Overshoot effects using Schroeder-phase harmonic maskers in listeners with normal hearing and with hearing impairment

Overshoot was examined in normal-hearing listeners and in listeners with sensorineural hearing loss using positive (m(+)) and negative (m(-)) Schroeder-phase harmonic maskers and brief (5-ms) 1000-Hz and 4000-Hz signals. Maskers were 460 ms in duration and contained equal-amplitude harmonics of a 100-Hz fundamental frequency. For each masker, probes were presented at temporal locations near the start of the masker (probe onsets 3, 5.5, 8, 10.5, and 13 ms following masker onset) and at the same positions (relative to masker fine structure) 150 ms later, near the temporal center of each masker. Probes were held constant at either 60 or 80 dB sound-pressure level (SPL) and masker levels were varied adaptively to determine masked thresholds at each position within the 10-ms masker period. Overshoot effects were greatest for conditions where cochlear processing was likely to be highly nonlinear, i.e., for normal-hearing listeners tested at moderate presentation levels (60 dB SPL probes). In addition, greater overshoot was observed for m(+) than for m(-) maskers. These findings are consistent with earlier suggestions that masking effectiveness of m(+) complexes is particularly influenced by cochlear nonlinearity (Summers, V. and Leek, M.R., 1998. Hear. Res. 188, 139-150) and with evidence linking overshoot to nonlinearity in peripheral auditory processing.