Peripheral and Central Influences on Auditory Temporal Processing & Speech Perception in Older Cochlear Implantees

Basic measurement of temporal processing - A masker stimulus encountered before a probe/target stimulus can affect the perception of the probe stimulus to a greater/lesser degree depending on their separation in time and their absolute and relative levels. Percent correct discrimination as a function of time separation and level manipulations, as measured from a behavioral response, will be reported.

Basic behavioral measurement of temporal processing - The ability to detect a silent gap within a stimulus typically varies depending on frequency and level characteristics of the stimulus in which the gap is embedded and also with the hearing history and age of the listener. Gap detection threshold is the shortest gap duration that can be reliably detected under a given set of conditions and is typically reported in milliseconds.

Basic measurement of temporal processing - Perceptual duration discrimination thresholds summarize a listener's ability to tell apart stimuli that differ in temporal extent. Percent correct discrimination as a function of duration difference, overall stimulus duration, and level manipulations, as measured from a behavioral response, will be reported.

Basic measurement of auditory processing - Perceptual amplitude discrimination thresholds summarize a listener's ability to tell apart stimuli that differ in level. Percent correct discrimination as a function of level difference size and average level, as measured from a behavioral response, will be reported.

Word discrimination, consonant, vowel, and sentence perception tests. The ability to discriminate between and identify recorded words, phonemic contrasts, and sentences will be assessed behaviorally. Results are reported in terms of percent correct words or phonemes.

Measure of ability to perceive amplitude modulation using modulation depth thresholds. Amplitude modulation detection performance summarizes a listener's ability to detect the presence of slower-changing amplitude variations applied to a faster-varying carrier signal. The modulation depth of the resulting combined signal can vary between 0 to 100% of the carrier signal with larger values indicating more extreme amplitude fluctuation. This research reports on the amount of modulation that can be detected as a function of different modulator and carrier frequencies, as well as overall stimulus level, as assessed via behavioral report.

ECAP amplitude growth function slopes will be used to predict perceptual performance. This measure uses clinically-available software to track the growth in auditory nerve response (peak-to-peak amplitude) as input level is varied from threshold to the maximal level at which the signal is comfortably loud. The slope of input-output function will be measured for each electrode along the electrode array of each CI study participant. Steeper slopes (measured in microvolts/current unit) will be interpreted as indicating better neural health of the associated auditory neurons.

Electrophysiological measurement of auditory nerve refractory time. This measure will be used to predict perceptual performance. Detection thresholds will be measured as masker and probe inputs are varied among a fixed set of levels and the interval between masker and probe is adjusted in duration.

Wave V from the ABR is a reflection of brainstem/midbrain processing. We will measure Wave V amplitude (microV) as the masker and probe levels and masker-to-probe interval are varied. This will be used to predict perceptual performance.

Wave V from the ABR is a reflection of brainstem/midbrain processing. We will measure Wave V latency (ms) as the masker and probe levels and masker-to-probe interval are varied. This will be used to predict perceptual performance.

Cortical (N1 and P2) amplitude (microV) in response to sound will be used to predict perceptual performance. This is an obligatory response from the auditory cortex that indicates sound detection.

Cortical (N1 and P2) latency (ms) in response to sound will be used to predict perceptual performance. This is an obligatory response from the auditory cortex that indicates sound detection. There is evidence that this latency varies as a function of aging.