  Most of the existing work in one-stage referring expression comprehension
(REC) mainly focuses on multi-modal fusion and reasoning, while the influence
of other factors in this task lacks in-depth exploration. To fill this gap, we
conduct an empirical study in this paper. Concretely, we first build a very
simple REC network called SimREC, and ablate 42 candidate designs/settings,
which covers the entire process of one-stage REC from network design to model
training. Afterwards, we conduct over 100 experimental trials on three
benchmark datasets of REC. The extensive experimental results not only show the
key factors that affect REC performance in addition to multi-modal fusion,
e.g., multi-scale features and data augmentation, but also yield some findings
that run counter to conventional understanding. For example, as a vision and
language (V&L) task, REC does is less impacted by language prior. In addition,
with a proper combination of these findings, we can improve the performance of
SimREC by a large margin, e.g., +27.12% on RefCOCO+, which outperforms all
existing REC methods. But the most encouraging finding is that with much less
training overhead and parameters, SimREC can still achieve better performance
than a set of large-scale pre-trained models, e.g., UNITER and VILLA,
portraying the special role of REC in existing V&L research.
