  We tackle the problem of learning object detectors without supervision.
Differently from weakly-supervised object detection, we do not assume
image-level class labels. Instead, we extract a supervisory signal from
audio-visual data, using the audio component to "teach" the object detector.
While this problem is related to sound source localisation, it is considerably
harder because the detector must classify the objects by type, enumerate each
instance of the object, and do so even when the object is silent. We tackle
this problem by first designing a self-supervised framework with a contrastive
objective that jointly learns to classify and localise objects. Then, without
using any supervision, we simply use these self-supervised labels and boxes to
train an image-based object detector. With this, we outperform previous
unsupervised and weakly-supervised detectors for the task of object detection
and sound source localization. We also show that we can align this detector to
ground-truth classes with as little as one label per pseudo-class, and show how
our method can learn to detect generic objects that go beyond instruments, such
as airplanes and cats.
