Tag Archives: NLP

Evaluating Syntactic Abilities of Language Models

In recent years, pre-trained language models, such as BERT and GPT-3, have seen widespread use in natural language processing (NLP). By training on large volumes of text, language models acquire broad knowledge about the world, achieving strong performance on various NLP benchmarks. These models, however, are often opaque in that it may not be clear why they perform so well, which limits further hypothesis-driven improvement of the models. Hence, a new line of scientific inquiry has arisen: what linguistic knowledge is contained in these models?

While there are many types of linguistic knowledge that one may want to investigate, a topic that provides a strong basis for analysis is the subject–verb agreement grammar rule in English, which requires that the grammatical number of a verb agree with that of the subject. For example, the sentence “The dogs run.” is grammatical because “dogs” and “run” are both plural, but “The dogs runs.” is ungrammatical because “runs” is a singular verb.

One framework for assessing the linguistic knowledge of a language model is targeted syntactic evaluation (TSE), in which minimally different pairs of sentences, one grammatical and one ungrammatical, are shown to a model, and the model must determine which one is grammatical. TSE can be used to test knowledge of the English subject–verb agreement rule by having the model judge between two versions of the same sentence: one where a particular verb is written in its singular form, and the other in which the verb is written in its plural form.

With the above context, in “Frequency Effects on Syntactic Rule-Learning in Transformers”, published at EMNLP 2021, we investigated how a BERT model’s ability to correctly apply the English subject–verb agreement rule is affected by the number of times the words are seen by the model during pre-training. To test specific conditions, we pre-trained BERT models from scratch using carefully controlled datasets. We found that BERT achieves good performance on subject–verb pairs that do not appear together in the pre-training data, which indicates that it does learn to apply subject–verb agreement. However, the model tends to predict the incorrect form when it is much more frequent than the correct form, indicating that BERT does not treat grammatical agreement as a rule that must be followed. These results help us to better understand the strengths and limitations of pre-trained language models.

Prior Work
Previous work used TSE to measure English subject–verb agreement ability in a BERT model. In this setup, BERT performs a fill-in-the-blank task (e.g., “the dog _ across the park”) by assigning probabilities to both the singular and plural forms of a given verb (e.g., “runs” and “run”). If the model has correctly learned to apply the subject–verb agreement rule, then it should consistently assign higher probabilities to the verb forms that make the sentences grammatically correct.

This previous work evaluated BERT using both natural sentences (drawn from Wikipedia) and nonce sentences, which are artificially constructed to be grammatically valid but semantically nonsensical, such as Noam Chomsky’s famous example “colorless green ideas sleep furiously”. Nonce sentences are useful when testing syntactic abilities because the model cannot just fall back on superficial corpus statistics: for example, while “dogs run” is much more common than “dogs runs”, “dogs publish” and “dogs publishes” will both be very rare, so a model is not likely to have simply memorized the fact that one of them is more likely than the other.

BERT achieves an accuracy of more than 80% on nonce sentences (far better than the random-chance baseline of 50%), which was taken as evidence that the model had learned to apply the subject–verb agreement rule. In our paper, we went beyond this previous work by pre-training BERT models under specific data conditions, allowing us to dig deeper into these results to see how certain patterns in the pre-training data affect performance.

Unseen Subject–Verb Pairs
We first looked at how well the model performs on subject–verb pairs that were seen during pre-training, versus examples in which the subject and verb were never seen together in the same sentence:

BERT’s error rate on natural and nonce evaluation sentences, stratified by whether a particular subject–verb (SV) pair was seen in the same sentence during training or not. BERT’s performance on unseen SV pairs is far better than simple heuristics such as picking the more frequent verb or picking the more frequent SV pair.

BERT’s error rate increases slightly for unseen subject–verb (SV) pairs, for both natural and nonce evaluation sentences, but it is still much better than naïve heuristics, such as picking the verb form that occurred more often in the pre-training data or picking the verb form that occurred more frequently with the subject noun. This tells us that BERT is not just reflecting back the things that it sees during pre-training: making decisions based on more than just raw frequencies and generalizing to novel subject–verb pairs are indications that the model has learned to apply some underlying rule concerning subject–verb agreement.

Frequency of Verbs
Next, we went beyond just seen versus unseen, and examined how the frequency of a word affects BERT’s ability to use it correctly with the subject–verb agreement rule. For this study, we chose a set of 60 verbs, and then created several versions of the pre-training data, each engineered to contain the 60 verbs at a specific frequency, ensuring that the singular and plural forms appeared the same number of times. We then trained BERT models from these different datasets and evaluated them on the subject–verb agreement task:

BERT’s ability to follow the subject–verb agreement rule depends on the frequency of verbs in the training set.

These results indicate that although BERT is able to model the subject–verb agreement rule, it needs to see a verb about 100 times before it can reliably use it with the rule.

Relative Frequency Between Verb Forms
Finally, we wanted to understand how the relative frequencies of the singular and plural forms of a verb affect BERT’s predictions. For example, if one form of the verb (e.g., “combat”) appeared in the pre-training data much more frequently than the other verb form (e.g., “combats”), then BERT might be more likely to assign a high probability to the more frequent form, even when it is grammatically incorrect. To evaluate this, we again used the same 60 verbs, but this time we created manipulated versions of the pre-training data where the frequency ratio between verb forms varied from 1:1 to 100:1. The figure below shows BERT’s performance for these varying levels of frequency imbalance:

As the frequency ratio between verb forms in training data becomes more imbalanced, BERT’s ability to use those verbs grammatically decreases.

These results show that BERT achieves good accuracy at predicting the correct verb form when the two forms are seen the same number of times during pre-training, but the results become worse as the imbalance between the frequencies increases. This implies that even though BERT has learned how to apply subject–verb agreement, it does not necessarily use it as a “rule”, instead preferring to predict high-frequency words regardless of whether they violate the subject–verb agreement constraint.

Conclusions
Using TSE to evaluate the performance of BERT reveals its linguistic abilities on syntactic tasks. Moreover, studying its syntactic ability in relation to how often words appear in the training dataset reveals the ways that BERT handles competing priorities — it knows that subjects and verbs should agree and that high frequency words are more likely, but doesn’t understand that agreement is a rule that must be followed and that the frequency is only a preference. We hope this work provides new insight into how language models reflect properties of the datasets on which they are trained.

Acknowledgements
It was a privilege to collaborate with Tal Linzen and Ellie Pavlick on this project.

Source: Google AI Blog


Grammar Correction as You Type, on Pixel 6

Despite the success and widespread adoption of smartphones, using them to compose longer pieces of text is still quite cumbersome. As one writes, grammatical errors can often creep into the text (especially undesirable in formal situations), and correcting these errors can be time consuming on a small display with limited controls.

To address some of these challenges, we are launching a grammar correction feature that is directly built into Gboard on Pixel 6 that works entirely on-device to preserve privacy, detecting and suggesting corrections for grammatical errors while the user is typing. Building such functionality required addressing a few key obstacles: memory size limitations, latency requirements, and handling partial sentences. Currently, the feature is capable of correcting English sentences (we plan to expand to more languages in the near future) and available on almost any app with Gboard1.

Gboard suggests how to correct an ungrammatical sentence as the user types.

Model Architecture
We trained a sequence-to-sequence neural network to take an input sentence (or a sentence prefix) and output the grammatically correct version — if the original text is already grammatically correct, the output of the model is identical to its input, indicating that no corrections are needed. The model uses a hybrid architecture that combines a Transformer encoder with an LSTM decoder, a combination that provides a good balance of quality and latency.

Overview of the grammatical error correction (GEC) model architecture.

Mobile devices are constrained by limited memory and computational power, which make it more difficult to build a high quality grammar checking system. There are a few techniques we use to build a small, efficient, and capable model.

  • Shared embedding: Because the input and output of the model are structurally similar (e.g., both are text in the same language), we share some of the model weights between the Transformer encoder and the LSTM decoder, which reduces the model file size considerably without unduly affecting accuracy.
  • Factorized embedding: The model splits a sentence into a sequence of predefined tokens. To achieve good quality, we find that it is important to use a large vocabulary of predefined tokens, however, this substantially increases the model size. A factorized embedding separates the size of the hidden layers from the size of the vocabulary embedding. This enables us to have a model with a large vocabulary without significantly increasing the number of total weights.
  • Quantization: To reduce the model size further, we perform post-training quantization, which allows us to store each 32-bit floating point weight using only 8-bits. While this means that each weight is stored with lower fidelity, nevertheless, we find that the quality of the model is not materially affected.

By employing these techniques, the resulting model takes up only 20MB of storage and performs inference on 60 input characters under 22ms on the Google Pixel 6 CPU.

Training the Model
In order to train the model, we needed training data in the form of <original, corrected> text pairs.

One possible approach to generating a small on-device model would be to use the same training data as a large cloud-based grammar model. While this data produces a reasonably high quality on-device model, we found that using a technique called hard distillation to generate training data that is better-matched to the on-device domain yields even better quality results.

