Comparing the effects of age on amplitude modulation and frequency modulation detection

Area of Science:

• Auditory Neuroscience
• Psychoacoustics
• Human Auditory Perception

Background:

• Auditory modulation detection is crucial for speech comprehension.
• Age-related changes in hearing can affect the processing of complex sounds.
• Understanding how ageing impacts the detection of frequency modulation (FM) and amplitude modulation (AM) is vital.

Purpose of the Study:

• To compare frequency modulation (FM) and amplitude modulation (AM) detection thresholds in young and older adults.
• To investigate the influence of modulation rate and the number of modulation cycles (N) on detection thresholds.
• To explore age-related differences in the use of excitation-pattern and temporal-fine-structure cues.

Main Methods:

• Participants: Young (22-28 yrs) and older (44-66 yrs) adults with normal audiograms.
• Stimuli: Carrier frequency of 500 Hz, modulation rates of 2 Hz and 20 Hz, and varying number of modulation cycles (N=2-9).
• Procedure: Detection thresholds for FM and AM were measured at 40 dB sensation level, with uninformative AM presented during FM detection to mask excitation-pattern cues.

Main Results:

• Both young and older listeners exhibited lower detection thresholds at 2 Hz compared to 20 Hz for both AM and FM.
• Detection thresholds decreased with an increasing number of modulation cycles (N) for both groups and modulation types.
• Older listeners generally had higher thresholds than younger listeners, particularly for 2 Hz FM detection, suggesting age-related decline in temporal-fine-structure cue utilization.

Conclusions:

• Ageing significantly impairs sensitivity to both excitation-pattern and temporal-fine-structure cues involved in auditory modulation detection.
• The decline in sensitivity is more pronounced for temporal-fine-structure cues compared to excitation-pattern cues.
• While temporal integration of modulation cues at low rates appears preserved, older adults show a greater benefit from increasing the number of modulation cycles at higher rates (20 Hz).