He Ning-ji, Mills John H, Ahlstrom Jayne B, Dubno Judy R
Department of Otolaryngology-Head and Neck Surgery, Medical University of South Carolina, MSC 550, Charleston, South Carolina 29425-5500, USA.
J Acoust Soc Am. 2008 Dec;124(6):3841-9. doi: 10.1121/1.2998779.
Detection of amplitude modulation (AM) in 500 and 4000 Hz tonal carriers was measured as a function of modulation frequency from younger and older adults with normal hearing through 4000 Hz. The modulation frequency above which sensitivity to AM increased ("transition frequency") was similar for both groups. Temporal modulation transfer function shapes showed significant age-related differences. For younger subjects, AM detection thresholds were generally constant for low modulation frequencies. For a higher carrier frequency, AM detection thresholds then increased as modulation frequency further increased until the transition frequency. In contrast, AM detection for older subjects continuously increased with increasing modulation frequency, indicating an age-related decline in temporal resolution for faster envelope fluctuations. Significant age-related differences were observed whenever AM detection was dependent on temporal cues. For modulation frequencies above the transition frequency, age-related differences were larger for the lower frequency carrier (where both temporal and spectral cues were available) than for the higher frequency carrier (where AM detection was primarily dependent on spectral cues). These results are consistent with a general age-related decline in the synchronization of neural responses to both the carrier waveform and envelope fluctuation.
对听力正常的年轻和年长成年人进行了测量，检测他们在500赫兹和4000赫兹音调载波中幅度调制（AM）随调制频率的变化情况，频率范围直至4000赫兹。两组对于幅度调制敏感度增加时的调制频率（“转折频率”）相似。时间调制传递函数的形状显示出与年龄相关的显著差异。对于年轻受试者，在低调制频率下，幅度调制检测阈值通常保持恒定。对于较高的载波频率，随着调制频率进一步增加直至转折频率，幅度调制检测阈值会升高。相比之下，年长受试者的幅度调制检测随着调制频率的增加而持续升高，这表明在更快的包络波动情况下，与年龄相关的时间分辨率下降。每当幅度调制检测依赖于时间线索时，就会观察到与年龄相关的显著差异。对于高于转折频率的调制频率，低频载波（同时存在时间和频谱线索）的年龄相关差异比高频载波（幅度调制检测主要依赖于频谱线索）更大。这些结果与神经反应对载波波形和包络波动同步的普遍年龄相关下降是一致的。
