Sensation and Perception (Unit 5)

sensation is…

the process by which our sensory receptors and nervous system receive and represent stimulus from our environment

perception is…

the process by which our brain organizes and interprets sensory input - allows us to recognize meaningful objects and events

taking the sensations and figuring out what they mean

bottom-up processing is…

processing which starts at the sensory receptors and works up to higher levels of processing

no context or understanding prior

ex. if you are guessing the drink you are drinking… it’s brown, it’s warm, it’s in a mug… it’s coffee!

top-down processing is…

perception constructed from the sensory input by drawing on our experience and expectations

context and understanding prior - coming from a place of comprehension, so you are drawing a conclusion from what you already know

ex. you look at the drink in the mug and automatically know it’s coffee because you already know what coffee looks like, smells like, tastes like, etc…

selective attention allows us to…

pinpoint our awareness

your brain is still unconsciously aware of other stimuli, it just filters out some input and pays attention to other input

ex. Cocktail Party Effect

describe/explain the Stroop Effect:

• participants read a list of words for colors, but the words are printed in a color different to the word itself

• it took longer for participants to state the color of the words rather than to read the text they were printed in

• this is because we are habitual readers - it’s easier to just read the words than process the colors - reading the words is so intuitive/routinely/embedded into our brains for us, it takes longer to do something else

• our brain must work harder to resolve differences

• other ways the test has been used:

  • emotion: emotionally charged words cause more interference when you must say the color instead of the word itself - harder for people that suffer from anxiety

  • mental disorders: used to test for schizophrenia and autism

inattentional blindness is (famous study?)…

failing to see visible objects when our attention is directed elsewhere

famous study: count the # of basketballs - did you see the gorilla? (Daniel J. Simons and Christopher Chabris)

change blindness is…

failing to notice change in the environment

choice blindness is…

after making a choice of a preferred food (french toast) people were given the non-preferred food (pancakes) and didn’t usually notice the swap

popout happens when…

even when we aren’t paying attention, some stimuli demand our attention/draw our eye

transduction is…

the process of converting one form of energy into another that your brain can use (sights, sounds, smells into neural impulses)

1. receive sensory info

2. transform stimulation into neural impulses

3. deliver into to the brain

what was Gustav Fechner’s significance?

absolute threshold

what is Fechner’s absolute threshold?

the minimum stimulation necessary to be able to detect a light, sound, pressure, taste, odor 50% of the time

faint stimuli we can just make out

ex. whispering someone’s name - they don’t hear you - continue to whisper incrementally louder until they can hear you - that volume is the absolute threshold for that faint stimuli

ex. the hearing test… “raise your hand if you hear a beep…”

what impacts the results of an absolute threshold? what is this theory called?

• signal strength (how loud? how bright? how strong a smell?)

• psychological state (sleeping? under the influence? mental disorder?)

• experience

• expectations (are you expecting someone? are you super locked into hearing a certain sound, like a knock at the door of your friend that’s picking you up?)

• motivation

• alertness (wide awake, or falling asleep? not paying attention?)

→ SIGNAL DETECTION THEORY (predicts when we will detect weak signals - when we will be less or more likely to hear that “whisper”… these are all predictors of this)

explain the signal detection theory:

predicts when we will detect weak signals

when we will be more or less likely to hear that “whisper“. . . loud surroundings, distracted, deaf, asleep, doing something else/preoccupied

expectation matters: if you are expecting something, you may hear a sound and assume it was the signal you want, but you could be wrong

explain subliminal stimuli:

stimuli you cannot detect 50% of the time

considered below your absolute threshold

expectation matters: if you are expecting something, you may hear a sound and assume it was the signal you want, but you could be wrong: measures “hits” and “misses”

explain subliminal sensations (messages/persuasion):

a sensation received by your brain but is not consciously noticed

hidden messages you don’t realize you’re intaking but you are… may be a subtle/fleeting effect

ex. quick slides during movie previews saying “thirsty” or “popcorn” subconsciously making you want to go buy a drink or some popcorn

explain difference thresholds:

the minimum difference a person can detect between any two stimuli 50% of the time

the larger the stimulus, the larger the difference threshold

• if one sound is just a little bit louder, they may sound the same

• if one shade of pink is just a little bit brighter than another, they may look the same

Weber’s Law discusses this (there must be a constant minimum percentage)

what does Weber’s Law state?

for an average person to perceive a difference, two stimuli must differ by a constant minimum percentage

sensory adaptation is…

constant exposure to a stimulus that does not change causes us to become less aware of it

