  Mutual gaze detection, i.e., predicting whether or not two people are looking
at each other, plays an important role in understanding human interactions. In
this work, we focus on the task of image-based mutual gaze detection, and
propose a simple and effective approach to boost the performance by using an
auxiliary 3D gaze estimation task during the training phase. We achieve the
performance boost without additional labeling cost by training the 3D gaze
estimation branch using pseudo 3D gaze labels deduced from mutual gaze labels.
By sharing the head image encoder between the 3D gaze estimation and the mutual
gaze detection branches, we achieve better head features than learned by
training the mutual gaze detection branch alone. Experimental results on three
image datasets show that the proposed approach improves the detection
performance significantly without additional annotations. This work also
introduces a new image dataset that consists of 33.1K pairs of humans annotated
with mutual gaze labels in 29.2K images.
