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.

From Sydney to Portland

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

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

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)

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

Cortical Response Auditory Brainstem Response Baer, 2003

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

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.

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)

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

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

CAEP Better Solution for Aided Testing Test occurs 50-300 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

HEARLab “Speech” Stimuli Unlike ABR, latency of the CAEP test (50-200 ms) allows the use of longer test stimuli better suited for use with hearing aids

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.

-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

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

HEARLab Example of CAEP Infant Response Adult Response

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

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.

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

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

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

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

Next: Demonstration of HEARLab ACA software!