300,584 research outputs found
Unsupervised 3D Pose Estimation with Geometric Self-Supervision
We present an unsupervised learning approach to recover 3D human pose from 2D
skeletal joints extracted from a single image. Our method does not require any
multi-view image data, 3D skeletons, correspondences between 2D-3D points, or
use previously learned 3D priors during training. A lifting network accepts 2D
landmarks as inputs and generates a corresponding 3D skeleton estimate. During
training, the recovered 3D skeleton is reprojected on random camera viewpoints
to generate new "synthetic" 2D poses. By lifting the synthetic 2D poses back to
3D and re-projecting them in the original camera view, we can define
self-consistency loss both in 3D and in 2D. The training can thus be self
supervised by exploiting the geometric self-consistency of the
lift-reproject-lift process. We show that self-consistency alone is not
sufficient to generate realistic skeletons, however adding a 2D pose
discriminator enables the lifter to output valid 3D poses. Additionally, to
learn from 2D poses "in the wild", we train an unsupervised 2D domain adapter
network to allow for an expansion of 2D data. This improves results and
demonstrates the usefulness of 2D pose data for unsupervised 3D lifting.
Results on Human3.6M dataset for 3D human pose estimation demonstrate that our
approach improves upon the previous unsupervised methods by 30% and outperforms
many weakly supervised approaches that explicitly use 3D data
A Theoretical Study of Inductive Biases in Contrastive Learning
Understanding self-supervised learning is important but challenging. Previous
theoretical works study the role of pretraining losses, and view neural
networks as general black boxes. However, the recent work of Saunshi et al.
argues that the model architecture -- a component largely ignored by previous
works -- also has significant influences on the downstream performance of
self-supervised learning. In this work, we provide the first theoretical
analysis of self-supervised learning that incorporates the effect of inductive
biases originating from the model class. In particular, we focus on contrastive
learning -- a popular self-supervised learning method that is widely used in
the vision domain. We show that when the model has limited capacity,
contrastive representations would recover certain special clustering structures
that are compatible with the model architecture, but ignore many other
clustering structures in the data distribution. As a result, our theory can
capture the more realistic setting where contrastive representations have much
lower dimensionality than the number of clusters in the data distribution. We
instantiate our theory on several synthetic data distributions, and provide
empirical evidence to support the theory
Combined self-learning based single-image super-resolution and dual-tree complex wavelet transform denoising for medical images
In this paper, we propose a novel self-learning based single-image super-resolution (SR) method, which is coupled with dual-tree complex wavelet transform (DTCWT) based denoising to better recover high-resolution (HR) medical images. Unlike previous methods, this self-learning based SR approach enables us to reconstruct HR medical images from a single low-resolution (LR) image without extra training on HR image datasets in advance. The relationships between the given image and its scaled down versions are modeled using support vector regression with sparse coding and dictionary learning, without explicitly assuming reoccurrence or self-similarity across image scales. In addition, we perform DTCWT based denoising to initialize the HR images at each scale instead of simple bicubic interpolation. We evaluate our method on a variety of medical images. Both quantitative and qualitative results show that the proposed approach outperforms bicubic interpolation and state-of-the-art single-image SR methods while effectively removing noise
Block sparsity and gauge mediated weight sharing for learning dynamical laws from data
Recent years have witnessed an increased interest in recovering dynamical
laws of complex systems in a largely data-driven fashion under meaningful
hypotheses. In this work, we propose a method for scalably learning dynamical
laws of classical dynamical systems from data. As a novel ingredient, to
achieve an efficient scaling with the system size, block sparse tensor trains -
instances of tensor networks applied to function dictionaries - are used and
the self similarity of the problem is exploited. For the latter, we propose an
approach of gauge mediated weight sharing, inspired by notions of machine
learning, which significantly improves performance over previous approaches.
The practical performance of the method is demonstrated numerically on three
one-dimensional systems - the Fermi-Pasta-Ulam-Tsingou system, rotating
magnetic dipoles and classical particles interacting via modified Lennard-Jones
potentials. We highlight the ability of the method to recover these systems,
requiring 1400 samples to recover the 50 particle Fermi-Pasta-Ulam-Tsingou
system to residuum of , 900 samples to recover the 50 particle
magnetic dipole chain to residuum of and 7000 samples to
recover the Lennard-Jones system of 10 particles to residuum
. The robustness against additive Gaussian noise is
demonstrated for the magnetic dipole system.Comment: 13 pages, 6 figure
The Influence of Observational Learning on Self-reported Physical Activity, Self-efficacy for Physical Activity, and Health-related Fitness Knowledge for Physical Activity
The obesity epidemic has caused tremendous burden to our economy and healthcare system. Physical activity is one method that can reduce the obesity rate. However, physical activity declines in high school and does not recover. The likelihood of adolescents continuing their involvement in physical activity depends on how they navigate the highs and lows of their physical activity experiences (Feltz & Magyar, 2006). The purpose of this study is to look at the role of observational learning in physical activity and behaviors in an adolescent population. Specifically, this research examines the influence of observational learning on self-reported physical activity, self-efficacy for physical activity, and health-related fitness knowledge, controlling for gender, ethnicity, and grade
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