Title: BETTER GENERALIZATION WITH ON-THE-FLY DATASET DENOISING

Abstract: Memorization in over-parameterized neural networks can severely hurt generalization in the presence of mislabeled examples. However, mislabeled examples are to hard avoid in extremely large datasets. We address this problem using the implicit regularization effect of stochastic gradient descent with large learning rates. By the loss statistics, we are able to identify mislabeled examples with remarkable success. Then, we discard the mislabeled examples on the fly and continue training with the rest of the examples. This leads to ON-THE-FLY DATA DENOISING (ODD), a simple yet effective algorithm that is robust to mislabeled examples, while introducing almost zero computational overhead. Empirical results demonstrate the effectiveness of ODD on several datasets containing artificial and real-world mislabeled examples.

1. INTRODUCTION:

Over-parametrized deep neural networks have remarkable generalization properties while achieving near-zero training error (Zhang et al., 2016) . However, the ability to fit the entire training set is highly undesirable, as a small portion of mislabeled examples in the dataset could severely hurt generalization (Zhang et al., 2016; Arpit et al., 2017) . Meanwhile, an exponential growth in training data size is required to linearly improve generalization in vision tasks (Sun et al., 2017) ; this progress could be hindered if there are mislabeled examples within the dataset.

Mislabeled examples are to be expected in large datasets that contain millions of examples. Webbased supervision produces noisy labels (Li et al., 2017a; Mahajan et al., 2018) ; whereas human labeled datasets sacrifice accuracy for scalability (Krishna et al., 2016) . Therefore, algorithms that are robust to various levels of mislabeled examples are warranted in order to further improve generalization for very large labeled datasets.

In this paper, we propose On-the-fly Data Denoising (ODD), a simple and robust method for training with noisy examples based on the implicit regularization effect of stochastic gradient descent. First, we train residual networks with large learning rate schedules and use the resulting losses to separate clean examples from mislabeled ones. This is done by identifying examples whose losses exceed a certain threshold. Reasonable thresholds can be derived from the loss distribution for uniform label noise which does not depend on the amount of mislabeled examples in the dataset. Finally, we remove these examples from the dataset and continue training until convergence. Empirically, ODD performs significantly better than previous methods in datasets containing artificial noise (Sections 4.1 and 4.2) or real-world mislabeled examples (Section 4.3), while achieving equal or better accuracy than the state-of-the-art on clean datasets (Sections 4.1 and 4.2). We further conduct ablation studies to demonstrate that ODD is robust w.r.t hyperparameters and artificial noise levels (Section 4.4). Our method is also able to detect mislabeled examples in the CIFAR-100 dataset without any additional supervision (Figure 1 ).

2. DENOISING DATASETS ON-THE-FLY:

The goal of supervised learning is to find a function f ∈ F that describes the probability of a random label vector Y ∈ Y given a random input vector X ∈ X , which has underlying joint distribution P (X, Y ). Given a loss function (y, ŷ), one could minimize the average of over P : R(f ) = (y, f (x)) dP (x, y)

The joint distribution P (X, Y ) is usually unknown, but we could gain access to its samples via a potentially noisy labeling process, such as crowdsourcing (Krishna et al., 2016) or web queries (Li et al., 2017a) . We denote the training dataset with N examples as

D = (x i , y i ) i∈[N ] = G ∪ B. G represents correctly labeled (clean) examples sampled from P (X, Y ). B represents mislabeled examples that are not sampled from P (X, Y ), but from another distribution Q(X, Y ); G ∩ B = ∅.

We aim to learn the function f from D without knowledge about B, G or their statistics (e.g. |B|).

A typical approach is to assume that B = ∅, i.e. all examples are i.i.d. from P (X, Y ), and minimizing the following objective: The working of the implicit regularization of gradient descent is by and large an open question that attracts much recent attentions (Neyshabur, 2017; Li et al., 2017b; Du et al., 2018) . Empirically, it has been observed that large learning rates are beneficial for generalization (Kleinberg et al., 2018) . Recent work has shown that the stationary distribution of SGD iterates corresponds to an Ornstein-Uhlenbeck process (Uhlenbeck & Ornstein, 1930) with noise proportional to the learning rate (Mandt et al., 2017) 

R(f ) = - 1 N N i=1 (y, f (x)) If B = ∅ is indeed true, then R(f ) → R(f ) as N → ∞.

EQUATION

ỹ = fc(relu(x)), x ∼ N (0, I), k ∼ Uniform{0, . . . , K}

where fc(•) is the final (fully connected) layer of the network, relu(x) = max(x, 0) is the Rectified Linear Unit, and k represents a random label from K classes. This represents the case where the model's prediction is uncorrelated with the labels. The actual noise distribution could skew to the left if the model overfits to the noise, and skew to the right if the model predicts a label different from the noisy one. We find that an identity covariance matrix for x is able to explain the noise distribution; this could result from well-conditioned objectives defined via deep residual networks (He et al., 2015a) and careful initialization (He et al., 2015b) . We qualitatively demonstrate the validity of our characterization on CIFAR-100 and ImageNet datasets in Figure 2 .

