你不需要过于复杂的假设:通过时间差异来实现视觉表示学习
You Don't Need Strong Assumptions: Visual Representation Learning via Temporal Differences
摘要
人工智能领域的进步在很大程度上得益于那些对假设要求较低的算法。随着计算能力和数据量的增加,那些依赖较弱归纳性假设的算法通常能够表现得更好。这一点在视觉表示学习领域尤为明显:过去,该领域的研究主要依赖于有监督学习;后来,弱监督学习方法逐渐流行起来;而现在,无需人类标注的自监督学习方法则得到了广泛应用。不过,即使是现代的自监督学习方法,仍然依赖于诸如增强、掩蔽或裁剪等强归纳性假设。如果这种趋势持续下去,那么这些剩余的假设因素最终也会成为研究的瓶颈——我们的实验也证实了这一点:随着数据量的增加,最优的归纳性假设强度会下降。因此,我们需要寻找那些依赖更少假设的算法。为此,我们提出了时间差分视觉技术——这是一种新的自监督学习方法,它避免了现有的归纳性假设,而是基于“过去决定未来”的因果假设来进行训练。时间差分视觉技术通过联合训练图像编码器和运动编码器来实现目标:当前帧的表示加上编码后的运动信息,最终得到下一帧的表示。尽管时间差分视觉技术没有使用任何强归纳性假设,但它能够在密集空间任务上达到与现有方法相当的效果,从而为无需强假设条件的表示学习奠定了基础。
English Abstract
Progress in AI has largely been driven by methods that assume less. As compute and data increase, approaches with weaker inductive biases generally outperform those with stronger assumptions. This is particularly characteristic of the field of Visual Representation Learning, where approaches have gone from being dominated by Supervised Learning, to Weakly Supervised Learning, to the now widespread success of Self-Supervised Learning without human labels. Yet, even modern Self-Supervised Learning approaches still depend on strong inductive biases such as augmentations, masking, or cropping. If this trend holds, even these remaining biases should become bottlenecks at scale -- and our experiments confirm this: the optimal strength of inductive biases decreases as data grows. This motivates the search for approaches that rely on fewer assumptions. To this end, we introduce Temporal Difference in Vision (TDV), a new paradigm for self-supervised learning from video that avoids existing inductive biases, relying instead on a causal assumption that the past causes the future. TDV functions by jointly training an image encoder and a motion encoder so that the current frame's representation plus the encoded motion equals the next frame's representation. Despite not leveraging any strong inductive biases, TDV matches state-of-the-art recipes on dense spatial tasks, laying the foundation for representation learning without strong assumptions.