• our nerve cells fire less frequently

• reduced sensitivity allows a focus of new stimuli

ex. you lifeguard at a pool - at first, the smell of chlorine is overwhelming, but with time you grow used to it and practically don’t even notice the smell anymore

through our experiences, we come to expect certain results called…

expectations

which can be influenced by motivation, emotion, and culture

what is perceptual set?

a mental predisposition to perceive one thing and not another

---

mental tendencies and assumptions that greatly affect what we perceive / the tendency of our perception to be influenced by our expectations, beliefs, and previous experiences

can influence what we see, hear, taste, and feel

→ the mental predisposition that shapes how we interpret and perceive sensory information and can also influence our interpretation and understanding of those stimuli.

explain expectation, a force that influences perceptual set:

the brain can work backwards in time to allow a later stimulus to determine how we perceive an earlier one

• what are we “expecting” the previous/earlier stimulus to be/mean?

**ex. reading "the phrase “eel is on the wagon” as “wheel is on the wagon” - your brain worked backwards and perceived “eel” to be “wheel” because that’s what makes sense in the sentence

ex. reading a sentence and failing to notice a duplication of words: “the the end of the marking period”

explain motivation/emotion, a force that influences perceptual set:

hearing sad rather than happy music can predispose people to perceive a sad meaning

desired objects, such as a water bottle when thirsty, seem closer - this perceptual bias energizes our going for it

ex. if you show a bunch of abstract images to someone that’s hungry, they may interpret them all as different kinds of food

explain culture, a force that influences perceptual set:

where you live in the world may influence your perception of certain things

ex. the picture of the man with the spear - which animal is he hunting?

ex. on page 165 of the textbook, there is a family sitting in a circle with a woman sitting under a box-like thing… East-Africans saw the woman balancing a metal box on her head while Westerners (more familiar with boxlike architecture) perceived her to be indoors, sitting under a window

how is our sensory experience of light determined?

wavelength (hue - the color we experience)

or…

intensity (the brightness/brilliance we experience)

compare/contrast wavelength vs. intensity (light):

wavelength and intensity both contribute to our sensory experience of light

wavelength is the distance from one wave peak to the next peak - determines the hue (the color we experience)

• violet is the shortest wavelength, red is the longest wavelength

intensity is the energy in light waves determined by amplitude/height - influences brightness

• ex. short amplitude: dull color or quiet sound, tall amplitude: bright color or loud sound

explain the step-by-step process of transduction through the eye:

1. light enters the eye through the cornea (protects the eye and bends light to provide focus)

2. the light passes through the pupil (a small, adjustable opening)

3. surrounding the pupil is the iris which dilates or constricts in response to light intensity and emotions

4. behind the pupil is the lens that focuses incoming light into an image on the retina (a tissue on the eyeball’s inner surface)

5. light moves from outer layer of retina to its buried receptor cells (rods and cones)

6. the light energy triggers chemical changes that spark neural signals (transduction) activating bipolar cells

7. bipolar cells activate ganglian cells who’s axons twine together to form the optic nerve

8. the optic nerve will carry the information to your brain where the thalamus is ready to distribute the information

beginning the process of transduction, light enters the eye through the…

cornea - protects the eye and bends light to provide focus

after the cornea bends the light for focus, the light passes through the…

pupil - a small adjustable opening that is small when there’s lots of light and big when there is little light (to let more light in) → (iris dictates this)

surrounding the pupil is the…

iris - a muscle that dilates or constricts in response to light intensity and emotions (controls pupil size)

behind the pupil is the…

lens - focuses incoming light into an image on the retina (a tissue on the eyeball’s inner surface)

light moves from the outer layer of the retina to…

rods and cones - its buried receptor cells

rode: black and white receptors

cones: color receptors

the light energy triggers what and thus activates what?

triggers chemical changes that spark neural signals (transduction), activating bipolar cells

the bipolar cells activated from chemical changes from light energy activate…

ganglion cells who’s axons twine together to form the optic nerve

the optic nerves, formed from ganglion cells’ axons that twine together, will…

carry the information to your brain where thalamus is ready to distribute the information

where the optic nerve leaves the eye there are…

no rods and cones (receptor cells), so we have a blind spot

cones cluster around the _____1_____, which is the retina’s area of _____2______

1. fovea

2. central focus

each cone transmits to a single bipolar cell that relays the cones messages to the…

visual cortex

cones are thus better able to detect fine detail!

