Hearing…It’s More Than You Think!

Karen J. Kushla, ScD, CCC-A/FAAAMorris County Chapter HLAA

Presentation January 9, 2016

Today’s Outline

• How do we hear?

– Anatomy and physiology of outer, middle, and inner ears

• Role of central auditory nervous system in hearing

• Sound and theories of hearing

• What can go wrong….

How Do We Hear?

We hear a sound…..how does it get from its location through our ears to our brain?

Let’s look at how sound travels through our auditory system

How We Hear…..

Outer ear → Acoustic energy

Middle ear → Mechanical energy

Inner ear → Neural energy

Three parts of the human ear

How We Hear….. (cont.)

Outer Ear: Acoustic Energy

Middle Ear: Mechanical Energy

Inner Ear:Neural Energy

How We Hear….. (cont.)

How We Hear….. (cont.)

Otoscopic evaluation

How We Hear….. (cont.)

How We Hear….. (cont.)

How We Hear….. (cont.)

• Human speech is produced between 100 Hz and about 6000 Hz…..this range of frequencies in human speech are most important for communication

– Not surprisingly, this range of frequencies is where we hear best, too!

– The outer and middle ears help to amplify this range of frequencies

How We Hear….. (cont.)

bony labyrinth

How We Hear….. (cont.)

membranous labyrinthAnalogy:

bicycle tube and tire filled with air

How We Hear….. (cont.)

How We Hear….. (cont.)

How We Hear….. (cont.)

7

How We Hear….. (cont.)

How We Hear….. (cont.)

• Okay….we’ve traveled through the outer, middle, and inner ears

• In order for sounds to be UNDERSTOOD, however, we must get these sounds from the ear to the brain for interpretation

– We call this the central auditory nervous system (CANS for short)

– The CANS actually begins at the cochlea, where the nerve fibers exit and begin their ascent to the brain

Role of the Central Auditory Nervous System in Hearing

Role of CANS in Hearing (cont.)

Primary auditory pathways1) Auditory nerve2) Cochlear nucleus3) Superior olivary complex4) Inferior colliculus5) Medial geniculate body6) Primary auditory cortex

Role of CANS in Hearing (cont.)

• First stop after the cochlea…..the cochlear nucleus

Role of CANS in Hearing (cont.)

• Next level, also in the brainstem……

– Superior olivary complex (in medulla)• Approximately two-thirds of the

nerve fibers leaving the cochlear nucleus cross over to the contralateral (opposite) side and begin their ascent to the brain

• Remaining one-third of nerve fibers ascend on the same side (ipsilaterally)

• Sound intensity and timing differences are encoded here

Role of CANS in Hearing (cont.)

Role of CANS in Hearing (cont.)

• The next areas up the CANS…….– Nucleus of lateral lemniscus (in pons)

• Temporal (timing) resolution occurs here, and is also sensitive to timing and amplitude changes of sound

– Inferior colliculus (in midbrain)

• Second crossover station

• Important in integration and routing of multi-modal sensory information (e.g., blinking at high-intensity sound)

– Medial geniculate body (in thalamus)

• Relays frequency, intensity, and binaural information via multiple small fibers (called auditory radiations) which run to auditory cortex in the temporal lobe of the brain

Role of CANS in Hearing (cont.)

the central nervous system consists of the brain and spinal cord

Auditory Cortex

Role of CANS in Hearing (cont.)

• Auditory cortex

– Primary auditory cortex• Lies in the posterior half

of the superior gyrus of the temporal lobe

• Divides into the lateral sulcus and Heschl’s gyrus

– Secondary auditory cortex• Around Wernicke’s area

on the posterior portion of the temporal lobe

Sound and Theories of Hearing

• How are the physical properties of sound processed by the auditory system?

– Through neural encoding of

• Frequency

• Intensity

• Phase

• Duration

Sound and Theories of Hearing (cont.)

• Frequency coding: two prevailing theories– Place theory: tonotopic

organization from the basilar membrane to neural fibers• Each auditory neuron has a

characteristic frequency to which it responds best

– Temporal theory: periodicity of the nerve discharge can be used to determine frequency of the stimulus (i.e., phase-locking)• For low-frequency tones (< 3000 Hz),

the auditory nerve fires at a particular phase of the stimulating tone

• For tones > 3000 Hz, phase-locking is weak

Sound and Theories of Hearing (cont.)

• Intensity coding

– At low intensity levels: increased intensity = increased firing rate (true for single nerve fibers)

– At high intensity levels: information is carried by several nerve fibers

Sound and Theories of Hearing (cont.)

• Localization: two different cues used– Interaural timing difference (ITD)

– Interaural intensity (level) difference (IID)

• Our neural system is exquisitely tuned in order to take both cues into account

Signal arriveshere first

Interaural intensity difference

Softer Louder

Interaural timing difference

Problems arise when there is hearing loss in one ear

only….the other ear may not be able to use these intensity

and timing cues effectively

What Can Go Wrong…..

• If the problem is found in the outer and/or middle ear, conductive hearing loss occurs– A reduction of sound intensity (but not of clarity)

occurs

• If a problem is found in the inner ear, sensorineural hearing loss occurs– A reduction in both sound intensity and clarity

occurs

What Can Go Wrong….. (cont.)

• With either type of hearing impairment, we may not be able to understand speech….even when we use the appropriate amplification

• Aural rehabilitation a good way to learn strategies to repair breakdowns in communication

What Can Go Wrong….. (cont.)

• AR teaches listeners with hearing loss to use different cues to further communication

– Examples of cues used

• Semantic cues (meaning)

• Syntactic cues (grammar)

• Phonemic/phonetic cues (speech sounds)

• Situational/environmental cues

• Stress, intonation cues (provide emphasis)

– We use these cues all the time to understand what is said, and to repair what we said in error

What Can Go Wrong…… (cont.)

• Many different types of AR

– Formal—working with an audiologist and/or speech–language pathologist• Top-down strategies (topic already known)

• Bottom-up strategies (figure out speech sounds=> syllables=>words=>phrases=>sentences=>paragraphs)

• Using computer-based programs (like LACE)

• Using programs found on all three cochlear implant websites

• Joining a community-based program (e.g., Westfield, NJ)

– Informal—working on your own or with a communication partner

What Can Go Wrong….. (cont.)

• Components of speechreading

– Using your residual hearing (with/without amplification)

– Watching the lips make speech sounds (aka lipreading)

– Gestures and body language

– Facial expressions

– Using situational cues

– Linguistic factors

What Can Go Wrong….. (cont.)

• Strategies to use to make communication go right

– If you understood none of the speech• Ask speaker to repeat

• Ask speaker to rephrase

• Ask speaker for key word

– If you understood some of the speech• Ask speaker to repeat part

• Ask speaker to rephrase part

• Ask for a specific and/or key word

• Ask a specific question

• Ask a general question

• Ask speaker to spell out troublesome word

What Can Go Wrong….. (cont.)

• Using anticipatory strategies in communication

– Be assertive….if you didn’t understand something, ask for repetition/rephrasing!

– Predict and remedy speaker-based and/or environmental problems

– Brainstorm and practice unfamiliar language

– Know your conversational topic (but give others a chance to talk, too)