Category: Machine Learning

Clinical Text Processing with Python

We are seeing a rise of Artificial Intelligence in medicine. This has potential for remarkable improvements in diagnosis, prevention and treatment in healthcare. Many of the existing applications are about rapid image interpretation using AI. We have many open opportunities in leveraging NLP for improving both clinical workflows and patient outcomes.

Python has become the language of choice for Natural Language Processing (NLP) in both research and development: from old school NLTK to PyTorch for building state-of-the-art deep learning models. Libraries such as Gensim and spaCy have also enabled production-ready NLP applications. More recently, Hugging Face has built a business around rapidly making current NLP research quickly accessible.

Yesterday, I presented on processing clinical text using Python at the local Python User Group meeting.

During the talk I discussed some opportunities in clinical NLP, mapped out fundamental NLP tasks, and toured the available programming resources– Python libraries and frameworks. Many of these libraries make it extremely easy to leverage state-of-the-art NLP research for building models on clinical text. Towards end of the talk, I also shared some data resources to explore and start hacking on.

It was a fun experience overall and I received some thoughtful comments and feedback — both during the talk and later also online. Special thanks to Pete Fein for organizing the meetup. It was probably the first time I had so many people put on a waitlist for attending one of my presentations. I am also sharing my slides from the talk in hope that they can be useful…


Machines learn to play Tabla, Part – 2

This is a followup on my earlier post on Machines Learn to play Tabla. You may wish it check it out first reading this one…

Three years ago, I published a post on using recurrent neural networks to generate tabla rhythms. Sampling music from machine learned models was not in vogue then. My post received a lot of attention on the web and became very popular. The project had been a proof-of-concept and I have wanted build on it for a long time now.

This weekend, I worked on making it more interactive and I am excited to share these updates with you. Previously, I was using a proprietary software to convert tabla notation to sound. That made it hard to experiment with sampled rhythms and I could share only a handful sounds. Taking inspiration from our friends at Vishwamohini, I am now able to convert bols into rhythm on the fly using MIDI.js.

Let me show off the new javascript synthesizer using a popular Delhi kaida. Hit the ‘play’ button to listen:

Now that you’ve heard the computer play, here’s an example of it being played by a tabla maestro:

Of course, the synthesized outcome is not much of a comparison to the performance by the maestro, but it is not too bad either…

Now to the more exciting part- Since our browsers have learned to play the tabla, we can throw in the char-rnn model that I built in the earlier post.  To do this, I used the RecurrentJS library and combined it with my javascript tabla player:

Feel free to play around with tempo and maximum character-limit for sampling. When you click on ‘generate’,  it will play a new rhythm every time. Hope you’ll enjoy playing with it as much as I did!

The player has a few kinks at this point I am working towards fixing them. You too can contribute to my repository on GitHub.

There are two areas that need major work:

Data: The models that I trained for my earlier post was done using a small amount of training data. I have been on a lookout for better dataset since then. I wrote a few emails, but without much success till now. I am interested in knowing about more datasets I could train my models on.

Modeling: Our model did a very good job of understanding the structure of TaalMala notations. Although character level recurrent neural networks work well, it is still based on very shallow understanding of the rhythmic structures. I have not come across any good approaches for generating true rhythms yet:

I think more data samples covering a range of rhythmic structures would only partially address this problem. Simple rule based approaches seem to outperform machine learned models with very little effort. Vishwamohini.com has some very good rule-based variation generators that you could check out.  They sound better than the ones created by our AI. After all the word for compositions- bandish, literally derived from ‘rules’ in Hindi. But on the other hand, there are only so many handcrafted rules that you can come up with which may lead to generating repetitive sounds.

Contact me if you have some ideas and if you’d like to help out! Hope that I am able to post an update on this sooner than three years this time 😀

Announcing NLPReViz…

Update – 5 Nov’18: Our paper was featured in AMIA 2018 Fall Symposium’s Year-in-Review!

NLPReViz - http://nlpreviz.github.io

We have released the source code for our NLPReViz project. Head to http://nlpreviz.github.io to checkout its project page.

Also, here’s our new JAMIA publication on it:

Gaurav Trivedi, Phuong Pham, Wendy W Chapman, Rebecca Hwa, Janyce Wiebe, Harry Hochheiser; NLPReViz: an interactive tool for natural language processing on clinical text. Journal of American Medical Informatics Association. 2017. DOI: 10.1093/jamia/ocx070.

