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52 Cards in this Set

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Sound as a stimulus

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.

Components of auditory signal

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

Frequency (pitch)

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

Amplitude (loudness)

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

Complexity (timbre)

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)

Amplitude and sound pressure

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.

Pure tone

When pressure changes occur in a sine wave pattern.

Fundamental frequency

the repetition rate of the complex tone

additive synthesis

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

periodicity pitch

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

Pitch

the perceptual quality associated with frequency

tone height

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

tone chroma

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

Timbre

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

Attack

build up at the beginning of the tone

decay

decrease in sound at the end of a tone.

the audibility curve

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.

The ear

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

The ossicles

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.

The cochlea

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.

Hair cells

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.

Inner hair cells

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

Outer hair cells

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.

Vestibular balance system

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

Semicircular canals

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.

Otolith organs

Head orientation and head tilt.

Utricle and saccule

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.

The vestibular pathway

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.

Frequency coding in the cochlea

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

Place coding theory

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

Place coding in the cochlea

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.

Envelope of the travelling wave

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.

Envelope as a function of frequency

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.

Neural frequency tuning curves

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

Auditory masking

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.

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

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

Place vs. Rate coding.

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

Phase locking

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.

Hearing loss and hair cell damage

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.

Drug induced hearing loss

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.

Noise induced hearing loss

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.

Leisure noise

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

The central auditory pathway

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.

Primary auditory cortex

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.

Dissociation in neurological patients : JG

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

Dissociation in neurological patients: ES

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

Neural correlates of pitch perception

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.

Pitch neurons

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.

Plasticity in auditory cortex

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.

Pitch perception: Individual differences.

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.

Cochlear implants

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



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.