Apparent auditory source width discrimination in normal-hearing and hearing-impaired individuals W. M. Whitmer*, B. U. Seeber§, & M. A. Akeroyd* *MRC Institute of Hearing Research, Glasgow Royal Infirmary, UK §MRC Institute of Hearing Research, University of Nottingham, UK Deficits in absolute azimuthal localization for hearing-impaired (HI) relative to normal-hearing (NH) listeners (e.g., Lorenzi et al., 1999) could be due in part to poorer representation of sound-source locations in the aged auditory pathway (Ross et al., 2007). If there are poor neural responses to location in aged and/or HI populations, there should be greater difficulties in discriminating auditory source width based on interaural cross-correlation. There is, however, little information on the interaural cross-correlation discrimination ability of the aged and/or hearing-impaired. Six young NH participants, six aged NH participants and ten aged HI participants compared the apparent auditory source width of broadband stimuli. Stimuli were comprised of third-octave narrow-band noises centered at 250-4000 Hz in octaves. The interaural cross-correlation of each noise was varied by mixing an uncorrelated sample of the same bandwidth and center frequency (Licklider & Dzendolet, 1948). Stimuli were presented over headphones with interaural time delays (ITDs) of -300, 0 and +300 µs. Correlation-difference thresholds (Δρ) were measured at six pedestal cross-correlations from 0.5 to 1 (i.e., diffuse to punctate) using a two-alternative adaptive- tracking procedure. Audibility was maintained by individually applying the half-gain rule to each component based on pure-tone audiometric thresholds at each center frequency. Results for young NH listeners corresponded to those of Pollack and Trippitoe (1959), with no effect of ITD on Δρ, corroborating some previous findings on ITD discrimination (Dominitz & Colburn, 1977). Results for aged NH and HI listeners will be discussed in terms of difficulties in apparent sound source-width discrimination, which imposes a limit on the potential localization ability of aged listeners. Acknowledgements Work supported by the Medical Research Council and the Chief Scientist Office. References Domnitz, R., Colburn, S. 1977. Lateral position and interaural discrimination. J Acoust Soc Am, 61, 1586–1598. Licklider, J., Dzendolet, E. 1948. Oscillographic scatterplots illustrating various degrees of correlation, Science, 107, 121-124. Lorenzi, C., Gatehouse, S., Lever, C. 1999. Sound localization in noise in hearing-impaired listeners. J Acoust Soc Am, 105, 3454- 3463. Pollack, I., Trittipoe, W. 1959a. Binaural listening and interaural noise correlation. J Acoust Soc Am, 31, 1250-1252. Ross, B., Fujioka, T., Tremblay, K., Picton, T. 2007. Aging in binaural hearing begins in mid-life: evidence from cortical auditory-evoked responses to changes in interaural phase. J Neurosci, 27, 11172-11178.