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Title: Collecting Entailment Data for Pretraining: New Protocols and Negative Results

Paper content:
Textual entailment (or NLI) data has proven useful as pretraining data for tasks requiring language understanding, even when building on an already-pretrained model like RoBERTa.
The standard protocol for collecting NLI was not designed for the creation of pretraining data, and it is likely far from ideal for this purpose.
With this application in mind we propose four alternative protocols, each aimed at improving either the ease with which annotators can produce sound training examples or the quality and diversity of those examples.
Using these alternatives and a simple MNLIbased baseline, we collect and compare five new 9k-example training sets.
Our primary results are largely negative, with none of these new methods showing major improvements in transfer learning.
However, we make several observations that should inform future work on NLI data, such as that the use of automatically provided seed sentences for inspiration improves the quality of the resulting data on most measures, and all of the interventions we investigated dramatically reduce previously observed issues with annotation artifacts.
The task of natural language inference (NLI; also known as textual entailment) has been widely used as an evaluation task when developing new methods for language understanding tasks, but it has recently become clear that high-quality NLI data can be useful in transfer learning as well.
Several recent papers have shown that training large neural network models on natural language inference data, then fine-tuning them for other language understanding tasks often yields substantially better results on those target tasks (Conneau et al., 2017; Subramanian et al., 2018) .
This result holds even when starting from large models like BERT (Devlin et al., 2019) that have already been pretrained extensively on unlabeled data (Phang et al., 2018; Clark et al., 2019; Liu et al., 2019b) .
The largest general-purpose corpus for NLI, and the one that has proven most successful in this setting, is the Multi-Genre NLI Corpus (MNLI Williams et al., 2018) .
MNLI was designed for use in a benchmark task, rather than as a resource for use in transfer learning and as far as we know, it was not developed on the basis of any kind of deliberate experimentation.
Further, data collected under MNLI's data collection protocol has known issues with annotation artifacts which make it possible to perform much better than chance using only one of the sentences in each pair (Tsuchiya, 2018; Gururangan et al., 2018; Poliak et al., 2018) .
This work begins to ask what would be involved in collecting a similar dataset that is explicitly designed with transfer learning in mind.
In particular, we consider four potential changes to the original MNLI data collection protocol that are designed to improve either the ease with which annotators can produce sound examples, or the quality and diversity of those examples, and evaluate their effects on transfer.
We collect a baseline dataset of about 10k examples that follows the MNLI protocol with our annotator pool, followed by four additional datasets of the same size which isolate each of our candidate changes.
We then compare all five in a set of transfer learning experiments that look at our ability to use each of these datasets to improve performance on the eight downstream language understanding tasks in the SuperGLUE (Wang et al., 2019b) benchmark.
All five of our datasets are consistent with the task definition that was used in MNLI, which is in turn based on the definition introduced by .
In this task, each example consists of a pair of short texts, called the premise and the hypothesis.
The model is asked to read both texts and make a three-way classification decision: Given the premise, would a reasonable person infer that hypothesis must be true (entailment), infer that that it must be false (contradiction), or decide that there is not enough information to make either inference (neutral).
While it is certainly not clear that this framing is optimal for pretraining, we leave a more broad-based exploration of task definitions for future work.
Our BASE data collection protocol ( Figure 1 ) follows MNLI closely in asking annotators to read a premise sentence and then write three corresponding hypothesis sentences in empty text boxes corresponding to the three different labels (entailment, contradiction, and neutral).
When an annotator follows this protocol, they produce three sentence pairs at once, all sharing a single premise.
Our PARAGRAPH protocol tests the effect of supplying annotators with complete paragraphs, rather than sentences, as premises.
Longer texts offer the potential for discourse-level inferences, the addition of which should yield a dataset which is more difficult, more diverse, and less likely to contain trivial artifacts.
However, reading full paragraphs adds a potential cost in added annotator time and effort, which could potentially be better spent constructing more sentence-level examples.
Our EDITPREMISE and EDITOTHER protocols test the effect of pre-filling a single seed text in each of the three text boxes that annotators are asked to fill out.
By reducing the raw amount of typing required, this could allow annotators to produce good examples more quickly.
By encouraging them to keep the three sentences similar, it could also encourage minimal-pair-like examples that minimize artifacts.
We test two variants of this idea: One uses a copy of the premise sentence as a seed text and the second retrieves a new sentence from an existing corpus that is similar to the premise sentence, and uses that.
Our CONTRAST protocol tests the effect of adding artificial constraints on the kinds of hypothesis sentences annotators can write.
Giving annotators difficult and varying constraints could encourage creativity and prevent annotators from falling into repeating ruts or patterns in their writing that could lead to easier, more repetitive data.
However, as with the use of longer contexts in BASE, this protocol risks substantially slowing the annotation process.
We experiment with a procedure inspired by that used to create the language-andvision dataset NLVR2 (Suhr et al., 2019) , in which in which annotators must write sentences that are valid entailments (or contradictions) for a given premise, but not valid entailments for a second, similar, distractor premise.
In evaluations on transfer learning with the SuperGLUE benchmark, all of these four methods offer substantial improvements in transfer ability over a plain RoBERTa model, but that only EDITOTHER and CONTRAST offering consistent improvements over BASE, and only by very small margins.
While this is largely a negative result for our primary focus on transfer, we also observe that all four of these methods are able to produce data of comparable subjective quality while significantly reducing the incidence of previously reported annotation artifacts, and that PARAGRAPH, EDITPREMISE, and EDITOTHER all accomplish this without significantly increasing the time cost of annotation.
Our chief results on transfer learning are negative: None of our four interventions consistently improve upon the base MNLI data collection protocol by more than a marginal degree, though we see suggestive evidence that methods that supply annotators with retrieved non-premise seed sentences for inspiration offer small improvements.
However, we also observe that all four of our interventions, and especially the use of longer contexts or pre-filled seed sentences, help reduce the prevalence of artifacts in the generated hypotheses that reveal the label, and the use of longer premises or seed sentences in particular do this without increasing the time cost of annotation.
This suggests that these methods may be valuable in the collection of high-quality evaluation data, if combined with additional validation methods to ensure high human agreement with the collected labels.
The need and opportunity that motivated this work remains compelling: Human-annotated data like MNLI has already proven itself as a valuable tool in teaching machines general-purpose skils for language understanding, and discovering ways to more effectively build and use such data could further accelerate the field's already fast progress toward robust, general-purpose language understanding technologies.
Further work along this line of research could productively follow a number of directions: General work on incentive structures and task design for crowdsourcing could help to address more general questions about how to collect data that is simultaneously creative and consistently labeled.
Machine learning methods work on transfer learning could help to better understand and exploit the effects that drive the successes we have seen with NLI data so far.
Finally, there remains room for further empirical work investigating the kinds of task definitions and data collection protocols most likely to yield positive transfer.

assistant: text: We propose four new ways of collecting NLI data. Some help slightly as pretraining data, all help reduce annotation artifacts.