The neural dynamics underlying brain activity are critical to understanding
cognitive processes and mental disorders. However, current voxel-based
whole-brain dimensionality reduction techniques fall short of capturing these
dynamics, producing latent timeseries that inadequately relate to behavioral
tasks. To address this issue, we introduce a novel approach to learning
low-dimensional approximations of neural dynamics by using a sequential
variational autoencoder (SVAE) that represents the latent dynamical system via
a neural ordinary differential equation (NODE). Importantly, our method finds
smooth dynamics that can predict cognitive processes with accuracy higher than
classical methods. Our method also shows improved spatial localization to
task-relevant brain regions and identifies well-known structures such as the
motor homunculus from fMRI motor task recordings. We also find that non-linear
projections to the latent space enhance performance for specific tasks,
offering a promising direction for future research. We evaluate our approach on
various task-fMRI datasets, including motor, working memory, and relational
processing tasks, and demonstrate that it outperforms widely used
dimensionality reduction techniques in how well the latent timeseries relates
to behavioral sub-tasks, such as left-hand or right-hand tapping. Additionally,
we replace the NODE with a recurrent neural network (RNN) and compare the two
approaches to understand the importance of explicitly learning a dynamical
system. Lastly, we analyze the robustness of the learned dynamical systems
themselves and find that their fixed points are robust across seeds,
highlighting our method's potential for the analysis of cognitive processes as
dynamical systems.

本文介绍了一种新方法，使用顺序变分自编码器（SVAE）和神经常微分方程（NODE）来学习神经动力学的低维逼近。该方法产生的光滑动态可以准确地预测认知过程，并显示出对任务相关的脑区的改善空间定位并识别出著名的结构，如 fMRI 运动任务记录中的运动全身像。

从全脑数据中学习低维度动力学提高任务捕获能力

Learning low-dimensional dynamics from whole-brain data improves task  capture

Traditional studies on voice conversion (VC) have made progress with parallel
training data and known speakers. Good voice conversion quality is obtained by
exploring better alignment modules or expressive mapping functions. In this
study, we investigate zero-shot VC from a novel perspective of self-supervised
disentangled speech representation learning. Specifically, we achieve the
disentanglement by balancing the information flow between global speaker
representation and time-varying content representation in a sequential
variational autoencoder (VAE). A zero-shot voice conversion is performed by
feeding an arbitrary speaker embedding and content embeddings to the VAE
decoder. Besides that, an on-the-fly data augmentation training strategy is
applied to make the learned representation noise invariant. On TIMIT and VCTK
datasets, we achieve state-of-the-art performance on both objective evaluation,
i.e., speaker verification (SV) on speaker embedding and content embedding, and
subjective evaluation, i.e., voice naturalness and similarity, and remains to
be robust even with noisy source/target utterances.

本研究提出利用自监督分离式语音表示学习的新视角进行零样本语音转换，通过在序列变分自编码器中平衡全局说话人表示和时变内容表示之间的信息流实现分离，并应用实时数据增强培训策略以使所学表示不受噪声干扰。在 TIMIT 和 VCTK 数据集上表现出了优越性能，不仅在客观评估上表现良好，而且在主观评估方面具有鲁棒性，即使在源 / 目标语音帧存在噪声的情况下仍能保持不错的性能。