On Interactive Machine Learning

When talking about machine learning, you may encounter many terminologies such as such as “online learning,” “active learning,” and “human in the loop” methods. Here are some of my thoughts on the relationship between interactive machine learning and machine learning in general. This is an extract from my answers to my comprehensive exam.

Traditionally machine-learning has been classified into supervised and unsupervised learning families. In supervised learning the training data, \mathcal{D}, consists of N sets of feature vectors each with a desired label provided by a teacher:

Training Set  \hspace{10pt} \mathcal{D} = \{(\textbf{x}_i, y_i)\}_{i=1}^{N}

where, \textbf{x}_i \in \mathcal{X} is a d-dimensional feature vector

and y_i \in \mathcal{Y} is the known label for it

The task is to learn a function, f : \mathcal{X} \to \mathcal{Y}, which can be used on unseen data.

In unsupervised learning, our data consists of vectors \textbf{x}_i, but no target label y_i. Common tasks under this category include clustering, density estimation and discovering patterns. A combination of these two is called semi-supervised learning, which has a mixture of labeled and unlabeled data in the training set. The algorithm assigns labels for missing data points using certain similarity measures.

While researchers are actively looking at improving the unsupervised learning techniques, supervised machine learning has been the dominant form of learning till date. However, traditional supervised algorithms assume that we have training data along with the labels readily available. They are not concerned with the process of obtaining the target values y_is for the training dataset. Often, obtaining labelled data is one of the main bottlenecks in applying these techniques in domain specific applications. Further, current approaches do not provide easy mechanisms for the end-users to correct problems when models deviate from the desired learning concept. NLP models are often built by experts in linguistics and/or machine learning, with limited or no scope for the end-users to provide input. Here the domain experts, or the end-users, provide input to models as annotations for a large batch of training data. This approach can be expensive, inefficient and even infeasible in many situations. This includes many problems in the clinical domain such as building models for analyzing EMR data.

“Human-in-the-loop” algorithms may be able to leverage the capabilities of a domain expert during the learning process. These algorithms can optimize their learning behavior through interaction with humans. Interactive Machine Learning (IML) is a subset of this class of algorithms. It is defined as the process of building machine learning models iteratively through end-user input. It allows the users to review model outputs and make corrections by giving feedback for building revised models. The users are then able to see model changes and verify them. This feedback loop allows end-users to refine the models further with every iteration. Some early examples for this definition include applications in image segmentation, interactive document clustering, document retrieval, bug triaging and even music composition. You can read more about this in the article titled "Power to the People: The Role of Humans in Interactive Machine Learning" (Amershi et.al., 2014).

Interactive machine learning builds on a variety of styles of learning algorithms:

  • Reinforcement Learning: In this class of learning we still want to learn f : \mathcal{X} \to \mathcal{Y} but we see samples of \textbf{x}_i but no target output y_i. Instead of y_i, we get a feedback from a critic about the goodness of the predicted output. The goal of the learner is to optimize for the reward function by selecting outputs that get best scores from the critics. The critic can be a human or any other agent. There need not be a human-in-the-loop for the algorithm to be classified under reinforcement learning. Several recent examples of this type include building systems that learn to play games such as Flappy Bird, Mario etc.
  • Active Learning:  Active learning algorithms try to optimize for the number of training examples. Such an algorithm would ask an oracle to give labels such that it can achieve higher accuracy with smallest number of queries. These queries contain a batch of examples to be labelled. For example, in SVMs, one could select training sets for labeling that are closest to the margin hyperplanes to reduce the number of queries.
  • Online Algorithms: Online learning algorithms are used when training data is available in sequential order, say due to the nature of the problem or memory constraints, as opposed to a batch learning technique where all the training data is available at once. The algorithm must adapt to the continuous stream of data made available to it. Formulating the learning problem to handle this situation forms the core of designing algorithms under this class.
    A commonly used example would be the online gradient descent method for linear regression: Suppose we are trying to learn the parameters \mathbf{w} for f(\mathbf{x}) = w_0 + w_1x_1 + \ldots w_d x_d . We update the weights when we receive the ith training example by taking the gradient of the defined error function:
    \mathbf{w}_{new} \leftarrow \mathbf{w} - \alpha \times \Delta_{\mathbf{w}} Error_i (\mathbf{w}). Where, \alpha is defined as the learning rate.
This is how the relationship between supervised, interactive machine learning, and human-in-the-loop algorithms may be represented in a Venn diagram.

