Psych 267 Chapter 11

Front 1

Sound as a stimulus

Back 1

When a speaker pushes out, it pushes the surrounding air molecules outward (condensation). When the speaker moves back in, air molecules spread out to fill the space (rarefraction). The alternating increase and decrease in pressure creates the sound waves.

Front 2

Components of auditory signal

Back 2

Frequency (pitch), Amplitude (loudness), and complexity (timbre).

Front 3

Frequency (pitch)

Back 3

The rate at which waves vibrate, measures as cycles per second, or hertz (Hz). Frequency roughly corresponds to our perception of pitch.

Front 4

Amplitude (loudness)

Back 4

The intensity of sound, usually measured in decibels (dB). Amplitude roughly corresponds to our perception of loudness.

Front 5

Complexity (timbre)

Back 5

Most sounds are a mixture of frequencies. The particular mixture determines the sounds timbre. Allows us to distinguish between the type of sound (piano vs violin on the same note)

Front 6

Amplitude and sound pressure

Back 6

Decibels and sound pressure. dB= 20xlog(p/p0). p= the sound pressure of the stimulus. p0= a standard sound pressure, 20 micropascals (near threshold). Pascal = a unit of pressure.

Front 7

Pure tone

Back 7

When pressure changes occur in a sine wave pattern.

Front 8

Fundamental frequency

Back 8

the repetition rate of the complex tone

Front 9

additive synthesis

Back 9

How complex tones are created. Using the fundamental and multiples of the fundamental.

Front 10

periodicity pitch

Back 10

the ability to distinguish tones when the fundamental has been removed.

Front 11

Pitch

Back 11

the perceptual quality associated with frequency

Front 12

tone height

Back 12

increases in pitch that is associated with increases in fundamental frequency.

Front 13

tone chroma

Back 13

letters of the notes repeat, notes with the same letters sound similar.

Front 14

Timbre

Back 14

is the quality that distingushes between two tones that have the same loudness, pitch, and duration.

Front 15

Attack

Back 15

build up at the beginning of the tone

Front 16

decay

Back 16

decrease in sound at the end of a tone.

Front 17

the audibility curve

Back 17

Humans are most sensitive to frequencies between 2000 - 4000 Hz which is the frequency range for most speech sounds. Loudness depends on both frequency and sound pressure.

Front 18

The ear

Back 18

The auditory canal has a resonant frequency from 1000 - 5000 Hz

Front 19

The ossicles

Back 19

The middle ear bones are needed to transfer sound waves from air to liquid. The ossicles work to amplify the sound by increasing the pressure by a factor of 20. Middle ear muscles are attached to the ossicles, the muscles contract at high intensities to prevent damage.

Front 20

The cochlea

Back 20

Filled with fluid. Hair cells - the sensory receptors in the ear. Basilar membrane - the membrane which contains the hair cells. Tectorial membrane - a membrane above the basilar, the 'shelf' for the cilia.

Front 21

Hair cells

Back 21

Cilia - some are attached to the tectorial membrane. Tip links - join adjacent cilia together. Force causes tip links to open cilia, allows Ca+2 and K+ to enter.

Front 22

Inner hair cells

Back 22

Are not attached to the tectorial membrane. Moved by the force of the fluid within the cochlea. Are responsible for transmitting the auditory signal.

Front 23

Outer hair cells

Back 23

Are attached to the tectorial membrane. Movement in tectorial membrane causes depolarization. Alter the mechanical characteristics of the basilar membrane. Act as a cochlear amplifier. thresholds for auditory neurons are drastically altered in the absence of outer hair cells.

Front 24

Vestibular balance system

Back 24

Important for balance and for coding rotation and tilt of the head. Also important for adjusting the eyes in response to head movement.

Front 25

Semicircular canals

Back 25

each responds to head rotations and angular acceleration in a single plane. contains hair cells that bend when movement in one plane is detected. Rotation causes endolymph to flow and cupula to move.

Front 26

Otolith organs

Back 26

Head orientation and head tilt.

Front 27

Utricle and saccule

Back 27

Responds to tilting of the head. Otoconia (otoliths) shift their weight when head is tilted, causes membrane to move and cilia to bend, K+ enters and action potentials are sent to the vestibular nerves.

Front 28

The vestibular pathway

Back 28

Information from the vestibular organs are carried to the vestibular nuclei in the medulla via cranial nerve 8 (vestibulo-cochlear nerve). Vestibular nuclei send information to areas in the spinal cord and cerebellum to control balance. Also sends information to cranial nerves that control eye movements.

Front 29

Frequency coding in the cochlea

Back 29

George von Bekesy (1899 - 1972). Won a nobel prize in 1961 for his work on the physiology of hearing. Place coding theory.

Front 30

Place coding theory

Back 30

The frequency of a sound is indicated by the place along the cochlea with the highest rate of firing.

