DHVT: Dynamic Hybrid Vision Transformer for Small Dataset Recognition.

The performance gap between Vision Transformers (ViTs) and Convolutional Neural Networks (CNNs) persists due to the lack of inductive bias, notably when training from scratch with limited datasets. This paper identifies two crucial shortcomings in ViTs: spatial relevance and diverse channel representation. Thus, ViTs struggle to grasp fine-grained spatial features and robust channel representation due to insufficient data. We propose the Dynamic Hybrid Vision Transformer (DHVT) to address these challenges. Regarding the spatial aspect, DHVT introduces convolution in the feature embedding phase and feature projection modules to enhance spatial relevance. Regarding the channel aspect, the dynamic aggregation mechanism and a groundbreaking design "head token" facilitate the recalibration and harmonization of disparate channel representations. Moreover, we investigate the choices of the network meta-structure and adopt the optimal multi-stage hybrid structure without the conventional class token. The methods are then modified with a novel dimensional variable residual connection mechanism to leverage the potential of the structure sufficiently. This updated variant, called DHVT2, offers a more computationally efficient solution for vision-related tasks. DHVT and DHVT2 achieve state-of-the-art image recognition results, effectively bridging the performance gap between CNNs and ViTs. The downstream experiments further demonstrate their strong generalization capacities.