Therefore, we could define a threshold via the p-th percentile of p n (l); it relates to approximately how much examples in B we would retain if Q(Y |X) is uniform. In Section 4.4, we show that this method is able to identify different percentages of uniform label noise with high precision.

2.3. A PRACTICAL ALGORITHM FOR ROBUST TRAINING:

We can utilize this implicit regularization effect to remove examples that might harm generalization, leading to On-the-fly Data Denoising (ODD), a simple algorithm robust to mislabeled examples:

1. Train all examples with large learning rates for E epochs.

2. Compute the p-th percentile of the distribution in Eq. ( 1), denoted as T p . ODD introduces three hyperparameters: E determines the amount of training that separates clean examples from noisy ones; p determines T p that specifies the trade-off between less noisy examples and more clean examples; h determines the window of averaged loss statistics to reduce variance from data augmentation. We do not explicitly estimate the portion of noise in the dataset, nor do we assume any specific noise model. In fact, the threshold T p could be used to accurately predict the portion of uniform noise in the dataset, and works quite well even on other types of label noise; we will demonstrate this in Section 4. Moreover, ODD is compatible with existing practices for learning rate schedules, such as stepwise (He et al., 2015a) or cosine (Loshchilov & Hutter, 2016) .

3.. Remove examples whose average loss of the past:



3. RELATED WORK:

Implicit Regularization of SGD The generalization of neural networks trained with SGD depend heavily on learning rate schedules (Loshchilov & Hutter, 2016) . It has been proposed that wide local minima2 could result in better generalization (Hochreiter & Schmidhuber, 1995; Chaudhari et al., 2016; Keskar et al., 2016) . Several factors could contribute to wider local optima and better generalization, such as smaller minibatch sizes (Keskar et al., 2016) , reasonable learning rates (Kleinberg et al., 2018) , and longer training time (Hoffer et al., 2017) . Moreover, solutions that are further away from the initialization may lead to wider local minima and better generalization (Hoffer et al., 2017) .

In the presence of mislabeled examples, changes in optimization landscape (Arpit et al., 2017) could result in bad local minima (Zhang et al., 2016) , although it is argued that larger batch sizes could mitigate this effect (Rolnick et al., 2017) .

Training with Mislabeled Examples One paradigm to robust training with noisy labels involves estimating the noise distribution (Liu & Tao, 2014) or confusion matrix (Sukhbaatar et al., 2014) .

Another line of methods propose to identify and clean the noisy examples through predictions of auxillary networks (Veit et al., 2017) or via binary predictions (Northcutt et al., 2017) ; the noisy labels are either pruned (Brodley et al., 1996) or replaced with model predictions (Reed et al., 2014) .

Our method is comparable to these approaches, but the key difference is that we leverage the implicit regularization effect of SGD to identify noisy examples. Other approaches propose to reweigh the examples via a pretrained network (Jiang et al., 2017) , meta learning (Ren et al., 2018) , or surrogate loss functions (Ghosh et al., 2017; Zhang & Sabuncu, 2018) . Some methods require a set of trusted examples (Xiao et al., 2015; Hendrycks et al., 2018) .

ODD has several appealing properties compared to existing methods. 

4. EXPERIMENTS:

We evaluate our method on clean and noisy versions of CIFAR-10, CIFAR-100, ImageNet (Russakovsky et al., 2015) and WebVision (Li et al., 2017a) datasets. We use stochastic gradient descent with momentum for training while following standard image preprocessing and data augmentation practices. We do not consider dropout (Srivastava et al., 2014) or model ensembles (Huang et al., 2017) in our experiments. We use h = 2 for all our ODD experiments; we observe that having h ∈ [2, 5] yields similar results.

4.1. CIFAR-10 AND CIFAR-100:

We first evaluate our method on the CIFAR-10 and CIFAR-100 datasets, which contain 50,000 training images and 10,000 validation images of size 32 × 32 with 10 and 100 labels respectively. During training, we follow the data augmentations in (Zagoruyko & Komodakis, 2016), which performs horizontal flips, takes random crops from 40 × 40 images padded by 4 pixels on each side, and fills missing pixels with reflections of the original images.

In our experiments, we train the wide residual network architecture (WRN-28-10) in (Zagoruyko & Komodakis, 2016) for 200 epochs with a minibatch size of 128, momentum 0.9 and weight decay 5×10 -4 . We consider a cosine annealing schedule as described in (Loshchilov & Hutter, 2016) with T 0 = 200, T mult = 1, η max = 0.1, η min = 10 -5 (no warm restarts), as we observe this schedule outperforms the traditional stepwise schedules on the clean dataset. We include results for two types of stepwise schedules in Appendix A.1. 2018)) that includes cross-entropy loss and mean absolute error (Ghosh et al., 2017) . We report the top-1 validation error in Table 1 , where denotes methods trained with knowledge of 1000 additional clean labels. Notably, ODD significantly outperforms all other algorithms (except for the oracle) when there is artificial noise, and is on-par with ERM even when there is no artificial noise. On the one hand, this suggests that ODD is able to distinguish the mislabeled examples and improve generalization; on the other hand, it would seem that removing certain examples even in the "clean" dataset does not seem to hinder generalization.

