LambdaNetworks: Modeling long-range Interactions without Attention

We present a framework for capturing long-range interactions between an input and structured contextual information (e.g. a pixel surrounded by other pixels). Our method, called the lambda layer, captures such interactions by transforming available contexts into linear functions, termed lambdas, and applying these linear functions to each input separately. Lambda layers may be implemented to model content and position-based interactions in global, local or masked contexts. As they bypass the need for expensive attention maps, lambda layers can routinely be applied to inputs of length in the thousands, enabling their applications to long sequences or high-resolution images. The resulting neural network architectures, LambdaNetworks, are computationally efficient and simple to implement using direct calls to operations available in modern neural network libraries. Experiments on ImageNet classification and COCO object detection and instance segmentation demonstrate that LambdaNetworks significantly outperform their convolutional and attentional counterparts while being more computationally efficient. Finally, we introduce LambdaResNets, a family of LambdaNetworks, that considerably improve the speed-accuracy tradeoff of image classification models. LambdaResNets reach state-of-the-art accuracies on ImageNet while being ∼4.5x faster than the popular EfficientNets on modern machine learning accelerators.