Batch construction and multitask learning in visual relationship recognition

An image can be described by the objects within it, as well as interactions between those objects. A pair of object labels together with an interaction label is known as a visual relationship, and is represented as a triplet of the form (subject, predicate, object). Recognising visual relationships in a given image is a challenging task, owing to the combinatorially large number of possible relationship triplets, which leads to an extreme classification problem, as well as a very long tail found typically in the distribution of those possible triplets. We investigate the effects of three strategies that could potentially address these issues. Firstly, instead of predicting the full triplet we opt to predict each element separately. Secondly, we investigate the use of shared network parameters to perform these separate predictions in a multitask setting. Thirdly, we consider a class-selective batch construction strategy to expose the network to more of the many rare classes during mini-batch training. Our experiments demonstrate that batch construction can improve performance on the long tail, possibly at the expense of accuracy on the small number of dominating classes. We also find that a multitask model neither improves nor impedes performance in any significant way, but that its smaller size may be beneficial.