ODD-train ODD-valid:

ODD-train ODD-valid Mislabeled examples in CIFAR-100 We run our methods on three random seeds, and find the examples that are considered mislabeled by all the three instances (598 in total); we demonstrate some examples3 in Figure 1 , which contains ambiguous / wrong labels. 3 , where ODD is able to outperform ERM in these settings where the input examples are not uniformly distributed. 

4.3. WEBVISION -A REAL-WORLD NOISY DATASET:

We further verify the effectiveness of our method on a real-world noisy dataset. The WebVision-2017 dataset (Li et al., 2017a) contains 2.4 million of real-world noisy labels, that are crawled from Google and Flickr using the 1,000 labels from the ImageNet-2012 dataset. We train two architectures, ResNet-50 and Inception ResNet-v2 (Szegedy et al., 2016) with the same procedure in the ImageNet experiments, except for Inception ResNet-v2 we train for 50 epochs and use input images of size 299×299. We use both WebVision and ImageNet validation sets for 1-crop validation, following the settings in Jiang et al. (2017) . We do not use a pretrained model or additional labeled data from ImageNet during training.

Our ODD method with p = 30 removes in the training set around 9.0% of the total examples with ResNet-50 and 9.3% of the total examples with Inception ResNet-v2 (Szegedy et al., 2016) . In the 20% and 40% noisy cases, the optimal trade-off for generalization is at p = 10, yet even when p = 50, the validation errors are still significantly better than ERM. When there is no artificial noise, generalization of ODD starts to match that of ERM as p ≥ 10. Therefore, ODD is not very sensitive to p in these cases, and empirically p = 10 represents the best trade-off. We include results for ResNet-152 in Appendix A.2.

Sensitivity Sensitivity to the amount of noise Finally, we evaluate the training error of ODD on CIFAR under input-agnostic label noise of {1%, 5%, 10%, 20%, 30%, 40%} with p = 5, E = 50 or 75. This reflects how much examples exceed the threshold and are identified as noise at epoch E. From Figure 5 , we observe that the training error is almost exactly the amount of noise in the dataset, which demonstrates that the loss distribution of noise can be characterized by our threshold regardless of the percentage of noise in the dataset. 

5. DISCUSSION:

We 

A ADDITIONAL EXPERIMENTAL RESULTS:



A.1 CIFAR INPUT-AGNOSTIC NOISE:

In addition to the existing experiments, we include results for ORACLE, ERM, ODD with two stepwise annealing schedules. In the stepwise schedules, the learning rate starts from 0.1 and is then divided by 5 after 60, 120, 160 epochs (stepwise-i, which is used in Zagoruyko & Komodakis ( 2016)) or after 100, 150, 175 epochs (stepwise-ii). We consider cosine schedule in Section 4 because it achieves better generalization performance on the clean dataset.

For the stepwise schedules, we set E to be the epoch at which learning rate begins to decay. For the cosine schedule, we set E = 100 for CIFAR-10 and E = 50 for CIFAR-100. We set p = 20 and p = 10 for CIFAR-10 and CIFAR-100 respectively for the clean datasets; p = 10 and p = 5 for noisy datasets. This is motivated by the fact that CIFAR-10 has less labels, so the threshold has to take into account random labels that happens to be correct. 3.39 ± 0.12 6.09 ± 0.27 9.26 ± 0.14

Tables 7 and 8 contain summary of the results. The cosine learning rate schedule generally outperforms the stepwise schedules. We note that for the stepwise schedules in ERM, the optimal validation error is achieved when the learning rate just starts to decay to 0.2, after that the model starts to overfit to noise, as demonstrated in Figure 3 . We also demonstrate random examples from the CIFAR-100 that are identified as noise in Figure 8 and those that are not identified as noise in Figure 9 . The examples identified as noise often contains multiple objects, and those not identified as noise often contains only one object that is less ambiguous in terms of identity. 

:

Validation error is 3.73 for 0% mislabeled case. Additional details for CIFAR-100 in Table1.

Although the notion of wideness is controversial(Dinh et al., 2017).

We include more examples in Appendix A.4.

Super-class information is available at https://www.cs.toronto.edu/ ˜kriz/cifar.html.

Figures and Tables:

Figure 1: Mislabeled examples in the CIFAR-100 training set detected by ODD.

h epochs exceeds T from the dataset. 4. Continue training the remaining examples from epoch E + 1.

Figure 3: Training curves of ERM and ODD with 40% artificially corrupted labels.

