  Learning from data in the quaternion domain enables us to exploit internal
dependencies of 4D signals and treating them as a single entity. One of the
models that perfectly suits with quaternion-valued data processing is
represented by 3D acoustic signals in their spherical harmonics decomposition.
In this paper, we address the problem of localizing and detecting sound events
in the spatial sound field by using quaternion-valued data processing. In
particular, we consider the spherical harmonic components of the signals
captured by a first-order ambisonic microphone and process them by using a
quaternion convolutional neural network. Experimental results show that the
proposed approach exploits the correlated nature of the ambisonic signals, thus
improving accuracy results in 3D sound event detection and localization.
