声音的响度辨别阈与信号时程的关系

本工作用两种方法研究了声音的响度辨别阈(△I/I)与信号时程(t)的关系.用信号比较法测得的△I/I不受t的长短的影响,即△I/I=K.用拍感受法测得的结果却有所不同:当t短于极限时间T时,△I/I与t的平方根成反比,即△I/I=K'(T/t)~(1/2);当t长于T时,△I/I趋于恒定,即△I/I=K';T约为150毫秒.用拍感受法测得的响度辨别阈与信号时程的关系,和以前测得的音调辨别阈与信号时程的关系十分相象.     

人耳正常鼓膜声顺图的频率特性

在人正常耳描记了不同频率的鼓膜声顺图并进行了比较。220—500赫的低频声顺图为“人”字形,其声顺最大的峰指向声阻抗小的一方。1000—1300赫的声顺图则为倒“人”字形,其声顺最大的峰指向声阻抗大的一方。2000赫的声顺图又倒转回低频时的形状,完成一个周期的演变。630、800及1400、1600赫的声顺图则为一些过渡型,有时出现双峰。鼓膜声顺的动态范围随频率的增加而变小。声顺图形状的变异及有关的一些问题,文中用声阻抗与声顺的非单调性关系进行了解释。     

人鼓膜声顺图的正常值

用国产中耳功能测定仪在171个正常耳描记了300赫的鼓膜声顺图并计算了各种声顺值。耳的声顺最大值在外耳道压力为0时其平均值为1.16毫升,在外耳道与中耳腔压力平衡时平均值为1.29毫升。鼓膜声顺的相对值平均为0.65毫升。96.1％的受试者中耳腔压力在±50毫米水柱以内。文中提出了声顺比CR(=ΔC_(ΔP)/ΔC_(200))的概念,以定量地表达声顺图中声顺变化的梯度。在ΔP为±50毫米水柱时,正常耳的声顺比值平均为0.5。     

重复短声的音调辨别阈与信号时程的关系

当重复频率为250,500或1000赫的重复短声信号的时程短于T时,重复短声的音调辨别閾△f_r与信号时程t的平方根成反比,即△f_r=C(T/t)~(1/2).当信号时程长于T时,重复短声的音调辨别閾即恒定在最低的水平,即△f_r=C.T是信息积累的极限时间,较为恒定,约为140毫秒.C为音调辨别閾的最低水平,其大小随受试者的不同及重复短声重复频率的不同而变化.     

强噪声等环境因素对人听觉功能的影响

本工作研究了在一次持续百余天的模拟试验中强噪声(95—110分贝,每天8小时)、高室温(35℃)等环境因素对人听觉功能的影响.9名受试者在进入模拟环境后,听力在30多天时下降最多达25—35分贝,以后即趋于稳定.音调辨别阈△F在60天后才开始增大,并有随时间而继续增大的趋势.响度辨别阈、声源定位误差、短期记忆正确率等在整个试验中均无明显的规律性变化.在离开模拟环境后,听力和△F在数天至一月内完全恢复正常.试验结果表明,所给的环境条件对人听觉功能的影响是暂时性的.文中讨论了环境因素对神经系统总功能状态的影响及其评定问题.     

SLOW CORTICAL RESPONSE EVOKED BY AMPLITUDE MODULATION OF SOUND AND RESPONSE THRESHOLDS IN GUINEA PIGS

AM-evoked slow cortical responses(SCR)were recorded in awake guinea pigs and the response thresholdin terms of amplitude increament in dB was determined.A quasi-rectangular pulse of 200 ms durationand with a repetition rate of 1/sec served as the modulating wave.The typical AM-evoked SCR assumes apositive-negative-positive triphasic waveform appearing 40—200ms after the on-set or off-set of modulation.For white noise,for repetitive clicks(1000pps)and for tones(125Hz—16kHz)in a very wide carrier levelrange(30—90 dB L_p),the values are only around 0.5 dB,quite close to those for human obtained bypsychophysical methods,suggesting that the SCR values can represent the intensity difference limens forthe animals.A guinea pig curve,i.e.,the functional curve of versus I,is constructed.This curve issupposed to be the first complete and convincing curve for animal.     

声音调幅诱发的豚鼠皮层慢反应及反应阈

在清醒豚鼠记录了声音调幅诱发的皮层慢反应(SCR),并测定了反应阈(△I,以加幅的dB数表示)。调制波是时程200ms的准矩形波,每秒一次。调幅诱发的典型SCR呈正负正三相波,出现在调制开始或结束后40—200ms内。用白噪声、重复短声和纯音作载波,在基幅强度30—90dBSPL的范围内△I仅0.5dB左右,和人的心理物理测试结果相近,表明用SCR测得的△I能代表动物的强度辨别阈。本实验所得的豚鼠△I与I的函数曲线,可算是动物第一条较完整的△I曲线。     

CHANGES OF CORTICAL FM-EVOKED RESPONSES IN GUINEA PIGS AFTER EXPOSURE TO INTENSIVE NOISE

After exposure either to a steady intensive noise(white noise,repetitive clicks,or narrow bandnoise.all of 110 dB SPL and 15 minute duration)or to impulse noise(300 impulses of 150 dB peak SPLand 50 ms impulse duration)amplitudes of the evoked potentials recorded from the primary audi-tory cortex of guinea pigs in response to frequency modulation of pure tones were found to be syste-matically augmented while the response threshods(△F_m) markedly lowered for most carrier fre-quencies and in most conditions.For all threshold lowering cases,the averaged △F_m shift was about1/2 of their pre-exposure values,with some extreme examples where post-exposure △F_m could beas small as only 1/5 of the pre-exposure ones or even lower.Post-exposure amplitude augmentationof evoked responses can be considered as a sign of certain cortical facilitation induced by noise.Lowering of △F_m tends to suggest that such cortical facilitation implies some temporary functionalchange in the sense of improving auditory discrimina     

强噪声暴露后豚鼠听皮层调频诱发反应的变化

在强噪声暴露后豚鼠听皮层对纯音调频的诱发电位振幅增大,对多数载波频率及在多数情况下调频诱发反应阈(△F_m)则明显地降低。以反应阈降低的全部数据计算,暴露后△F_m平均约降至暴露前的一半,在少数例子中降至暴露前的1/5,甚至更低。噪声暴露后诱发电位振幅的增大可以认为是由噪声引起的皮层活动某种易化的表现△F_m的降低则倾向于提示,此种皮层易化反映暂时的功能变化,它使听觉分辨暂时得到改善。     

NORMAL VALUES OF HUMAN TYMPANOGRAMS

Acoustic compliance was measured and calculated on tympanograms taken from 171 otologicallynormal ears with the MEFM-Apparatus,the test frequency being 300 Hz.The averaged maximumcompliance was found to be 1.16 ml at zero ear-canal pressure(C_0),and 1.29 ml at the point wherepressure in the ear canal equaled that in the tympanic cavity(C_e).The range of relative compliancechange in the tympanogram was 0.65 ml in average.For the majority(96.1%)of the tested ears,pressure in the tympanic cavity did not exceed ±50 mm H_2O.A new term of compliance variation(CR=ΔC_(Δp)/ΔC_(200))is introduced as a measurable parameter to express the gradient of compliancechange.It is proposed to take ±50 and ±100 mm H_2O for Δp in routine compliance ratio measure-ment and comparison.Normal CR is approximately 0.5 when Δp is ±50 mm H_2O.