4.1.3 GENERALIZATION ON NON-HOMOGENEOUS LABELSWe evaluate ERM and ODD on a setting without mislabeled examples, but the ratio of classes could vary. To prevent the model from utilizing the number of examples in a class, we combine multiple classes of CIFAR-100 into a single class, creating the CIFAR-20 and CIFAR-50 tasks. In CIFAR-50, we combine an even class with an odd class while we remove c% of the examples in the odd class. In CIFAR-20, we combine 5 classes in CIFAR-100 that belong to the same super-class 4 while we remove c% of the examples in 4 out of 5 classes. This is performed for both training and validation datasets. Results for ERM and ODD with p = 10 and E = 75 are shown in Table

Figure 4: Validation errors of ODD on CIFAR with different values of E.

Figure 5: Training errors of ODD on CIFAR with different values of E.

IMAGES IN CIFAR-100 CLASSIFIED AS NOISE We display the examples in CIFAR-100 training set for which our ODD methods identify as noise across 3 random seeds. One of the most common label such examples have is "leopard"; in fact, 21 of 50 "leopard" examples in the training set are perceived as hard, and we show some of them in Figure 7. It turns out that a lot of the "leopard" examples contains images that clearly contains tigers and black panthers (CIFAR-100 has a label corresponding to "tiger").

Figure 7: Examples with label "leopard" that are classified as noise.

Figure 9: Random CIFAR-100 examples that are not classified as noise.

4.1.1 GENERALIZATION ON INPUT-AGNOSTIC LABEL NOISEWe first consider label noise that are agnostic to inputs. FollowingZhang et al. (2016), We randomly replace a 0%/20%/40%) of the training labels to uniformly random ones, and evaluate generalization error on the clean validation set. We compare with the following baselines: ORACLE, where the model knows the true identity of clean examples and only trains on them; Empirical Risk Minimization (ERM,Goyal et al. (2017)) which assumes all examples are clean; MENTORNET(Jiang et al., 2017), which pretrains an auxiliary model that predicts weights for each example based on its input features; REN(Ren et al., 2018), which optimizes the weight of examples via meta-learning; mixup(Zhang et al., 2017), a data augmentation approach that trains neural networks on convex combinations of pairs of examples and their labels; and Generalized Cross Entropy (GCE, Zhang & Sabuncu (

Table content: <table/>

Minimum validation error throughout training (in percentage).

Table content: <table><tr><td/><td/><td/><td>CIFAR-10</td><td/><td/><td/><td>CIFAR-100</td></tr><tr><td>Method</td><td>0</td><td colspan="3">% of Mislabeled Examples 20</td><td>40</td><td>0</td><td>% of Mislabeled Examples 20</td><td>40</td></tr><tr><td>ORACLE</td><td>-</td><td/><td>4.25 ± 0.05</td><td colspan="2">5.06 ± 0.05</td><td>-</td><td>20.42 ± 0.20</td><td>23.64 ± 0.27</td></tr><tr><td>ERM</td><td colspan="2">3.73 ± 0.13</td><td>11.53 ± 0.06</td><td colspan="2">15.57 ± 0.45</td><td colspan="2">18.41 ± 0.17</td><td>30.38 ± 0.14</td><td>44.35 ± 0.53</td></tr><tr><td>ODD</td><td colspan="2">3.80 ± 0.10</td><td>5.33 ± 0.04</td><td colspan="2">7.16 ± 0.20</td><td colspan="2">18.19 ± 0.10</td><td>22.79 ± 0.10</td><td>27.61 ± 0.38</td></tr><tr><td>mixup</td><td colspan="2">3.04 ± 0.05</td><td>6.09 ± 0.27</td><td colspan="2">9.26 ± 0.14</td><td colspan="2">18.61 ± 0.33</td><td>28.78 ± 0.27</td><td>40.58 ± 0.35</td></tr><tr><td>GCE</td><td>-</td><td/><td>10.13 ± 0.20</td><td colspan="2">12.87 ± 0.22</td><td>-</td><td>33.19 ± 0.42</td><td>38.23 ± 0.24</td></tr><tr><td>REN</td><td>-</td><td/><td>-</td><td colspan="2">13.08 ± 0.19</td><td>-</td><td>-</td><td>38.66 ± 2.06</td></tr><tr><td>MENTORNET</td><td>-</td><td/><td>9</td><td/><td>23</td><td>-</td><td>28</td><td>44</td></tr><tr><td>MENTORNET</td><td>-</td><td/><td>8</td><td/><td>11</td><td>-</td><td>27</td><td>32</td></tr></table>

Results on input-dependent label noise experiments.Images from some classes could be harder to label correctly than that from other classes. To simulate this, we perform experiments on settings where the label noise only comes from certain types of input data. Specifically, we remove a portion of classes from the dataset (e.g. class 9 in CIFAR-10), and assign the labels of all its examples to the remaining classes randomly (e.g. a class 9 example has a class 0 -8 random label). This reduces the total number of classes, so on the validation set we only consider the classes that are not removed (e.g. classes 0 -8). We compare ERM and ODD on datasets with 10% or 20% of the examples mislabeled, and summarize the results in Table2. ODD is still able to significantly outperform ERM under such input-dependent noise.

