Interaural attenuation

the amount of reduction in intensity that occurs as a signal crosses over the head (is transmitted by bone conduction) from one ear to the other ear; the point at which the better ear begins to respond:

a.   about 40 - 50dB for air conduction (depending on phones)

b.  at 0dB for bone conduction

c.   also the loss of intensity of a sound introduced to one ear and heard by the other.

Masking

a way to remove the nontest ear from the test procedure when cross-hearing is suspected.  The difference for air conduction is based on the BC of the better ear to the AC of the worse ear.

Noises used for pure tones are:

Rule for AC masking:

If the thresholds from the test ear exceed the bone conduction threshold of the nontest ear by the amount of minimum interaural attenuation, then masking MUST be used.

Rule for BC masking:

Always use masking in the non-test ear during bone conduction testing if there is any difference at all between ears.

Overmasking 

the noise presented is so loud that it crosses back over to the other (test) ear and masks the test ear.  

Central masking  

a small shift in threshold with the introduction of masking and the shift continues to increase with increased noise.

Effective Masking 

the level where increased masking noise will no longer result in a shift of threshold

Masking dilemma  

occurs when the difference between the BC threshold in the test ear and the AC threshold in the non-test ear approaches the amount of interaural attenuation.  Most often seen in bilateral conductive hearing loss.

So What does the audiogram tell us?

1.    gives the degree of hearing loss (mild, moderate, severe, profound)

2.    describes shape of loss (flat, sloping, low frequency, high frequency, precipitous, cookie-bite, reverse slope or rising)

3.    measures interaural symmetry (the difference between ears)

4.    differentiates hearing loss (conductive, sensori-neural, mixed)

0 – 25dB         normal hearing

25 – 40dB              mild hearing loss

40 – 60dB              moderate hearing loss

60 – 90dB              severe hearing loss

90dB+            profound hearing loss

Speech tests

The goal is to quantify a patient’s ability to understand everyday communication at suprathreshold levels.

Why?

- Gives us a threshold to crosscheck against our pure tone

   average

- Measurement of threshold for speech

- Assists in differential diagnosis

- Assesses central auditory processing

- Gives estimates of communicative function, aided as well as

   unaided

Speech reception or recognition threshold (SRT) 

The lowest level at which speech can be detected or recognized.  The minimum level where spondee words that they have been familiarized with can be correctly detected 50% of the time.  AKA Speech detection threshold or speech recognition threshold

the point where they are able to repeat 50% (2 out of 4) of the spondee words (compound words of equal emphasis) correctly after they have been familiarized with the words.  ASHA recently recommended this be changed to speech recognition threshold.

Speech recognition or discrimination 

the percentage correct of 50 or 25 monosyllabic word lists presented at some level above the SRT, usually 30 – 40SL (SL meaning above the minimum hearing threshold of the spondee threshold).

The ability to perceive and recognize speech

Lets us know the prognosis with amplification

Speech detection threshold (SDT) = Speech awareness threshold (SAT) 

lowest level at which a speech signal is audible or detected 50% of the time; this is used when the individual cannot speak, has a profound hearing loss, or is a child who cannot communicate, this may be used in place of SRT if they cannot repeat spondees.

The SDT requires that the client merely detect the present of speech, the SRT requires that the client recognize the words.  So the STD may often be at a somewhat better threshold than the SRT as it often reflects the best threshold.

for a child who cannot repeat or an individual who cannot discriminate words, the point at which they are able to detect the speech and respond by raising their hand or pushing a button.

MLV – monitored live voice: 

Taped 

Ways to deliver speech stimuli?

a.    through the headphones

b.   via bone conductor

c.    via speakers for sound field testing

Sound field testing (SF)

when the stimuli, whether speech or pure tone or noise, are delivered through speakers in the room.  This maybe used to check the efficacy of hearing aids or to test children who won’t tolerate headphones.  May also be used for localization for infants and toddlers.

With children, pictures of the spondees may be used and the child will point for the response.

