian corpuscle do
Large encapsulations and found in subcutaneous tissue (and gut). Onionlike
capsule and fluid filled inner space, with one or more rapidly adapting
afferent axons. Capsule acts like a filter that allows only transient,
high-frequency disturbances (250-350 Hz) to active the nerve
endings. Stimulation introduces a sense of vibration and/or tickle. 10-
15% of cutaneous receptors in the hand. Similar structure in the bills of
ducks and geese, legs of cranes & herons, and in wings of soaring birds.
Rapid adaptation, large receptive field (detects over a large area but has poor sensitivity - large recetive area)
What does the ruffini organ do
Ruffini’s corpuscles aren’t well understood. Elongated,
spindle shaped structures are located deep in the skin, as
well as in the ligaments and tendons. Long axis is usually
aligned parallel to the stretch lines in the skin, and are
particularly responsive to stretching. They account for ~20%
of the receptors in the hand, they don’t elicit any particular
feeling when stimulated.
Slow adaptation, large receptive fields
What do the merkel disks do
Located in the epidermis. ~25% of the receptors in hand, and
are particularly dense in the fingertips, lips, and external
genitalia. Stimulation introduces a sense of light pressure.
Slow adaptation, small receptive fields
What do the meissner corpuscles do
Elongated receptors that contain one or more afferent nerve fibers that
generate rapidly adapting action potentials following minimal skin
depression. Found just beneath the epidermis of fingers, palms, and
soles. Most common receptors of glabrous skin (the smooth and hairless
type). Account for ~40% innervation of the human hand, and respond
best in the range of low-frequency vibrations (30-50 Hz)
Rapid adaptation, small receptive fields
What causes the two waves of pain
The A delta and C pain fibres.
Explain the difference between A delta and C pain fibres
A delta pain fibres are myelinated –> convey pain really quickly, providing the immediate sensation of pain
C fibres aren’t myelinated –> convey pain at a slower rate, providng the lingering, hurting sensation of pain
What distinguishes pain senstivity to all other senses
Pain is the only sense that exhibits an enhanced sensitivity to stimuli over time; all other senses exhibit adaptation –> chronic pain can growin in intensity over time
What is referred pain? WHy does it occur?
It is where pain in one area of the body is perceived as coming from a different area. This happens as nerves from different parts of the body converge on same pathway in spinal cord –> brain can misinterpret pain source
What are thermoreceptors
These are basically detectors of heat/cold
They work by comparing a certain temperature to the idea of a physiological zero. So, when we say something is cold, it is just saying it is colder than physiological zero
What are proprioceptors
These are specialised sensory receptors in muscles, tendons and joints which convey info about body position, movement and spatial orientation, which is essneitla for proprioception, or our ‘sense of self’ in space which helps us to detect and control limb position, movement etc without relying on visual cues
What are the types of proprioceptors
Muscles spindles
Golgi tendon organs
Joint receptors
What information do muscle spindles convey
These provide info about muscle length. They are embedded within muscle fibres and detects muscle length and changes in muscle length
Ultimately informs brain about how stretched or contracted a muscle is
What information do golgi tendon organs convey
Provides information about muscle tensions. They are located in tendons, where muscle fibres connect to bone.
GOlgi tendon detects muscle tension or force. Ultimately providingfeedback on force exerted by muslces, helping prevent excessive force that could lead to injry
What information do joint receptors convey
Provide info about the positions and tensions on the joints (4 different types of receptors)
Located in the connective tissue of joints, and they sense joint angle, rotation and pressure around the joint
Informs brain about position and movement of the joints which is essnetial for coordinated movements
What is the two point threshold - what does it convey?
Basically getting two pins and placing them close to each other, and then placing it on skin on certain parts of the body. We find that some parts of the body are more sensitive than others
Ultimately, shows that the fingers can tell that they are separate, whereas its harder for the arm or thigh to be able to tell etc
Ultiately provides info about the size of the receptive fields (the regions on the skin a neuron responds to)
Why are certain parts more sensitive than others?
Normally some parts of the body have more receptors like the hands and face, normally based on how much we need to use them (i.e. we have to control it a lot = more receptors = increased sensitivity)
Explain somatosensory and motor homunculi
A motor homunculus represents a map of brain areas dedicated to motor processing for different anatomical divisions of the body. - we have a lot of brain areas dedicated to face and fingers
What are the 3 general parts of an ear
Outer, middle and inner ear
What is the function of the outer ear
Includes the pinna and ear canal. Main function is to capture sound waves from environment and direct them into the ear canal towards the eardrum for sound processing
What is the function of the middle ear
Contains the 3 smallest bones called the ossicles, and the eardrum
The middle ear amplifies and transmits sound waves from outer to inner ear
What is the function of the inner ear
Includes the cochlea and the vestibular system (responsible for balance)
Converts sound vibrations into electrical signals, which are sent to brain via auditory nerve, allowingus to perceive sound
Vestibular system detects head movements and position changes, which helps us maintain balance
What is the vestibular sense organ? WHat is it’s function?
