Contribution of temporal fine structure information to comodulation masking release Robert H. Pierzycki and Bernhard U. Seeber MRC Institute of Hearing Research, Nottingham, NG7 2RD Patients with cochlear implants (CIs) demonstrate an increase in speech reception thresholds in the presence of modulated noise compared to normal hearing, which is also present in simulated CI-processing (Qin & Oxenham, 2003). The ability to use temporal fine structure (TFS) information is reduced in many hearing-impaired subjects including those with CIs, and this has been connected to the loss of resistance against noise (Lorenzi et al., 2006). Simulations of CIs extract the envelope in frequency channels and modulate carrier signals, e.g. band-pass noises, with it. Recent studies with simulated stimuli demonstrate a specific contribution of fine-structure information to perception of speech stimuli in modulated background maskers (Gnansia et al., 2008). Modulation of flanking bands of noise can reduce detection thresholds of a tone when masked by a coherently modulated on-frequency noise masker. This effect has been termed comodulation masking release (CMR) (Hall et al., 1984). We question whether this process requires TFS information or solely relies on envelope information. In the latter case the effect should be present with CI- simulations that remove TFS information. A CMR paradigm using co-modulated and anti-modulated flanking bands was adapted to measure detection thresholds of a tone in the presence of bands of amplitude-modulated noise maskers with removed TFS. In the baseline condition, tone and maskers were presented unprocessed similar to classical CMR experiments, whereas in the processed condition tone and on-frequency masker were summed and processed using a CI-simulation. Preliminary results show that CMR is greatly reduced due to the processing, but in some conditions it is not completely abolished. This suggests that evaluation of TFS is essential for CMR. Acknowledgements Work supported by the intramural programme of the Medical Research Council. References Gnansia, D., Jourdes, V. & Lorenzi, C. 2008. Effect of masker modulation depth on speech masking release. Hear Res, 239, 60-68. Hall, J.W., Haggard, M.P. & Fernandes, M.A. 1984. Detection in noise by spectro- temporal pattern analysis. J Acoust Soc Am, 76, 50-56. Lorenzi, C., Gilbert, G., Carn, H., Garnier, S. & Moore, B.C.J. 2006. Speech perception problems of the hearing impaired reflect inability to use temporal fine structure. Proc Natl Acad Sci U S A, 103, 18866-18869. Qin, M.K. & Oxenham, A.J. 2003. Effects of simulated cochlear-implant processing on speech reception in fluctuating maskers. J Acoust Soc Am, 114, 446-454.