Times when the SRT/SDT will not agree with the PTA

a.   when there is a precipitous drop of hearing in the high frequencies (e.g., hearing is normal at 500Hz and then drops to 70 at 1000Hz, etc) – SRT better than PTA, closer to the best 2 frequency average.

b.  When there is a central auditory problem, the elderly may have a problem in recognizing words and thus cannot get 50% correct – the SRT is poorer than PTA

c.   In pseudohypacusis – anything goes here:  NOTE: often, in the case of spondees, they will give half the word correct and not the other half.

d.  SAT or SDT usually matches the single best frequency.

MCL – most comfortable listening level or most comfortable loudness level: 

just talk to them and tell them to tell you when your voice is comfortable or “just right”.  I like to tell them to tell me when my voice is at a level where they would like to listen to television for 2 hours.

UCL or ULL– uncomfortable listening level or uncomfortable loudness level akaTD (threshold of discomfort) and LDL (loudness discomfort level):                                                                                                                 

Dynamic Range 

Tests to measure speech discrimination

a.   Phonetically balanced words (PB): These are word lists and tested using 50 or 25 words.  There are a number of sets.

b. CNC (consonant-nucleus-consonant)

c. High frequency emphasis

d. Nonsense-syllable lists – CVCV

e.  Closed set response lists

Adaptation

Recruitment

an unusually rapid growth of loudness of an impaired ear.  Loudness grows more rapidly than normal at intensity levels just above threshold in an ear with a cochlear problem.  It may also be defined as a disproportionate increase in loudness as a function of intensity of the impaired ear.  This is symptomatic of the majority of hearing losses that are sensory.  There are other variations of recruitment – SENSORY (IN THE NERVE)

partial recruitment 

 hyperrecruitment  

The impaired ear not only catcher up to the better ear

but appears to be louder in the impaired ear than the normal ear with the same high intensity.

ABLB – Alternate Binaural Loudness Balance Test

This is a standard measurement of recruitment.  We perform this test at 2 frequencies, a low frequency (usually 500Hz) and a high frequency (usually 2kHz).  The bad ear is compared to the good ear as intensity is increased until they are equal.  Usually, the intensity required for equal loudness is less for the impaired ear than the normal ear.  

AMLB (Alternate Monaural Loudness Balance Test)               

  SBLB (Simultaneous Binaural Loudness Balance Test)           

This test presents the tone simultaneously to both ears.  It was found that this was not a good test for recruitment. When recruitment is found, it is suggestive of a cochlear disorder.

SISI – Short Increment Sensitivity Index

This was another popular test of recruitment.

This procedure tests the patient’s ability to detect the presence of a 1dB increment superimposed on a tone that is presented at 20SL.  It is a suprathreshold test so beware of crossover.  Again, this is presented at a low freq. and a high freq.  The high frequency scores are greater, suggestive of a cochlear disorder. 

Example:  Threshold of the poorer ear is 20dB at 500 and 40dB at 2kHz.  A tone is presented at 500Hz with an intensity of 40dB and every so often, it is increased by 1dB as a blip.  They are to raise their finger every time they hear it.  We score for 20 blips.  The same is done at 2kHz with an intensity of 60dB.  They will hear the blip much more often at 2kHz than at 500Hz.  A score over 50% indicative of recruitment and so a cochlear disorder.

TDT or Tone Decay Test

This is a test of adaptation.

This test represents a sustained tone to the ear.  Even normal ears will change threshold at soft levels to the sustained tone.  As with the other tests, this is performed with a low frequency (500Hz) tone and a high frequency (2kHz) tone. A major change may be indicative of a CNS disorder.  This is a test of adaptation.  In adaptation, we know that a normal ear will adapt to ongoing sound, especially at near threshold levels, and eventually the sound is inaudible but higher intensity sounds will remain audible.  We also know that with a retrocochlear disorder, audibility will be lost much faster, even at loud levels, due to excessive auditory adaptation. NEURAL OR CENRAL DISORDER

Generalizations:

Most decay is noted for high frequencies.  Thus, usually a low frequency and high frequency is tested.

Decay was very significant when there is 30dB or more in one minute.  Only moderate with 20 – 25dB of decay.