Hard distillation works as follows: We first collected hundreds of millions of English sentences from across the public web. We then used the large cloud-based grammar model to generate grammar corrections for those sentences. This training dataset of <original, corrected> sentence pairs is then used to train a smaller on-device model that can correct full sentences. We found that the on-device model built from this training dataset produces significantly higher quality suggestions than a similar-sized on-device model built on the original data used to train the cloud-based model.

Before training the model from this data, however, there is another issue to address. To enable the model to correct grammar as the user types (an important capability of mobile devices) it needs to be able to handle sentence prefixes. While this enables grammar correction when the user has only typed part of a sentence, this capability is particularly useful in messaging apps, where the user often omits the final period in a sentence and presses the send button as soon as they finish typing. If grammar correction is only triggered on complete sentences, it might miss many errors.

This raises the question of how to decide whether a given sentence prefix is grammatically correct. We used a heuristic to solve this — if a given sentence prefix can be completed to form a grammatically correct sentence, we then consider it grammatically correct. If not, it is assumed to be incorrect.

What the user has typed so far       Suggested grammar correction
She puts a lot
She puts a lot of
She puts a lot of effort
She puts a lot of effort yesterday   Replace "puts" with "put in".
GEC on incomplete sentences. There is no correction for valid sentence prefixes.

We created a second dataset suitable for training a large cloud-based model, but this time focusing on sentence prefixes. We generated the data using the aforementioned heuristic by taking the <original, corrected> sentence pairs from the cloud-based model’s training dataset and randomly sampling aligned prefixes from them.

For example, given the <original, corrected> sentence pair:

Original sentence: She puts a lot of effort yesterday afternoon.
Corrected sentence: She put in a lot of effort yesterday afternoon.

We might sample the following prefix pairs:

Original prefix: She puts
Corrected prefix: She put in

Original prefix: She puts a lot of effort yesterday
Corrected prefix: She put in a lot of effort yesterday

We then autocompleted each original prefix to a full sentence using a neural language model (similar in spirit to that used by SmartCompose). If a full-sentence grammar model finds no errors in the full sentence, then that means there is at least one possible way to complete this original prefix without making any grammatical errors, so we consider the original prefix to be correct and output <original prefix, original prefix> as a training example. Otherwise, we output <original prefix, corrected prefix>. We used this training data to train a large cloud-based model that can correct sentence prefixes, then used that model for hard distillation, generating new <original, corrected> sentence prefix pairs that are better-matched to the on-device domain.

Finally, we constructed the final training data for the on-device model by combining these new sentence prefix pairs with the full sentence pairs. The on-device model trained on this combined data is then capable of correcting both full sentences as well as sentence prefixes.

Training data for the on-device model is generated from cloud-based models.

Grammar Correction On-Device
Gboard sends a request to the on-device grammar model whenever the user has typed more than three words, whether the sentence is completed or not. To provide a quality user experience, we underline the grammar mistakes and provide replacement suggestions when the user interacts with them. However, the model outputs only corrected sentences, so those need to be transformed into replacement suggestions. To do this, we align the original sentence and the corrected sentence by minimizing the Levenshtein distance (i.e., the number of edits that are needed to transform the original sentence to the corrected sentence).

Extracting edits by aligning the corrected sentence to the original sentence.

Finally, we transform the insertion edits and deletion edits to be replacement edits. In the above example, we transform the suggested insertion of "in" to be an edit that suggests replacing "puts" with "put in". And we similarly suggest replacing “effort on” with “effort”.

Conclusion
We have built a small high-quality grammar correction model by designing a compact model architecture and leveraging a cloud-based grammar system during training via hard distillation. This compact model enables users to correct their text entirely on their own device without ever needing to send their keystrokes to a remote server.

Acknowledgements
We gratefully acknowledge the key contributions of the other team members, including Abhanshu Sharma, Akshay Kannan, Bharath Mankalale, Chenxi Ni, Felix Stahlberg, Florian Hartmann, Jacek Jurewicz, Jayakumar Hoskere, Jenny Chin, Kohsuke Yatoh, Lukas Zilka, Martin Sundermeyer, Matt Sharifi, Max Gubin, Nick Pezzotti, Nithi Gupta, Olivia Graham, Qi Wang, Sam Jaffee, Sebastian Millius, Shankar Kumar, Sina Hassani, Vishal Kumawat, and Yuanbo Zhang, Yunpeng Li, Yuxin Dai. We would also like to thank Xu Liu and David Petrou for their support.


1The feature will eventually be available in all apps with Gboard, but is currently unavailable for those in WebView

Source: Google AI Blog


Two New Datasets for Conversational NLP: TimeDial and Disfl-QA

A key challenge in natural language processing (NLP) is building conversational agents that can understand and reason about different language phenomena that are unique to realistic speech. For example, because people do not always premeditate exactly what they are going to say, a natural conversation often includes interruptions to speech, called disfluencies. Such disfluencies can be simple (like interjections, repetitions, restarts, or corrections), which simply break the continuity of a sentence, or more complex semantic disfluencies, in which the underlying meaning of a phrase changes. In addition, understanding a conversation also often requires knowledge of temporal relationships, like whether an event precedes or follows another. However, conversational agents built on today’s NLP models often struggle when confronted with temporal relationships or with disfluencies, and progress on improving their performance has been slow. This is due, in part, to a lack of datasets that involve such interesting conversational and speech phenomena.

To stir interest in this direction within the research community, we are excited to introduce TimeDial, for temporal commonsense reasoning in dialog, and Disfl-QA, which focuses on contextual disfluencies. TimeDial presents a new multiple choice span filling task targeted for temporal understanding, with an annotated test set of over ~1.1k dialogs. Disfl-QA is the first dataset containing contextual disfluencies in an information seeking setting, namely question answering over Wikipedia passages, with ~12k human annotated disfluent questions. These benchmark datasets are the first of their kind and show a significant gap between human performance and current state of the art NLP models.

TimeDial
While people can effortlessly reason about everyday temporal concepts, such as duration, frequency, or relative ordering of events in a dialog, such tasks can be challenging for conversational agents. For example, current NLP models often make a poor selection when tasked with filling in a blank (as shown below) that assumes a basic level of world knowledge for reasoning, or that requires understanding explicit and implicit inter-dependencies between temporal concepts across conversational turns.

It is easy for a person to judge that “half past one” and “quarter to two” are more plausible options to fill in the blank than “half past three” and “half past nine”. However, performing such temporal reasoning in the context of a dialog is not trivial for NLP models, as it requires appealing to world knowledge (i.e., knowing that the participants are not yet late for the meeting) and understanding the temporal relationship between events (“half past one” is before “three o’clock”, while “half past three” is after it). Indeed, current state-of-the-art models like T5 and BERT end up picking the wrong answers — “half past three” (T5) and “half past nine” (BERT).

The TimeDial benchmark dataset (derived from the DailyDialog multi-turn dialog corpus) measures models’ temporal commonsense reasoning abilities within a dialog context. Each of the ~1.5k dialogs in the dataset is presented in a multiple choice setup, in which one temporal span is masked out and the model is asked to find all correct answers from a list of four options to fill in the blank.

In our experiments we found that while people can easily answer these multiple choice questions (at 97.8% accuracy), state-of-the-art pre-trained language models still struggle on this challenge set. We experiment across three different modeling paradigms: (i) classification over the provided 4 options using BERT, (ii) mask filling for the masked span in the dialog using BERT-MLM, (iii) generative methods using T5. We observe that all the models struggle on this challenge set, with the best variant only scoring 73%.

Model   2-best Accuracy
Human   97.8%
BERT - Classification   50.0%
BERT - Mask Filling   68.5%
T5 - Generation   73.0%

Qualitative error analyses show that the pre-trained language models often rely on shallow, spurious features (particularly text matching), instead of truly doing reasoning over the context. It is likely that building NLP models capable of performing the kind of temporal commonsense reasoning needed for TimeDial requires rethinking how temporal objects are represented within general text representations.

Disfl-QA
As disfluency is inherently a speech phenomenon, it is most commonly found in text output from speech recognition systems. Understanding such disfluent text is key to building conversational agents that understand human speech. Unfortunately, research in the NLP and speech community has been impeded by the lack of curated datasets containing such disfluencies, and the datasets that are available, like Switchboard, are limited in scale and complexity. As a result, it’s difficult to stress test NLP models in the presence of disfluencies.

Disfluency   Example
Interjection   When is, uh, Easter this year?
Repetition   When is EasEaster this year?
Correction   When is Lent, I mean Easter, this year?
Restart   How much, no wait, when is Easter this year?
Different kinds of disfluencies. The reparandum (words intended to be corrected or ignored; in red), interregnum (optional discourse cues; in grey) and repair (the corrected words; in blue).

Disfl-QA is the first dataset containing contextual disfluencies in an information seeking setting, namely question answering over Wikipedia passages from SQuAD. Disfl-QA is a targeted dataset for disfluencies, in which all questions (~12k) contain disfluencies, making for a much larger disfluent test set than prior datasets. Over 90% of the disfluencies in Disfl-QA are corrections or restarts, making it a much more difficult test set for disfluency correction. In addition, compared to earlier disfluency datasets, it contains a wider variety of semantic distractors, i.e., distractors that carry semantic meaning as opposed to simpler speech disfluencies. 