Interactive machine learning methods can include all or some of these learning techniques. The common property between all the interactive machine learning methods is the tight interaction loop between the human and the learning algorithm. Most of the effort in interactive machine learning has been about designing interactions for each step of this loop. My work on interactive clinical and legal text analysis also follows this pattern. You are welcome to check out those posts as well!

References

  1. Amershi et.al. (2014), Power to the People: The Role of Humans in Interactive Machine Learning. Available: https://www.microsoft.com/en-us/research/publication/power-to-the-people-the-role-of-humans-in-interactive-machine-learning/.

Using Machine learning to help Manage Diabetes

I participated in the PennApps hackathon in Philadelphia this weekend. While most of the city was struck with a bad snow storm, a group of hackers holed up inside the Penn engineering buildings to work on some cool hacks. My team consisting of three other hackers: Daniel, Alex and Madhur, decided to work on an app that could predict blood glucose levels of diabetes patients by building machine learning models.

Our proof-of-concept. We have our own logo!
We have our own logo!

We used the OneTouch Reveal API to gather some data provided by the Johnson & Johnson’s company. They are the manufacturers of OneTouch glucose monitors for diabetes patients. They also give their patients an app for tagging events like exercise (light, moderate, heavy etc.), when they eat food and use insulin (different kinds – fast acting, before/after meals etc.). Our team thought that it might be a good idea to hack on this dataset to find out whether we could predict patients’ glucose levels without them having them to punch a hole in their fingers. A real world use case for this app would be to alert a patient when we predicted unusual glucose levels or have them do an actual blood test when the confidence on our predictions falls low.

We observed mixed results for the patients in our dataset. We did reasonably well for those with more data, but others had very few data points to make good predictions. We also saw that our predictions became more precise as we considered more data. Another issue was that the OneTouch API did not give sufficient information about food and exercise events for any of the patients – mostly without additional event tagging. As a result, our models were not influenced much by them.

The trend line is our blood glucose prediction based on past data. The shaded region indicates our prediction range. Whenever this region is broader, our confidence in prediction goes down.
The pink trend-line is our blood glucose predictions based on prior data. The shaded region indicates the prediction range. Whenever this region is broader, our confidence in prediction goes down.

We believe that in the near future, it would be common for the patients to have such monitors communicate with other wearable sensors such as smart watches. Such systems would be able to provide ample information about one’s physical activity etc., to make more meaningful predictions possible. Here’s a video demonstrating our proof-of-concept:

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Interactive Natural Language Processing for Legal Text

Update: We received the best student paper award for our paper at JURIX’15!

In an earlier post, I talked about my work on Natural Language Processing in the clinical domain. The main idea behind the project is to enable domain experts to build machine learning models for analyzing text. We do this by designing usable tools for NLP without really having the need to send datasets to machine learning experts or understanding the inner working details of the algorithms. The post also features a demo video of the prototype tool that we have built.

I was presenting this work at my program’s bi-weekly meetings where Jaromir, a fellow ISP graduate student, pointed out that such an approach could be useful for his work as well. Jaromir also holds a degree in Law and works on building AI systems for legal applications. As a result, we ended up collaborating on a project on using the approach for statutory analysis. While, the main topic of discussion in the project is on the framework in which a human experts cooperate with a machine learning text classification algorithm, we also ended up augmenting our approach with a new way of capturing and re-using knowledge. In our tool datasets and models are treated separately and our not tied together. So, if you were building a classification model for say statutes from the state of Alaska, when you need to analyze laws from Kansas you need not start from scratch. This allows us to be in a better starting place in terms of all the performance measures and build a model using fewer training examples.

