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目的探讨以听觉系统对调幅信号响应幅值随调制频率的改变计算等调制深度时问调制转换函数(temporal modulation transfer function,TMTF)来客观评估听觉系统时间分辨率的可行性。方法豚鼠下丘和听皮层分别埋植慢性电极,记录正弦调幅纯音(载频为8 kHz,调制深度固定为100%)诱发电位,反应幅值经快速傅立叶变换(fast Fourier transform,FFT)得出相对反应幅值,并以相对反应幅值和调制频率绘制出等调制深度 TMTF。记录正弦调幅纯音每个调制频率的调制深度从100%至10%的诱发电位,得出与传统的调制深度阈值 TMTF 方法相当的等幅值 TMTF,与等调制深度 TMTF 相比较,判断等调制深度 TMTF 方法的有效性。结果豚鼠下丘和听皮层的等调制深度TMTF 与等幅值 TMTF 都分别表现为带通和低通特性;等调制深度 TMTF 的截止频率与等幅值 TMTF的截止频率差异无统计学意义(P 值均>0.05)。豚鼠听皮层等调制深度 TMTF 的截止频率与传统的行为学结果基本一致。结论以100%调制深度的正弦调幅纯音诱发反应幅值与调制频率绘制等调制深度 TMTF 是一种有效的客观评估听觉系统时间分辨率的方法,其中豚鼠听皮层的等调制深度TMTF 可用于行为学预测。
Objective To investigate the feasibility of objectively assessing the time resolution of auditory system by calculating the modulation depth of temporal modulation function (TMTF) by adjusting the response amplitude of amplitude modulation signal with the modulation of the hearing system. Methods Chronic electrodes were implanted into the inferior colliculus and auditory cortex of guinea pigs. Evoked potentials were recorded by sinusoidal amplitude-modulated pure tone (carrier frequency was 8 kHz, modulation depth was fixed at 100%). The response amplitude was obtained by fast Fourier transform (FFT) Relative response amplitude, and to the relative modulation amplitude and modulation amplitude of the modulation depth TMTF. Record the amplitude modulation depth of each sine wave amplitude modulation modulation from 100% to 10% of the evoked potential, resulting in the traditional modulation depth threshold TMTF method equivalent amplitude TMTF, compared with the equal modulation depth TMTF, to determine the equal modulation depth The effectiveness of TMTF method. Results The equal modulation depth (TMTF) and equal amplitude (TMTF) of the inferior colliculus and auditory cortex of guinea pig showed band-pass and low-pass characteristics respectively. There was no significant difference between the cutoff frequency of TMTF and the cutoff frequency of TMTF Value> 0.05). The cutoff frequency of modulation depth TMTF in the auditory cortex of guinea pig is basically consistent with the traditional behavioral results. Conclusion Modulation depth (TMTF) can be effectively estimated by sinusoidal amplitude-pure tone induced response amplitude and modulation frequency at 100% modulation depth. The equal modulation depth (TMTF) of auditory cortex in guinea pigs can be used for behavioral prediction.