Auditory evoked response to gaps in noise: older adults

Abstract

Objective: The objective of this study was to describe the auditory evoked response to silent gaps for a group of older adults using stimulus conditions identical to those used in psychophysical studies of gap detection.

Design: The P1-N1-P2 response to the onsets of stimuli (markers) defining a silent gap for within-channel (spectrally identical markers) and across-channel (spectrally different markers) conditions was examined using four perceptually-equated gap durations.

Study sample: A group of 24 older adults (mean age = 63 years) with normal hearing or minimal hearing loss participated.

Results: Older adults exhibited neural activation patterns that were qualitatively different and more frontally oriented than those observed in a previous study (Lister et al., 2007) of younger listeners. Older adults showed longer P2 latencies and larger P1 amplitudes than younger adults, suggesting relatively slower neural travel time and altered auditory inhibition/arousal by irrelevant stimuli.

Conclusion: Older adults appeared to recruit later-occurring T-complex-like generators for gap processing, compared to earlier-occurring T-complex-like generators by the younger group. Early and continued processing of channel cues with later processing of gap cues may represent the inefficiency of the aging auditory system and may contribute to poor speech understanding in noisy, real-world listening environments.

Figure 1

Pure tone thresholds for each participant for the ear tested. Test ear was the ear with the better pure-tone threshold (11 right). Dark black line indicates mean.

Figure 2

Representative auditory evoked responses (AEPs) following each marker onset recorded from electrode Fz for a single participant. The stimulus condition was within-channel, supra-threshold gap. Narrow-band noise (NBN) marker time waveforms are shown below AEPs. Gray area represents duration of gap, which varied across listeners and conditions.

Figure 3

Group mean responses to the first marker recorded from electrode Fz (younger n = 12, older n = 24).

Figure 4

Group mean responses to the second marker recorded from electrode Fz (younger n = 12, older n = 24). Solid lines represent within-channel. Dotted lines represent across-channel. Black lines represent younger listeners (Lister et al, 2007). Gray lines represent older listeners. Panel A shows standard gap. Panel B shows sub-threshold gap. Panel C shows GDT gap. Panel D shows supra-threshold gap.

Figure 5

Individual waveforms for the older listeners (n = 24) for the first and second marker for the within-channel GDT gap condition recorded from Fz. Left panel represents first marker responses. Right panel represents second marker responses. The dark black line represents the average response for the young control group (Lister et al, 2007) for the same conditions.

Figure 6

Summary of channel (within, across) and channel by group (right ear, left ear) effects identified via a temporal-spatial principal component analysis (PCA). Temporal factors, shown with peak latencies (in ms, middle), indicate time windows during which channel effects were detected. Scalp maps (top) indicate topographic regions at which channel effects were detected within each time window. The maps are organized loosely by region. Spatial factor loadings range in amplitude from +1 (extreme red) to −1 (extreme blue). Darker areas on each map denote high spatial factor loadings (electrodes with higher loadings have a more prominent role in defining the topographic region of interest associated with each spatial factor).

Figure 7

Summary of main effects of gap duration as well as interactions between gap duration and channel condition or gap duration and ear of stimulation identified via temporal-spatial principal component analysis. Temporal factors, shown with peak latencies (in ms, middle), indicate time windows during which gap effects were detected. Scalp maps (top) indicate topographic regions at which gap effects were detected within each time window. The maps are organized loosely by region. Spatial factor loadings range in amplitude from +1 (extreme red) to −1 (extreme blue). Darker areas on each map denote high spatial factor loadings (electrodes with higher loadings have a more prominent role in defining the topographic region of interest associated with each spatial factor).