Passage: …The Normans (Norman: Nourmands; French: Normands; Latin: Normanni) were the people who in the 10th and 11th centuries gave their name to Normandy, a region in France. They were descended from Norse ("Norman" comes from "Norseman") raiders and pirates from Denmark, Iceland and Norway who, under their leader Rollo, …
Q1:   In what country is Normandy located? France ✓
DQ1:   In what country is Norse found no wait Normandy not Norse? Denmark X
Q2:   When were the Normans in Normandy? 10th and 11th centuries ✓
DQ2:   From which countries no tell me when were the Normans in Normandy? Denmark, Iceland and Norway X
A passage and questions (Qi) from SQuAD dataset, along with their disfluent versions (DQi), consisting of semantic distractors (like “Norse” and “from which countries”) and predictions from a T5 model.

Here, the first question (Q1) is seeking an answer about the location of Normandy. In the disfluent version (DQ1) Norse is mentioned before the question is corrected. The presence of this correctional disfluency confuses the QA model, which tends to rely on shallow textual cues from the question for making predictions.

Disfl-QA also includes newer phenomena, such as coreference (expression referring to the same entity) between the reparandum and the repair.

SQuAD  Disfl-QA
Who does BSkyB have an operating license from?  Who removed [BSkyB’s] operating license, no scratch that, who do [they] have [their] operating license from?

Experiments show that the performance of existing state-of-the-art language model–based question answering systems degrades significantly when tested on Disfl-QA and heuristic disfluencies (presented in the paper) in a zero-shot setting.

Dataset   F1
SQuAD   89.59
Heuristics   65.27 (-24.32)
Disfl-QA   61.64 (-27.95)

We show that data augmentation methods partially recover the loss in performance and also demonstrate the efficacy of using human-annotated training data for fine-tuning. We argue that researchers need large-scale disfluency datasets in order for NLP models to be robust to disfluencies.

Conclusion
Understanding language phenomena that are unique to human speech, like disfluencies and temporal reasoning, among others, is a key ingredient for enabling more natural human–machine communication in the near future. With TimeDial and Disfl-QA, we aim to fill a major research gap by providing these datasets as testbeds for NLP models, in order to evaluate their robustness to ubiquitous phenomena across different tasks. It is our hope that the broader NLP community will devise generalized few-shot or zero-shot approaches to effectively handle these phenomena, without requiring task-specific human-annotated training datasets, constructed specifically for these challenges.

Acknowledgments
The TimeDial work has been a team effort involving Lianhui Qi, Luheng He, Yenjin Choi, Manaal Faruqui and the authors. The Disfl-QA work has been a collaboration involving Jiacheng Xu, Diyi Yang, Manaal Faruqui.

Source: Google AI Blog


Two New Datasets for Conversational NLP: TimeDial and Disfl-QA

A key challenge in natural language processing (NLP) is building conversational agents that can understand and reason about different language phenomena that are unique to realistic speech. For example, because people do not always premeditate exactly what they are going to say, a natural conversation often includes interruptions to speech, called disfluencies. Such disfluencies can be simple (like interjections, repetitions, restarts, or corrections), which simply break the continuity of a sentence, or more complex semantic disfluencies, in which the underlying meaning of a phrase changes. In addition, understanding a conversation also often requires knowledge of temporal relationships, like whether an event precedes or follows another. However, conversational agents built on today’s NLP models often struggle when confronted with temporal relationships or with disfluencies, and progress on improving their performance has been slow. This is due, in part, to a lack of datasets that involve such interesting conversational and speech phenomena.

To stir interest in this direction within the research community, we are excited to introduce TimeDial, for temporal commonsense reasoning in dialog, and Disfl-QA, which focuses on contextual disfluencies. TimeDial presents a new multiple choice span filling task targeted for temporal understanding, with an annotated test set of over ~1.1k dialogs. Disfl-QA is the first dataset containing contextual disfluencies in an information seeking setting, namely question answering over Wikipedia passages, with ~12k human annotated disfluent questions. These benchmark datasets are the first of their kind and show a significant gap between human performance and current state of the art NLP models.

TimeDial
While people can effortlessly reason about everyday temporal concepts, such as duration, frequency, or relative ordering of events in a dialog, such tasks can be challenging for conversational agents. For example, current NLP models often make a poor selection when tasked with filling in a blank (as shown below) that assumes a basic level of world knowledge for reasoning, or that requires understanding explicit and implicit inter-dependencies between temporal concepts across conversational turns.

It is easy for a person to judge that “half past one” and “quarter to two” are more plausible options to fill in the blank than “half past three” and “half past nine”. However, performing such temporal reasoning in the context of a dialog is not trivial for NLP models, as it requires appealing to world knowledge (i.e., knowing that the participants are not yet late for the meeting) and understanding the temporal relationship between events (“half past one” is before “three o’clock”, while “half past three” is after it). Indeed, current state-of-the-art models like T5 and BERT end up picking the wrong answers — “half past three” (T5) and “half past nine” (BERT).

The TimeDial benchmark dataset (derived from the DailyDialog multi-turn dialog corpus) measures models’ temporal commonsense reasoning abilities within a dialog context. Each of the ~1.5k dialogs in the dataset is presented in a multiple choice setup, in which one temporal span is masked out and the model is asked to find all correct answers from a list of four options to fill in the blank.

In our experiments we found that while people can easily answer these multiple choice questions (at 97.8% accuracy), state-of-the-art pre-trained language models still struggle on this challenge set. We experiment across three different modeling paradigms: (i) classification over the provided 4 options using BERT, (ii) mask filling for the masked span in the dialog using BERT-MLM, (iii) generative methods using T5. We observe that all the models struggle on this challenge set, with the best variant only scoring 73%.

Model   2-best Accuracy
Human   97.8%
BERT - Classification   50.0%
BERT - Mask Filling   68.5%
T5 - Generation   73.0%

Qualitative error analyses show that the pre-trained language models often rely on shallow, spurious features (particularly text matching), instead of truly doing reasoning over the context. It is likely that building NLP models capable of performing the kind of temporal commonsense reasoning needed for TimeDial requires rethinking how temporal objects are represented within general text representations.

Disfl-QA
As disfluency is inherently a speech phenomenon, it is most commonly found in text output from speech recognition systems. Understanding such disfluent text is key to building conversational agents that understand human speech. Unfortunately, research in the NLP and speech community has been impeded by the lack of curated datasets containing such disfluencies, and the datasets that are available, like Switchboard, are limited in scale and complexity. As a result, it’s difficult to stress test NLP models in the presence of disfluencies.

Disfluency   Example
Interjection   When is, uh, Easter this year?
Repetition   When is EasEaster this year?
Correction   When is Lent, I mean Easter, this year?
Restart   How much, no wait, when is Easter this year?
Different kinds of disfluencies. The reparandum (words intended to be corrected or ignored; in red), interregnum (optional discourse cues; in grey) and repair (the corrected words; in blue).

Disfl-QA is the first dataset containing contextual disfluencies in an information seeking setting, namely question answering over Wikipedia passages from SQuAD. Disfl-QA is a targeted dataset for disfluencies, in which all questions (~12k) contain disfluencies, making for a much larger disfluent test set than prior datasets. Over 90% of the disfluencies in Disfl-QA are corrections or restarts, making it a much more difficult test set for disfluency correction. In addition, compared to earlier disfluency datasets, it contains a wider variety of semantic distractors, i.e., distractors that carry semantic meaning as opposed to simpler speech disfluencies. 

Passage: …The Normans (Norman: Nourmands; French: Normands; Latin: Normanni) were the people who in the 10th and 11th centuries gave their name to Normandy, a region in France. They were descended from Norse ("Norman" comes from "Norseman") raiders and pirates from Denmark, Iceland and Norway who, under their leader Rollo, …
Q1:   In what country is Normandy located? France ✓
DQ1:   In what country is Norse found no wait Normandy not Norse? Denmark X
Q2:   When were the Normans in Normandy? 10th and 11th centuries ✓
DQ2:   From which countries no tell me when were the Normans in Normandy? Denmark, Iceland and Norway X
A passage and questions (Qi) from SQuAD dataset, along with their disfluent versions (DQi), consisting of semantic distractors (like “Norse” and “from which countries”) and predictions from a T5 model.

Here, the first question (Q1) is seeking an answer about the location of Normandy. In the disfluent version (DQ1) Norse is mentioned before the question is corrected. The presence of this correctional disfluency confuses the QA model, which tends to rely on shallow textual cues from the question for making predictions.

Disfl-QA also includes newer phenomena, such as coreference (expression referring to the same entity) between the reparandum and the repair.

SQuAD  Disfl-QA
Who does BSkyB have an operating license from?  Who removed [BSkyB’s] operating license, no scratch that, who do [they] have [their] operating license from?

