Response to Reviewer QwNu
Thanks for your constructive comments. We provide our feedback as follows.
**Q1: Comparison between Vision Mamba and Vision RWKV.**
**A1:** Vision Mamba\[1\](Vim) and Vision RWKV (VRWKV) are both linear complexity models, but they differ in terms of model structure and scalability. We have added a comparison with Vim in Section A.3 in the Appendix.
As demonstrated in Table 7, Vim exhibits superior Top-1 Accuracy in classification tasks for tiny and small sizes, whereas the base size models deliver similar performance. Benefitting from our careful stability design, VRWKV can scale up to larger models, while Vim encounters instability during training such as #issue30 in their official repository.
When reproducing Vim-T for detection tasks, we encountered the same issue as described in #issue30, where the loss became NaN, and the final $AP_{box}$ was 25.5 before the training diverged. In contrast, **VRWKV did not exhibit any instability issues across models ranging from tiny to large** and achieved higher detection scores compared to ViT using window attention.
Furthermore, we compare the inference speed of three attention mechanisms: Vanilla Attn, Bi-WKV, and Vision Mamba, shown in Figure 5 in the Appendix. As the input resolution increases, the inference cost of vanilla attention quickly surpasses that of Bi-WKV and Vision Mamba. With our optimizations and design on CUDA, our Bi-WKV demonstrates faster speeds than Vision Mamba at the same input resolution.
**Q2: Innovation of Vision RWKV.**
**A2:** As described in lines 46-53 of our paper, the direct application of the language model RWKV to the visual domain presents two significant challenges: (1) RWKV lacks a global receptive field in its attention mechanism, which is essential in the vision domain. (2) Ensuring the training stability of RWKV when the model scales up requires a more carefully designed approach.
To address the first issue, we designed a bidirectional attention mechanism, Bi-WKV, which maintains linear complexity while achieving a global reception field. We also rewrote the operation at the CUDA level for better optimization. We also modified RWKV's shift method to better suit visual tasks.
**In Table 5 presented in the ablation study, our implementation yielded a 4-point improvement in Top-1 Accuracy compared to directly employing the original RWKV model.**
For the second issue, we have identified the appropriate key position to add normalization layers, making our model scale up stably while showing consistent improvement in model capacity.
[1] Zhu, L., Liao, B., Zhang, Q., Wang, X., Liu, W., & Wang, X. (2024). Vision mamba: Efficient visual representation learning with bidirectional state space model. arXiv preprint arXiv:2401.09417.