Abstract
OBJECTIVES: Sensorineural hearing loss is common with advancing age, but even with normal or near-normal hearing in older persons, performance deficits are often seen for suprathreshold listening tasks such as understanding speech in background noise or localizing sound direction. This suggests there is also a more central source of the problem. Objectives of this study were to examine as a function of age (young adult to septuagenarian) performance on: 1) a spatial acuity task examining localization ability, and a spatial speech-in-noise (SSIN) recognition task, both measured in a hemi-anechoic sound field using a circular horizontal-plane loudspeaker array, and 2) a suprathreshold auditory temporal processing task and a spectro-temporal processing task, both measured under headphones. Further, we examined any correlations between age, hearing thresholds including extended high frequency (EHF: >8000 Hz), and these measures. DESIGN: Subjects were 48 adults, aged 21 to 78, with either normal hearing or only a mild sensorineural hearing loss through 4000 Hz. The localization task measured minimum audible angle (MAA) for 500 and 4000 Hz 1/3 (rd) octave narrowband noise (NBN) in diffuse background noise for both an on-axis (reference source 0°) and off-axis (reference source 45°) listening condition at signal-to-noise ratios (SNRs) of -3, -6, -9, and -12 dB. SSIN testing was also completed for key word recognition in sentences in multi-talker babble noise; specifically, the separation between speech and noise loudspeakers was adaptively varied to determine the difference needed for 40% and 80% correct performance levels. Finally, auditory temporal processing ability was examined using the Temporal Fine Structure (TFS) test, and the Spectro-Temporal Modulation (STM) test. RESULTS: Spatial acuity was poorer (larger MAAs) in older compared to younger subjects, particularly in the more adverse listening conditions (off-axis, and poorer SNRs). The SSIN data also showed declining mean performance with age at both criterion levels, emerging in the middle age group (> 40 years), but was not correlated with standard audiometric hearing thresholds. Decreased performance on the TFS and STM tasks was dependent on age, emerging only in the older (> 60 years) and middle (>40 years) age groups, respectively; neither was dependent on hearing thresholds. Results of multiple regression analyses suggest that SSIN recognition scales with the ability of the subjects to use both low-frequency binaural temporal fine structure as well as higher-frequency binaural envelope cues, both of which are impacted by aging but not necessarily audiometric hearing thresholds. Finally, EHF range hearing thresholds significantly decreased with age, but performance on tasks remained significantly correlated with age when controlled for EHF hearing. CONCLUSIONS: Particularly for more adverse listening conditions, age-related deficits, but not hearing-threshold-related deficits, were found on both of the spatial hearing tasks and in temporal and spectro-temporal processing abilities. It may be that deficits in temporal processing ability contribute to poorer spatial hearing performance in older subjects due to inaccurate coding of binaural/interaural timing information sent from the periphery to the binaural brainstem. In addition, EHF hearing loss may be a coexisting factor in the reduced performance seen in older subjects.