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Title: Semi-supervised classification by reaching consensus among modalities

Paper content:
Deep learning has demonstrated abilities to learn complex structures, but they can be restricted by available data.
Recently, Consensus Networks (CNs) were proposed to alleviate data sparsity by utilizing features from multiple modalities, but they too have been limited by the size of labeled data.
In this paper, we extend CN to Transductive Consensus Networks (TCNs), suitable for semi-supervised learning.
In TCNs, different modalities of input are compressed into latent representations, which we encourage to become indistinguishable during iterative adversarial training.
To understand TCNs two mechanisms, consensus and classification, we put forward its three variants in ablation studies on these mechanisms.
To further investigate TCN models, we treat the latent representations as probability distributions and measure their similarities as the negative relative Jensen-Shannon divergences.
We show that a consensus state beneficial for classification desires a stable but imperfect similarity between the representations.
Overall, TCNs outperform or align with the best benchmark algorithms given 20 to 200 labeled samples on the Bank Marketing and the DementiaBank datasets.
Deep learning has demonstrated impressive capacities to learn complicated structures from massive data sets.
However, acquiring sufficient labeled data can be expensive or difficult (e.g., for specific pathological populations BID10 ).
Transductive learning (a set of semi-supervised algorithms) uses intrinsic structures among unlabeled data to boost classifier performance.
In the real world, data can spread across multiple modalities (e.g., visual, acoustic, and text) in typical tasks, although many existing transductive algorithms do not exploit the structure across these modalities.
Co-training [3] and tri-training BID23 use one classifier per modality to supervise each other, but they can only apply to two and three modalities respectively.Recently, Consensus Networks (CNs) BID24 incorporated the idea of co-training.
Not limited by the number of modalities, CNs showed promising results on detecting cognitive impairments from multi-modal datasets of speech.
A consensus network contains several interpreters (one per modality), a discriminator, and a classifier.
The interpreters try to produce low-dimensional representations of input data that are indistinguishable by the discriminator.
The classifier makes predictions based on these representation vectors.Despite promising results, CN is limited by the amount of available training data.
This motivates our extension into semi-supervised learning with our Transductive Consensus Network (TCN).TCNs
operate in two mechanisms: as consensus or classifier. The
consensus mechanism urges the modality representations to resemble each other (trained on the whole dataset without using labels), and the classifier mechanism optimizes the networks to retain information useful for classification (trained on the labeled dataset). To
illustrate the importance of these two mechanisms in an ablation study, we also put forward its three variants: TCN-embed, TCN-svm, and TCN-AE in §3. By
this ablation study, we show that both mechanisms should function together via iterative training.To further reveal the mechanisms of TCN, we formulate in §3.5 the similarity between latent representations using negative Jensen-Shannon divergences. By
monitoring their similarities, we show that a meaningful consensus state prefers representations to have suboptimal similarities.In experiments ( §4), we compare TCN to its three variants, TCN's multimodal supervised learning counterpart (CN), and several other semi-supervised learning benchmark algorithms on two datasets: Bank Marketing (from the UCI repository) and DementiaBank (a dataset of pathological speech in multiple modalities). On
both datasets, the F-scores of TCN align with the best benchmark models when there are more labeled data available, and outperform benchmarks (including tri-training) given as few as 20 labeled points.
In this paper, we present Transductive Consensus Networks (TCNs) that extend consensus networks with semi-supervised learning.
We identify two mechanisms in which TCNs function, i.e., the consensus and classifier mechanisms.
With three TCN variants in an ablation study, we show the importance of both mechanisms.
Moreover, by treating the representations as probability distributions and defining their similarity as negative relative JS divergences, we show that although the consensus mechanism urges high similarities, a good consensus state might not need perfect similarities between modality representations.In the future, several avenues may be considered.
To start with, building consensus networks using other types of neural networks may be considered.
In addition, more exploration could be done to find a more explainable metric to describe the extent of agreement.
Currently, we use −

assistant: text: TCN for multimodal semi-supervised learning + ablation study of its mechanisms + interpretations of latent representations