Age-related differences in binaural masking level differences: behavioral and electrophysiological evidence

Abstract

The effects of aging and stimulus configuration on binaural masking level differences (BMLDs) were measured behaviorally and electrophysiologically, using the frequency-following response (FFR) to target brainstem/midbrain encoding. The tests were performed in 15 younger normal-hearing (<30 yr) and 15 older normal-hearing (>60 yr) participants. The stimuli consisted of a 500-Hz target tone embedded in a narrowband (50-Hz bandwidth) or wideband (1,500-Hz bandwidth) noise masker. The interaural phase conditions included NoSo (tone and noise presented interaurally in-phase), NoSπ (noise presented interaurally in-phase and tone presented out-of-phase), and NπSo (noise presented interaurally out-of-phase and tone presented in-phase) configurations. In the behavioral experiment, aging reduced the magnitude of the BMLD. The magnitude of the BMLD was smaller for the NoSo-NπSo threshold difference compared with the NoSo-NoSπ threshold difference, and it was also smaller in narrowband compared with wideband conditions, consistent with previous measurements. In the electrophysiology experiment, older participants had reduced FFR magnitudes and smaller differences between configurations. There were significant changes in FFR magnitude between the NoSo to NoSπ configurations but not between the NoSo to NπSo configurations. The age-related reduction in FFR magnitudes suggests a temporal processing deficit, but no correlation was found between FFR magnitudes and behavioral BMLDs. Therefore, independent mechanisms may be contributing to the behavioral and neural deficits. Specifically, older participants had higher behavioral thresholds than younger participants for the NoSπ and NπSo configurations but had equivalent thresholds for the NoSo configuration. However, FFR magnitudes were reduced in older participants across all configurations. NEW & NOTEWORTHY Behavioral and electrophysiological testing reveal an aging effect for stimuli presented in wideband and narrowband noise conditions, such that behavioral binaural masking level differences and subcortical spectral magnitudes are reduced in older compared with younger participants. These deficits in binaural processing may limit the older participant's ability to use spatial cues to understand speech in environments containing competing sound sources.

Keywords: aging; binaural masking level difference; frequency-following response; perception.

Fig. 1.

Average hearing thresholds for right and left ears are plotted from 125 to 8,000 Hz for young normal-hearing (YNH; black circles) and older normal-hearing (ONH; gray squares) participants. HL, hearing level. Errors bars = ±1 SD.

Fig. 2.

Stimulus waveforms and spectra are displayed for of a single frozen iteration of each of the wideband (WB; A and C) and narrowband (NB; B and D) noise stimuli. These particular stimuli were used for all experiments; a.u., arbitrary units.

Fig. 3.

Thresholds for the wideband (WB; A) and narrowband (NB; B) noise conditions for younger (circles) and older (squares) participants. Open symbols show the individual thresholds; closed symbols show the average thresholds with error bars that are ±1 SD in length. NoSo, tone and noise presented interaurally in-phase; NoSπ, noise presented interaurally in-phase and tone presented out-of-phase; NπSo, noise presented interaurally out-of-phase and tone presented in-phase.

Fig. 4.

Group average perceptual binaural masking level differences (BMLDs) for young normal-hearing (YNH; black circles) and older normal-hearing (ONH; gray squares) groups for noise presented interaurally in-phase and tone presented out-of-phase (NoSπ; closed symbols) and noise presented interaurally out-of-phase and tone presented in-phase (NπSo; open symbols) configurations. Error bars are ±1 SD in length. WB, wideband; NB, narrowband.

Fig. 5.

Effects of aging on frequency-following-response magnitudes and response amplitudes in the various test configurations with continuous background noise. Note that group averages are based on 15 participants for each age group, except for the tone in quiet in the dichotic condition (Sπ) for which there are 7 participants in the young normal-hearing (YNH) group and 5 participants in the older normal-hearing (ONH) group. NoSo, tone and noise presented interaurally in-phase; NoSπ, noise presented interaurally in-phase and tone presented out-of-phase; NπSo, noise presented interaurally out-of-phase and tone presented in-phase; So, tone in quiet; WB, wideband; NB, narrowband. *P < 0.05, **P < 0.01.

Fig. 6.

Frequency-following-response magnitudes for the wideband (WB; A) and narrowband (NB; B) noise conditions for younger (circles) and older (squares) participants. Open symbols show the individual magnitude values; closed symbols show the average magnitude values with error bars that are ±1 SD in length. NoSo, tone and noise presented interaurally in-phase; NoSπ, noise presented interaurally in-phase and tone presented out-of-phase; NπSo, noise presented interaurally out-of-phase and tone presented in-phase.

Fig. 7.

Frequency-following-response magnitude differences (in dB) between configurations displayed for young normal-hearing (YNH; black circles) and older normal-hearing (ONH; gray squares) participants for noise presented interaurally in-phase and tone presented out-of-phase (NoSπ; closed symbols) and noise presented interaurally out-of-phase and tone presented in-phase (NπSo; open symbols) configurations. WB, wideband; NB, narrowband. Error bars are ±1 SD in length.

Fig. 8.

Effects of configuration on frequency-following-response magnitudes in young normal-hearing (YNH; A and C) vs. older normal-hearing (ONH; B and D) participants. Grand averaged spectra from individual waveforms are overlaid for tone in quiet (So; black), tone and noise presented interaurally in-phase (NoSo; gray), noise presented interaurally in-phase and tone presented out-of-phase (NoSπ; red dashed), and noise presented interaurally out-of-phase and tone presented in-phase (NπSo; blue dotted) in the wideband (WB) and narrowband (NB) conditions.

Fig. 9.

Grand average response waveforms and spectra derived from individual waveforms are displayed for 10 young normal-hearing (YNH) participants in responses to binaural stimuli presented in phase or 180° out of phase between ears for tone only, narrowband noise only, and tone-in-noise condition. NoSo, tone and noise presented interaurally in-phase; NoSπ, noise presented interaurally in-phase and tone presented out-of-phase; NπSo, noise presented interaurally out-of-phase and tone presented in-phase; So, tone in quiet; Sπ, tone in quiet presented interaurally out-of-phase.

Fig. 10.

Scatter plots among perceptual thresholds and frequency-following-response (FFR) magnitudes among the younger normal-hearing (YNH; black circles) and older normal-hearing (ONH; gray squares) participants. Note that no correlations were significant after correcting for multiple comparisons. NoSo, tone and noise presented interaurally in-phase; NoSπ, noise presented interaurally in-phase and tone presented out-of-phase; NπSo, noise presented interaurally out-of-phase and tone presented in-phase; WB, wideband; NB, narrowband.

Fig. 11.

Scatter plots among behavioral and binaural masking level differences (BMLDs) and frequency-following-response magnitude differences among the younger normal-hearing (YNH; black circles) and older normal-hearing (ONH; gray squares) participants. NoSo, tone and noise presented interaurally in-phase; NoSπ, noise presented interaurally in-phase and tone presented out-of-phase; NπSo, noise presented interaurally out-of-phase and tone presented in-phase; WB, wideband; NB, narrowband.