rods share bipolar cells with other rods sending…

combined messages to the visual cortex

rods are less sensitive to details!

why are words further to the left or right of your field of vision probably blurry? what type of vision is this?

their image is hitting the outer area of your retina where rods are plentiful, but cones (the fine detail finders) are not

→ this is your peripheral vision

describe peripheral vision images:

you can see them in general before you can see them in sharp focus

compare and contrast: cones vs. rods

cones:

• 6 million

• center of retina

• allow us to perceive color

• struggle in dim light, doesn’t work well in the dark

• better able to detect/catch fine detail

rods:

• 120 million

• periphery of retina

• allow us to perceive black and white

• sensitive in dim light, works better in the dark than cones

• less sensitive to detail

how do your eyes adapt to light changes?

your pupils dilate to allow more light to the retina

• could take 20 minutes or more to fully adapt

• dilated pupils or rapid involuntary movement of the eyeball is also a common sign of certain drug use

how do the eye and brain process visual info?

entry level of processing - retina’s neural layers - brain tissue that has migrated to the eye during fetal development

→ these layers both pass along electrical information plus encode and analyze sensory information

the pathway…

1. rods and cones

2. light energy → transduction → bipolar cells

3. ganglion cells’ axons create optic nerve

4. optic nerve

5. brain (thalamus → visual cortex)

feature detectors are (and who’s experiments discovered them?)…

specialized neurons in occipital lobe’s visual cortex that receive info from ganglion cells in retina

respond to edges, lines, angles, movements, etc. and pass info to other cortical areas where supercell clusters respond to more complex patterns

**experiments by David Hubel and Thorsten Weisel

what do supercell clusters respond to?

the more complex patterns

true or false: different brain areas activate when people view various objects - faces, houses, shoes, etc.

TRUE!

ex. prosopagnosia causes people to never recognize a face - only a certain brain area is damaged causing this, they can still recognize other things

what is prosopagnosia?

no facial recognition

every face is a stranger to them - even their parents, spouse, anyone

explain parallel processing and how is applies to analyzing a visual scene:

our brain does many things at once

to analyze a visual scene - our brain divides it into subdimensions (motion, form, depth, color) and works on each part simultaneously

ex. that’s a bird: it’s flying, it has wings, a beak, feathers (you’re thinking about all of those separate parts at the same time)

**perception occurs when we integrate this separate but parallel work

Is a tomato RED?

. . .

NO!! But why not?

objects reject or reflect the wavelengths of the color they “look like”

seeing red occurs because the tomato rejects or reflects the long wavelengths of red

explain color vision:

color is a mental construction - it is from our brain, not the object itself

most of us can see 1,000,000 color variations! (low difference threshold)

we can probably see shapes before colors in peripheral vision since image is hitting rods and not cones (think of the colored pencil demo we did in class)

explain the Young-Helmholtz trichromatic theory (trichromatic = three color):

knowing any color can be created by combining the light waves of three colors (red, green, blue)…

…they inferred the retina in the eye must have 3 color receptors which, when we stimulate combinations of these cones, create other colors

how did the Young-Helmholtz trichromatic theory explain the vision of people who are color deficient?

they lack functioning red or green cones (or both)

their vision is monochromatic or dichromatic instead of trichromatic

questions remained…

• how do people blind to red and green still see yellow?

• why does yellow appear pure (unlike purple)?

explain Hering’s Opponent Processing Theory:

three sets of opponent retinal processes enable color vision:

• red/green, yellow/blue, black/white

---

• the thalamus has neurons only turned on by red and off by green and vice versa…

• since red and green (or yellow/blue, or black/white) messages cannot travel simultaneously, we do not see “reddish green”

  • but we could see a “bluish green”, or a “greenish blue” (not an opposing pair)

explaining after images:

• when staring at green, we fire “green green green”

• when one member of the color pair is “fatigued” by extended use, inhibition of its corresponding pair member is reduced “green is so tired, red perks up”

• this increases the activity level of the unfatigued pair member and results in its color being perceived “red gets rolling…”

• this is why we may see an after image of red after staring at a green square before it disappears

** REMEMBER: AFTER IMAGES = HERING’S OPPONENT PROCESSING THEORY

color perception is in 2 stages which are…

1. Retina’s Red, Green, Blue cones respond in varying degrees to different stimuli (Young-Helmholtz)

2. Signals are processed by the nervous system’s opponent-process theory

explain the visual cliff experiment/discoveries:

• a laboratory device for testing depth perception in infants and young animals

• when researchers placed infants on the edge of a safe canyon and had the infant’s mother coax them to crawl out onto the glass, most infants refused to do so, indicating that they could perceive depth…helped researchers (Gibson and Walk) discover that depth perception is partly innate - kids are somewhat predisposed to fear heights

why is touch so important?

animals deprived of touch as infants…

• less growth hormone

• slower metabolic rate

• monkey unhappiness

how do we sense touch?

