Bacon S P, Gleitman R M
Department of Speech and Hearing Science, Arizona State University, Tempe.
J Speech Hear Res. 1992 Jun;35(3):642-53. doi: 10.1044/jshr.3503.642.
Modulation detection thresholds were measured as a function of modulation frequency in 5 normal-hearing subjects and in 8 subjects with relatively flat, slight-to-moderate hearing losses. The carrier was a broadband noise that was sinusoidally amplitude modulated (SAM) in one of two observation intervals. The spectrum level of the carrier ranged from -10 to 50 dB SPL, and, for a given carrier level, modulation frequency varied from 2 to 1024 Hz. The temporal modulation transfer functions (TMTFs) were fitted very well with a simple equation describing a low-pass filter function. The TMTFs from the normal-hearing subjects were relatively independent of carrier level, although the derived time constant tended to increase slightly with decreases in carrier level, from an average value of 2.5 msec at 30 dB SPL to 6.0 msec at -10 dB SPL. In addition, sensitivity to amplitude modulation (AM) decreased by about 4 dB as the pressure spectrum level of the carrier was decreased from 0 to -10 dB SPL. The TMTFs from 7 of the 8 hearing-impaired subjects were similar to those from the normal-hearing subjects when the carriers were presented at equal SPLs, except that the derived time constants were slightly larger in the subjects with hearing impairment. When comparisons were made at comparable sensation levels (SLs), however, the TMTFs from the two groups of subjects were quantitatively similar, with the exception that at the lowest SL (20 dB), hearing-impaired subjects typically were more sensitive to AM than normal-hearing subjects, and the derived time constants from their TMTFs were somewhat smaller. These results, taken together with previously published results, suggest that a broad listening bandwidth is important for normal performance on a temporal resolution task. That the time constant from one of the hearing-impaired subjects was significantly longer than normal, regardless of whether the comparisons were made at equal SPL or equal SL, indicates that other factors can also be important.
在5名听力正常的受试者和8名患有相对平坦、轻度至中度听力损失的受试者中，测量了调制检测阈值作为调制频率的函数。载波是一种宽带噪声，在两个观察间隔之一中进行正弦幅度调制（SAM）。载波的频谱水平范围为-10至50 dB SPL，并且对于给定的载波水平，调制频率从2变化到1024 Hz。用描述低通滤波器函数的简单方程很好地拟合了时间调制传递函数（TMTF）。听力正常受试者的TMTF相对独立于载波水平，尽管导出的时间常数倾向于随着载波水平的降低而略有增加，从30 dB SPL时的平均值2.5毫秒增加到-10 dB SPL时的6.0毫秒。此外，随着载波的压力频谱水平从0降低到-10 dB SPL，对幅度调制（AM）的敏感度降低了约4 dB。当以相等的SPL呈现载波时，8名听力受损受试者中的7名的TMTF与听力正常受试者的TMTF相似，只是听力受损受试者中导出的时间常数略大。然而，当在可比的感觉水平（SL）下进行比较时，两组受试者的TMTF在数量上相似，不同之处在于在最低SL（20 dB）时，听力受损受试者通常比听力正常受试者对AM更敏感，并且从他们的TMTF导出的时间常数略小。这些结果与先前发表的结果一起表明，宽的聆听带宽对于时间分辨率任务的正常表现很重要。一名听力受损受试者的时间常数明显长于正常水平，无论比较是在相等的SPL还是相等的SL下进行，这表明其他因素也可能很重要。
