NEURO -ADV SENSATION AND PERCEPTION hearing

Frequency vs Amplitude

Frequency = pitch (Hz) and Amplitude = loudness (dB).

Frequency

-Number of cycles that a wave completes in a given amount of time

-Measured in Hertz: Cycles per second

-Corresponds to our perception of pitch

-Low pitch: low frequency

-High pitch: high frequency

lose frequencies with age

Amplitude

-The intensity of a sound stimulus, usually measured in decibels (dB)

-The magnitude of change in air-molecule density

-Corresponds to our perception of loudness

-Soft sound: Low amplitude

-Loud sound: High amplitude

complexity

--Pure tones

Sounds with a single frequency

--Complex tones

Sounds with a mixture of frequencies

Complex sounds can be

¡broken down into their component frequencies

¡A sound contains a fundamental, or basic, frequency—harmonics are multiples of that frequency.

Timbre

Characteristic sound quality of an instrument, related to the intensities of harmonics.

Sound waves

consist of wave-like changes in air pressure

pure tone

described by amplitude or intensity

-percieved as loudness

—decibel (dB); a measure of sound intensity

Frequency

number of cycles per second of vibration

—percieved as pitch

—measured in hertz (Hz)

pinna

this and the external ear funnel soundwaves into the ear canal

middle ear

concentrates sound energies

The middle ear connects

tymphanic membrane (eardrum) to oval window via ossicles (hammer, anvil and stirrup)

Steps of middle ear sound 

1. pinna catches sound waves deflecting them into ear canal

2. waves are amplified and directed to the ear drum causing it to vibrate

3. which in turn vibrates ossicles

4. ossicles amplify and convey vibrations to the oval window

5. vibration of the oval window sends waves through cochlea fluid

6. causing the basilar and tectorial membranes to bend

7. which in turn cause cilia of inner hair cells to bend. this bending generates neural activity in hair cells

Oval window

is a membrane in the cochlea that separates the scala tympani from the middle of the ear

Cochlea

Mammals have a fluid-filled cochlea, a spiral structure with a base and an apex

—-the base is the nearest oval window membrane

The cochlea has 3 parallel canals

scala vestibuli — vestibular canal

scala media —middle canal

scala tympani — tympanic canal

tectorial membrane

in cochlea —- overlying hair cells

basilar membrane

receptor surface in the cochlea that transduces sound waves to neural activity

organ of corti

Has 3 rows or outer hair cells

1 row of inner hair cells

outer hair cells

amplify waves providing an energy source that enhances cochlear sensitivity and frequency selectivity

outer hair cells can

contract and relax to change stiffness of tectorial membrane

inner hair cells

only these acts as auditory sensory receptors

sound vibrations cause

the basilar membrane to oscillate 

different parts respond to different frequences:

high frequency sound

displaces the narrow base of basilar membrane. (narrow base is tuned for high frequencies)

low frequency sound

displaces wider apex (a wide, thin apex is tuned for low-frequencies)

medium soundwaves

cause peak bending of the basilar membrane in between the narrow base and wide apex

transduction of sound waves

to neural activity takes place in the hair cells

-movement of the basilar membrane stimulates the hair cells via bending and shearing action

-movement of cilia on hair cells changes membrane potential via influx of ions, and allows neurotransmitter release

tip links (cochlea)

thin fibers that run across the tips of the hair cell’s stereocilia

vibration

makes stereocilia sway, creating tension on the tip links that then open the ion channels they are attached to 

the hair cell depolarizes and calcium influx at the base causes neurotransmitter release

Primary auditory cortex (A1)

¡) lies within Heschl’s gyrus, surrounded by secondary cortical areas( A2).

wernicke’s area

¡(posterior speech zone): On the left hemisphere, has a role in formed speech

Heschl’s gyrus

¡On the  right hemisphere has a special role in analyzing music.

30% of left handed people have the two flipped

output of the cochlear nuclei travels to multiple targets

superior olivary nuclei — receive bilateral input

inferior colliculi — in the midbrain

then to the medial geniculate nuclei in the thalamus

then to auditory cortical areas

60% of information goes to

contralateral auditory cortex

All levels of the auditory pathway have

tonotopic organization

they are arranged in a map according to the frequencies to which they respond 

—PET and fMRI show that the main activation is in the primary auditory cortex (A1) on the superior temporal lobes

tonotopic representation

¡Low frequencies are processed first by cells on the apex of the basilar membrane and eventually by cells located in the anterior portion of A1

¡High frequencies are processed first by cells on the base of the basilar membrane and eventually by cells located in the posterior portion of A1