1. Introduction to Cortical Auditory Evoked Potentials (CAEP)
Manufactured by Frye Electronics
Many thanks to the researchers at NAL who put together much of the information of this presentation.

2. From Sydney to Portland

3. Clinical Uses of HEARLab ACA
Verifying the effectiveness of hearing aid fittings on infants and adults or older children with disabilities in addition to hearing loss
Estimating audiometric thresholds in adults who may not cooperate in conventional hearing test (worker’s compensation)
Testing infants and children with auditory neuropathy

4. First: How does HEARLab work?
Sound stimulus  Generates neural activity  Measured by electrodes  Analyzed by HEARLab

5. What is an Auditory Evoked Potential?
The human brain generates random electrical activity continually
We can record this electrical activity using electrodes on the scalp (EEG)
Sound stimulates neural activity in the brain that we can extract from the total EEG
The electrical activity generated from exposure to sound is called an Auditory Evoked Potential (AEP)

6. Auditory Evoked Potentials
Auditory Brainstem Response (ABR)
Cortical Auditory Evoked Potential (CAEP)
From: Katz, J (Ed.) Handbook of Clinical Audiology 4th Ed (Chpt 22)

7. Cortical Response
Auditory Brainstem Response
Baer, 2003

8. Electrode Placement
From: Hall, J.W. (1992) Handbook of Auditory Evoked Potentials

9. Obligatory CAEPs: Adult responses from several sites
From:Vaughan, H.G., Ritter, W. (1970) The sources of auditory evoked responses recorded
from the human scalp. Electroencephalography and Clinical Neurophysiology.
Vol 28.

10. Test Stimuli ABR HEARLab CAEP Broadband clicks (1 ms)
Frequency-specific pips (1 ms)
HEARLab CAEP
Speech stimuli - /m/ /g/ /t/ (30 ms)
Highly frequency-specific tone bursts (30 ms)

11. ABR vs Audiometer Stimuli
ABR click
Audiometer tone
ABR pip
From: Abramovich (1990) ERA in Clinical Practice.

12. ABRs Unsuitable for Aided Testing
ABR test occurs 1-5 ms after stimulus
Digital hearing aids have digital processing delay (2-15 ms)
Hearing aids respond poorly to ABR clicks

13. CAEP Better Solution for Aided Testing
Test occurs ms after stimulus
Stimulus uses speech stimulus (30 ms)
Frequency emphasis speech sounds
/m/ - Low frequency emphasis
/g/ - Mid frequency emphasis
/t/ - High frequency emphasis

14. HEARLab “Speech” Stimuli
Unlike ABR, latency of the CAEP test ( ms) allows the use of longer test stimuli better suited for use with hearing aids

15. Auditory Neuropathy
Outer hair cells within the cochlea are functional, but sound information is not transmitted to the auditory nerve and brain properly.
Diagnosis:
Positive Otoacoustic Emissions (OAE)
Negative ABR
Some Auditory Neuropathy patients have relatively normal hearing levels. Others may have severe hearing losses
CAEP can be used to assess audibility of highly-frequency specific tones.

16. -100 100 200 300 400 500 600 ms Subj: normal hearing adult Stim: /g/
No. of responses: 100 (and replicated)
30 dB SL
20 dB SL
10 dB SL
2.5 µV
-100
100
200
300
400
500
600 ms

17. Infant CAEPs with Maturity
From: Steinschneider, M., et al., (1992) Event–related potentials in developmental Neuropsychology. In Handbook of Neuropsychology Vol 6 Elsevier Science

18. HEARLab Example of CAEP
Infant Response
Adult Response

19. Traditional Problems with CAEP
Unlike ABR, CAEP waveforms vary from individual to individual
Requires experience interpreting CAEP traces for clients of different ages to decide whether the sounds are likely audible to the patient

20. Solution!
Statistical Analysis using Multivariate Analysis of Variance (MANOVA) with Hotellings T2
As the HEARLab test runs, an ongoing statistical analysis of the results are performed. If the results are < 0.05, there is a high probability a response is present.

21. NAL Research shows Hotellings T2 works!
Study done comparing a group of experts on CAEP to the Hotellings analysis
Results shows that Hotellings is at least equal to, if not more able, than the “composite” examiner to differentiate a CAEP from random noise at sensation levels of 10 dB or more

22. Example of HEARLab Test
Test Controls
Most recent epoch
Average
Statistics
Residual Noise

23. Clinical Use of HEARLab ACA
Aided testing with speech sounds (infants, mentally disabled)
Frequency-specific threshold estimation (multiply disabled, worker’s compensation, auditory neuropathy)
Customer base:
Hospitals
Nursing homes
Hearing aid clinics

24. Early Hearing Intervention programs
Screening ABR/OAE 
Diagnostic ABR 
RECD/Simulated Real-ear 
NEW!!! HEARLab ACA

25. Next: Demonstration of HEARLab ACA software!