Sensation and Perception Quiz 3

How we hear

every natural sound we hear is composed of multiple frequencies, we hear a lot at once

wavelength is the inverse of

frequency

Sinusoid wave

represents pure tones, regular periods of sound condensation 

sound waves

created by alternating patterns of high and low density air molecules generated by movement of a stimulus 

Unit of frequency

measured in Hertz (Hz)

Frequency

number of waves per unit of time

frequency is the inverse of

wavelength

frequency is determined by

rate at which air is compressed (ex. speaker diaphragm) 

Well spaced molecules

low frequency

Closer together molecules

high frequency

we hear different frequencies as having different

pitches

Amplitude

amount of energy in the wave, how big it is 

how we perceive amplitude

loudness

Phase

sound waves position in the cycle, technology behind noise cancelling headphones

how noise cancelling headphones work

match incoming noise with complete opposite phase noise, which cancel each other out and we perceive nothing

constructive interference

 two sounds add together and we get a louder sound than two original, occurs when waves are in phase

Deconstructive interference

we add two sounds out of phase 180 degrees we get no sound (noise cancelling headphones)

Timbre

distinguished sound quality: ev vocal note vs guitar note

Waveform

graphical representation of a wave against time

Spectrum

amplitude against frequency (shows amplitude on y axis and frequency on x axis)

how speakers work

produce sound by moving diaphragm inward and outward, alternating pattern of refraction and compression that creates wave

compression

 high density sound

refraction

low density sound

Sound level

an vary from whisper to explosion, expressed on decibel scale 

• Every change in 10db is a tenfold increase in sound power

humans are most sensitive to what range

20-20 000 Hz, mostly around the 3-4 thousand range

Pinna

outermost part of ear, funnels sound into ear canal, varies across species (elaphans have huge ears)

Ear Canal and drum

pinna funnels sound into ear canal, vibration vibrates eardrum that creates the signal sent to brain

Ossicles

3 smallest bones in body

hammer, anvil, stirrup 

role of the ossicles

Transmits and amplifies sound even more because inner ear is fluid filled

fluid makes it harder to translate into signals

how sound gets amplified by ossicles

small movements of malleus amplified into larger movement by the time they reach the stapes 

Stapes rests on the oval window, pushes it in and out in response to tympanic membrane

how sound gets transducted

• Movement of oval window causes cochlear fluid to move like waves

• Movement causes displacement of basilar membrane

• Basilar membrane lined with hair cells that respond to waves and generate electric potentials 

basilar membrane located in

the center of cochlea

Hair cells at base sensitive to

high frequencies

Apex has hair cells sensitive to

low frequency

Organ of Corti

• Region of sound transduction 

• contains rows of hair cells 

Inner hair cells

• depolarize and send signals in response to their preferred frequency 

outer hair cells

amplify sound signals

organ of court is covered by

• techtorial membrane

Spiral ganglia

first neurons in auditory pathway, they exit cochlea at auditory nerve

Audiogram

measure of how well someone can hear

• Uses method of limits

• 
  

hearing loss due to noise exposure (audiogram)

has higher threshold

Presbycusis

age related hearing loss, hair cells degrade over time especially for high frequency sounds, 

Hyperacusis

makes everyday sounds feel too loud, caused by a variety of things like drugs, head injury, mental health, surgery, infection

Tinnitus

hearing sounds that aren't there, ears ringing 

Amplification

 a hearing aid to help amplify sounds and reverse hearing loss

compression technology

compress sound info to lower its pitch so it's received by an intact region of the ear, distorts harmonic arrangement of a sound and affects its timbre

Cochlear implants

microphone worn on back of ear, transmits sound info through skull to electrode in cochlea, directly stimulates spiral ganglion initiating signaling. For people whose hair cells don't work

Ascending auditory pathway

• Neurons of cochlear nucleus project to superior olivary complex on contralateral side

• Then project to inferior colliculus

• And then to medial geniculate nucleus 

• More crosstalk than visual pathway

Efferent fibres

 carry info away from brain

Afferent fibres

 carry info toward the brain

8th cranial nerve

vestibular and cochlear area, transmits sound and balance and orientation 

Tonotopic organization

different sound frequencies are processed by different neurons located in specific places

• Present at each point along pathway to preserve brain's ability to discriminate sounds based on pitch
  

Where pathway

• heads toward parietal lobe to integrate with visual stream, tracks location and movement

What pathway

• travels along ventralateral temporal lobe to the front brain, integrates with attention memory and emotion discernation 

Cues to segregation/fusion

• Other parameters can affect whether they are bound or separated

• When the time between them is short were more likely to perceive two sounds

• If theyre more slow we perceive a single sound source

• ADD INFO!

Harmonic structure/ timing cues

• Most sounds harmonic in nature

• If they all have the same onset and onset times, we perceive them as together

• If we change spacing of a frequency so its not a multiple of the harmonic we’ll perceive two diff sounds

Sound Localization

How we tell where things are

Interaural time difference cues

etween ears, there are time differences between what we hear by a 10th of a second because one ear is closer, the head also blocks some noise (acoustic shadow)

location with biggest ITD

Source 90 degrees to right or left

Interaural difference in the superior olive

• Give our brain ability to encode interaural time differences

Jeffers Model

• If a sound is on your right, it'll reach right ear before left 

• if Electrical activity at right superior olive arrives first it results in electrical activity at ITD sensitive cell in that location 

Source Confusion

• There are places we can't discriminate between ex. 60 degrees and 120 degrees on the same side since they have the same Interaural difference 

• We have to use other cues like prior knowledge 

• Human pinna helps because it funnels info differently from different elevations, helps judge adobe and below 

High frequency sound and object tracking

• Some species are better than others ex. bats and echolocation