Experiments show that the performance of existing state-of-the-art language model–based question answering systems degrades significantly when tested on Disfl-QA and heuristic disfluencies (presented in the paper) in a zero-shot setting.

Dataset   F1
SQuAD   89.59
Heuristics   65.27 (-24.32)
Disfl-QA   61.64 (-27.95)

We show that data augmentation methods partially recover the loss in performance and also demonstrate the efficacy of using human-annotated training data for fine-tuning. We argue that researchers need large-scale disfluency datasets in order for NLP models to be robust to disfluencies.

Conclusion
Understanding language phenomena that are unique to human speech, like disfluencies and temporal reasoning, among others, is a key ingredient for enabling more natural human–machine communication in the near future. With TimeDial and Disfl-QA, we aim to fill a major research gap by providing these datasets as testbeds for NLP models, in order to evaluate their robustness to ubiquitous phenomena across different tasks. It is our hope that the broader NLP community will devise generalized few-shot or zero-shot approaches to effectively handle these phenomena, without requiring task-specific human-annotated training datasets, constructed specifically for these challenges.

Acknowledgments
The TimeDial work has been a team effort involving Lianhui Qi, Luheng He, Yenjin Choi, Manaal Faruqui and the authors. The Disfl-QA work has been a collaboration involving Jiacheng Xu, Diyi Yang, Manaal Faruqui.

Source: Google AI Blog


Constructing Transformers For Longer Sequences with Sparse Attention Methods

Natural language processing (NLP) models based on Transformers, such as BERT, RoBERTa, T5, or GPT3, are successful for a wide variety of tasks and a mainstay of modern NLP research. The versatility and robustness of Transformers are the primary drivers behind their wide-scale adoption, leading them to be easily adapted for a diverse range of sequence-based tasks — as a seq2seq model for translation, summarization, generation, and others, or as a standalone encoder for sentiment analysis, POS tagging, machine reading comprehension, etc. The key innovation in Transformers is the introduction of a self-attention mechanism, which computes similarity scores for all pairs of positions in an input sequence, and can be evaluated in parallel for each token of the input sequence, avoiding the sequential dependency of recurrent neural networks, and enabling Transformers to vastly outperform previous sequence models like LSTM.

A limitation of existing Transformer models and their derivatives, however, is that the full self-attention mechanism has computational and memory requirements that are quadratic with the input sequence length. With commonly available current hardware and model sizes, this typically limits the input sequence to roughly 512 tokens, and prevents Transformers from being directly applicable to tasks that require larger context, like question answering, document summarization or genome fragment classification. Two natural questions arise: 1) Can we achieve the empirical benefits of quadratic full Transformers using sparse models with computational and memory requirements that scale linearly with the input sequence length? 2) Is it possible to show theoretically that these linear Transformers preserve the expressivity and flexibility of the quadratic full Transformers?

We address both of these questions in a recent pair of papers. In “ETC: Encoding Long and Structured Inputs in Transformers”, presented at EMNLP 2020, we present the Extended Transformer Construction (ETC), which is a novel method for sparse attention, in which one uses structural information to limit the number of computed pairs of similarity scores. This reduces the quadratic dependency on input length to linear and yields strong empirical results in the NLP domain. Then, in “Big Bird: Transformers for Longer Sequences”, presented at NeurIPS 2020, we introduce another sparse attention method, called BigBird that extends ETC to more generic scenarios where prerequisite domain knowledge about structure present in the source data may be unavailable. Moreover, we also show that theoretically our proposed sparse attention mechanism preserves the expressivity and flexibility of the quadratic full Transformers. Our proposed methods achieve a new state of the art on challenging long-sequence tasks, including question answering, document summarization and genome fragment classification.

Attention as a Graph
The attention module used in Transformer models computes similarity scores for all pairs of positions in an input sequence. It is useful to think of the attention mechanism as a directed graph, with tokens represented by nodes and the similarity score computed between a pair of tokens represented by an edge. In this view, the full attention model is a complete graph. The core idea behind our approach is to carefully design sparse graphs, such that one only computes a linear number of similarity scores.

Full attention can be viewed as a complete graph.

Extended Transformer Construction (ETC)
On NLP tasks that require long and structured inputs, we propose a structured sparse attention mechanism, which we call Extended Transformer Construction (ETC). To achieve structured sparsification of self attention, we developed the global-local attention mechanism. Here the input to the Transformer is split into two parts: a global input where tokens have unrestricted attention, and a long input where tokens can only attend to either the global input or to a local neighborhood. This achieves linear scaling of attention, which allows ETC to significantly scale input length.

In order to further exploit the structure of long documents, ETC combines additional ideas: representing the positional information of the tokens in a relative way, rather than using their absolute position in the sequence; using an additional training objective beyond the usual masked language model (MLM) used in models like BERT; and flexible masking of tokens to control which tokens can attend to which other tokens. For example, given a long selection of text, a global token is applied to each sentence, which connects to all tokens within the sentence, and a global token is also applied to each paragraph, which connects to all tokens within the same paragraph.

An example of document structure based sparse attention of ETC model. The global variables are denoted by C (in blue) for paragraph, S (yellow) for sentence while the local variables are denoted by X (grey) for tokens corresponding to the long input.

With this approach, we report state-of-the-art results in five challenging NLP datasets requiring long or structured inputs: TriviaQA, Natural Questions (NQ), HotpotQA, WikiHop, and OpenKP.

Test set result on Question Answering. For both verified TriviaQA and WikiHop, using ETC achieved a new state of the art.

BigBird
Extending the work of ETC, we propose BigBird — a sparse attention mechanism that is also linear in the number of tokens and is a generic replacement for the attention mechanism used in Transformers. In contrast to ETC, BigBird doesn’t require any prerequisite knowledge about structure present in the source data. Sparse attention in the BigBird model consists of three main parts:

  • A set of global tokens attending to all parts of the input sequence
  • All tokens attending to a set of local neighboring tokens
  • All tokens attending to a set of random tokens
BigBird sparse attention can be seen as adding few global tokens on Watts-Strogatz graph.

In the BigBird paper, we explain why sparse attention is sufficient to approximate quadratic attention, partially explaining why ETC was successful. A crucial observation is that there is an inherent tension between how few similarity scores one computes and the flow of information between different nodes (i.e., the ability of one token to influence each other). Global tokens serve as a conduit for information flow and we prove that sparse attention mechanisms with global tokens can be as powerful as the full attention model. In particular, we show that BigBird is as expressive as the original Transformer, is computationally universal (following the work of Yun et al. and Perez et al.), and is a universal approximator of continuous functions. Furthermore, our proof suggests that the use of random graphs can further help ease the flow of information — motivating the use of the random attention component.

This design scales to much longer sequence lengths for both structured and unstructured tasks. Further scaling can be achieved by using gradient checkpointing by trading off training time for sequence length. This lets us extend our efficient sparse transformers to include generative tasks that require an encoder and a decoder, such as long document summarization, on which we achieve a new state of the art.

Summarization ROUGE score for long documents. Both for BigPatent and ArXiv datasets, we achieve a new state of the art result.

Moreover, the fact that BigBird is a generic replacement also allows it to be extended to new domains without pre-existing domain knowledge. In particular, we introduce a novel application of Transformer-based models where long contexts are beneficial — extracting contextual representations of genomic sequences (DNA). With longer masked language model pre-training, BigBird achieves state-of-the-art performance on downstream tasks, such as promoter-region prediction and chromatin profile prediction.

On multiple genomics tasks, such as promoter region prediction (PRP), chromatin-profile prediction including transcription factors (TF), histone-mark (HM) and DNase I hypersensitive (DHS) detection, we outperform baselines. Moreover our results show that Transformer models can be applied to multiple genomics tasks that are currently underexplored.

Main Implementation Idea
One of the main impediments to the large scale adoption of sparse attention is the fact that sparse operations are quite inefficient in modern hardware. Behind both ETC and BigBird, one of our key innovations is to make an efficient implementation of the sparse attention mechanism. As modern hardware accelerators like GPUs and TPUs excel using coalesced memory operations, which load blocks of contiguous bytes at once, it is not efficient to have small sporadic look-ups caused by a sliding window (for local attention) or random element queries (random attention). Instead we transform the sparse local and random attention into dense tensor operations to take full advantage of modern single instruction, multiple data (SIMD) hardware.

To do this, we first “blockify” the attention mechanism to better leverage GPUs/TPUs, which are designed to operate on blocks. Then we convert the sparse attention mechanism computation into a dense tensor product through a series of simple matrix operations such as reshape, roll, and gather, as illustrated in the animation below.

Illustration of how sparse window attention is efficiently computed using roll and reshape, and without small sporadic look-ups.

Recently, “Long Range Arena: A Benchmark for Efficient Transformers“ provided a benchmark of six tasks that require longer context, and performed experiments to benchmark all existing long range transformers. The results show that the BigBird model, unlike its counterparts, clearly reduces memory consumption without sacrificing performance.

