week 6: sensation and perception

sensation

detecting physical energy with our sense organs (eyes, ears, skin, nose, tongue)

perception

the brain’s interpretation of the raw sensory information

illusion

the way we perceive a stimulus doesn’t match its physical reality; illusions tell us that perception involves some processing of information (and we can make errors)

transduction

conversion of an external stimulus into a neural signal

sensory receptors

specialized cells designed to convert a certain kind of external information into a neural signal

sensory adaptation

sensory neurons adjust their sensitivity based on recent stimulus history; examples: perceiving smells, adjusting to dark vs. light conditions, etc

aftereffects

opposing sensory or perceptual distortions that occur after adaptation

for sound, what psychological sensation corresponds to the wavelength of a sound wave

pitch

for light, what psychological sensation corresponds to the wavelength of a light wave

color

shorter wavelength characteristics

high frequency, high energy

longer wavelength characteristics

low frequency, low energy

perception of sound waves

louder = higher amplitutde, higher pitch = higher frequency

perception of light waves

brighter = higher amplitutde

a longer wavelength of visible light are what colors

red, orange, or yellow

psychophysics

the study of how our sensations (psychological events) correspond to physical events in the world

absolute threshold

the lowest level of a stimulus needed for the nervous system to detect a change 50% of the time; something vs. nothing; the level detected 50% of the time

just noticeable difference (jnd)

something vs. something; the smallest change in the intensity of a stimulus that we can detect (again, 50% of the time)

weber’s law

the stronger the stimulus, the bigger the change needed to detect it; the same added amount can be obvious or invisible, what matters is the fraction

signal detection theory

how stimuli are detected under different conditions; difficulty of detecting the signal depends on the strength of the signal in relation to the strength of the noise

when stimulus is present and the answer is true

hit (true positive)

when stimulus is present and the answer is false

miss (false negative)

when stimulus is absent and the answer is true

false alarm (false positive)

when stimulus is absent and the answer is false

correct rejection (true negative)

dichotic listening

play different information through each ear of headphones, information reported only from the attended ear

cocktail party effect

when important information pops out in a conversation that you are not attending; ex: your name

inattentional blindness

occurs when unattended stimuli are ignored as if they weren’t there

change blindness

occurs when you fail to detect obvious changes in your environment

bottom-up processing

constructing a representation from parts and basic features

top-down processing

processing influenced by previous experience and knowledge

perceptual sets

set formed when our expectations influence our perceptions, is a readiness to perceive something in a particular way

pupil

circular hole where light enters

iris

colored portion of the eye that controls pupil size (letting in more or less light)

sclera

white part

cornea

curved, transparent layer covering the iris and pupil that helps focus light

lens

oval shaped disc that bends light

acommodation

changing of the lens shape to focus on near/far objects

myopia

eye is too long (nearsightedness); near is clear

hyperopia

eye is too short (farsightedness); far is clear

retina

membrane at the back of the eye responsible for converting light into a neural signal; contains two kinds of photoreceptors: rods and cones, has a high density of cones (photoreceptors)

fovea

central portion of the retina, responsible for visual acuity; very small, about 1% of retinal size; highly represented in the brain

acuity

sharpness of vision

saccades

small jerky movements of the eye allowing for rapid hanges of focus; puts the fovea on a new location

rods

respond under low levels of light, not color sensitive, more common outside of fovea

cones

sensitive to fine detail, primarily located in fovea, color sensitive, less plentiful than rods

optic nerve

bundle of axons that travels from the retina to the brain

blind spot

area of the retina where the optic nerve exits the eye

left eye sees which visual field

right

right eye sees which visual field

left

dorsal, “where” stream

spatial processing; parietal lobe

ventral, “what” stream

object processing; temporal lobe

hue

color of light which corresponds to wavelength

trichromatic theory

color vision is based on three primary colors: blue, green, red (types of cones)

opponent process theory

we perceive colors in terms of three pairs of opponent colors: red-green, blue0yellow, black-white

color blindness

inability to see some or all colors due to loss of one or more types of cones

depth perception

ability to judge distance and spatial relations

binocular depth cues

involves two eyes; binocular disparity (each eye sees slightly different images, brain can judge depth) and convergence (eyes converge to see near objects)

monocular depth cues

involves one eye: relative size (distant objects look smaller than closer objects), texture gradient (texture is more clear on closer objects), interposition (closer objects appear in front of distant objects), linear perspective (parallel lines converge with distance), height in plane (distant objects appear higher than closer objects), light and shadow (shadows can tell us about form), and motion parallax (closer objects pass more quickly than distant objects)

perceptual constancy

perceive stimuli as consistent across varied conditions: size, shape, color

gestalt principles

rules that govern how we perceive objects as wholes within their overall context

figure-ground separation

figures are integrated units of percption; visual system automatically tries to identify figure through cues that converge (ex: motion, depth, patterns, etc)

proximity (gestalt principles)

elements placed close together are interpreted as a related group, often overriding similarity

similarity (gestalt principles)

objects that share visual traits—like color, shape, size, or texture—are perceived as belonging to the same group

continuity (gestalt principles)

following the smoothest, most continuous path (straight or curved lines) rather than sharp, abrupt turns

closure (gestalt principles)

brain automatically fills in gaps, missing lines, or incomplete shapes to perceive a complete object

figure-ground (gestalt principles)

mind separates a dominant foreground (figure) from its background (ground) to establish focus

symmetry (gestalt principles)

symmetrical, balanced elements as a single, unified group

connectedness (gestalt principles)

brain automatically groups visual elements together when they are physically or visually linked

simplicity (gestalt principles)

naturally simplifies complex, ambiguous, or cluttered visual stimuli into the most basic, orderly, and recognizable shapes possible.

common fate

objects moving at the same direction and at the same speed are perceived as a group

synchrony

stimuli that are perceived to occur at the same time are perceived as part of the same event

common region

naturally simplifies complex, ambiguous, or cluttered visual stimuli into the most basic, orderly, and recognizable shapes possible.

sound

vibration; mechanical energy that travels through some medium (air, water, …); without a medium there is no sound

timbre

quality or complexity of a sound

outer

funnels sound to the ear drum; pinna, ear canal, ear drum

middle

transmit sounds from ear drum to inner ear; hammer, anvil, stirrup

inner

transduces sound; cochlea (transduction accomplished by movement of hair cells [cilia])

place theory

specific locations on the basilar membrane match tones with specific pitches (base vibrates to high-frequency sounds, end vibrates to low-frequency sounds)

frequency theory

neuron firing rate matches pitch (sound frequency corresponds to action potential frequency)

volley principle

clusters of nerve cells can fire together (modification of frequency theory)

binaural cues

depending on having two ears

interaural level difference

sound coming from right side is more intense in right ear (because it doesn’t have to pass through your head)

interaural timing difference

sound from the right side reaches the right ear first (just a little)

conductive deafness

malfunctioning of the ear drum or ossicles

sensorineural hearing loss

neural signals are not transmitted from cochlea

noise-induced hearing loss

damage to hair cells due to loud noises