MCAT p/s

Visual cues

allows us to perceptually organize by taking into account the following cues: depth, form, motion, constancy

depth, form, motion, constancy

Visual cues

Retinal disparity

Eyes are ~2.5 inches apart which allows humans to get slightly different views of objects of world around. Gives humans an idea on depth

depth

Binocular cues give a sense of ______

Convergence

Gives humans an idea of depth based on how much eyeballs are turned

relaxed

Convergence

Things far away–muscles of eyes ______

contract

Convergence

Things close to us–muscles of eyes _______

Monocular cues

• Humans also have visual cues they receive which they do not need two eyes for

• These give humans a sense of form of an object

  • Relative size, interposition, relative height, shading and contour

• Give sense of constancy

  • Size, shape, colour constancy

• Give sense of motion

  • Motion parallax

form, motion, constancy

Monocular cues give sense of

Relative size

Monocular cue

• an infer with one eye

• The closer an object it is perceivedas being bigger

• Gives us an idea of form

Interposition (overlap)

Monocular cue

• Perception that tone object is in front of another

• An object that is in the front is closer

Relative height

Monocular cue

things higher are perceived to be farther away than those that are lower

Shading and contour

Monocular cue

using light and shadows to perceive form depth/contours–crater/mountain

Motion parallax

Monocular cue

“relative motion” Things farther away move slower, closer moves faster

Constancy

Monocular cue

• Our perception of object doesn’t change even if the image cast on the retina is different.

• Size, shape, color

Sensory adaptation

Our senses are adaptable and they can change their sensitivity to stimuli

contract

Sensory adaptation

Hearing adaptation-inner ear muscle: higher noise = muscle ____ (this dampens vibrations in inner ear, protects ear drum.)

desensitize

Sensory adaptation - touch and smell receptors ______ over time

Proprioception

the sense of the position of the body in space i.e.“sense ofbalance/where you are in space

Down regulation

Sensory adaptation to light

light adaptation

When it is bright out, pupils constrict (less light enters back of eye), and the desensitization of rods and cones become desensitized to light)

Up regulation

Sensory adaptation to light

dark regulation

Pupils dilate-, rods and cones start synthesizing light sensitive molecules

just noticeable difference (JND)/difference threshold

• The threshold at which you’re able to notice a change in any sensation

• smallest difference that can be detected 50% of the time

deltaI = Ik

Weber’s Law

Weber’s Law

ΔI (JND)/I (initial intensity) = k (constant)

predicts alinear relationshipbetween incremental threshold and background intensity.

Absolute threshold of sensation

• The minimum intensity of stimulus needed to detect a particular stimulus 50% of the time

• Different that JND/difference threshold

  • This is about intensity, JND is about difference in intensity

• Can change, influenced by:

  • Expectations

  • Experience

  • Motivation

  • Alertness

Subliminal stimuli

stimuli below the absolute threshold of sensation

Somatosensation

the sense of touch, encompasses all sensations received from the skin, mucous membranes, limbs, and joints

• Receive info about type, intensity, timing, and location

• Location relies on dermatomes

Thermoception

Temperature Somatosensation

Mechanoception

Pressure Somatosensation

Nociception

Pain Somatosensation

Proprioception

Position Somatosensation

Intensity

how quickly neurons fire for us to notice. Slow =low intensity, fast = highintensity

Non-adaptive

Timing for somatosensation

neuron consistency fires at a constant rate

Slow-adapting

Timing for somatosensation

neuron fires in beginning of stimulus and calms downafter awhile

Fast-adapting

Timing for somatosensation

neuron fires as soon as stimulus start...then stopsfiring. Startsagain when stim stops)

Vestibular system

• For balance and spatial orientation

• Inner ear, particularly semi-circular canals

Endolymph

Semi-circular Canal is filled with ________, and when we rotate the fluid shifts in the semi circular canals–allows us to detect what direction our head is moving in, and because we can detect how quickly the _______ is moving we can determine the strength of rotation

Otolithic organs (utricle and saccule)

• help us to detect linear acceleration and head positioning

• In these are CaCO3 (Calcium carbonate) crystals attached to hair cells in viscous gel

• If we go from lying down to standing up, they move, and pull on hair cells,which triggers AP.

• These would not work very well w/o gravity! Buoyancy can haveeffects as well, particularly without visual cues on which way is up/down

Signal Detection Theory

• Looks at how we make decision under conditions of uncertainty

• Discerning between important stimuli and unimportant “noise

• Options: hit/miss/false alarm/correct rejection

>, <

Strength (d’) in signal detection theory

hit __ miss (when there is strong signal)

miss __ hit (weak signal)

Strategy (c)

Seen as a threshold

Want to minimize miss and false alarm

When C = 0, participant is ideal observer. If <1 - liberal. If >1 - conservative

Beta strategy

set value of threshold to the ratio of height of signal distribution to height of noise distribution

i.e. ln ___ = d’ x C = 1 x 1.5 = 1.5. So e^1.5 = beta= 4.48

Strength (d’)

Difference between the means or noise and signal distribution

So if signal shifted to right, d’would be big and easyto detect. If left, d’ very small and more difficult to detec

Conservation strategy

Strategy (c) in signal detection theory

always say no unless 100% sure signal ispresent. Bad thing is might get some misses

Liberal strategy

Strategy (c) in signal detection theory

always sayyes, even if get false alarms

Bottom up Processing

Begins with stimulus. Stimulus influences what we perceive

• No preconceived cognitive constructs of the stimulus (never seen it before)

• Data driven. And the stimulus directs cognitive awareness of what you’re lookingat (object)

• InductiveReasoning. Always correct

Top-down Processing

uses background knowledge influences perception

• Theory driven

• Perception influenced by our expectation

• DeductiveReasoning

• ex.creating a cube when it’s not there! Not always correc

Gestalt Principles

Tries to explain how we perceivethings the way we do

• Similarity, Pragnanz, Proximity, Continuity, Closure, Symmetry

Similarity

Gestalt Principle

• items similar to one another grouped together by brain

• Ex:The brainautomatically organizes these squares and circles in columns, and not in rows

Pragnanz

Gestalt Principle

• Reality organized reduced to simplest form possible.