Table content: <table><tr><td colspan="2">% of Corrupted Labels Method</td><td>CIFAR10</td><td>CIFAR100</td><td>Network</td></tr><tr><td>10</td><td>ERM ODD</td><td colspan="2">4.31 ± 0.26 19.9 ± 0.12 4.2 ± 0.02 18.79 ± 0.05</td><td>WRN-28-10</td></tr><tr><td>20</td><td>ERM ODD</td><td colspan="2">4.85 ± 0.23 24.69 ± 0.25 4.65 ± 0.19 18.05 ± 0.01</td></tr><tr><td colspan="4">4.1.2 GENERALIZATION ON INPUT-DEPENDENT LABEL NOISE</td></tr></table>

Results on CIFAR-50 and CIFAR-20 tasks.

Table content: <table><tr><td>Task</td><td>Method</td><td>30</td><td>c% of Removed Labels 50</td><td>70</td><td>Network</td></tr><tr><td>CIFAR-50</td><td>ERM ODD</td><td colspan="3">21.52 ± 0.13 22.03 ± 0.05 22.45 ± 0.10 21.05 ± 0.16 21.39 ± 0.18 21.87 ± 0.08</td><td>WRN-28-10</td></tr><tr><td>CIFAR-20</td><td>ERM ODD</td><td colspan="3">13.61 ± 0.20 14.86 ± 0.08 15.51 ± 0.32 13.37 ± 0.27 14.63 ± 0.26 15.44 ± 0.24</td><td/></tr><tr><td>4.2 IMAGENET</td><td/><td/><td/><td/><td/></tr><tr><td colspan="6">We conduct additional experiments on the ImageNet-2012 classification dataset (Russakovsky et al.,</td></tr><tr><td colspan="6">2015). The dataset contains 1.28 million training images and 50,000 validation images from 1,000</td></tr><tr><td colspan="6">classes. Input-agnostic random noise of 0%, 20%, 40% are considered. We follow standard data</td></tr><tr><td colspan="6">augmentation practices during training, including scale and aspect ratio distortions, random crops,</td></tr><tr><td colspan="5">and horizontal flips. We only use the center 224 × 224 crop for validation.</td><td/></tr></table>

Results on ImageNet validation set. MENTORNET results from(Jiang et al., 2017).

Table content: <table><tr><td/><td/><td colspan="4">% of Mislabeled Examples</td><td/><td/></tr><tr><td>Method</td><td>0</td><td/><td>20</td><td/><td>40</td><td/><td>Network</td></tr><tr><td/><td colspan="6">Top-1 Top-5 Top-1 Top-5 Top-1 Top-5</td><td/></tr><tr><td colspan="2">ERM ODD (p = 10) 23.37 23.39</td><td>6.77 6.94</td><td>26.23 25.05</td><td>8.51 7.89</td><td colspan="2">29.61 10.52 27.51 9.25</td><td>ResNet-50</td></tr><tr><td colspan="2">ERM ODD (p = 10) 21.35 21.31</td><td>5.69 5.98</td><td>23.9 22.49</td><td>7.12 6.45</td><td>27.39 25.22</td><td>9.16 7.91</td><td>ResNet-152</td></tr><tr><td>ERM MENTORNET</td><td>23 -</td><td>--</td><td>--</td><td>--</td><td>-34.9</td><td>-14.1</td><td>Inception ResNet-v2</td></tr></table>

Validation errors on WebVision / ImageNet validation sets while training on WebVision.

Table content: <table><tr><td>Method</td><td colspan="2">WebVision Top-1 Top-5</td><td>Top-1</td><td>ImageNet</td><td>Top-5</td><td>Network</td></tr><tr><td>ERM ODD</td><td colspan="6">27.90 ± 0.11 10.94 ± 0.08 34.71 ± 0.12 14.87 ± 0.05 ResNet-50 27.49 ± 0.22 10.79 ± 0.09 34.48 ± 0.01 14.75 ± 0.01</td></tr><tr><td>ERM ODD</td><td>25.71 25.38</td><td>9.30 9.37</td><td>33.62 33.27</td><td/><td>13.97 13.68</td><td>Inception ResNet-v2</td></tr><tr><td>MENTORNET</td><td>29.2</td><td>12.0</td><td>37.5</td><td/><td>17.0</td></tr></table>

Table 5 suggests that our method is able to outperform both ERM and MENTORNET when the training dataset is noisy, even as we remove a notable portion of examples. We include more results in Appendix A.3. In comparison, we removed around 1.1% of examples in ImageNet (Table 10, Appendix A.2); this may suggest that WebVision labels are indeed much noisier. We first evaluate noisy ImageNet classification with ResNet-50 where p ∈ {1, 10, 30, 50, 80} and E = 60 in Table 6. A higher p includes more clean examples at the cost of involving more noisy examples.