Present the tone at 20dBSL.  As soon as they hear it the finger goes up and down when it disappears.  Record how long they hear it at 20dL and increase level by 5dB without interrupting the tone.  Continue in this way until they hear it for a full minute or until 30dB above the starting level has been reached.

STAT – suprathreshold adaptation test 

Bekesy Audiometry

This was another way to measure adaptation.

This was once a popular test and had its own type of audiometer.  It also measures auditory adaptation.  It is a patient controlled test.  They press a button and let go, depending on whether or not they hear the tone.  A comparison is made between continuous and pulsed tones.  

1.  Type I:  normal and conductive hearing loss.  The tracings overlap almost completely.

2.  Type II:  above 1kHz, the tracing for continuous tone drops below the interrupted tone and this is indicative of cochlear pathology.

3.  Type III:  the continuous trace shows a pronounced separation for all frequencies and is associated with problems beyond the cochlea (neural or central).  This is the most dramatic tracing.  That is because the continuous tone shows adaptation and so it is fading as would be seen with a tone decay test.

4.  Type IV:  Similar to type II but the breakaway is at 500Hz and the separation between the 2 tracings is 20+dB.  This may be cochlear or neural.

5.  Type V:  this is most often seen with nonorganic disorders.  The continuous tracing is better than the pulsed tracing (they tend to run parallel).

Masking Level Differences – MLDs

This is another test still used.  It measures lower brainstem function.  It measures binaural release from masking due to interaural phase relationships.  First, an identical, in-phase, low frequency tone is present to both ears.  Then noise is added to each ear until the tone is masked.  If the phase of the tone to one ear is reversed, the tone should become audible again.  We look at the difference in threshold between the in-phase and out-of-phase conditions.  MLDs should be greater than 7dB.

Electrophysiological tests

a.   serve as an indication of peripheral sensitivity

b.  serve as an indicator for site-of-lesion within the system

c.   is objective and requires no subjective response from the patient.

IMMITTANCE AUDIOMETRY

A test battery that has become as common as pure tones and speech is acoustic immittance.  This is a term that can be used to refer to acoustic impedance or acoustic admittance.  Either terminology is correct, but acoustic impedance is the inverse of acoustic immittance.  It is now accepted that the BEST  measure of middle ear disorder is this battery of tests. 

It has 4 main functions:

1.  it is very sensitive to middle ear disorder

2.  it can separate out cochlear from retrocochlear involvement

3.  it may help estimate hearing sensitivity

4.  it may help confirm your audiometric results 

describe eardrum membrane impedance, compliance, or admittance.  It is also known as middle-ear measurements.  All the measures of ME function are indirect as they are determined by measurements made in the plane of the eardrum membrane.  It assesses how energy flows through the outer and middle ears to the cochlea.  It indirectly assess the appropriateness of the flow of energy throughout the system.

Immittance  

In general, it is a measure of how readily a system can be set into vibration by a force.

So immittance is a term encompassing both the concepts of impedance and admittance.

Admittance

the ease with which energy will flow through the vibrating system; the total energy flow through a system

Compliance 

static acoustic compliance or immitance: 

tympanometry

  Acoustic reflexes 

acoustic reflex decay 

Resistance 

 determined by the ligaments supporting the ossicles

Resistance, mass, and stiffness make up the impedance of the system: Mass affects the high frequencies. Stiffness affects the low frequencies.

Mass  

Stiffness  

load of fluid pressure from the inner ear on the stapes

By combining the mass and stiffness, we can obtain the measurements needed for acoustic immittance.

C2 (eardrum at maximum compliance)

-   C1 (eardrum stiffened with +200 pressure

    C3 (total compliance of the TM)

.3 is the minimum compliance for normal ears

1.6 to 1.75 is the maximum compliance for normal ears

If the system is below the norm, there is less than normal mobility and the system is stiff.  Some examples that could cause this problem are otitis media or otosclerosis where the stapes is fixed.

hypercompliant 

If the system exceeds the norm, then there is greater than normal mobility.  Some examples that could cause this problem are a separation of the ossicles (disarticulation) or a very thin eardrum characterized by abnormal elasticity (monomeric membrane).  This may occur due to a healed perforation.

