Reading Notes - Text Preprocessing in Neural Network Architectures

I came across this short paper today in the ArXiv digest. This post is a quick summary.

Title: On the Role of Text Preprocessing in Neural Network Architectures: An Evaluation Study on Text Categorization and Sentiment Analysis

Authors: Jose Camacho-Collados and Mohammad Taher Pilehvar

Read online here

Word embeddings, and neural networks are being commonly used in various text processing tasks in the past 3-4 years (Read Sebastian Ruder’s article series to know more on embeddings). There is some discussion on how to do hyper-parameter tuning for embeddings, how to combine word level embedding representations to get document embeddings etc in literature. However, there is little analysis about how pre-processing decisions can affect end results (e.g., in text classification) when using embedding representations. This article works on performing such an analysis.

They look at four pre-processing operations: tokenization, lowercasing, lemmatising and multi-word grouping, and how these affect a CNN’s text classification performance on 9 benchmark datasets (4 relate to topic classification, 5 are sentiment classification). Their main conclusions is as follows:

“In general a simple tokenized corpus works equally or better than more complex preprocessing techniques such as lemmatization or multiword grouping, except for a dataset corre- sponding to a specialized domain, like health, in which sole tokenization performs poorly. Addi- tionally, word embeddings trained on multiword-grouped corpora perform surprisingly well when applied to simple tokenized datasets.”

I have been working on embedding representations with three different kinds of text datasets (one stylistic, one biomed literature, one forum postings) in the past few months and I have often thought on this issue of what is a better pre-processing? what is a better resource to train embeddings? etc. Not as much about parameter tuning, as we have been relying on cross-validation to choose the best parameters. However, in my experience with using n-gram representations and any text classification in general, the performance of a learner is very sensitive to several pre-processing decisions and choice of tools (e.g., taggers, parsers etc).

So, I think this kind of empirical research into how such choices influence the eventual performance will perhaps make researchers in general think more in the direction of whether their ultra-complex model is giving a marginally better performance because of engineering marvel or is there a simpler explanation such as these simpler choices. I am very much looking forward to read more of this kind of work on analysing the models.

One other recent work that I found useful in this context:

An Empirical Evaluation of doc2vec with Practical Insights into Document Embedding Generation by Lau and Baldwin.

Read online here

Written on July 7, 2017