• skin pressure, warmth, cold, pain

• different body parts more sensitive to different stimuli

how do we understand pain?

• pain signals a problem

• people who don’t feel pain can really hurt themselves

• women more pain sensitive than men

what influences pain sensitivity?

• genes, psychology, experience, attention, culture

• both bottom-up AND top-down

biological influences on pain include:

• different nociceptors (sensory receptors for painful stimuli) detect temperatures, pressure, chemicals

• gate control theory

explain Robert Melzack and Patrick Wall’s Gate Control Theory:

the spinal cord contains a neurological “gate” that either blocks pain signals or allows them to continue on to the brain:

• spinal cord contains nerve fibers that conduct most pain signals

• contains a neurological “gate” which is activated by injured tissue and closed by large neural fibers to end pain

often used to explain phantom pains

what if we stimulate “gate closing” - would this end people’s pain?

it could: massage, acupuncture, electric stimulation

what other factors can influence pain, aside from biological influences?

• if we are distracted, we may feel less pain (psychological)

• endorphin releases ease pain (biological)

what do phantom pains (limb amputees), phantom noises (ringing in the ears called tinnitus), phantom sights in blind, taste phantoms, and phantom smells conclude for the brain?

we see, hear, taste, feel, and smell with our brain which can sense without functioning senses -signals are sent as though the limb is there

people believe they’re having a sensation when they’re not actually

ex. a limb amputee may sense pain in their left leg, even though they got it removed… sensing pain without there being any real pain

psychological influences on pain include…

• distraction allows people to play through pain

• we tend to overlook duration of pain in hindsight as well

• but, we REMEMBER peak pain and end pain

• if we can ease your pain at the end of a procedure, people recall it as less severe (taper-down)

social-cultural influences on pain include…

we perceive more pain when others are experiencing pain too

how can pain be controlled?

• drugs

• surgery

• acupuncture

• electrical stimulation

• massage

• hypnosis

• relaxation training

• thought distraction

• sometimes, even believing becomes reality… placebo effect

what flavors can you taste?

sour, sweet, salty, bitter, umami (newest flavor)

why do we have flavor receptors tied to these flavors? evolutionary value?

attracted people to energy or protein rich foods

the tongue has 200+ taste buds on each…

bump of your tongue

what are taste buds / what do they do?

• they have antenna like hairs that sense food molecules and catch food chemicals

• they have specialized receptors (for each flavor) - sweet, salty, etc.

• send signals to the temporal lobe

• regenerate every week or two - ex. if you burn your tongue

• however, they decline with age

how can expectations influence taste (GUSTACION)?

your perception of taste can affect how it tastes to you

ex. $8 wine vs. $100 wine - if you’ve been informed of the value of each wine, you’ve now been primed to assume that the more expensive wine will taste better

ex. if someone has previously told you deviled eggs are disgusting, you may expect them to be disgusting, and if you try it you may greatly dislike it because of your previous expectations regarding deviled eggs.

how does smell (OLFACTION) work?

• molecules of a substance (an odor/smell) carried in the air reaches a cluster of the 20 million receptor cells at the top of the nasal cavity

• lock and key relationship between odors and receptors BUT not a one-to-one relationship…

• some odors trigger a combination of receptors

• these receptor cells alert the brain (since smell is primitive, the first sense developed, they skip the thalamus)

• learned associations of smell matter! good and bad memories associated with certain smells

which sense is the least acute (you have to be closer to sense it): seeing, hearing, or smelling?

sense of smell is less acute than seeing and hearing

ex. you have to be a lot closer to smell a flower than to see it

kinesthesia (proprioception) is…

your sense of the position/location and movement of your limbs

explain your vestibular sense:

EARS AND BALANCE WORK TOGETHER!