• Ex. Olympic rings, where the brain automatically organizes these into 5 circles, instead of more complex shapes

Proximity

Gestalt Principle

• objects that are close are grouped together,we naturally group the closerthings together rather thanthings that are farther apart.

Continuity

Gestalt Principle

lines are seen as following the smoothestpath

Closure

Gestalt Principle

objects grouped together are seen as a whole. Mind fills inmissing information.

Ex. You fill in the triangle even though there is none

Symmetry

Gestalt Principle

the mind perceives objects as being symmetrical and forming around acenter point

Law of Common Fate

Gestalt Principle

• elements moving together in the same direction or at the same speed are perceived as a group

• For example, if there are an array ofdots and half the dots aremoving upward while the other half are moving downward, we would perceive theupward moving dots and the downward moving dots as two distinct units.

Law of Past Experiences

Gestalt Principle

• Under somecircumstances visual stimuli are categorized according to past experience

• If two objectstend to be observed within close proximity, or small temporal intervals, the objects aremore likely to be perceived together.

• or example, the English language contains 26letters that are grouped to form words using a set of rules. If an individual reads anEnglish word they have never seen, they use the law of past experience to interpret theletters "L" and "I" as two letters beside each other, rather than using thelaw of closureto combine the letters and interpret the object as an uppercase U

Contextual effects

Gestalt Principle

the context in which stimuli are presented and the processes ofperceptual organization contribute to how people perceive those stimuli (and also that the context can establish the way in which stimuli are organized

Conjunctiva

Part of the eye

thin layer of cells that lines the inside of your eyelids from the eye

Cornea

Part of the eye

transparent thick sheet of fibrous tissue, anterior 1/6th; starts to bends light, first part of eye light hits

Anterior chamber

Part of the eye

space filled with aqueous humour, which provides pressure to maintain shape of eyeball; allows nutrients and minerals to supply cells of cornea/iris.

Pupil

Part of the eye

• opening in the middle of the iris

• The size can get bigger/smaller based on the iris relaxing/contracting respectively

• Modulates the amount of light able to enter the eyeball

Iris

Part of the eye

• Gives the eye color

• The muscle that constricts/relaxes to change the size of the pupil

Lens

Part of the eye

• bends the light so it goes to back of eyeball–focuses light specifically on the fovea of the retina

• Adjust how much it bends the light by changing its shape, using thesuspensory ligaments

Suspensory ligaments

Part of the eye

• attached to a ciliary muscle

• These two things together form theciliary body, what secrets the aqueous humor

Posterior chamber

Part of the eye

area behind the iris to the back of lens; also filled with aqueous humor

Vitreous chamber

Part of the eye

filled with vitreous humour, a jelly-like substance to provide pressure to eyeball and gives nutrients to inside of eyeball

Retina

Part of the eye

inside, back area filled with photoreceptors, where the ray of light is converted from a physical waveform to a electrochemical impulse that the brain can interpret

Macula

Part of the eye

• special part of retina rich in cones, but there are also rods

Fovea

Part of the eye

• special part of macula

• Completely covered in cones,no rods.

• *Rest of the retina is covered in primarily rods

Choroid

Part of the eye

• pigmented black in humans, is a network of blood vessels that helps nourish the retina

• If black all light is absorbed.

• Some animals have a different colored choroid which gives them better night vision

Sclera

Part of the eye

• Usually absorbs by the time the light gets to this

• The whites of the eye, thick fibrous tissue that covers posterior 5/6th of eyeball(cornea covers the anterior 1/6)

• Attachment point for muscles

• Extra layer of protection and structure of eyeball

• Lined with the conjunctiva.

Rod

Photoreceptor - Detect light

• Night vision

• 120 million

• Light comes in, goes through pupil, and hits ___. Normally __ is turned on, but when light hits turns off

• When ___ is off, it turns on a bipolar cell, which turns on a retinal ganglion cell, which goes into the optic nerve and enters the brain

Cone

Photoreceptor - detect color and discern high level of detail

• 6-7 million

• 3 types: red, green, blue

• Mostly on fovea (center of macula)

Transmisson

electrical activation of one neuron by another neuron

Perception

conscious sensory experience of neural processing

Processing

neural transformation of multiple neural signals into a perception

Transduction

Occurs whenever E is transformed from one form to another

Light E to electrical E by rods and cones

Sensation

requires a physical stimulus to be converted into a neural impulse

Light

• Electromagnetic wave

• In the middle of EM spectrum

  • Violet (400nm)–Red (700nm). Highest to lowest wavelength: ROYGBV

• Sun = most common source

Phototransduction cascade

what happens when light hits rod/cone

• Light hits rods(which causes rod turns off) → bipolar cell(turns on) → retinal ganglion cell (turns on) → optic nerve → BRAIN

• The phototransduction cascade is the process of rod turning from ON toOFF

Light → rod (off) → bipolar cell (on) → ganglion cell (on) → optic nerve → brain

Order of phototransduction cascade

Bipolar cells

• In retina

• Send visual signals from rods and cones to ganglion cells

Ganglion cells

• In retina

• Receive signals from bipolar cells and send to optic nerve

Optic nerve

• Receive signals from ganglion cells

• Signals brought to brain

• Axons of ganglion cells

• Blind spot