Need for cortical evoked potentials Assessment and determination of amplification benefit in actual hearing aid users is an issue that continues to be a major challenge to audiologists worldwide. Hearing aid technology continues to evolve at a rapid pace but evaluation tools often lag behind changes in hearing aid design and struggle to keep pace with technology developments. Speech-evoked cortical auditory event-related potentials (ERPs) are measures of the neural detection of acoustic cues that relate to speech perception and hence offer promise as a tool to evaluate the neural representation of amplified speech.

Auditory Brainstem Response Cortical Response Baer, 2003

The complex is made up of: 1) P1, a vertex-positive peak seen around 50 milliseconds (msec) after stimulus onset, 2) N1, a negative peak occurring approximately 100 msec after stimulus presentation, and 3) P2, a positive peak occurring approximately 200 msec after stimulus presentation. P1-N1-P µV P1 N1 P2

ORIGIN OF HEARLAB The need for a new measurement tool Evaluation of aided functioning in infants Universal new born screening Early fitting of hearing aids Need for an evaluation method Cochlear implants Hearing aids

Harvey Dillon et. al., NAL

2. Differential amplification Inverting Non-inverting + - Ground NAL : Dillon, Van Dun, Carter, Gardner-Berry Electrode input:+-Ground Pre-ampActiveReferenceGround Non-invertingInvertingReference

Hearlab options  ACA: “Aided Cortical Assessment” Free field Speech sounds Can be tested aided or unaided Focused on infants  CTE: “Cortical Threshold Evaluation” With insert phones Tone-bursts Only unaided Focused on adults

WP ASA HEARING LEVELS IN DECIBELS FREQUENCY (Hz) m g t m g t

LTA: /m/

LTA: /g/

LTA: /t/

Specific aims The current study investigated the effects of digital amplification technology in new hearing aid users with sensorineural hearing loss amplitudes and latencies of cortical ERPs generated by speech sounds from different frequency ranges (/m/, /g/, /t/), b) changes in cortical processing of speech sounds /m/, /g/, /t/ from unaided to aided conditions, and c) aided speech detection versus discrimination of speech sounds from different frequency ranges (/m/, /g/, /t/).

Subjects All subjects were new hearing aid users and had no prior experience with wearing amplification. Subjects consisted of 3 males and 4 females from the ages of 66 to 77 years (mean age of 72y). Subjects with normal otoscopic findings, normal tympanograms, mild to moderately-severe SNHL, word recognition >70% in both ears. Each subject was required to score 23 or greater on the Mini Mental State Examination (MMSE) to ensure normal cognitive function. Each subject underwent ABR testing to ensure normal brainstem function

Procedure Each speech token was presented in the soundfield of a soundproof booth at levels of 65 dB SPL and 75 dB SPL in the aided and unaided conditions via a speaker placed one meter in front of the participant at 0º A. Our test protocol required that each speech token reach 100 accepted epochs before moving on to the next testing condition. Prior to beginning the ACA assessment, the soundfield was calibrated and electrodes were placed on the subject’s forehead (ground electrode), mastoid (reference electrode), and vertex (active electrode). Listener’s own hearing aids used

Test Condition Speech Sounds Stimulus Level Test Condition X Speech Sounds Test Condition X Stimulus Level Speech Sounds X Stimulus Level Test Condition X Speech Sounds X Stimulus Level (unaided vs aided) (/m/ vs /t/ vs /g/) 65 vs 75 dB F dfdf pF dfdf pF dfdf pF dfdf pF dfdf pF dfdf pFdfp P N P Latency effects

Test Condition Speech Sounds Stimulus Level Test Condition X Speech Sounds Test Condition X Stimulus Level Speech Sounds X Stimulus Level Test Condition X Speech Sounds X Stimulus Level (unaided vs aided) (/m/ vs /t/ vs /g/) 65 vs 75 dB F dfdf pF dfdf pF dfdf pF dfdf pF dfdf pF dfdf pFdfp P N P Amplitude effects

Amplitudes /m/ /t/ /g/ Test ConditionP1N1P2P1N1P2P1N1P2 Aided Mean SD Unaided Mean SD

Effects of amplification on latency and amplitude of CAEPs No significant differences were also seen between amplitudes of CAEPs recorded under unaided and aided conditions. Tremblay et al. (2006) found that distinct neural patterns elicited by different speech stimuli were evident in aided conditions showed no significant differences between aided and unaided cortical (N1) responses in response to either speech stimulus when adding 20-dB of gain. Billings et al. (2007) also found that similar to the Tremblay et al. (2006) findings, adding 20-dB of hearing aid gain did not result in an amplitude increase or latency decrease compared with unaided cortical responses at the same input level.

Why no significant unaided versus aided effects? Both measures at suprathreshold levels (65 dB and 75 dB SPL): physiological saturation of cortical neurons? Increasing audibility under the aided conditions does not alter neural patterns differentially from those in the unaided conditions? Since P1-N1-P2 responses are more reflective of onset and steady state portions of CV stimuli, they may be too short to characterize hearing aid gain across unaided and aided conditions Do digital signal processing hearing aid strategies alter the stimulus characteristics across unaided and aided conditions in such a way that unaided and aided responses are not neurally distinct?

Individual effects

Subject 1Subject 2Subject 3Subject 4Subject 5Subject 6Subject 7 UAUAUAUAUAUAUA /m/ vs. /t/ /m/ vs. /g/ /t/ vs. /g/ Discrimination-75 dB (U= unaided, A= aided)

Clinical implications No /t/ response Amplification effects No /g/ response No /m/ response Review HF gain or loss estimate Review mid-freq gain or loss estimate Review LF gain or loss estimate