Conclusion
We show that carefully designed sparse attention can be as expressive and flexible as the original full attention model. Along with theoretical guarantees, we provide a very efficient implementation which allows us to scale to much longer inputs. As a consequence, we achieve state-of-the-art results for question answering, document summarization and genome fragment classification. Given the generic nature of our sparse attention, the approach should be applicable to many other tasks like program synthesis and long form open domain question answering. We have open sourced the code for both ETC (github) and BigBird (github), both of which run efficiently for long sequences on both GPUs and TPUs.

Acknowledgements
This research resulted as a collaboration with Amr Ahmed, Joshua Ainslie, Chris Alberti, Vaclav Cvicek, Avinava Dubey, Zachary Fisher, Guru Guruganesh, Santiago Ontañón, Philip Pham, Anirudh Ravula, Sumit Sanghai, Qifan Wang, Li Yang, Manzil Zaheer, who co-authored EMNLP and NeurIPS papers.

Source: Google AI Blog


Constructing Transformers For Longer Sequences with Sparse Attention Methods

Natural language processing (NLP) models based on Transformers, such as BERT, RoBERTa, T5, or GPT3, are successful for a wide variety of tasks and a mainstay of modern NLP research. The versatility and robustness of Transformers are the primary drivers behind their wide-scale adoption, leading them to be easily adapted for a diverse range of sequence-based tasks — as a seq2seq model for translation, summarization, generation, and others, or as a standalone encoder for sentiment analysis, POS tagging, machine reading comprehension, etc. The key innovation in Transformers is the introduction of a self-attention mechanism, which computes similarity scores for all pairs of positions in an input sequence, and can be evaluated in parallel for each token of the input sequence, avoiding the sequential dependency of recurrent neural networks, and enabling Transformers to vastly outperform previous sequence models like LSTM.

A limitation of existing Transformer models and their derivatives, however, is that the full self-attention mechanism has computational and memory requirements that are quadratic with the input sequence length. With commonly available current hardware and model sizes, this typically limits the input sequence to roughly 512 tokens, and prevents Transformers from being directly applicable to tasks that require larger context, like question answering, document summarization or genome fragment classification. Two natural questions arise: 1) Can we achieve the empirical benefits of quadratic full Transformers using sparse models with computational and memory requirements that scale linearly with the input sequence length? 2) Is it possible to show theoretically that these linear Transformers preserve the expressivity and flexibility of the quadratic full Transformers?

We address both of these questions in a recent pair of papers. In “ETC: Encoding Long and Structured Inputs in Transformers”, presented at EMNLP 2020, we present the Extended Transformer Construction (ETC), which is a novel method for sparse attention, in which one uses structural information to limit the number of computed pairs of similarity scores. This reduces the quadratic dependency on input length to linear and yields strong empirical results in the NLP domain. Then, in “Big Bird: Transformers for Longer Sequences”, presented at NeurIPS 2020, we introduce another sparse attention method, called BigBird that extends ETC to more generic scenarios where prerequisite domain knowledge about structure present in the source data may be unavailable. Moreover, we also show that theoretically our proposed sparse attention mechanism preserves the expressivity and flexibility of the quadratic full Transformers. Our proposed methods achieve a new state of the art on challenging long-sequence tasks, including question answering, document summarization and genome fragment classification.

Attention as a Graph
The attention module used in Transformer models computes similarity scores for all pairs of positions in an input sequence. It is useful to think of the attention mechanism as a directed graph, with tokens represented by nodes and the similarity score computed between a pair of tokens represented by an edge. In this view, the full attention model is a complete graph. The core idea behind our approach is to carefully design sparse graphs, such that one only computes a linear number of similarity scores.

Full attention can be viewed as a complete graph.

Extended Transformer Construction (ETC)
On NLP tasks that require long and structured inputs, we propose a structured sparse attention mechanism, which we call Extended Transformer Construction (ETC). To achieve structured sparsification of self attention, we developed the global-local attention mechanism. Here the input to the Transformer is split into two parts: a global input where tokens have unrestricted attention, and a long input where tokens can only attend to either the global input or to a local neighborhood. This achieves linear scaling of attention, which allows ETC to significantly scale input length.

In order to further exploit the structure of long documents, ETC combines additional ideas: representing the positional information of the tokens in a relative way, rather than using their absolute position in the sequence; using an additional training objective beyond the usual masked language model (MLM) used in models like BERT; and flexible masking of tokens to control which tokens can attend to which other tokens. For example, given a long selection of text, a global token is applied to each sentence, which connects to all tokens within the sentence, and a global token is also applied to each paragraph, which connects to all tokens within the same paragraph.

An example of document structure based sparse attention of ETC model. The global variables are denoted by C (in blue) for paragraph, S (yellow) for sentence while the local variables are denoted by X (grey) for tokens corresponding to the long input.

With this approach, we report state-of-the-art results in five challenging NLP datasets requiring long or structured inputs: TriviaQA, Natural Questions (NQ), HotpotQA, WikiHop, and OpenKP.

Test set result on Question Answering. For both verified TriviaQA and WikiHop, using ETC achieved a new state of the art.

BigBird
Extending the work of ETC, we propose BigBird — a sparse attention mechanism that is also linear in the number of tokens and is a generic replacement for the attention mechanism used in Transformers. In contrast to ETC, BigBird doesn’t require any prerequisite knowledge about structure present in the source data. Sparse attention in the BigBird model consists of three main parts:

  • A set of global tokens attending to all parts of the input sequence
  • All tokens attending to a set of local neighboring tokens
  • All tokens attending to a set of random tokens
BigBird sparse attention can be seen as adding few global tokens on Watts-Strogatz graph.

In the BigBird paper, we explain why sparse attention is sufficient to approximate quadratic attention, partially explaining why ETC was successful. A crucial observation is that there is an inherent tension between how few similarity scores one computes and the flow of information between different nodes (i.e., the ability of one token to influence each other). Global tokens serve as a conduit for information flow and we prove that sparse attention mechanisms with global tokens can be as powerful as the full attention model. In particular, we show that BigBird is as expressive as the original Transformer, is computationally universal (following the work of Yun et al. and Perez et al.), and is a universal approximator of continuous functions. Furthermore, our proof suggests that the use of random graphs can further help ease the flow of information — motivating the use of the random attention component.

This design scales to much longer sequence lengths for both structured and unstructured tasks. Further scaling can be achieved by using gradient checkpointing by trading off training time for sequence length. This lets us extend our efficient sparse transformers to include generative tasks that require an encoder and a decoder, such as long document summarization, on which we achieve a new state of the art.

Summarization ROUGE score for long documents. Both for BigPatent and ArXiv datasets, we achieve a new state of the art result.

Moreover, the fact that BigBird is a generic replacement also allows it to be extended to new domains without pre-existing domain knowledge. In particular, we introduce a novel application of Transformer-based models where long contexts are beneficial — extracting contextual representations of genomic sequences (DNA). With longer masked language model pre-training, BigBird achieves state-of-the-art performance on downstream tasks, such as promoter-region prediction and chromatin profile prediction.

On multiple genomics tasks, such as promoter region prediction (PRP), chromatin-profile prediction including transcription factors (TF), histone-mark (HM) and DNase I hypersensitive (DHS) detection, we outperform baselines. Moreover our results show that Transformer models can be applied to multiple genomics tasks that are currently underexplored.

Main Implementation Idea
One of the main impediments to the large scale adoption of sparse attention is the fact that sparse operations are quite inefficient in modern hardware. Behind both ETC and BigBird, one of our key innovations is to make an efficient implementation of the sparse attention mechanism. As modern hardware accelerators like GPUs and TPUs excel using coalesced memory operations, which load blocks of contiguous bytes at once, it is not efficient to have small sporadic look-ups caused by a sliding window (for local attention) or random element queries (random attention). Instead we transform the sparse local and random attention into dense tensor operations to take full advantage of modern single instruction, multiple data (SIMD) hardware.

To do this, we first “blockify” the attention mechanism to better leverage GPUs/TPUs, which are designed to operate on blocks. Then we convert the sparse attention mechanism computation into a dense tensor product through a series of simple matrix operations such as reshape, roll, and gather, as illustrated in the animation below.

Illustration of how sparse window attention is efficiently computed using roll and reshape, and without small sporadic look-ups.

Recently, “Long Range Arena: A Benchmark for Efficient Transformers“ provided a benchmark of six tasks that require longer context, and performed experiments to benchmark all existing long range transformers. The results show that the BigBird model, unlike its counterparts, clearly reduces memory consumption without sacrificing performance.

Conclusion
We show that carefully designed sparse attention can be as expressive and flexible as the original full attention model. Along with theoretical guarantees, we provide a very efficient implementation which allows us to scale to much longer inputs. As a consequence, we achieve state-of-the-art results for question answering, document summarization and genome fragment classification. Given the generic nature of our sparse attention, the approach should be applicable to many other tasks like program synthesis and long form open domain question answering. We have open sourced the code for both ETC (github) and BigBird (github), both of which run efficiently for long sequences on both GPUs and TPUs.

