Clinical NeuroscienceA method to dynamically control unwanted loudness cues when measuring amplitude modulation detection in cochlear implant users

- Unwanted loudness cues may contribute to cochlear implant (CI) users' modulation detection thresholds (MDTs).
- A method to control for amplitude-modulated (AM) loudness cues was used in an adaptive modulation detection task.
- The level of non-AM stimuli was adjusted to match the loudness of AM stimuli, followed by roving the level of all stimuli.
- Absolute MDTs were poorer after controlling for AM loudness cues.
- Effects of presentation level and modulation rate were unchanged by the new method, with an interaction with carrier rate.

BackgroundAmplitude modulation (AM) detection is a measure of temporal processing that has been correlated with cochlear implant (CI) users' speech understanding. For CI users, AM stimuli have been shown to be louder than steady-state (non-AM) stimuli presented at the same reference current level, suggesting that unwanted loudness cues might contribute to CI users' AM sensitivity as measured in a modulation detection task. In this paper, a new method is introduced to dynamically control unwanted AM loudness cues when adaptively measuring modulation detection thresholds (MDTs) in CI users.MethodsMDTs were adaptively measured in 9 CI subjects using a three-alternative, forced-choice procedure, with and without dynamic control of unwanted AM loudness cues. To control for AM loudness cues during the MDT task, the level of the steady-state (non-AM) stimuli was increased to match the loudness of the AM stimulus using a non-linear amplitude scaling function, which was obtained by first loudness-balancing non-AM stimuli to AM stimuli at various modulation depths. To further protect against unwanted loudness cues, ±0.75 dB of level roving was also applied to all stimuli during the MDT task.ResultsAbsolute MDTs were generally poorer when unwanted AM loudness cues were controlled. However, the effects of modulation frequency and presentation level on modulation sensitivity were fundamentally unchanged by the availability of AM loudness cues.ConclusionsThe data suggest that the present method controlling for unwanted AM loudness cues might better represent CI users' MDTs, without changing fundamental effects of modulation frequency and presentation level on CI users' modulation sensitivity.