John J Galvin1, Qian-Jie Fu2, Sandy Oba2, Deniz Başkent3. 1. Division of Communication and Auditory Neuroscience, House Research Institute, Los Angeles, CA, USA; University of California Los Angeles, David Geffen School of Medicine Department of Head and Neck Surgery, Los Angeles, CA, USA; Department of Otorhinolaryngology, Head and Neck Surgery, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands; Research School of Behavioral and Cognitive Neurosciences, Graduate School of Medical Sciences, University of Groningen, Groningen, The Netherlands. Electronic address: JGalvin@mednet.ucla.edu. 2. Division of Communication and Auditory Neuroscience, House Research Institute, Los Angeles, CA, USA; University of California Los Angeles, David Geffen School of Medicine Department of Head and Neck Surgery, Los Angeles, CA, USA. 3. Department of Otorhinolaryngology, Head and Neck Surgery, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands; Research School of Behavioral and Cognitive Neurosciences, Graduate School of Medical Sciences, University of Groningen, Groningen, The Netherlands.
Abstract
BACKGROUND: Amplitude 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. METHODS: MDTs 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, ±0.75dB of level roving was also applied to all stimuli during the MDT task. RESULTS: Absolute 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. CONCLUSIONS: The 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.
BACKGROUND: Amplitude 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. METHODS:MDTs 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, ±0.75dB of level roving was also applied to all stimuli during the MDT task. RESULTS: Absolute 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. CONCLUSIONS: The 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.