psych ch 4: ear (auditory)

sensations and perceptions

sound waves

vibrations of molecules - sound waves are usually generated by vibrating objects (ex: guitar strings, vocal chords)

3 physical dimensions of sound

• frequency

• amplitude

• complexity

frequency

corresponds to our perception of pitch

amplitude

corresponds to our perception of loudness

complexity

corresponds to our perception of timbre 

these 3 things determine what we hear:

• pitch

• loudness

• timbre

the purity or complexity of a sound influences how timbre is perceived. to understand timbre, think of a note with precisely the same loudness and pitch played on a piano and on violin . difference you perceive between the sounds is a difference in tiembre.

human ear divided into 3 sections:

• external ear

• middle ear

• inner ear

external ear

vibration of air molecules

middle ear

vibrations of moveable bones

inner ear

depends on waves in fluid (which are finally converted into a stream of neural signals sent to the brain)

external ear

consists mainly of the pinna, a sound collecting cone (when you cup your hand behind your ear to try to hear better, you are augmenting that cone

sound waves collected by the pinna are funneled along the auditory canal toward the eardrum, a taut membrane that vibrates in response.

in middle ear, vibrations of the eardrum are transmitted inward by a mechanical chain made up of the 3 tiniest bones in your body 

hammer, anvil, stirrup - known as ossicles 

ossicles form a 3 stage lever system that converts relatively large movements with little force into smaller motions with greater force- serves to amplify tiny changes in air pressure

pinna

outer, visible part of the ear

external ear’s sound collecting cone

ossicles

which are three tiny bones in the middle ear that convert the

eardrum’s vibration (amplifies sound) 

semi circular canals 

chat : The semicircular canals are three tiny, curved tubes in your inner ear that are part of your vestibular system (your balance and motion-sensing system).

They help your brain detect rotational (angular) movement — basically, when and how your head is turning

auditory canal

google:

function is to collect sound waves from the environment and channel them to the eardrum

eardrum

google: process of hearing- sound transmission

cochlea

inner ear consists largely of the cochlea, a fluid-filled, coiled tunnel that contains the receptors for hearing (looks like a snail)

basilar membrane

(ear’s neural tissue) runs the length of the spiral cochlea, holds the auditory receptors, called hair cells

(waves in the fluid of the inner ear stimulate the hair cells )

hair cells convert this physical stimulation into neural impulses that are sent to the brain

signals routed through thalamus to auditory cortex, located mostly in the temporal lobes of the brain

two influential theories of pitch perception:

place theory and frequently theory

place thorey:

holds that perception of pitch corresponds to the vibration of different portions, or places, along the basilar membrane

place theorey assumes that hair cells at various locations respond independently, and that different sets of hair cells are vibrated by different sound frequencies. the brain then detects the frequency of a tone according to which area along the basilar membrane is most active.

frequency theory

alternative pitch perception theory:

holds that perception of pitch corresponds to the rate, or frequency, at which the entire basilar membrane vibrates (theory: whole membrane vibrates in response to sounds) 

auditory location

locating the source of a sound in space

ex: ambulance wailing - you glancing around to see if it’s behind you, front of you)

2 important cues:

• the intensity (loudness)

• timing of sounds arriving at each ear

intensity difference between the two ears is greatest when the sound source is well to one side (farther ear takes longer for sound to reach)

evidence suggests people depend primarily on timing differences to localize low frequency sounds, and on intensity differences to localize high frequency sounds

Gustatory system

sensory system for taste

• gustatory receptors are clusters of taste cells found in the taste buds

• taste cells only last about 10 days, and are constantly being replaced- new cells are born at the edge of the taste bud and migrate inward to die at the center

4 primary tastes: sweet, sour, bitter, salty

scientists recognizing a 5th primary taste called umami (savory taste)

taste signals are routed through the thalamus and sent onto the insular cortex in the frontal lobe, where initial cortical processing takes place.

sensitivity to certain tastes —- > matter of genetic inheritance 

non tasters= tends to have about ¼ as many taste buds per square cm as do people at the other end of the spectrum - 25%

(super tasters)- 25%

medium tasters- 50%

super tasters- more sensitive to certain sweet and bitter substances - this taste sensitivity influences people’s eating habits in ways that can have repercussions for their physical health 

ex: supertasters less likely fond of sweets and tend to consume fewer high fat foods → likely to reduce their risk for cardiovascular disease 

sensory adaptation

a gradual decline in sensitivity to prolonged stimulation 

(placing a flavored substance in a single spot on your tongue, taste will fade until it vanishes)

