In this paper, (supra-threshold) stochastic resonance phenomenon of noise-enhanced information transmission is studied in detail through the numerical calculation and the computer simulation in a non-linear multilevel threshold neural networks system, which is affected by both additive noise and multiplicative noise, then the mutual information is used to characterize the phenomenon. The mutual information as a function of additive noise intensity or multiplicative noise intensity brings on convex changes under a suitable system threshold and a fixed multiplicative noise intensity or additive noise intensity, which shows that the (supra-threshold) stochastic resonance phenomenon occurs. The increases in the number of the system threshold units can enhance the effectiveness of information transmission; the increase of the system threshold can increase the signal components that are under the threshold, and thus the supra-threshold stochastic resonance takes place more easily. In addition, by changing the additive noise intensity the supra-threshold stochastic resonance occurs more easily than by changing the multiplicative noise intensity. The above results show that both the existence of the supra-threshold stochastic resonance and the effectiveness of noise-improved the signal transmission are closely related to multiplicative or additive noise intensity, the number of threshold units, and the system threshold level.%以互信息为测度，通过数值计算和计算机仿真比较详细地讨论了在加性和乘性噪声共同作用下的一类非线性神经网络中噪声改善信息传输的(阈上)随机共振现象。在一定的系统阈值和固定的乘性(或加性)噪声强度下，互信息随着加性(或乘性)噪声强度的增加显示出上凸变化，(阈上)随机共振出现；系统阈值单元数目的增加可增强信息传输的效果；系统阈值的增加使得信号处在阈下的成分增多，(阈上)随机共振现象更容易发生。另外，改变加性噪声强度比改变乘性强度时(阈上)随机共振更容易发生。以上结果说明(阈上)随机共振现象的存在性和噪声改善信息传输的效果与乘性或加性噪声强度、阈值单元数以及系统阈值水平密切相关。
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