Front 31

Place coding in the cochlea

Back 31

Vibrating motion of the basilar membrane is similar to a wave. Base is thick and narrow, apex is thin and wide. The base is 100 times stiffer than the apex. The base of the basilar membrane codes high frequency sounds, the apex (end) codes lower frequency sounds.

Front 32

Envelope of the travelling wave

Back 32

Is the maximum displacement that the wave causes at each point along the basilar membrane. The point of maximum displacement will cause the hair cells on the portion of the membrane to have the highest firing rates.

Front 33

Envelope as a function of frequency

Back 33

Bekesy (1960) made two important observations. 1. The envelope has a peak amplitude at one point on the basilar membrane. Hair cells at this position will have the highest firing rates. 2. The position of the peak on the membrane is a function of the frequency of the sound. Observations were made on postmortem cochleas.

Front 34

Neural frequency tuning curves

Back 34

Nerve fibers along different parts of the basilar membrane also respond preferentially to specific frequencies of sound.

Front 35

Auditory masking

Back 35

If you are trying to hear a sound at a particular frequency, another loud sound at a similar frequency can cause interference. The masking effect is largest when it is the same frequency as the sound you are trying to hear, but the effect also spreads.

Front 36

How are two similar frequencies able to be distinguished from one another on the basis of place coding?

Back 36

Outer hair cells act as a cochlear amplifier by elongating and contradicting to alter the mechanical characteristics of the basilar membrane.

Front 37

Place vs. Rate coding.

Back 37

Signals in the CNS are transmitted by both the presence and rate of neural firing. Phase locking

Front 38

Phase locking

Back 38

Inner hair cells fire at the peak of the pressure change and stop firing at the trough in synchrony with the frequency of the stimulus. Place coding and phase locking are used for frequencies up to 4000 Hz. Place coding is used for frequencies above 4000 Hz. Different frequencies cause different temporal patterns of firing.

Front 39

Hearing loss and hair cell damage

Back 39

We are born with all of the hair cells we will ever have. Over time hair cells die and lead to hearing loss. Hair cell loss can occur from normal aging (presbycusis). 40-50% of people over the age of 75 are affected. Hearing loss tends to be worse for higher frequencies. Tends to be worse in males.

Front 40

Drug induced hearing loss

Back 40

certain antibiotics are toxic to hair cells in the cochlea and vestibular system (ototoxicity). Typically associated with high frequency hearing loss. Aminoglycosides are a primary culprit.

Front 41

Noise induced hearing loss

Back 41

Loud noises in the environment can also cause hearing loss. Loud work environments, noise pollution in crowded urban environments. playing in a band. Regulations have mandated that workers should not be exposed to sound levels in excess of 85dB for an 8 hour shift.

Front 42

Leisure noise

Back 42

Listening to MP3 players at a high volume can lead to hearing loss. Attending loud events can also lead to hearing damage.

Front 43

The central auditory pathway

Back 43

Auditory information crosses at the superior olives. each auditory cortex receives binaural inputs. Unilateral deafness can only occur following damage to the cochlea or auditory nerve.

Front 44

Primary auditory cortex

Back 44

A1 = primary auditory cortex. Activated by pure tones. Hierarchical organization. Signals travel from A1 to the belt and parabelt regions. Belt and parabelt regions are higher level auditory processing regions. Respond to more complex sounds.

Front 45

Dissociation in neurological patients : JG

Back 45

Patient JG. Damage to the temporal cortex resulted in poor recognition.

Front 46

Dissociation in neurological patients: ES

Back 46

Patient ES. damage to fronto-parietal cortex, was impaired at localization, but intact recognition.

Front 47

Neural correlates of pitch perception

Back 47

Studies a patient with bilateral damage to the auditory cortex. Duration discrimination and line orientation judgements were normal. The patients ability to judge the direction of a frequency change and differences in pitch between two tones was impaired.

Front 48

Pitch neurons

Back 48

Recorded from neurons that respond similarly to pure and complex tones with the same fundamental frequency. Recorded responses frmo the same neurons when the fundamental was removed and only a portion of the harmonics were available. Neurons did not respond when only a single harmonic was presented.

Front 49

Plasticity in auditory cortex

Back 49

Neurons in auditory cortex are tuned based on input and experience. Monkeys were trained to discriminate tones near 2,500 Hz. Following training more of A1 was dedicated to processing tones near 2,500 Hz.

Front 50

Pitch perception: Individual differences.

Back 50

Some people detect changes in pitch using changes in the fundamental frequency, whereas others detect changes in the harmonics (spectral pitch). This effect seems to be related to the organization of the auditory cortex (left: fundamental pitch, right: spectral pitch). Patients with right temporal lobe damage are not able to detect changes in pitch when the fundamental frequency is filtered out.

Front 51

Cochlear implants

Back 51

Cochlear implants can help reverse hearing loss. Speech perception improves most following cochlear implants. Results are better for people who could hear previously.

Front 52

Back 52

1. Microphone 2. sound processor 3. transmitter 4. receiver implanted on mastoid bone 5. electrical signals from the receiver are sent to nerve fibres at different places along the cochlea.