When testing, one of the measurements obtained is the ear canal volume is ECV.  If the overall volume is greater than 5.0, or if one ear’s volume is twice that of the other ear, then the ear probably has a perforation or a patent ventilation tube.

Tympanogram

this is a chart that shows your curve of compliance.

To measure this, we start at +200daPa (aka mmH₂O), measure the compliance, and gradually change the pressure until –200daPa.  This highest peak shows the point of greatest compliance.  A low-frequency probe tone of 220 or 226Hz is used to bounce off the TM and measure the distance back to determine compliance at each point of the tympanogram.

  type A:  

 type A_s 

type A_D  

type B  

type C 

Gradient 

(slope):  the ratio of the height and width of the tymp.

                      Width

                      Height

ECV 

COMP

MEP

• Tympanometry

• Absent reflex 

• Abnormal middle ear system
• Severe sensitivity loss
• VIII nerve lesion
• Ipsilateral VII nerve lesion
• Some otherwise "normal" ears

• Elevated threshold 

ART (Acoustic reflex threshold) 

Ipsilateral reflex pathway

 a sound in that ear evokes a response from the same ear.

Sound Þ OE Þ ME Þ cochlea (IE) Þ along 8^th nerve and to the brainstem.  In the brainstem, it is received by CN Þ SOC Þ facial nerve (VII) ipsilaterally, and descends to innervate the stapedius muscle.

Contralateral reflex pathway

the sound goes in the ear opposite the probe and the reflex is picked up by the ear with the probe.

Sound Þ OE Þ ME Þ cochlea (IE) Þ along 8^th nerve and to the brainstem.  In the brainstem, it is received by CN Þ SOC and crosses over to the opposite SOC Þ facial nerve (VII) contralaterally, and descends to innervate the stapedius muscle, thus evoking a contralateral reflex.

Sensitivity Prediction by the acoustic Reflex (SPAR):

This is a popular test for predicting hearing sensitivity.  It is based on the difference between acoustic reflex thresholds to the pure

tones and the reflex threshold to broad band noise (BBN).

AEP – Auditory Evoked Potentials

There are neuroelectric events; they are measured from the scalp via electrodes.  The electroencephalograph (EEG) is used and looks for a change in activity.  All waves, except for the change associated with the introduction of the click stimulus, are then filtered out.  They are subdivided based on where and when they occur:

ECoG or Electrocochleography

1.  ABR (Auditory Brainstem Response) 

aka BAER (brainstem Auditory “Evoked Response aka BERA (brainstem evoked Response Audiometry):  This occurs in the first 10 – 15 ms and the response comes from the 8^th nerve and brainstem to the midbrain.  It is the most commonly used test of the the evoked potentials.  There are 5 waves we measure.  We can approximate hearing sensitivity for high frequency click stimuli from this.  It is also a good test for neonates, and until recently, the gold standard for newborn screening in the screening version called is the AABR (Automated Auditory Brainstem Response).  

  AMLR (Auditory Middle Latency Response)

 LLR (late latency response) or (ALR - Auditory Late Response) 

STACKED ABR 

AUDITORY STEADY STATE RESPONSE (ASSR): 

Otoacoustic Emissions Audiometry

This test is a preneural response giving information up to but not including the auditory nerve.  They are an active byproduct of the outer hair cell system.  If there is a compromise in the outer or middle ear, the response will be affected and most likely be absent.  Remember, this is not a direct measure of hearing. 

1.  OAE – Otoacoustic Emissions 

TOAE (transient otoacoustic emissions)  

aka as TEOAE (transient evoked otoacoustic emissions) – These are produced by brief acoustic stimuli such as tone pips or clicks.  The response is usually all or none.  Anyone with normal hearing and normal ear structures should have emissions.  A middle ear problem or hearing loss greater than 35 - 40dB will eliminate the response. 

Both the TOAE and DPOAE give a measure of outer hair cell function.  That is why they are sensitive to cochlear vs retrocochlear pathology for hearing loss below 65dBHL.

DPOAE (distortion product otoacoustic emissions)

 SOAE (spontaneous otoacoustic emissions)