Instrumentation 2/22/00

Magnetic Resonance Imaging Magnetic field through tissue Pass radio waves through tissue –Protons absorb some energy & change direction –They then move back to the original position when the charge is shut off Release absorbed energy to create an image Tissues have different densities (absorb different amounts of protons)

MRI Purpose: Acquiring images inside body- no radiation Detailed information about anatomical structures Speech: –Precise measurements of the entire vocal tract without radiation effects –Well defined pharyngeal cavity- measurements –Central control and the actual speech events that result

Electromyography (EMG) Purpose: Record the action potential of muscles during contraction Investigation in pathology of muscles Speech: –Provide information about speech control mechanisms & speech gestures in natural units –Central nervous system control of muscles

Auditory System

Hearing: Mechanoreceptors Hearing = sensitivity to mechanical vibrations transmitted through air. Mechanoreceptors= mechanical sensitivity; monitor mechanical stimuli such as pressure, position & movement. –Hair cell= sensory receptor for audition & balance –Site of mechanoelectric transduction

Ear: Three Parts Outer Ear –Visible externally –Captures vibrations in the air & funnels them into the ear canal (External Auditory Meatus) Middle Ear –Starts at the ear drum (Tympanic Membrane) –Contains ossicles (Stapes, Incus, Malleus) Inner Ear –Sensory end organ of hearing (Cochlea) –Fluid filled

Outer ear Pinna Outer Ear Middle Ear Eustachian Tube External Auditory Meatus Inner Ear Auditory Nerve Ear Anatomy

Electrical Events Bending hair cells are responsible for the generation of neural impulses –Transmits signal to brain –Signals can be recorded Otoacoustic Emission –Faint sounds produced by the cochlea as it responds to acoustic stimuli –Emissions recorded in the human ear –Miniature probe placed in EAM

Otoacoustic Emission Two types of emission: –1. Spontaneous otoacoustic emission- weak tonal signals that occur naturally, without acoustic stimuli –2. Evoked otoacoustic emission- occur in almost everyone; elicited with low to moderate level test sounds Clinical application

Otoacoustic Emission Reflect the biomechanical activity of the outer hair cells –outer hair cells are susceptible to: 1) Disease, 2) Damage due to loud sounds, Provides a means to test hearing in infants & subjects who cannot complete behavioral tests of auditory function Otoacoustic emissions are absent in some disorders of the cochlea

Energy & Information Flow in the Auditory System Both energy & information have two paths of travel Acoustic stimulation in the environment = flow of energy from the outer ear to inner ear Reverse flow= otoacoustic emission –Allows the brainstem to influence actions in the inner ear

Inner Hair cells Acoustic Reflex Efferent System AuditoryCortex Middle ear Nerve Fibers Brain Stem Center Outer ear Inner Ear Flow of Information & Energy in the Auditory System

Auditory Function: Comparative Frequency range –Humans: 20-20,000 Hz Greatest sensitivity at 1000 Hz –Dogs: 20-60,000 Hz –Elephants: better low frequency range as low as 12 Hz Auditory frequencies most important to humans –100 Hz-5000Hz (Speech frequencies)

Life Course Considerations Auditory system development: –5 1/2 months after conception –Cochlea is the last structure to reach maturity –Auditory function in the fetus (Heper & Shahidullah, 1994): Fetuses: weeks gestation Pure tones (100, 250, 500, 1000, 5000) presented with speaker Fetal response: ultrasound of movement 19 weeks- Response to 500 Hz With maturation: response spread to low frequencies (27 weeks) than high (33-35 weeks)

Audition: Age Hearing high frequencies: Decline after the age of 20 years 30 Years: Hearing in men declines 2x as rapidly as women’s Hearing low frequencies: Declines in the 7th decade Older women have more sensitive hearing than older men

Risk factors: Hearing Loss Industrial noise Aging Combination of aging and noise exposure Diet Medications (ototoxic drugs) –Aspirin –Some antibiotics (Streptomyocin) –Alcohol Cardiovascular disease