Table content: <table><tr><td>4.4 ABLATION STUDIES</td></tr><tr><td>Sensitivity to p</td></tr></table>

Ablation studies over the hyperparameter p on ImageNet.

Table content: <table><tr><td/><td/><td colspan="4">% of Mislabeled Examples</td><td/></tr><tr><td>Method</td><td>0</td><td/><td>20</td><td/><td>40</td><td/><td>Network</td></tr><tr><td/><td colspan="6">Top-1 Top-5 Top-1 Top-5 Top-1 Top-5</td></tr><tr><td>ODD (p = 1)</td><td>23.74</td><td>7.17</td><td>25.33</td><td>8.13</td><td>27.96</td><td>9.89</td></tr><tr><td colspan="2">ODD (p = 10) 23.37</td><td>6.94</td><td>25.05</td><td>7.89</td><td>27.51</td><td>9.25</td></tr><tr><td colspan="2">ODD (p = 30) 23.48 ODD (p = 50) 23.52</td><td>6.89 6.89</td><td>25.05 25.31</td><td>7.77 7.92</td><td>27.75 28.63</td><td>9.4 9.4</td><td>ResNet-50</td></tr><tr><td colspan="2">ODD (p = 80) 23.31</td><td>6.74</td><td>25.93</td><td>8.33</td><td colspan="2">29.41 10.43</td></tr><tr><td colspan="8">relatively small where the learning rate is high, but is unable to perform well when the learning rate</td></tr><tr><td colspan="3">decreases at later stages of the training.</td><td/><td/><td/><td/></tr></table>

have proposed ODD, a straightforward method for robust training with mislabeled examples. ODD utilizes the implicit regularization effect of stochastic gradient descent to prune examples that potentially harm generalization. Empirical results demonstrate that ODD is able to significantly outperform related methods on a wide range of datasets with artificial and real-world mislabeled examples, maintain competitiveness with ERM on clean datasets, as well as detecting mislabeled examples automatically in CIFAR-100.The implicit regularization of stochastic gradient descent opens up other research directions for implementing robust algorithms. For example, we could consider using a smaller network to remove examples, removing examples not only once but multiple times, retraining from scratch with the denoised dataset, or other data-augmentation approaches such as mixup(Zhang et al., 2017). Moreover, it would be interesting to understand the implicit regularization over mislabeled examples from a theoretical viewpoint.

Table content: <table/>

Minimum validation error throughout training (in percentage) on CIFAR10.

Table content: <table><tr><td>Method</td><td>0</td><td colspan="2">% of Mislabeled Examples 20</td><td>40</td><td>Network</td></tr><tr><td>ORACLE (cosine)</td><td>-</td><td>4.25 ± 0.05</td><td colspan="2">5.06 ± 0.05</td></tr><tr><td>ORACLE (stepwise-i)</td><td>-</td><td>4.45 ± 0.06</td><td colspan="2">5.29 ± 0.01</td></tr><tr><td>ORACLE (stepwise-ii)</td><td>-</td><td>4.44 ± 0.03</td><td colspan="2">5.14 ± 0.15</td></tr><tr><td>ERM (cosine)</td><td colspan="4">3.73 ± 0.13 11.53 ± 0.06 15.57 ± 0.45</td></tr><tr><td>ERM (stepwise-i) ERM (stepwise-ii)</td><td colspan="4">3.75 ± 0.02 8.39 ± 0.24 10.77 ± 0.26 3.93 ± 0.10 7.79 ± 0.03 10.12 ± 0.27</td><td>WRN-28-10</td></tr><tr><td>ODD (cosine)</td><td colspan="2">3.80 ± 0.10 5.33 ± 0.04</td><td colspan="2">7.16 ± 0.20</td></tr><tr><td>ODD (stepwise-i)</td><td colspan="2">3.92 ± 0.09 5.47 ± 0.16</td><td colspan="2">7.50 ± 0.15</td></tr><tr><td>ODD (stepwise-ii)</td><td colspan="2">4.06 ± 0.15 5.52 ± 0.08</td><td colspan="2">7.42 ± 0.05</td></tr><tr><td>MIXUP (α = 1.0)</td><td colspan="4">3.04 ± 0.05 10.55 ± 0.31 25.14 ± 0.08</td></tr><tr><td>MIXUP (α = 8.0)</td><td/><td/><td/><td/></tr></table>

Minimum validation error throughout training (in percentage) on CIFAR100.We evaluate precision and recall for examples classified as noise on CIFAR10 and CIFAR100 for different noise levels(1, 5, 10, 20, 30, 40)  in Figure6. The recall values are around 0.84 to 0.88 where as the precision values range from 0.88 to 0.92. This demonstrates that ODD is able to achieve good precision/recall with default hyperparameters even at different noise levels.We include the ImageNet ablation experiments on the hyperparameter p on the ResNet-152 architecture in Table9. Compared to the ResNet-50 experiments, we can draw similar conclusions here: p = 10 generally represents the best trade-off. We show the percentage of examples discarded by NOISE CLASSIFIER in Table10; the percentage of discarded examples by p = 10 is very close to the actual noise level. Moreover, the percentage of discarded examples does not vary significantly when we change our architecture from ResNet-50 to ResNet-152.

