Jonathan Regev1, Johannes Zaar1,2, Helia Relaño-Iborra1,3, Torsten Dau1
1Hearing Systems Section, Department of Health Technology, Technical University of Denmark, Kgs. Lyngby, Denmark
2Eriksholm Research Centre, Snekkersten, Denmark
3Cognitive Systems Section, Department of Applied Mathematics and Computer Science, Technical University of Denmark, Kgs. Lyngby, Denmark
The concept of a modulation filterbank has been shown to account well for psychophysical data from experiments assessing temporal envelope processing acuity in young normal-hearing (NH) listeners. Recent studies using functional imaging and physiological measurements observed a loss of modulation tuning in older listeners and acoustically-traumatized animals, suggesting that modulation frequency selectivity may be adversely affected by ageing or hearing impairment. However, behavioural evidence of reduced modulation frequency selectivity in older and/or hearing-impaired (HI) listeners has not yet been provided. The present study investigated modulation frequency selectivity in older NH and HI listeners, as compared to young NH listeners, using psychophysical paradigms. Data were collected in conditions of amplitude modulation (AM) detection, AM frequency discrimination, and modulation masking. All conditions used sinusoidal modulations applied on a sinusoidal carrier, with target modulation rates of 4, 16, 64, and 128 Hz. Masked modulation thresholds were obtained for fixed-bandwidth noise modulation maskers (bandwidth corresponding to ½ octave when on-frequency) centered at frequencies ranging from -5 to 2 octaves relative to the target modulation frequency. The results suggested a reduction in modulation frequency selectivity at all target modulation frequencies in older NH listeners as compared to the young NH group, particularly at the target modulation frequency of 4 Hz. Preliminary data indicate that modulation frequency selectivity is predominantly affected at low modulation rates in HI listeners. To quantify modulation frequency selectivity, the envelope power spectrum model of masking (EPSM) was used to derive modulation filters that account for the masking data. The differences in modulation filter shape and selectivity across listener groups are discussed and analyzed in connection to the AM detection and AM frequency discrimination data. A loss of modulation frequency selectivity, as observed in the present study, might have detrimental effects on higher-level tasks, such as speech intelligibility or stream segregation.