Recurrent neural networks (RNNs) are powerful architectures to model sequential data, due to their capability to learn short and long-term dependencies between the basic elements of a sequence. Nonetheless, popular tasks such as speech or images recognition, involve multi-dimensional input features that are characterized by strong internal dependencies between the dimensions of the input vector. We propose a novel quaternion recurrent neural network (QRNN) that takes into account both the external relations and these internal structural dependencies with the quaternion algebra. Similarly to capsules, quaternions allow the QRNN to code internal dependencies by composing and processing multidimensional features as single entities, while the recurrent operation reveals correlations between the elements composing the sequence. We show that the QRNN achieves better performances in both a synthetic memory copy task and in a realistic application of phoneme recognition. Finally, we show that the QRNN reduces by a factor of 3x the number of free parameters needed, compared to RNNs to reach equal or even better results, leading to a more compact representation of the relevant information.

研究提出了一种用四元数代替实数的递归神经网络来处理多维特征，从而更好地模拟长期依赖，并在语音识别应用中表现出更好的性能和更紧凑的表示方式。

四元数循环神经网络