Table content: <table><tr><td>Method</td><td>0</td><td>% of Mislabeled Examples 20</td><td>40</td><td>Network</td></tr><tr><td>ORACLE (cosine)</td><td>-</td><td colspan="2">20.42 ± 0.20 23.64 ± 0.27</td><td/></tr><tr><td>ORACLE (stepwise-i)</td><td>-</td><td colspan="2">20.21 ± 0.22 24.18 ± 0.04</td><td/></tr><tr><td>ORACLE (stepwise-ii)</td><td>-</td><td colspan="2">20.99 ± 0.25 23.79 ± 0.05</td><td/></tr><tr><td>ERM (cosine)</td><td colspan="3">18.41 ± 0.17 30.38 ± 0.14 44.35 ± 0.53</td><td/></tr><tr><td>ERM (stepwise-i) ERM (stepwise-ii)</td><td colspan="3">18.77 ± 0.33 28.81 ± 0.48 33.93 ± 0.26 18.80 ± 0.15 29.28 ± 0.27 36.72 ± 0.49</td><td>WRN-28-10</td></tr><tr><td>ODD (cosine)</td><td colspan="3">18.19 ± 0.10 22.79 ± 0.10 27.61 ± 0.38</td><td/></tr><tr><td>ODD (stepwise-i)</td><td colspan="3">18.82 ± 0.14 22.95 ± 0.19 28.01 ± 0.15</td><td/></tr><tr><td>ODD (stepwise-ii)</td><td colspan="3">18.53 ± 0.10 23.27 ± 0.34 28.79 ± 0.03</td><td/></tr><tr><td>MIXUP (α = 1.0)</td><td colspan="3">18.61 ± 0.33 28.78 ± 0.27 44.43 ± 0.31</td><td/></tr><tr><td>MIXUP (α = 8.0)</td><td colspan="3">20.50 ± 0.27 28.86 ± 0.17 40.58 ± 0.35</td><td/></tr></table>

Ablation studies over the hyperparameter p on ImageNet-2012.

Table content: <table><tr><td/><td/><td colspan="4">% of Mislabeled Examples</td><td/><td/></tr><tr><td>Method</td><td>0</td><td/><td>20</td><td/><td>40</td><td/><td>Network</td></tr><tr><td/><td colspan="6">Top-1 Top-5 Top-1 Top-5 Top-1 Top-5</td><td/></tr><tr><td>ERM</td><td>21.31</td><td>5.69</td><td>23.9</td><td>7.12</td><td>27.39</td><td>9.16</td><td/></tr><tr><td>ODD (p = 1)</td><td>21.50</td><td>6.08</td><td>22.87</td><td>6.61</td><td>25.6</td><td>8.42</td><td/></tr><tr><td>ODD (p = 5)</td><td>21.40</td><td>5.98</td><td>22.67</td><td>6.54</td><td>25.43</td><td>8.01</td><td>ResNet-152</td></tr><tr><td colspan="2">ODD (p = 10) 21.35</td><td>5.98</td><td>22.49</td><td>6.45</td><td>25.22</td><td>7.91</td><td/></tr><tr><td colspan="2">ODD (p = 30) 21.45</td><td>5.78</td><td>22.68</td><td>6.52</td><td>25.77</td><td>8.24</td><td/></tr><tr><td colspan="2">ODD (p = 50) 21.04</td><td>5.7</td><td>22.78</td><td>6.5</td><td>26.73</td><td>8.9</td><td/></tr></table>

Percentage of example discraded by ODD on ImageNet-2012.We include the WebVision ablation experiments on the hyperparameter p on the ResNet-50 and Inception ResNet-v2 architecture with E = 60 in Tables11 and 12, where we report top-1 and top-5 validation errors on WebVision and ImageNet validation sets respectively, as well as how many examples are discarded by our method at epoch 60. Similar to the results in ImageNet, generalization performance is generally insensitive to the hyperparameter p, except for p = 1, which discarded 25.3% of the examples. We use 2 seeds for each experiment setting. Notice that at each p, WebVision has more examples discarded compared to ImageNet (with 0% artificial noise), which further suggests that it has more mislabeled examples than ImageNet. Again, the percentage of discarded examples does not vary significantly across different architectures.