It is part of the inner ear which assists in control of gaze and posture.
Also responsible for detecting balance, spatial orientation and head movement
Contains sensory structures with receptor cells that detect gravitational forces, including angular and linear head accelerations in space
What do the vestibular sense organs contain? How does this relate to how the vestibular sense organ works?
Three semicircular canals (Angular accelerometry) (Each canal is oriented at right angles to each other, and detect rotational movements of the head) ( Works when the head rotates, the fluid inside semicircular canals lag slightly due to inertia –> bending the cilia within the capula. This bending causes electrical signals which is sent to brain for direction and speed of head rotation interpretation)
Two otolith organs (detect linear movements and head position relative to gravity) (When head moves linearly or tilts, gravity causes otoliths to shift, bending hair cells which inform brain about changes in linear acceleration)
What does a vestibular hair cell do
Bending a vestibular hair cell in its preferred direction excites a neuron, which is able to deliver the brain a direction, whilst bending it in the opposite direction inhibits the neuronal activation–> delivers the brain a sense of direction as well
Does the vestibular system detect motion or acceleration
Acceleration
Why does spinning cause feelings of dizziness
Normally after being spun, it could lead to dizziness and feelings of being spun even after falling down. This is largely because fluid within the semicircular canals continues flowing. This bends the hair cells continuouly –> sense of movement
What is the vestibular ocular reflex? How does it work?
VOR is a reflex that stabilises gaze by moving the eyes in the opposite direction of head movements, allowing for a clear and steady view of the environment when our head moves (saccadic eye movement )
It works by detecting head movement –> sending signals to brainstem to process direction and speed of head movement –> eye movement correction
What happens if VOR overcompensates for head movements
The eyes move too far in the opposite direction co counterbalance movement –> perception of the scene doing a ‘jump’
What happens if VOR undercompensates for head movements
The eyes don’t move far enough in opposite direction to counterbalance movement –> perception of visual ‘slip’ or blurriness
What is sound
Sound is a form of energy that travels as a mechanical wave through a medium (like air or water or solids). It is created by vibrations which cause particles in medium to compress and decompress
How is sound transmitted into the inner ear
Pinna and eardrum (directional microphone)–> middle ear (Impedance matching and overload protection)–> inner ear (frequency analysis)
WHat is any complicated wave made up of?
A combination of different sine waves
What is the process of sound entering the ear (and being perceived (?!))
Sound waves enter the outer ear through the pinna which help funnel sound into ear canal –> hits ear drums
the vibrations from the eardrum are transferred into small bones of middle ear called the ossicles which aimplify the sound vibrations and transmits it to the inner ear
In the inner ear, the cochlea receives the vibrations and creates pressure waves in cochlear fluid, which causes hair cells to bend, and triggers an electrical signal which then gets sent via auditory nerve to brain, where it is processed for sound
What are the different dimensions of sound and what does it mean for the perception of sound
Frequency = gives rise to perception of pitch
Amplitude = gives rise to perception of loudness
Purity = “timbre” of an instrument (gives it a “colour” - what makes that note unique to the instrument)
Why is decibels measured on a log scale
Better reflects how humans perceive changes in loudness, and accommodates raise of sound intensities we hear
I.e. a greater jump in intensity to have a different sensation of hearing
explain how we describe sounds in terms of decibels - how does it work
When we describe things in terms of decibels, it is in reerence to an agreeed upon reference sound called I-0. This was chosen to be the closest to the minimum detectable sound level for humans at a particular frequency
Explain the equal loudness curves as functions of frequency
Describes how human ear perceives sounds at diff frequencies and intensities. Illustrates that sounds of different frequencies must be played at varying intensities to be perceived as equally loud
What is the function of the middle ear? How does it work?
Main function is impedance (resistance) matching
Essential for amplifying sounds received from outer to inner ear. This is important because strong sound waves are needed for the cochlea in the inner ears which is filled with fluid (for the fluid to move and generate the perception of sound)
Vibrations from outer ear are transferred to the ossicles. The ossicles then amplify the sound vibrations due to lever-like actions –> increased pressure exerted on oval window which is 20x smaller than the ear drum —> energy amplifcation (as there is an increased energy amount per unit)
Moreover, for transduction to occur, the air pressure in middle ear must be the same as the atmospheric pressure outside eardrum –> role of Eustachian tube is to equalise pressure on both sides of the ear
(basically, its function is to amplify the sound waves because the fluid in the cochlea is very dense so there is increased resistance, and thus how to amplify waves? Put the same waves into a small area –> high energy per unit, and thus greater mechanical energy)
The oval window is 20x smaller than eardrum
What is white noise?