The results of the cold start (Kansas) and the knowledge re-use (Alaska) experiment. In the Figure KS stands for Kansas, AK for Alaska, 1p and 2p for the first (ML model-oriented) and second (interaction-oriented) evaluation perspectives, P for precision, R for recall, F1 for F1 measure, and ROC with a number for an ROC curve of the ML classifier trained on the specified number of documents.
The results of the cold start (Kansas) and the knowledge re-use (Alaska) experiment. In the Figure KS stands for Kansas, AK for Alaska, P for precision, R for recall, F1 for F1 measure, and ROC with a number for an ROC curve of the ML classifier trained on the specified number of documents.

We will be presenting this work at JURIX’15 during the 28th year of the conference focusing on legal information systems. Previously, we had presented portions of this work at the AMIA Summit on Clinical Research Informatics and at the ACM IUI Workshop on Visual Text Analytics.

References

Jaromír Šavelka, Gaurav Trivedi, and Kevin Ashley. 2015. Applying an Interactive Machine Learning Approach to Statutory Analysis. In Proceedings of the 28th International Conference on Legal Knowledge and Information Systems (JURIX ’15). Braga, Portugal. [PDF] – Awarded the Best Student Paper (Top 0.01%).

Machines learn to play Tabla

Update: This post now has a Part 2.

If you follow machine learning topics in the news, I am sure by now you would have come across Andrej Karpathy‘s blog post on The Unreasonable Effectiveness of Recurrent Neural Networks.[1] Apart from the post itself, I have found it very fascinating to read about the diverse applications that its readers have found for it. Since then I have spent several hours hacking with different machine learning models to compose tabla rhythms:

Although Tabla does not have a standardized musical notation that is accepted by all, it does have a language based on the bols (literally, verbalize in English) or the sounds of the strokes played on it. These bols may be expressed in written form which when pronounced in Indian languages sound like the drums. For example, the theka for the commonly used 16-beat cycle – Teental is written as follows:

Dha | Dhin | Dhin | Dha | Dha | Dhin | Dhin | Dha 
Dha | Tin  | Tin  | Ta  | Ta  | Dhin | Dhin | Dha

For this task, I made use of Abhijit Patait‘s software – TaalMala, which provides a GUI environment for composing Tabla rhythms in this language. The bols can then be synthesized to produce the sound of the drum. In his software, Abhijit extended the tabla language to make it easier for users to compose tabla rhythms by adding a square brackets after each bol that specify the number of beats within which it must be played. You could also lay more emphasis on a particular bol by adding ‘+’ symbols which increased their intensity when synthesized to sound. Variations of standard bols can be defined as well based on different the hand strokes used:

Dha1 = Na + First Closed then Open Ge

Now that we are armed with this background knowledge, it is easy to see how we may attempt to learn tabla like a language model using Natural Language Processing techniques. Predictive modeling of tabla has been previously explored in "N-gram modeling of tabla sequences using variable-length hidden Markov models for improvisation and composition" (Avinash Sastry, 2011). But, I was not able to get access to the datasets used in the study and had to rely on the compositions that came with the TaalMala software.[2] This is comparatively a much smaller database than what you would otherwise use to train a neural network: It comprises of 207 rhythms with 6,840 bols in all. I trained a char-rnn and sampled some compositions after priming it with different seed text such as “Dha”, “Na” etc. Given below is a minute long composition sampled from my network. We can see that not only the network has learned the TaalMala notation but it has also understood some common phrases used in compositions such as the occurrence of the phrase “TiRa KiTa“, repetitions of “Tun Na” etc.:

