Attention Mechanisms in NLP – Let’s Understand the What and Why

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Author

Wissen Team

Date

April 24, 2024

For the advancement of AI and natural language processing (NLP), the attention mechanism has emerged as a vital component or capability. As a replacement for the previous encoder-decoder model, the attention mechanism has enabled neural networks to easily cope with long input sequences.

As is well known in the NLP domain, elements of the source text have a different context depending on the assigned task. For instance, cue words like “good” and “bad” are relevant in sentiment analysis, but not for other aspects. Similarly, in visualized tasks, background pixels are relevant to describing the image or “scenery.”

Among the valuable breakthroughs, the attention mechanism pioneered the development of the transformer architecture and Google's BERT framework. Other NLP-powered tasks like language modeling, machine translation, and text summarization have also used the attention mechanism.

In this blog, let's understand the what and why of the attention mechanism in NLP.

What is the Attention Mechanism in NLP?

The attention mechanism helps focus AI and NLP models on the most relevant portion of the input data. The attention model in NLP searches for the most relevant information in the source sentences. This is similar to the human cognitive process of concentrating on one (or few) elements while ignoring the rest of the information.

For instance, humans have the cognitive ability to count the number of seated children in a school's group photo, while ignoring the rest of the elements in the photo. Similarly, in NLP, the attention mechanism enables AI models to add weightage to various input components and allocate more importance to specific components. 

Also known as intra-attention, self-attention is a form of attention mechanism where the neural model focuses attention on different positions of the input text sequence and compares each text position with the other text positions in the input. This enables the model to focus on the input components that are most relevant to the assigned task.

Here are the various types of attention mechanisms used in NLP applications:

  1. Scaled dot-product attention

This is a commonly used type of self-attention that assigns attention weights for each position in the input sequence. It represents the input sequence in the form of:

  • The query matrix indicates the current position of the input sequence.
  • The key matrix displays all the other positions in the input sequence.
  • The value matrix shows the output information for each position in the input sequence.

  1. Multi-head attention

This is a variant of the scaled dot-product attention mechanism, where multiple attention heads in parallel learn to attend to a different input representation. This technique divides the input sequence into multiple representations (or heads), which can compute the attention weight for each head. The benefit is that each head can focus on a different aspect of the input.

  1. Additive attention

Similar to scaled dot-product attention, the additive attention technique calculates the attention weight differently. For instance, it computes the similarity between the query and key vectors. After representing each input sequence as a query, key, and value vector, the attention weights are fed into a feed-forward neural network to produce a scalar output. This technique is most useful for NLP models to self-learn a non-linear similarity measure between key and query vectors.

  1. Location-based attention

This form of attention mechanism enables NLP models to focus on specific input regions. It uses a convolutional neural network (CNN) to learn the attention weights. In this method, the input sequence is first passed through the CNN to produce feature maps. A feature map represents the input at different scales and positions and computes a set of attention weights for each position. Location-based attention is useful for focusing on specific input regions, instead of individual positions.

Benefits of using Attention Mechanism in NLP

Why is the attention mechanism important in NLP? Here are some of its benefits or advantages:

  • Improves model performance by enabling them to focus on relevant parts of the input sequence.
  • Reduces workload by breaking down lengthy sequences into smaller manageable components.
  • Improves decision-making by enhancing the interpretability of the AI and NLP models.

Why is the attention mechanism better than the previous encoder-decoder architecture? Here’s how the encoder-decoder technique in NLP works:

  • The encoder processes the input sequence and summarizes the information into a fixed-length context vector.
  • The decoder component is initialized with the context vector, following which it generates the output information.

Thus, the fixed-length context vector design is designed for shorter input sequences. Frequently, this technique "forgets" the earlier part of a longer input sequence after processing the entire sequence. The attention mechanism overcomes this limitation.

Conclusion

To summarize, the attention mechanism is highly effective in the world of NLP as compared to previous techniques. Hopefully, this blog has been a comprehensive guide on the working of attention mechanisms in NLP.

At Wissen, we work with customers looking for the best solutions in AI and machine learning. We also have a proven track record in using NLP solutions across a range of industry applications. Here’s a customer case study of how our NLP expertise enabled a global financial company to provide specific information from their research reports.

Are you looking to improve your NLP model capabilities? We can help you. Contact us now.

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