Audiometry

We've now talked about 'objective' hearing tests

• Otoscopy, Tympanometry, Acoustic Reflex Testing, OAEs, and ABR Testing

• Let's bring the human element back

Audiometry characterizes how effectively people are able to hear sounds

• How well you can hear sounds at different frequencies and amplitudes

  • Pure tone audiometry

• How well you can hear speech at different amplitudes

  • Speech Audiometry

• Both test your ability to use your hearing

  • These are 'subjective' tests

Today's Plan

• Audiometric Testing Equipment

• Pure-tone Audiometry

• Speech Audiometry

• Reading an audiogram

Audiometric Testing Equipment

Sound Booth

Sound Booths are crucial

• Lowers the 'noise floor'

• The signals being presented will have no 'competition'

• You can only test sounds > RoomNoise - AttenuationOfHeadphones

• Don't trust the low end of a test done in a noisy booth!

Audiometer

Basic Audiometer Functions

• Adjust the amplitude of the tone

• Adjust the frequency of the tone

• Send the tone

Audiometers can be basic or complex

Complex Audiometer Functions

• Talk and listen to the patient inside the booth

• Masking noise

• Choice of transducers

• Choice of stimulus type

  • Speech vs. Puretone vs. Warble Tone vs. Pulse Tone

Software-based Audiometry

Transducers

• Audiologists refer to 'headphones' as transducers

• These turn output from the audiometry box into sound

• Different transducers for different goals

• Audiological transducers are very 'flat' by design

  • They produce all relevant frequencies at the same levels

Supraural Transducers

In-Ear Transducers

High-Frequency Headphones

Bone Conduction

Sound Field

• Generally not advised!

Calibration is key!

• 60 dB in software is meaningless when transducers and outputs vary

• Professional calibration guarantees that the 60dB setting generates 60dB tones

  • Each transducer type must be calibrated separately

  • Calibration should be done yearly, ~$100 USD

• Without calibration, all you know is relative frequency results

• This is why online or DIY tests aren't very reliable!

Pure-tone Audiometry

Pure-tone audiometry

• Measures the amplitude required to hear a "pure tone" at a variety of frequencies.

  • Pure tones are simple waves, not complex

• "Press the button when you hear a beep"

Types of Tones

• Pure Tones

  • Just a vanilla sine wave at Frequency f

• Warble Tones

  • 'Frequency modulated' tones, where the sound goes between (e.g.) f +/- 5% at 5 Hz

• Pulsed Tones

  • 'Amplitude pulsed' tones, where the puretone is played (e.g.) for 200ms, then off, then played...

• Pulsed Tones and Warble Tones are more easily distinguished from tinnitus'

  • They also avoid 'standing waves' when played with speakers

• Pick one and use it, thresholds aren't comparable across tone types

Examples (800 Hz)

Pure:

Pulsed (200ms):

Warble (3 Hz):

The goal is to establish a 'threshold'

• "What is the lowest amplitude sound this patient can hear by frequency?"

• Thresholds are usually taken between 250-8000Hz

• The end result is an audiogram

The procedure

• Play a tone at a given frequency

• Wait for participant response

• If they hear it, go quieter

• If they don't, go louder

• ... but you need to make sure they're not cheating!

Patients will give false responses!

• False positives are responses when no tone is audible

• False negatives are failures to respond to a tone they can hear

Precautions to avoid biased tests

• Randomly timing your presses to avoid guessing

• Facing the patient away from you

• Using a testing paradigm to arrive at the proper measurement

• Not allowing patients to measure their own hearing

  • Again, this is why online tests aren't great

'5 Down 10 Up' Paradigm

The threshold is determined by a 50% response rate

• Patients should respond at least 50% of the time to that tone for that to 'count'

This creates an 'audiogram'

• Audiograms show the quietest tone reliably responded to across frequencies

You'll likely want to test bone conduction as well as air conduction!

You'll want to use masking

• Contralateral masking helps prevent one ear from 'helping' the other

  • If HL exceeds interaural attenuation

• See the 'Masking' video for details there

• Or Chapter 9 in your textbook

You might test higher frequencies too!

• High frequency audiograms go above 8000 Hz

• This requires more specialized equipment

• Useful for monitoring some kinds of ototoxic drugs and detecting loss early

• Also has some generalized benefits

We're going to stop here with pure tones!

• The book goes into more details about testing kids, procedures, and other complexities!

• Chapter 6 is your friend!

Speech Audiometry

Pure tones capture one aspect of hearing

• Raw ability to hear frequencies

• ... but often, poor speech intelligibility is the biggest complaint

• Why not test speech perception directly?

Speech Audiometry has three aspects

• How loud does speech need to be for them to hear that speech is being produced?

  • The 'Speech Detection Threshold' (SDT)

• How loud does speech need to be to be understandable?

  • The 'Speech Recognition Threshold' (SRT)

• How accurately are they recognizing the words?

  • The 'Word Recognition Score' (WRS)

Speech Audiometry Procedure

• Read words aloud with the level limited to certain amplitudes

• Ask the participant to repeat the words back

• Score...

  • Whether they heard the word (SDT)

  • Whether they accurately heard the word (SRT)

  • Individual Phoneme Errors (WRS)

• Repeat the task with masking noise to check perception in noise

Not all words are equally understandable

• Attempting to use words which are familiar to everybody

  • Or are they?

• Audiologists use monosyllables and "spondees", words with two stressed syllables

Sample Audiology Spondees

• Words from the NU-6 Listing: sidewalk, birthday, cupcake, airplane, railroad, baseball, playground, cowboy, sunset, hotdog, outside...

• A new list: smartphone, hashtag, upload, bikeshare, cashcow, laptop, iPad, flashmob, backpack, deadbeat, bandwidth, roadrage...

Testing follows a fixed procedure

• This is complicated, and there are many moving parts

• You can use masking if the required level exceeds interaural attenuation

• You can also do recognition in noise to get a better sense of in-the-world recogition

• These are detailed in Chapter 8

Reported Results

• Generally you'll report SDT and SRT in dB

• You'll report maximum "PB" (phonetically balanced word recognition) and associated level for SRT

• More detailed tests give more detailed results

These audiometric data give great information

• What is the nature, severity, and distribution of hearing loss?

• What of this loss is present in bone conduction as well?

• How does this loss affect their ability to hear speech?

All of this is recorded and reported in the audiogram

Reading Audiograms

Audiograms give us data about thresholds, by frequency, with and without masking

Looking at an audiogram gives us information about hearing loss

• We know what frequencies and amplitudes exist in the world

• We see the difference between masked and unmasked

• Sounds which are 'above the line' are not going to be audible

• This gives rise to...

The Speech Banana (lol)

Audiograms can then be interpreted for diagnostic purposes

• ... and interpreting the audiogram is a skill we'll be working on

• Often, audiograms (with the other tests we've discussed) provide key diagnostic information

• Reading Chapter 7 is important!

Let's look at a sample audiogram

---

Wrapping up

• Audiometric Testing Equipment is specialized and expensive

• Puretone Audiometry gives us absolute thresholds for hearing by frequency

• Speech Audiometry gives us a better sense of how speech is perceived

• Audiograms give us all the information we need in one convenient place

Thank you!