• occurs in other senses as well 

• can leave after effects 

ex: adaptation of a sour solution makes water taste sweet. sweet →bitter 

smell makes a significant contribution to the experience of flavor 

flavor declines when odor cues are absent 

ex: when you eat food, and the food tastes bland because your stuffy nose impaired your sense of smell 

olfactory system 

the sensory system for smell 

receptors for smells (olfactory cilia), hairlike structures located in the upper portion of the nasal passages 

receptors for pain: 2 pathways that pass through different areas in the thalamus

1. fast pathway

2. slow pathway

fast pathway

(registers localized pain and relays it to the cortex in a fraction of a second) system that hits you with sharp pain when you first cut your finger

slow pathway 

• routed through the limbic system, that lags a second or two behind the fast system

• longer lasting aching or burning pain that comes after the initial injury

how are incoming pain signals blocked ? 

gate control - theory holds that incoming pain sensations must pass through a “gate” in the spinal chord that can be closed, thus blocking ascending pain signals 

patterns of neural activity that inhibits incoming pain signals 

certain type of glial cells may contribute to the regulation of pain 

sensory integration

norm in perceptual experience

Perceiving Pitch
- Area A1
- Normal range
• 20 - 16,000 Hz
- Place code
- Temporal code

Pitch is how we perceive the “highness” or “lowness” of a sound — it’s related to the frequency of a sound wave (measured in Hertz, Hz).

• A1 stands for Primary Auditory Cortex, located in the temporal lobe of your brain.

• It’s the first cortical area that processes sound information coming from the ears.

• Within A1, different neurons are tuned to respond best to specific sound frequencies (like piano keys laid out in your brain)

typical range for human hearing

place code:

The place theory of pitch perception says that different frequencies activate different places along the cochlea (the spiral structure in the inner ear).

• High frequencies activate hair cells near the base of the cochlea.

• Low frequencies activate hair cells near the apex (tip).

• The brain can tell what pitch you’re hearing based on which part of the cochlea is active — that’s the “place code.”

temporal code:

• The temporal theory says that pitch is also encoded by timing — specifically, how often neurons fire in sync with the sound wave.

• For low frequencies (< ~4000 Hz), neurons can fire in rhythm with the wave (e.g., 500 times per second for a 500 Hz tone).

• The brain interprets this firing rate pattern as the pitch — that’s the “temporal code.”

Touch
- Haptic perception – up
close & personal!
- Thermoreceptors
- Neural representation of
the body’s surface
• contralateral organization
• somatosensory representation
(fingers vs. back)

This slide is about how your body senses and interprets touch, temperature, and texture — what’s called haptic perception.

Haptic Perception – “Up Close & Personal!”

using touch to perceive and identity objects

• “Haptic” means active touch — when you explore the world through direct contact (using your hands, skin, etc.).

• For example: feeling the texture of fabric or identifying an object in the dark by touching it.

• It’s called “up close and personal” because it requires physical contact with objects, unlike vision or hearing which can work from a distance.

Thermoreceptors

• These are sensory receptors in your skin that detect temperature changes.

• There are two main types:

  • Warm receptors – respond when skin temperature rises.

  • Cold receptors – respond when skin temperature drops.

• They send signals through sensory neurons to your brain, helping you tell if something is hot, cold, or changing temperature.

• “Contralateral” means opposite sides.

• Touch sensations from the right side of your body are processed in the left hemisphere of your brain,
  and sensations from the left side are processed in the right hemisphere.

• This cross-wiring also happens for vision and motor control.

🖐 Somatosensory Representation

• The somatosensory cortex (in the parietal lobe) contains a map of your entire body called the somatotopic map or homunculus.

• Body parts with more nerve endings and finer touch sensitivity (like your fingers and lips) take up more space in this map.

• Less sensitive areas (like your back or legs) take up less space.

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thermal grill illusion

The thermal grill illusion happens when warm and cool sensations are applied together to the skin in an alternating pattern (like warm–cool–warm–cool metal bars touching your hand).

“cool receptors and warm receptors”

Touch something, warm cells and cool cells respond equal amounts- the temperature of thing that I am touching is where they cross. ~25-30 

Thermal grill illusion- nothing is damaged. Both warm and cool 

vestibular system

the sensory system that provides information about spatial orientation and balance

smell :

- Only sense directly connected to forebrain
- Olfactory receptor neurons (ORNs)
• glomerulus
• 350 different ORNs (humans)
- Olfactory bulb
- Pheromones

glomerulus: a structure in the olfactory bulb that receives signals from similar olfactory receptor neurons

pheromones: chemical signals released by an animal that communicate information

taste:

Identifying things that are “bad” for you
- Most of taste perception is really smell.
• Orthonasal vs retronasal olfaction
- Taste buds (5 different types)
• salt
• sour
• bitter
• sweet
• umami (savory)
• each contains several types of taste receptors (microvilli)
that react with tastant molecules in food

orthonasal vs retronasal olfaction:

chat:

Orthonasal olfaction: Smelling odors that enter through the nostrils

Retronasal olfaction: Smelling odors that travel from your mouth → up the throat → into the nasal cavity while you eat