Acknowledgements
This research resulted as a collaboration with Amr Ahmed, Joshua Ainslie, Chris Alberti, Vaclav Cvicek, Avinava Dubey, Zachary Fisher, Guru Guruganesh, Santiago Ontañón, Philip Pham, Anirudh Ravula, Sumit Sanghai, Qifan Wang, Li Yang, Manzil Zaheer, who co-authored EMNLP and NeurIPS papers.

Source: Google AI Blog


RxR: A Multilingual Benchmark for Navigation Instruction Following

A core challenge in machine learning (ML) is to build agents that can navigate complex human environments in response to spoken or written commands. While today’s agents, including robots, can often navigate complicated environments, they cannot yet understand navigation goals expressed in natural language, such as, “Go past the brown double doors that are closed to your right and stand behind the chair at the head of the table.”

This challenge, referred to as vision-and-language navigation (VLN), demands a sophisticated understanding of spatial language. For example, the ability to identify the position “behind the chair at the head of the table requires finding the table, identifying which part of the table is considered to be the “head”, finding the chair closest to the head, identifying the area behind this chair and so on. While people can follow these instructions easily, these challenges cannot be easily solved with current ML-based methods, requiring systems that can better connect language to the physical world it describes.

To help spur progress in this area, we are excited to introduce Room-Across-Room (RxR), a new dataset for VLN. Described in “Room-Across-Room: Multilingual Vision-and-Language Navigation with Dense Spatiotemporal Grounding”, RxR is the first multilingual dataset for VLN, containing 126,069 human-annotated navigation instructions in three typologically diverse languages — English, Hindi and Telugu. Each instruction describes a path through a photorealistic simulator populated with indoor environments from the Matterport3D dataset, which includes 3D captures of homes, offices and public buildings. To track progress on VLN, we are also announcing the RxR Challenge, a competition that encourages the machine learning community to train and evaluate their own instruction following agents on RxR instructions.

Language Instruction
en-US Starting next to the long dining room table, turn so the table is to your right. Walk towards the glass double doors. When you reach the mat before the doors, turn immediately left and walk down the stairs. When you reach the bottom of the stairs, walk through the open doors to your left and continue through the art exhibit with the tub to your right hand side. Down the length of the table until you reach the small step at the end of the room before you reach the tub and stop.
  
hi-IN अभी हमारे बायीं ओर एक बड़ा मेज़ है कुछ कुर्सियाँ हैं और कुछ दीपक मेज़ के ऊपर रखे हैं। उलटी दिशा में घूम जाएँ और सिधा चलें। अभी हमारे दायीं ओर एक गोल मेज़ है वहां से सीधा बढ़ें और सामने एक शीशे का बंद दरवाज़ा है उससे पहले बायीं ओर एक सीढ़ी है उससे निचे उतरें। निचे उतरने के बाद दायीं ओर मुड़े और एक भूरे रंग के दरवाज़े से अंदर प्रवेश करें और सीधा चलें। अभी हमारे दायीं ओर एक बड़ा मेज़ है और दो कुर्सियां राखी हैं सीधा आगे बढ़ें। हमारे सामने एक पानी का कल है और सामने तीन कुर्सियां दिवार के पास रखी हैं यहीं पर ठहर जाएँ।
  
te-IN ఉన్న చోటు నుండి వెనకకు తిరిగి, నేరుగా వెళ్తే, మీ ముందర ఒక బల్ల ఉంటుంది. దాన్ని దాటుకొని ఎడమవైపుకి తిరిగితే, మీ ముందర మెట్లు ఉంటాయి. వాటిని పూర్తిగా దిగండి. ఇప్పుడు మీ ముందర రెండు తెరిచిన ద్వారాలు ఉంటాయి. ఎడమవైపు ఉన్న ద్వారం గుండా బయటకు వెళ్ళి, నేరుగా నడవండి. ఇప్పుడు మీ కుడివైపున పొడవైన బల్ల ఉంటుంది. దాన్ని దాటుకొని ముందరే ఉన్న మెట్ల వద్దకు వెళ్ళి ఆగండి.

Examples of English, Hindi and Telugu navigation instructions from the RxR dataset. Each navigation instruction describes the same path.

Pose Traces
In addition to navigation instructions and paths, RxR also includes a new, more detailed multimodal annotation called a pose trace. Inspired by the mouse traces captured in the Localized Narratives dataset, pose traces provide dense groundings between language, vision and movement in a rich 3D setting. To generate navigation instructions, we ask guide annotators to move along a path in the simulator while narrating the path based on the surroundings. The pose trace is a record of everything the guide sees along the path, time-aligned with the words in the navigation instructions. These traces are then paired with pose traces from follower annotators, who are tasked with following the intended path by listening to the guide’s audio, thereby validating the quality of the navigation instructions. Pose traces implicitly capture notions of landmark selection and visual saliency, and represent a play-by-play account of how to solve the navigation instruction generation task (for guides) and the navigation instruction following task (for followers).

Example English navigation instruction in the RxR dataset. Words in the instruction text (right) are color-coded to align with the pose trace (left) that illustrates the movements and visual percepts of the guide annotator as they move through the environment describing the path.
The same RxR example with words in the navigation instruction aligned to 360° images along the path. The parts of the scene the guide annotator observed are highlighted; parts of the scene ignored by the annotator are faded. Red and yellow boxes highlight some of the close alignments between the textual instructions and the annotator's visual cues. The red cross indicates the next direction the annotator moved.

Scale
In total, RxR contains almost 10 million words, making it around 10 times larger than existing datasets, such as R2R and Touchdown/Retouchdown. This is important because, in comparison to tasks based on static image and text data, language tasks that require learning through movement or interaction with an environment typically suffer from a lack of large-scale training data. RxR also addresses known biases in the construction of the paths that have arisen in other datasets, such as R2R in which all paths have similar lengths and take the shortest route to the goal. In contrast, the paths in RxR are on average longer and less predictable, making them more challenging to follow and encouraging models trained on the dataset to place greater emphasis on the role of language in the task. The size, scope and detail of RxR will expand the frontier for research on grounded language learning while reducing the dominance of high resource languages such as English.

Left: RxR is an order of magnitude larger than similar existing datasets. Right: Compared to R2R, the paths in RxR are typically longer and less predictable, making them more challenging to follow.

Baselines
To better characterize and understand the RxR dataset, we trained a variety of agents on RxR using our open source framework VALAN, and language representations from the multilingual BERT model. We found that results were improved by including follower annotations as well as guide annotations during training, and that independently trained monolingual agents outperformed a single multilingual agent.

Conceptually, evaluation of these agents is straightforward — did the agent follow the intended path? Empirically, we measure the similarity between the path taken by the VLN agent and the reference path using NDTW, a normalized measure of path fidelity that ranges between 100 (perfect correspondence) and 0 (completely wrong). The average score for the follower annotators across all three languages is 79.5, due to natural variation between similar paths. In contrast, the best model (a composite of three independently trained monolingual agents, one for each language) achieved an NDTW score on the RxR test set of 41.5. While this is much better than random (15.4), it remains far below human performance. Although advances in language modeling continue to rapidly erode the headroom for improvement in text-only language understanding benchmarks such as GLUE and SuperGLUE, benchmarks like RxR that connect language to the physical world offer substantial room for improvement.

Results for our multilingual and monolingual instruction following agents on the RxR test-standard split. While performance is much better than a random walk, there remains considerable headroom to reach human performance on this task.

Competition
To encourage further research in this area, we are launching the RxR Challenge, an ongoing competition for the machine learning community to develop computational agents that can follow natural language navigation instructions. To take part, participants upload the navigation paths taken by their agent in response to the provided RxR test instructions. In the most difficult setting (reported here and in the paper), all the test environments are previously unseen. However, we also allow for settings in which the agent is either trained in or explores the test environments in advance. For more details and the latest results please visit the challenge website.

PanGEA
We are also releasing the custom web-based annotation tool that we developed to collect the RxR dataset. The Panoramic Graph Environment Annotation toolkit (PanGEA), is a lightweight and customizable codebase for collecting speech and text annotations in panoramic graph environments, such as Matterport3D and StreetLearn. It includes speech recording and virtual pose tracking, as well as tooling to align the resulting pose trace with a manual transcript. For more details please visit the PanGEA github page.

Acknowledgements
The authors would like to thank Roma Patel, Eugene Ie and Jason Baldridge for their contributions to this research. We would also like to thank all the annotators, Sneha Kudugunta for analyzing the Telugu annotations, and Igor Karpov, Ashwin Kakarla and Christina Liu for their tooling and annotation support for this project, Austin Waters and Su Wang for help with image features, and Daphne Luong for executive support for the data collection.

Source: Google AI Blog


Navigating Recorder Transcripts Easily, with Smart Scrolling

Last year we launched Recorder, a new kind of recording app that made audio recording smarter and more useful by leveraging on-device machine learning (ML) to transcribe the recording, highlight audio events, and suggest appropriate tags for titles. Recorder makes editing, sharing and searching through transcripts easier. Yet because Recorder can transcribe very long recordings (up to 18 hours!), it can still be difficult for users to find specific sections, necessitating a new solution to quickly navigate such long transcripts.

