• Your CARL Pro (CARL Basic is not compatible with Audiometry)
• CARL Pro ears
• Computer to access CARL software (a Chromebook was included with 1st generation Audio CARL)
• Audiometer of your choosing
• Transducer of your choosing
• Sound booth or other approach for minimizing noise floor

Setting up your CARL Pro for Audiometry includes a few steps:

1. Pick the correct environment for your CARL Pro
   
   Your CARL will be responding like a hearing test like a patient. This means the noise level of the environment must be taken into account. In ideal cases CARL Pro can be set up in a sound booth. If this is not possible, ensure the hearing losses you give CARL are severe enough so they are above the noise floor of the environment you are in.
   
   
2. Calibrate your CARL Pro
   
   CARL Pro's calibration functionality must be conducted whenever CARL is in a new environment, or if a new transducer is used.
   
   For a full in depth video of how to calibrate your CARL Pro, please see see our YouTube Video.
   
   
3. Use the CARL Pro software to upload a hearing loss into CARL!
   
   CARL is now ready to have his hearing tested! Instead of clicking a button or raising his hand, CARL will blink the LEDs in his shoulders to tell you he's heard a tone.

Note: All transducer types should be compatible with CARL. Ensure that your CARL Pro is calibrated for the specific transducer in which you are using for this test.

The following competency checks can be used as checkpoints / tasks for standardized training of Audiometry on CARL:

1. Explanation of the procedure
2. Transducer selection and contraindications
3. Proper placement of transducer
4. Confirm CARL hears tone
5. Hughson-Westlake procedure
6. Tone-length standard
7. Optimal length of time between tones for efficient timing of test
8. Requirements for masking per transducer
9. Core masking competency including finding a masking plateau
10. Barriers in patients to completing masking
11. Overmasking and undermasking
12. Utilizing various audiometer and transducer models

Full hearing assessments provide information regarding auditory function and overall health of the outer, middle and inner ear. There are many components to a hearing assessment including case history, consent, otoscopic exam, acoustic immittance measures, pure-tone audiometry, speech audiometry, bone-conduction audiometry, and counseling. For the purposes of this guide, we will focus on pure-tone audiometry through air-conduction as this provides a threshold for frequency specific data for each ear and is the foundation of a typical hearing assessment.

Pure-tone audiometry assesses the auditory system by introducing a tone into the ear canal via a transducer. The tone then passes through the tympanic membrane, ossicles, cochlea, cochlear nerve then finally the auditory cortex1. The pure-tone test alone does not allow for the determination of which part of the auditory system is affected. Other tests that are normally part of the hearing assessment battery of tests will determine which part of the system is abnormal and the exact type of hearing loss present (such as conductive, sensorineural or mixed).

After the tone is presented, the patient indicates they have heard the tone in several ways which may include pressing a response button, raising a hand, clapping or a verbal response. In the case of using CARL, the lights on the shoulder area indicate a response is heard.

Modifications must be made for patients who are not able to reliably give a response as pure-tone audiometry requires a reliable behavioral response. Possible modifications may include visual reinforcement audiometry or conditioned play; these are commonly used when a child is under 5-years-old or those who experience cognitive challenges.

See other guides on cerumen management, foreign body removal, transducers, and masking.

When performing a pure-tone air-conduction test, CARL can be placed inside a sound-treated booth for standardization and to reduce interference from other sounds. CARL can also be used outside of the booth if in a quiet environment and a hearing level of 40dB or more is present per frequency. The booth should be calibrated to American National Standards Institute (ANSI) standards for reliability. A transducer such as insert headphones will be placed in CARLs ears (remember to obtain his consent! ;). Then, a series of tones will be presented, and CARL will be instructed to respond to these tones in a developmentally and cognitively appropriate way. CARL responds by lights flashing at his left or right shoulder.

Step 1: Up 5, Down 10 Method

Beginning with a presentation tone of 1000 Hz to the better ear, is most commonly the beginning point of the test. The tone is presented at what is likely an easily audible tone for CARL (usually based on case history or previous test results). When a response is observed by the flashing lights, following the recommended Hughson-Westlake procedure, the tone is then decreased by 10dB and then presented again. When a response isn’t present in CARL (no lights), increasing the tone by 5dB is the standard until a response is obtained. The hearing threshold at a specific frequency is obtained when CARL responds at least 2 out of 3 times to the softest ascending presentation of the tone.

Step 2: Range

A presentation of a range of frequencies from 250-8000kHz is obtained, usually ascending octaves from 1k-8k then below 1 k. Inter-octaves are often obtained, depending on the purpose of the test and especially in cases when there is a significant drop in threshold between octaves.

Step 3: Audiogram

The responses are plotted a graph called anaudiogram, where the X axis is Frequency (Hz) and the Y axis is Loudness (dB). Key responses on a typical air conduction measurement are O (indicating the right ear) and X (indicating the left ear). See sample below.

When assessing hearing, it is important to be able to obtain ear-specific information. In other words, it is pivotal to make sure the information gathered is for the ear that is being tested and is not influenced by a better hearing ear; This can be the case when there is a significant asymmetrical hearing loss present, and the better ear hears the tone instead of the ear that is being tested. To isolate the ear that is being tested, masking is necessary in certain cases.

Cross-over can occur when the pure-tone, air-conduction thresholds are greater than 55dB between ears for insert headphones and 40dB between ears for circumaural or supra-aural headphones (this standard will vary based on your country, region, and governing body). Therefore, if there is a gap between ears at any one frequency that is outside of these numbers, masking is needed at that frequency to confirm the threshold is heard by the ear being tested.

Considerations

Ability of the patient to condition to the task. Age/Cognitive level/understanding of English or language used during test; Tinnitus. Choice of transducer and amount of cross-over. Auditory processing difficulties.

Technique

After the unmasked, pure-tone air-conduction thresholds are obtained masking may be required when there is potential for cross-over hearing. At the time of masking, there will be a presentation of narrowband noise that centres around ½ to 1/3 octave of the tone in the other ear2; the ear that is presented with the masked signal is known as the ‘non-test ear’. The ear being tested is known as the ‘test ear’, which will be presented with pure tones. CARL will ignore the narrowband noise and respond only when hearing the pure tones.

Procedure

Step 1: Present and condition

Begin at the frequency in need of masking. Present the pure tone without masking to the test ear to re-establish the pure-tone threshold and re-orient CARL to the task of listening for tones again.

Next introduce the masking sound in the non-test ear at the tonal threshold of the non-test ear at that frequency you are testing. Once the CARL lights up in response, proceed by increasing the masking sound by 10dB and presenting the pure tone in the test ear (do not change the level of the pure tone presentation). If CARL does not hear the tone and does not light up in response, increase the pure tone by 5dB while not changing the masked signal level. A masked threshold is obtained when three successive levels of masking (a minimum of 20dB) produce a heard response by CARL.

Step 2: Range

Unlike pure-tone, air-conduction audiometry, the range of the masked frequencies being tested are related to the crossover hearing effect of the transducer used. There may not be any thresholds that require masking, there may be a few or there may be the requirement of masking at all octaves. This will be determined by looking at the transducer used and whether there is a large enough asymmetry between the ears to have crossover.

If you are using CARL, the crossover of CARL is fine tuned to the average crossover of humans. See the chart below for reference.

Step 3: Audiogram

The responses are plotted the audiogram, where the X axis is Frequency (Hz) and the Y axis is Loudness (dB). Key responses on a typical masked air conduction measurement is a hollow triangle (indicating the right ear) and a hollow square (indicating the left ear). This icon can be selected within the CARL software, on a hand-drawn audiogram plot, or on all major audiometers.