It describes sound which is of all frequencies at approx the same amplitude
It helps mask all other sounds
What is a low pass filtered white noise
This is where white noise is filtered to only allow for low frequencies to pass, but high frequencies to be cut out
How is white noise filtered
FIltered by decreasing the frequencies required to pass –> a more ‘gentle’ noise than the harsh noise heard in white noise
How do musical instruments that play the same note somehow sound different?
Basically, when a note is played, there is the fundamental (lowest frequency), and the harmonics/overtones (1/2, 1/3, 1/4 …of lowest frequency).
Each instrument stimulates the fundamental as well as all harmonics to a certain extent. However, they differ in relative amplitudes of these component frequencies they produce. The amplitudes of the upper harmonics (or overtones) contribute to the quality of the notes
The pitch of an instrument is conveyed by the fundamental frequency, and timbre by the relative amplitudes of overtones (each instrument has diff amplitude of overtone)
What is harmonic singing
Normal humans can generate one note of given pitch when singing which consits of fundamental frequency and upper harmonics. However, some people can increase ampltitude of certain harmonics or decrease the amplitude of others by shaping mouth cavity –> makes certain harmonic frequencies stand out against fundamental to generate perception of multiple notes
Explain how pitch can be visualised/perceived
As a helix. It wraps around to the same note an octave higher, over the range of audible frequencies
Our experience of pitch is shaped like a helix. EVery time we do a loop in the helix it goes up an octave (thats how the brain organises it)
Pitch of different frequencies is also logarithmic
How does the inner ear convert sound to electrical impulses
Basic idea is that there are vibrations on the oval window which creates waves in fluid of cochlea –> causes basilar membrane to wiggle –> hair cells move in response –> hair cells move in response –> voltage changes when electrical signals are carried up the auditory nerve to the brain
An early theory as to why basilar membrane wiggles in response to sound is the whole thing moves at once, like a diaphragm, but the basilar membrane varies in thickness and stiffness –> can’t move all at once
How are different frequencies of sound detected in the cochlea
Vibrations of the oval window induce pressure changes in cochlear fluid that result in a travelling wave on the basilar membrane.
The wave peaks in different places of the basilar membrane, depending on the frequency content
Low frequencies peak closer to the apex of the cochlea, whereas high frequencies is closer to the base
The waves cause basilar membrane to vibrate at specific points along its length
High frequency causes hair cells at base to bend, whereas low frequency causes hair cells at apex to bend
The bends in hair opens ion channels in hair cells, allowing ions to flow in —> triggers release of neurotransmitters –> electrical signals to auditory nerve fibres –> caries these signals to the brain
What is phase locking of neural responses
Mechanism where neurons fire action potentials in a synchronised manner with specific phases of a sound wave. The timing of neural firing corresponds to certain points in the waveform –> auditory system to encode info about sound’s frequency
What frequencies undergo phase locking
Typically low frequencies, as frequency increases, the phase locking decreases
What are cues to frequencies in a sound
The place of execution in cochlea
Frequency of firing
Explain the maps of tones in body
Tonotopy
The auditory cortex has a map of different frequencies as well. Certain parts of it are used to respond and interpret certain frequencies
What is light
FOrm of electromagnetic radiation, which has properties of both waves and particles - it has a dual nature
Why is light different in terms of how waves normally behave
Light is strange because it moves in straight lines
What are the 3 stages of image formation
Sample optical structure
Transduce light energy into electrical impulses
Transmit this info to brain for interpretation through electrical impulses
What are the 4 types of eyes we look out
Compound, concave(?! or convex) mirror, pinhole and single chambered eyes
Explain what compound eyes do/ how they work
Made up of many individual eyes called ommatidia, and each one functions as a tiny, independent visual receptor –> mosaic lke image
They haave a wide field of view, especially as there are so many ommatidia
Explain what concave(?! or convex) mirror eyes do/ how they work
Inward curved surface, which causes light rays hitting it to reflect inwards
When the light hits and reflects in, it converges at a single point called the focal point. This can magnify focus on a single point of light and allow for vision
Explain what pinhole eyes do/ how they work
Small opening instead of wide pupil –> limited light –> no lens to focus light, so only allows a narrow beam of light in, which enables retina to preserve spatial layout of an image –> prevents overlapping and thus projects a dim but focussed image
Because the pinhole naturally limits light, there isn’t a need for lens to focus image
What is the general principle of image formation
For image formation, there must be one ‘point’ of the world mapping onto one receptor
Every point on an object emits light in all directions. To form a clear image, light rays from each point must be redirected so they converge at a corresponding point on a surface (normally achieved through a pinhole)
The image mapped is a flipped image
Why don’t humans use pinhole eyes
Because there isn’t much light (causes everything to be dim)
Would only work in bright light scenarios
Why don’t we use big holes in the eyes
These can cause a blur because different light waves of the same thing can be projected to the same point
Light rays from one point overlap with light rays from other points —> received mixed lighting from multiple points –> blurred image
Explain what single chambered eyes do/ how they work.