To increase the navigability of content, we introduce Smart Scrolling, a new ML-based feature in Recorder that automatically marks important sections in the transcript, chooses the most representative keywords from each section, and then surfaces those keywords on the vertical scrollbar, like chapter headings. The user can then scroll through the keywords or tap on them to quickly navigate to the sections of interest. The models used are lightweight enough to be executed on-device without the need to upload the transcript, thus preserving user privacy.

Smart Scrolling feature UX

Under the hood
The Smart Scrolling feature is composed of two distinct tasks. The first extracts representative keywords from each section and the second picks which sections in the text are the most informative and unique.

For each task, we utilize two different natural language processing (NLP) approaches: a distilled bidirectional transformer (BERT) model pre-trained on data sourced from a Wikipedia dataset, alongside a modified extractive term frequency–inverse document frequency (TF-IDF) model. By using the bidirectional transformer and the TF-IDF-based models in parallel for both the keyword extraction and important section identification tasks, alongside aggregation heuristics, we were able to harness the advantages of each approach and mitigate their respective drawbacks (more on this in the next section).

The bidirectional transformer is a neural network architecture that employs a self-attention mechanism to achieve context-aware processing of the input text in a non-sequential fashion. This enables parallel processing of the input text to identify contextual clues both before and after a given position in the transcript.

Bidirectional Transformer-based model architecture

The extractive TF-IDF approach rates terms based on their frequency in the text compared to their inverse frequency in the trained dataset, and enables the finding of unique representative terms in the text.

Both models were trained on publicly available conversational datasets that were labeled and evaluated by independent raters. The conversational datasets were from the same domains as the expected product use cases, focusing on meetings, lectures, and interviews, thus ensuring the same word frequency distribution (Zipf’s law).

Extracting Representative Keywords
The TF-IDF-based model detects informative keywords by giving each word a score, which corresponds to how representative this keyword is within the text. The model does so, much like a standard TF-IDF model, by utilizing the ratio of the number of occurrences of a given word in the text compared to the whole of the conversational data set, but it also takes into account the specificity of the term, i.e., how broad or specific it is. Furthermore, the model then aggregates these features into a score using a pre-trained function curve. In parallel, the bidirectional transformer model, which was fine tuned on the task of extracting keywords, provides a deep semantic understanding of the text, enabling it to extract precise context-aware keywords.

The TF-IDF approach is conservative in the sense that it is prone to finding uncommon keywords in the text (high bias), while the drawback for the bidirectional transformer model is the high variance of the possible keywords that can be extracted. But when used together, these two models complement each other, forming a balanced bias-variance tradeoff.

Once the keyword scores are retrieved from both models, we normalize and combine them by utilizing NLP heuristics (e.g., the weighted average), removing duplicates across sections, and eliminating stop words and verbs. The output of this process is an ordered list of suggested keywords for each of the sections.

Rating A Section’s Importance
The next task is to determine which sections should be highlighted as informative and unique. To solve this task, we again combine the two models mentioned above, which yield two distinct importance scores for each of the sections. We compute the first score by taking the TF-IDF scores of all the keywords in the section and weighting them by their respective number of appearances in the section, followed by a summation of these individual keyword scores. We compute the second score by running the section text through the bidirectional transformer model, which was also trained on the sections rating task. The scores from both models are normalized and then combined to yield the section score.

Smart Scrolling pipeline architecture

Some Challenges
A significant challenge in the development of Smart Scrolling was how to identify whether a section or keyword is important - what is of great importance to one person can be of less importance to another. The key was to highlight sections only when it is possible to extract helpful keywords from them.

To do this, we configured the solution to select the top scored sections that also have highly rated keywords, with the number of sections highlighted proportional to the length of the recording. In the context of the Smart Scrolling features, a keyword was more highly rated if it better represented the unique information of the section.

To train the model to understand this criteria, we needed to prepare a labeled training dataset tailored to this task. In collaboration with a team of skilled raters, we applied this labeling objective to a small batch of examples to establish an initial dataset in order to evaluate the quality of the labels and instruct the raters in cases where there were deviations from what was intended. Once the labeling process was complete we reviewed the labeled data manually and made corrections to the labels as necessary to align them with our definition of importance.

Using this limited labeled dataset, we ran automated model evaluations to establish initial metrics on model quality, which were used as a less-accurate proxy to the model quality, enabling us to quickly assess the model performance and apply changes in the architecture and heuristics. Once the solution metrics were satisfactory, we utilized a more accurate manual evaluation process over a closed set of carefully chosen examples that represented expected Recorder use cases. Using these examples, we tweaked the model heuristics parameters to reach the desired level of performance using a reliable model quality evaluation.

Runtime Improvements
After the initial release of Recorder, we conducted a series of user studies to learn how to improve the usability and performance of the Smart Scrolling feature. We found that many users expect the navigational keywords and highlighted sections to be available as soon as the recording is finished. Because the computation pipeline described above can take a considerable amount of time to compute on long recordings, we devised a partial processing solution that amortizes this computation over the whole duration of the recording. During recording, each section is processed as soon as it is captured, and then the intermediate results are stored in memory. When the recording is done, Recorder aggregates the intermediate results.

When running on a Pixel 5, this approach reduced the average processing time of an hour long recording (~9K words) from 1 minute 40 seconds to only 9 seconds, while outputting the same results.

Summary
The goal of Recorder is to improve users’ ability to access their recorded content and navigate it with ease. We have already made substantial progress in this direction with the existing ML features that automatically suggest title words for recordings and enable users to search recordings for sounds and text. Smart Scrolling provides additional text navigation abilities that will further improve the utility of Recorder, enabling users to rapidly surface sections of interest, even for long recordings.

Acknowledgments
Bin Zhang, Sherry Lin, Isaac Blankensmith, Henry Liu‎, Vincent Peng‎, Guilherme Santos‎, Tiago Camolesi, Yitong Lin, James Lemieux, Thomas Hall‎, Kelly Tsai‎, Benny Schlesinger, Dror Ayalon, Amit Pitaru, Kelsie Van Deman, Console Chen, Allen Su, Cecile Basnage, Chorong Johnston‎, Shenaz Zack, Mike Tsao, Brian Chen, Abhinav Rastogi, Tracy Wu, Yvonne Yang‎.

Source: Google AI Blog


Measuring Gendered Correlations in Pre-trained NLP Models

Natural language processing (NLP) has seen significant progress over the past several years, with pre-trained models like BERT, ALBERT, ELECTRA, and XLNet achieving remarkable accuracy across a variety of tasks. In pre-training, representations are learned from a large text corpus, e.g., Wikipedia, by repeatedly masking out words and trying to predict them (this is called masked language modeling). The resulting representations encode rich information about language and correlations between concepts, such as surgeons and scalpels. There is then a second training stage, fine-tuning, in which the model uses task-specific training data to learn how to use the general pre-trained representations to do a concrete task, like classification. Given the broad adoption of these representations in many NLP tasks, it is crucial to understand the information encoded in them and how any learned correlations affect performance downstream, to ensure the application of these models aligns with our AI Principles.

In “Measuring and Reducing Gendered Correlations in Pre-trained Models” we perform a case study on BERT and its low-memory counterpart ALBERT, looking at correlations related to gender, and formulate a series of best practices for using pre-trained language models. We present experimental results over public model checkpoints and an academic task dataset to illustrate how the best practices apply, providing a foundation for exploring settings beyond the scope of this case study. We will soon release a series of checkpoints, Zari1, which reduce gendered correlations while maintaining state-of-the-art accuracy on standard NLP task metrics.

Measuring Correlations
To understand how correlations in pre-trained representations can affect downstream task performance, we apply a diverse set of evaluation metrics for studying the representation of gender. Here, we’ll discuss results from one of these tests, based on coreference resolution, which is the capability that allows models to understand the correct antecedent to a given pronoun in a sentence. For example, in the sentence that follows, the model should recognize his refers to the nurse, and not to the patient.

The standard academic formulation of the task is the OntoNotes test (Hovy et al., 2006), and we measure how accurate a model is at coreference resolution in a general setting using an F1 score over this data (as in Tenney et al. 2019). Since OntoNotes represents only one data distribution, we also consider the WinoGender benchmark that provides additional, balanced data designed to identify when model associations between gender and profession incorrectly influence coreference resolution. High values of the WinoGender metric (close to one) indicate a model is basing decisions on normative associations between gender and profession (e.g., associating nurse with the female gender and not male). When model decisions have no consistent association between gender and profession, the score is zero, which suggests that decisions are based on some other information, such as sentence structure or semantics.

BERT and ALBERT metrics on OntoNotes (accuracy) and WinoGender (gendered correlations). Low values on the WinoGender metric indicate that a model does not preferentially use gendered correlations in reasoning.