• the semicircle canals and vestibular sacs in your inner ear contain fluid that moves when your head rotates or tilts

• this stimulates hair-like receptors which send messages to your cerebellum allowing you to sense body position and balance

• when the fluid in your ear gets jostled around, you wobble back and forth with it, causing a loss of balance

ex. ever play dizzy bats? your brain is fooled into feeling like you are still spinning - it takes your body a moment to return to the balance feeling

ex. riding a roller coaster causes the fluid in your ears to shake all around, which is why you may feel disoriented when the ride is over

how do we sense our body’s position and movement?

• kinesthesia

• vestibular sense

how do our senses interact?

• smell + texture + taste = flavor

→ we often use vision to assess the taste of food

• vision and hearing act together too:

  • “look at me so I can hear what you’re saying” or turning on closed captioning while watching something

• tactile and social judgements:

  • a person holding a warm drink rates people more warmly

  • called embodied cognition - brain circuits responsible for cognition connect with those responsible for sensation

sensory interaction is at work all the time

what is Gestalt Psychology?

focuses on how people perceive and experience the world as organized wholes, rather than just the sum of their individual parts

emphasizes the importance of context, patterns, and the mind's tendency to perceive objects as complete and meaningful entities.

(This approach was developed by Max Wertheimer, Wolfgang Köhler, and Kurt Koffka in the early 20th century)

explain figure ground:

the organization of the visual field into objects (the figure) that stand out from their surroundings (the ground) - we tend to segment our visual world into these two things (figure = object or person) (ground = background or anything besides the focus)

*helps us recognize objects through vision

ex. the optical illusions of “do you see the young woman or the old woman?” - based on where you focus you eyes to see the figure versus the background, the image is different

explain grouping (in general):

the perceptual tendency to organize stimuli into coherent groups

explain proximity (grouping):

we group nearby figures together

ex. 6 lines are side by side: I I I I I I … we see not 6 separate lines, but 3 sets of 2 lines

explain continuity (grouping):

we perceive smooth, continuous patterns rather than discontinuous ones

explain closure (grouping):

we fill in gaps to create a complete, whole object

explain relative size/size constancy:

smaller objects seem further away

if we assume 2 objects are similar in size, most perceive the one that casts the smaller retinal image as farther away

explain relative height:

we perceive objects higher in our field of vision as farther away…

higher images seem farther away

also, shorter objects seem farther away

explain shape constancy:

perceiving objects as unchanging even as illumination and retinal images change

ex. looking at the tile floor from different angles, some squares may not always keep that perfect square shape, but we still know they are all perfect squares, the same shape

explain overlap (interposition):

interpose = “come between”

an object blocking the view of another seems in front / closer

explain linear perspective:

parallel lines appear to meet in the distance

the sharper the angle of convergence, the greater the perceived distance

gives a sense of depth

explain light and shadow:

shading produces a sense of depth

for DIMENSION! not just any shadow you see.

explain relative motion:

when we move, objects at rest appear to move

ex. driving in the car and looking out the window and seeing the mountains, trees, and houses that look like they’re moving

→ objects farther away appear to be moving slower and objects closer appear to be moving faster (motion parallax)

explain stroboscopic motion:

brain’s perception of movement in a rapid series of slightly varying images

ex. cartoons, stop motion animation, flip-books

explain motion parallax:

objects moving across the frame will appear to move a greater amount if they are closer to an observer and at a slower amount if they are a greater distance away

ex. driving in the car, the trees right next to you appear to be moving more rapidly than the mountains off in the distance

explain the phi phenomenon:

an illusion of movement created when 2 or more adjacent lights blink on and off in succession

ex. ever been to a light show? things appear to be moving, like a snowman waving his arm, but really it’s just lights rapidly turning on and off one by one to create the sense of motion

explain binocular cues:

retinal disparity between the 2 eyes’ images

visual information taken in by two eyes that enables us a sense of depth perception

retinal disparity = a difference in the angle or position of an object as seen by both eyes … the space between the eyes creates a different perspective for each eye

explain retinal disparity:

a difference in the angle or position of an object as seen by both eyes

one of the many ways in which humans can perceive depth

the way that your left eye and your right eye view slightly different images… the two slightly different images produced in both eyes are blended into one view when both eyes are open, and this is one of the ways in which human depth perception is possible

the space between the eyes creates a different perspective for each eye

explain the Muller-Lyer Illusion and the Ponzo Illusion:

Muller-Lyer: which line body is longer? (middle of arrow vs. arrowheads turned upside down)

Ponzo: which yellow line is longer? (railroad track)

both argued that most people judge a shape (in this case, size) by its surroundings - in this case, people were misusing the size constancy principle

audition/hearing is…

adaptive