To create neural representations of external stimuli, the brain performs a number of processing steps that transform its inputs. For fundamental attributes, such as stimulus contrast, this involves one or more nonlinearities that are believed to optimise the neural code to represent features of the natural environment. Here we ask if the same is also true of more complex stimulus dimensions, such as emotional facial expression. We report the results of three experiments combining morphed facial stimuli with electrophysiological and psychophysical methods to measure the function mapping emotional expression intensity to internal response. The results converge on a nonlinearity that accelerates over weak expressions, and then becomes shallower for stronger expressions, similar to the situation for lower level stimulus properties. We further demonstrate that the nonlinearity is not attributable to the morphing procedure used in stimulus generation.

中文翻译：

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情绪面部表情的非线性转导。

为了创建外部刺激的神经表示，大脑执行许多处理步骤来转换其输入。对于基本属性（例如刺激对比），这涉及一种或多种非线性，这些非线性被认为可以优化神经代码以表示自然环境的特征。在这里，我们问更复杂的刺激维度（如情感表情）是否也是如此。我们报告了结合变形的面部刺激与电生理学和心理物理方法来测量映射情感表达强度到内部反应的功能的三个实验的结果。结果收敛于非线性，该非线性在弱表达式上加速，然后对于较强的表达式变浅，类似于较低级别的刺激特性的情况。