Ti [0.50] | Ra | Ki | Te | Dha [0.50] | Ti [0.25] | Ra | Ki
| Ta | Tun [0.50] | Na | Dhin | Na 
| Tun | Na | Tun | Na | Dha | Dhet | Dha | Dhet | Dha | Dha
| Tun | Na | Dha | Tun | Na | Ti | Na | Dha | Ti | Te | Ki |
Ti | Dha [0.50] | Ti [0.25] | Ra | Ki | Te | Dhin [0.50] |
Dhin | Dhin | Dha | Ge | Ne | Dha | Dha | Tun | Na | Ti
[0.25] | Ra | Ki | Ta | Dha [0.50] | Ti [0.25] | Ra | Ki |
Te | Dha [1.00] | Ti | Dha | Ti [0.25] | Ra | Ki | Te | Dha
[0.50] | Dhet | Dhin | Dha | Tun | Na | Ti [0.25] | Ra | Ki
| Ta | Dha [0.50] | Ti [0.25] | Ra | Ki | Te | Ti | Ka | Tra
[0.50] | Ti | Ti | Te | Na [0.50] | Ki [0.50] | Dhin [0.13]
| Ta | Ti [0.25] | Ra | Ki | Te | Tra | Ka | Ti [0.25] | Ra
| Ki | Te | Dhin [0.50] | Na [0.25] | Ti [0.25] | Ra | Ki |
Te | Tra | Ka | Dha [0.34] | Ti [0.25] | Ra | Ki | Ta | Tra
| Ka | Tra [0.50] | Ki [0.50] | Tun [0.50] | Dha [0.50] | Ti
[0.25] | Ra | Ki | Ta | Tra | Ka | Ta | Te | Ti | Ta | Kat |
Ti | Dha | Ge | Na | Dha | Ti [0.25] | Ra | Ki | Te | Dha
[0.50] | Dhin | Dhin | Dhin | Dha | Tun | Na | Ti | Na | Ki
| Ta | Dha [0.50] | Dha | Ti [0.50] | Ra | Ki | Te | Tun
[0.50] | Tra [0.25] | Ti [0.25] | Ra | Ki | Te | Tun | Ka |
Ti [0.25] | Ra | Ki | Te | Dha [0.50] | Ki [0.25] | Ti | Dha
| Ti | Ta | Dha | Ti | Dha [0.50] | Ti | Na | Dha | Ti
[0.25] | Ra | Ki | Te | Dhin [0.50] | Na | Ti [0.25] | Ra |
Ki | Te | Tra | Ka | Dha [0.50] | Ti [0.50] | Ra | Ki | Te |
Tun [0.50] | Na | Ki [0.25] | Te | Dha | Ki | Dha [0.50] |
Ti [0.25] | Ra | Ki | Te | Dha [0.50] | Ti [0.25] | Ra | Ki
| Te | Dha [0.50] | Tun | Ti [0.25] | Ra | Ki | Te | Dhin
[0.50] | Na | Ti [0.25] | Te | Dha | Ki [0.25] | Te | Ki |
Te | Dhin [0.50] | Dhin | Dhin | Dhin | Dha | Dha | Tun | Na
| Na | Na | Ti [0.25] | Ra | Ki | Ta | Ta | Ka | Dhe [0.50]
| Ti [0.25] | Ra | Ki | Te | Ti | Re | Ki | Te | Dha [0.50]
| Ti | Dha | Ge | Na | Dha | Ti [0.25] | Ra | Ki | Te | Ti |
Te | Ti | Te | Ti | Te | Dha [0.50] | Ti [0.25] | Te | Ra |
Ki | Te | Dha [0.50] | Ki | Te | Dha | Ti [0.25]

Here’s a loop that I synthesized by pasting a composition sampled 4 times one after the another:

Of course, I also tried training n-gram models and the smoothing methods using the SRILM toolkit. Adding spaces between letters is a quick hack that can be used to train character level models using existing toolkits. Which one produces better compositions? I can’t tell for now but I am trying to collect more data and hope to add updates to this post as and when I find time to work on it. I am not confident if simple perplexity scores may be enough to judge the differences between two models, specially on the rhythmic quality of the compositions. There are many ways in which one can extend this work. One there is a possibility of training on different kinds of compositions: kaidas, relas, laggis etc., different rhythm cycles and also from different gharanas. All of this would required collecting a bigger composition database:

And then there is a scope for allowing humans to interactively edit compositions at places where AI goes wrong. You could also use the samples generated by it as an infinite source of inspiration.

Finally, here’s a link to the work in progress playlist of the rhythms I have sampled till now.

References

  1. Avinash Sastry (2011), N-gram modeling of tabla sequences using variable-length hidden Markov models for improvisation and composition. Available: https://smartech.gatech.edu/bitstream/handle/1853/42792/sastry_avinash_201112_mast.pdf?sequence=1.

Footnotes

  1. If you encountered a lot of new topics in this post, you may find this post on Understanding natural language using deep neural networks and the series of videos on Deep NN by Quoc Le helpful. ^
  2. On the other hand, Avinash Sastry‘s work uses a more elaborate Humdrum notation for writing tabla compositions but is not as easy to comprehend for tabla players. ^