Table content: <table><tr><td>% Mislabeled</td><td>1</td><td colspan="3">Hyperparameter p 10 30 50</td><td>80</td><td>Network</td></tr><tr><td>0%</td><td>6.2</td><td>2.6</td><td>1.1</td><td>0.7</td><td>0.5</td></tr><tr><td>20%</td><td colspan="5">24.4 21.1 19.3 17.6 11.5</td><td>ResNet-50</td></tr><tr><td>40%</td><td colspan="5">44.8 40.3 36.2 28.1 7.8</td></tr><tr><td>0%</td><td>5.5</td><td>2.3</td><td>1.1</td><td>0.7</td><td>0.4</td></tr><tr><td>20%</td><td colspan="5">23.8 20.8 19.2 17.5 0.7</td><td>ResNet-152</td></tr><tr><td>40%</td><td colspan="5">44.1 40.2 36.2 27.6 0.6</td></tr></table>

Ablation studies on WebVision with ResNet-50. ERM 27.90 ± 0.11 10.94 ± 0.08 34.71 ± 0.12 14.87 ± 0.05 -ODD (p = 1) 28.03 ± 0.03 11.45 ± 0.05 34.68 ± 0.03 15.05 ± 0.08 25.3 ODD (p = 10) 27.45 ± 0.01 11.07 ± 0.01 34.47 ± 0.01 14.80 ± 0.01 15.1 ODD (p = 30) 27.49 ± 0.22 10.79 ± 0.09 34.48 ± 0.01 14.75 ± 0.01 9.0 ODD (p = 50) 27.59 ± 0.01 10.77 ± 0.01 34.40 ± 0.03 14.81 ± 0.02 5.8 ODD (p = 80) 27.53 ± 0.02 10.82 ± 0.01 34.27 ± 0.04 14.81 ± 0.02 2.5

Table content: <table><tr><td>Method</td><td>WebVision Top-1 Top-5</td><td>Top-1</td><td>ImageNet</td><td>Top-5</td><td>% Discarded</td></tr></table>

Ablation studies on WebVision with Inception ResNet-v2.

Table content: <table><tr><td>Method</td><td colspan="4">WebVision Top-1 Top-5 Top-1 Top-5 ImageNet</td><td>% Discarded</td></tr><tr><td>ERM</td><td>25.71</td><td>9.3</td><td colspan="2">33.62 13.97</td><td>-</td></tr><tr><td>ODD (p = 1)</td><td colspan="3">25.99 10.07 34.23</td><td>14.6</td><td>25.7</td></tr><tr><td colspan="2">ODD (p = 10) 25.69</td><td>9.45</td><td colspan="2">33.91 14.14</td><td>15.2</td></tr><tr><td colspan="2">ODD (p = 30) 25.38</td><td>9.37</td><td colspan="2">33.27 13.68</td><td>9.3</td></tr><tr><td colspan="2">ODD (p = 50) 25.57</td><td>9.22</td><td colspan="2">33.42 13.79</td><td>6.1</td></tr><tr><td colspan="2">ODD (p = 80) 25.50</td><td>9.21</td><td colspan="2">33.27 13.76</td><td>2.8</td></tr></table>

Peer review (iclr2019):
 Thanks for the rebuttal. But, I am still not very convinced with the proposed results. For CIFAR-100 (0%), you get about 0.2% gain, for ImageNet (0%), you get about 0.2% loss in top-5 accuracy, and for WebVision, you get about 0.3% gain. I am not sure whether you can call these as statistically significant gains. I believe such gain/loss can be obtained with many other tweaks, such as the learning rate scheduling, as the authors have done. I believe extensive testing the proposed method on many real noisy datasets, not the synthetically generated ones, and showing the consistent gains would much strengthen the paper. But, at the current version, the only such result is Table 5, which is, again, not very convincing to me. So, I still keep my rating. ======= Summary: The authors propose a simple empirical method for cleaning the dataset for training. By using the implicit regularization property of SGD-based optimization method, the authors come up with a method of setting a threshold for the training loss statistics such that the examples that show losses above the threshold are regarded as noisy examples and are discarded. Their empirical results show that ODD (their method) can outperform other baselines when artificial random label noise is injected. They also show ablation studies on the hyperparameters and show the final result seems to be robust to those parameters. Pros: - The method is very simple - The empirical results, particularly on the synthetic noisy training data, seems to be encouraging. - The ablation study argues that the method is robust to the hyperparameters, p, E, and h. Cons: - I think the results remains to be highly empirical. While it is interesting to see the division of the loss statistics in Figure 2, I am not very convinced about the real usage of the proposed method. The result in Table 5 shows that ODD can outperform ERM for real world datasets, but the improvement seems to be marginal. Moreover, the hyperparameter p was set to 30 for that experiment, but how did the authors choose that parameter? Clearly, if you choose wrong p, I think the performance will degrade, and it is not clear how you can choose p in real applications. The ablation studies are only with synthetic noisy label data, so I think the result is somewhat limited. - I think the paper shows interesting results, but my concern is that it seems to be quite empirical. The positive results are particularly on the synthetic data case.