Explain the convex of single chambered eyes
Convex lens enables it to bend light rays inwards as they pass through –> all converge towards a single point
Lens focus light from each point on an object onto a corresponding point on the retina. Because of convergence –> rays meet on retinaa to form a clear, sharp image of object which is inverted
Different parts of the lens diverge the light and helps focus it
Focal points vary as a function of lens curvature and object distance
As the lens gets thicker and more curved, the focal point becomes less distant –> short sight, when the lensget thinner –> focal point becomes more distant –> far sight
Convex lens ensure light rays from each point of object focus to specific points on retina –> formation of detailed image. By adjusting shape, lens can change focus
Why is myopia increasing at an alrming rate
In most cases, it is developed over lifetime, not at birth
It is probably due to body adapting to more nearsighted activities, such as looking at a phone or reading .
Ultimately, myopia rates have doubled since 2000,
Ultimately occurs when eyes become too long due to adaptation –> light rays can’t hit the retina (or it has too much curvature)
What are the different mechanisms of light accomodation
Far and near accomodation
Done to focus objects at different distances
What is far accomodation
Lens become ‘flatter’ to focus light from a distant object on the retina
Near objects become focused behind the retina resulting in blurring the image
What is near accomodation
Lens become ‘rounder’ to focus light from a near object on the retina
Light from far objects become focussed in front of retina –> blurred at the retina
What is the tilt shift illusion
Fixating on something relatively close causes far and near things to be blurred
Brain uses this fact to infer perceived size (causes things to seem smaller)
What is the duplicity theory of vision
Suggests that we use two different classes of photosensitive receptors that operate in different luminance regimes
Scotopic vision: low-light, rod dominated
Photopic vision: high-light, cone dominated
How many rods and cones do we have
We have 3 cones and 1 rod
The rod is very sensitive
How many rods and cones do we need to determine colour
At least 2
Thus, in dim light, we can’t see colour as we are using rods, but we only have one rod in proportion to 3 –> thus not useful
Explain function of cones vs rods
Cones = high light vision
Rods = low light vision
What is the ratio of rods to cones that we have
20:1
120 million rods, 6 million cones, 1 million optic nerve fibres
What happens when we look at a dim object? Why do we have to look to the side to see a few stars in the nigth sky
When looking at a dim object (kinda like a star in the sky, the image falls on the fovea, where there are only cones which are only good in high light –> thus faint object may seem to disappear when looked directly at)
Meanwhile, sides of the fovea are rod dominated –> thus you see dim things like stars in the night sky in your peripheral (rods are very sensitive asw)
How are rods and cones distributed across the retina
Fovea (the ‘focus’ for our eyes) is very much cone dominated. However, the sides of the fovea are rod dominated
What does it mean by our eyes being organised backwards?
We have the blood vessels in front of our eyes, and separated from photoreceptors
What are the perceptual consequences of our eyes being ‘organised backwards’
We somehow ignore the blood vessels when we see
Visual processing delay as light has to pass through a few cells before reachign photoreceptors
Blind spot where optic nerve exits eyes (no photoreceptors there)?
(from chatgpt)
Why can we just use three coloured lights to generate all of our experiences of colour
Because R,G,B stimulates photoreceptors in different proportions and allow us to create different colours - generating basically all colours if you mix any proportion of the lights
What is the theory of trichromacy
Colour is closely related to proportions of responses of three diff types of cones receptors
S-cones sensitive to blue (short wl)
M-cones sensitive to green (med wl)
L- cones sensitive to red (long wl)
What is the Opponent Processes theory?
Focuses on how colours are perceived in terms of opposing pairs - visual system processes colour info so some colours are perceived as opposites (black vs white, yelow vs blue, red vs green)
Evidence is that we can’t have a reddish green or bluish yellow or a blackish white
Is trichromacy or opponent process corect?
Both are actually correct
