IB Assessment Statements Option I-1, The Ear and Hearing: I.1.1.Describe the basic structure of the human ear. I.1.2.State and explain how sound pressure variations in the air are changed into larger pressure variations in the cochlear fluid. I.1.3.State the range of audible frequencies experienced by a person with normal hearing. I.1.4.State and explain that a change in observed loudness is the response of the ear to a change in intensity.

IB Assessment Statements Option I-1, The Ear and Hearing: I.1.5.State and explain that there is a logarithmic response of the ear to intensity. I.1.6.Define intensity and intensity level (IL). I.1.7.State the approximate magnitude of the intensity level at which discomfort is experienced by a person with normal hearing.

IB Assessment Statements Option I-1, The Ear and Hearing: I.1.8.Solve problems involving intensity levels. I.1.9.Describe the effects on hearing of short- term and long-term exposure to noise. I.1.10.Analyze and give a simple interpretation of graphs where IL is plotted against the logarithm of frequency for normal and for defective hearing.

Objectives:  Lesson Objectives. By the end of this class you should be able to:  Describe the basic components of the human ear  Define sound intensity and the sound intensity scale based on the decibel  Perform calculations with intensity and the decibel scale

Objectives:  Understand how the ear functions  Describe how the ear separates sound according to frequency in the cochlea  State the meaning of the terms threshold of hearing and audiogram

Introductory Video

Macroscopic View of the Ear

 Ear is sensitive to sounds ranging from 20 Hz to 20,000 Hz  At 1000 Hz, the ear can pick up sound vibrations that displace the eardrum by 1/10 th the diameter of a hydrogen atom

 Outer ear  Middle ear  Inner ear

 Eustachian tube serves to equalize pressure  Airplanes  Scuba Diving

 Semicircular canals do not contribute to hearing  Provide us with a sense of balance

The Ear and Balance

Schematic Diagram of the Ear

Figure I1.2, Schematic Diagram of the Ear  Ossicles are three small bones: malleus, incus and stapes – smallest in human body  Purpose is to amplify amplitude of sound waves by a factor of 1.5

Figure I1.2, Schematic Diagram of the Ear  Area difference between eardrum and oval window increases amplification by 13  Total amplification = 20x  Acoustic reflex – muscles limit ossicle movement  Does not protect from instantaneous sound

Figure I1.2, Schematic Diagram of the Ear  Cochlea is where hearing takes place  Vestibular, Helicotrema and Tympanic canals (2cm long)  Round window is pressure release point

Figure I1.2, Schematic Diagram of the Ear  Scala media or cochlean duct runs between canals  Covered by the basilar membrane  Contains nerve endings which convert sound waves into electrical signals sent to the brain

Figure I1.2, Schematic Diagram of the Ear  Basilar membrane  Organ of Corti responsible for converting vibrations into electrical signals  Different parts are sensitive to different frequency ranges

Mismatch of Impedances  Sound travels differently in different media  In hearing, sound goes from air to the fluid in the inner ear  The term impedance is used to describe the difference in sound in different media  Acoustic Impedance:  ρ is density  c is speed of sound

Mismatch of Impedances  When sound transitions to a new media, differences in impedances will cause some of the sound to be reflected  More sound is transmitted when impedances are matched  Impedance before oval window is 450 kg/m 2 s  Impedance after oval window is 1.5 x 10 6 kg/m 2 s

Mismatch of Impedances  Because of the difference in the impedances, the sound must be amplified by the ossicles and by the differences in area between the eardrum and the oval window

Complex Sounds

 Any periodic function can be written as a sum of harmonic functions  Complex sounds can be decomposed into component frequencies of the harmonic function  This is what is done in the cochlea  The sound is then reconstructed in the brain

Intensity of Sound

Sensation of Hearing  Hearing does not increase linearly with intensity  It is a logarithmic function  Increase in hearing is proportional to the fractional increase in intensity (Weber- Fechner law)  This give us the decibel scale

Sensation of Hearing  An increase of 10 dB equates to an increase in intensity by a factor of 10  I 0 refers to the threshold of hearing, 1 x W/m 2

Frequency Response and Loudness  The normal hearing range is 20 Hz to 20,000 Hz  The threshold of hearing reduces with age

Frequency Response and Loudness  The threshold of hearing of 1 x W/m 2 is based on 1000 Hz  Sounds of greater or lesser intensity may be heard depending on frequency

Threshold of Hearing Curve

Threshold of Hearing

 Hearing sensitivity can best be understood based on resonance in the ear canal  Think of it as a closed-end tube where the fundamental wavelength is 4L

Threshold of Hearing  The length of the ear canal is 2.8 cm

Pitch  Subjective  How high or low a sound is  Primarily determined by frequency, but also by intensity

Frequency Separation in Cochlea  The basilar membrane decreases in stiffness along its length (35mm)  Velocity of sound is high at the beginning of the canal and drops along the length  Response by the organ of Corti is greatest to sounds that are resonant

Frequency Separation in Cochlea

Hearing Defects  Sensory Nerve Deafness  Damage to hair cells and neural pathways  Tumors of the acoustic nerve or meningitis  Conduction Deafness  Damage to the middle ear  Blockage (full or partial) of the auditory canal  Bone disease to the ossicles  Hearing tested with an audiogram

Hearing Loss  Aging  Gently curved with smaller loss in decibels  Damage  More substantial loss, especially in higher frequencies

Required Amplification

Audiogram  Steep curve  Large high frequency loss indicates damage due to over- exposure  Aging would show shallow curve, less overall loss

Audiogram  Circles for air  Triangles for bone  Gap between the two indicates a conduction problem in middle or outer ear

Audiogram  When the bone and air graphs nearly coincide, the problem is most likely a cochlear or nerve problem in the inner ear

Hearing Aids  Used for conductive hearing loss where inner ear is still functioning  Amplifies sound within a limited range  Mainly the range of human speech  Doesn’t work well for much else

Cochlear Implant  For sensory loss in the inner ear  Consists of:  Microphone  Signal processor to convert sound to electrical signals  Electrodes surgically implanted in the cochlea  Mimics the function of the cochlea

Objectives:  Lesson Objectives. By the end of this class you should be able to:  Describe the basic components of the human ear  Define sound intensity and the sound intensity scale based on the decibel  Perform calculations with intensity and the decibel scale

Objectives:  Understand how the ear functions  Describe how the ear separates sound according to frequency in the cochlea  State the meaning of the terms threshold of hearing and audiogram

IB Assessment Statements Option I-1, The Ear and Hearing: I.1.1.Describe the basic structure of the human ear. I.1.2.State and explain how sound pressure variations in the air are changed into larger pressure variations in the cochlear fluid. I.1.3.State the range of audible frequencies experienced by a person with normal hearing. I.1.4.State and explain that a change in observed loudness is the response of the ear to a change in intensity.

IB Assessment Statements Option I-1, The Ear and Hearing: I.1.5.State and explain that there is a logarithmic response of the ear to intensity. I.1.6.Define intensity and intensity level (IL). I.1.7.State the approximate magnitude of the intensity level at which discomfort is experienced by a person with normal hearing.

IB Assessment Statements Option I-1, The Ear and Hearing: I.1.8.Solve problems involving intensity levels. I.1.9.Describe the effects on hearing of short- term and long-term exposure to noise. I.1.10.Analyze and give a simple interpretation of graphs where IL is plotted against the logarithm of frequency for normal and for defective hearing.

#1-9 Homework