In this study, we see that neither the (Large) BERT or ALBERT public model achieves zero score on the WinoGender examples, despite achieving impressive accuracy on OntoNotes (close to 100%). At least some of this is due to models preferentially using gendered correlations in reasoning. This isn’t completely surprising: there are a range of cues available to understand text and it is possible for a general model to pick up on any or all of these. However, there is reason for caution, as it is undesirable for a model to make predictions primarily based on gendered correlations learned as priors rather than the evidence available in the input.

Best Practices
Given that it is possible for unintended correlations in pre-trained model representations to affect downstream task reasoning, we now ask: what can one do to mitigate any risk this poses when developing new NLP models?

  • It is important to measure for unintended correlations: Model quality may be assessed using accuracy metrics, but these only measure one dimension of performance, especially if the test data is drawn from the same distribution as the training data. For example, the BERT and ALBERT checkpoints have accuracy within 1% of each other, but differ by 26% (relative) in the degree to which they use gendered correlations for coreference resolution. This difference might be important for some tasks; selecting a model with low WinoGender score could be desirable in an application featuring texts about people in professions that may not conform to historical social norms, e.g., male nurses.
  • Be careful even when making seemingly innocuous configuration changes: Neural network model training is controlled by many hyperparameters that are usually selected to maximize some training objective. While configuration choices often seem innocuous, we find they can cause significant changes for gendered correlations, both for better and for worse. For example, dropout regularization is used to reduce overfitting by large models. When we increase the dropout rate used for pre-training BERT and ALBERT, we see a significant reduction in gendered correlations even after fine-tuning. This is promising since a simple configuration change allows us to train models with reduced risk of harm, but it also shows that we should be mindful and evaluate carefully when making any change in model configuration.
    Impact of increasing dropout regularization in BERT and ALBERT.
  • There are opportunities for general mitigations: A further corollary from the perhaps unexpected impact of dropout on gendered correlations is that it opens the possibility to use general-purpose methods for reducing unintended correlations: by increasing dropout in our study, we improve how the models reason about WinoGender examples without manually specifying anything about the task or changing the fine-tuning stage at all. Unfortunately, OntoNotes accuracy does start to decline as the dropout rate increases (which we can see in the BERT results), but we are excited about the potential to mitigate this in pre-training, where changes can lead to model improvements without the need for task-specific updates. We explore counterfactual data augmentation as another mitigation strategy with different tradeoffs in our paper.

What’s Next
We believe these best practices provide a starting point for developing robust NLP systems that perform well across the broadest possible range of linguistic settings and applications. Of course these techniques on their own are not sufficient to capture and remove all potential issues. Any model deployed in a real-world setting should undergo rigorous testing that considers the many ways it will be used, and implement safeguards to ensure alignment with ethical norms, such as Google's AI Principles. We look forward to developments in evaluation frameworks and data that are more expansive and inclusive to cover the many uses of language models and the breadth of people they aim to serve.

Acknowledgements
This is joint work with Xuezhi Wang, Ian Tenney, Ellie Pavlick, Alex Beutel, Jilin Chen, Emily Pitler, and Slav Petrov. We benefited greatly throughout the project from discussions with Fernando Pereira, Ed Chi, Dipanjan Das, Vera Axelrod, Jacob Eisenstein, Tulsee Doshi, and James Wexler.



1 Zari is an Afghan Muppet designed to show that ‘a little girl could do as much as everybody else’.

Source: Google AI Blog


Measuring Gendered Correlations in Pre-trained NLP Models

Natural language processing (NLP) has seen significant progress over the past several years, with pre-trained models like BERT, ALBERT, ELECTRA, and XLNet achieving remarkable accuracy across a variety of tasks. In pre-training, representations are learned from a large text corpus, e.g., Wikipedia, by repeatedly masking out words and trying to predict them (this is called masked language modeling). The resulting representations encode rich information about language and correlations between concepts, such as surgeons and scalpels. There is then a second training stage, fine-tuning, in which the model uses task-specific training data to learn how to use the general pre-trained representations to do a concrete task, like classification. Given the broad adoption of these representations in many NLP tasks, it is crucial to understand the information encoded in them and how any learned correlations affect performance downstream, to ensure the application of these models aligns with our AI Principles.

In “Measuring and Reducing Gendered Correlations in Pre-trained Models” we perform a case study on BERT and its low-memory counterpart ALBERT, looking at correlations related to gender, and formulate a series of best practices for using pre-trained language models. We present experimental results over public model checkpoints and an academic task dataset to illustrate how the best practices apply, providing a foundation for exploring settings beyond the scope of this case study. We will soon release a series of checkpoints, Zari1, which reduce gendered correlations while maintaining state-of-the-art accuracy on standard NLP task metrics.

Measuring Correlations
To understand how correlations in pre-trained representations can affect downstream task performance, we apply a diverse set of evaluation metrics for studying the representation of gender. Here, we’ll discuss results from one of these tests, based on coreference resolution, which is the capability that allows models to understand the correct antecedent to a given pronoun in a sentence. For example, in the sentence that follows, the model should recognize his refers to the nurse, and not to the patient.

The standard academic formulation of the task is the OntoNotes test (Hovy et al., 2006), and we measure how accurate a model is at coreference resolution in a general setting using an F1 score over this data (as in Tenney et al. 2019). Since OntoNotes represents only one data distribution, we also consider the WinoGender benchmark that provides additional, balanced data designed to identify when model associations between gender and profession incorrectly influence coreference resolution. High values of the WinoGender metric (close to one) indicate a model is basing decisions on normative associations between gender and profession (e.g., associating nurse with the female gender and not male). When model decisions have no consistent association between gender and profession, the score is zero, which suggests that decisions are based on some other information, such as sentence structure or semantics.

BERT and ALBERT metrics on OntoNotes (accuracy) and WinoGender (gendered correlations). Low values on the WinoGender metric indicate that a model does not preferentially use gendered correlations in reasoning.

In this study, we see that neither the (Large) BERT or ALBERT public model achieves zero score on the WinoGender examples, despite achieving impressive accuracy on OntoNotes (close to 100%). At least some of this is due to models preferentially using gendered correlations in reasoning. This isn’t completely surprising: there are a range of cues available to understand text and it is possible for a general model to pick up on any or all of these. However, there is reason for caution, as it is undesirable for a model to make predictions primarily based on gendered correlations learned as priors rather than the evidence available in the input.

Best Practices
Given that it is possible for unintended correlations in pre-trained model representations to affect downstream task reasoning, we now ask: what can one do to mitigate any risk this poses when developing new NLP models?

  • It is important to measure for unintended correlations: Model quality may be assessed using accuracy metrics, but these only measure one dimension of performance, especially if the test data is drawn from the same distribution as the training data. For example, the BERT and ALBERT checkpoints have accuracy within 1% of each other, but differ by 26% (relative) in the degree to which they use gendered correlations for coreference resolution. This difference might be important for some tasks; selecting a model with low WinoGender score could be desirable in an application featuring texts about people in professions that may not conform to historical social norms, e.g., male nurses.
  • Be careful even when making seemingly innocuous configuration changes: Neural network model training is controlled by many hyperparameters that are usually selected to maximize some training objective. While configuration choices often seem innocuous, we find they can cause significant changes for gendered correlations, both for better and for worse. For example, dropout regularization is used to reduce overfitting by large models. When we increase the dropout rate used for pre-training BERT and ALBERT, we see a significant reduction in gendered correlations even after fine-tuning. This is promising since a simple configuration change allows us to train models with reduced risk of harm, but it also shows that we should be mindful and evaluate carefully when making any change in model configuration.
    Impact of increasing dropout regularization in BERT and ALBERT.
  • There are opportunities for general mitigations: A further corollary from the perhaps unexpected impact of dropout on gendered correlations is that it opens the possibility to use general-purpose methods for reducing unintended correlations: by increasing dropout in our study, we improve how the models reason about WinoGender examples without manually specifying anything about the task or changing the fine-tuning stage at all. Unfortunately, OntoNotes accuracy does start to decline as the dropout rate increases (which we can see in the BERT results), but we are excited about the potential to mitigate this in pre-training, where changes can lead to model improvements without the need for task-specific updates. We explore counterfactual data augmentation as another mitigation strategy with different tradeoffs in our paper.

What’s Next
We believe these best practices provide a starting point for developing robust NLP systems that perform well across the broadest possible range of linguistic settings and applications. Of course these techniques on their own are not sufficient to capture and remove all potential issues. Any model deployed in a real-world setting should undergo rigorous testing that considers the many ways it will be used, and implement safeguards to ensure alignment with ethical norms, such as Google's AI Principles. We look forward to developments in evaluation frameworks and data that are more expansive and inclusive to cover the many uses of language models and the breadth of people they aim to serve.

Acknowledgements
This is joint work with Xuezhi Wang, Ian Tenney, Ellie Pavlick, Alex Beutel, Jilin Chen, Emily Pitler, and Slav Petrov. We benefited greatly throughout the project from discussions with Fernando Pereira, Ed Chi, Dipanjan Das, Vera Axelrod, Jacob Eisenstein, Tulsee Doshi, and James Wexler.



1 Zari is an Afghan Muppet designed to show that ‘a little girl could do as much as everybody else’.

Source: Google AI Blog