Deep Learning from Scratch (Part 5) – History 3

Not Every Deep Learning Model Solves the Same Problem

After learning what a neural network is, it’s tempting to imagine that deep learning is built around one universal model.

It isn’t. “Deep learning” is really a collection of architectures, each designed with different kinds of data and different kinds of problems in mind. They all rely on neural networks, but they don’t all process information the same way.

If every problem looked identical, we probably wouldn’t have needed so many architectures in the first place.

The type of data often determines the kind of model that makes sense.

Take images, for example. An image isn’t just a long list of numbers. Nearby pixels usually contain related information. Edges, textures, and shapes appear because neighboring pixels have meaningful spatial relationships. Models designed for computer vision take advantage of that structure instead of treating every pixel independently.

Diagram illustrating CNN process for image classification with a cat image.
Step-by-step diagram of CNN image classification process.

Text presents a different challenge.

Words appear in a sequence, and their meaning depends heavily on context. Changing the order of just a few words can completely change the meaning of a sentence. Models built for language need to understand relationships across sequences rather than across space.

This is why architectures such as RNNs, LSTMs, and later Transformers became so important for natural language processing.

Diagram showing AI models from RNN to Transformer with timeline and features.
Visual comparison of RNN, LSTM, and Transformer models in AI development from 1980s to 2017.

Time series data introduces another set of challenges.

Stock prices, weather measurements, sensor readings, or repeated health assessments all depend on time. The order of observations matters. A measurement taken today often means something different depending on what happened yesterday or last month.

This makes forecasting fundamentally different from classifying an image.

Graph showing past data, trend, forecast, and uncertainty in time series analysis.
Illustration of the time series forecasting process.

Some data doesn’t naturally fit into either category.

Tables are everywhere: customer records, financial transactions, medical histories, survey responses. Structured data remains one of the most common types of data in industry, and surprisingly, traditional machine learning models often remain very competitive on these problems.

Deep learning can certainly work with tabular data, but it isn’t automatically the best choice simply because it’s newer. That’s an important lesson that’s easy to miss when most online discussions revolve around large language models.

Then there are models that generate entirely new content.

Instead of predicting a label or recognizing an object, these models learn to produce text, images, audio, or video that resembles their training data. Generative AI didn’t introduce deep learning, but it dramatically changed how visible deep learning became to the public.

Illustration of text and image generation with AI models and prompts.
Diagram showing the process of text and image generation using AI models and prompts.

Different data carries different kinds of structure. Images have spatial patterns. Language has sequential relationships. A time series evolves over time. Tables organize information into columns.

Each of these characteristics influences how researchers design a model.

As the field evolved, researchers didn’t simply build larger neural networks. They built architectures that better matched the data they wanted to learn from.

The next question naturally becomes, if there are so many different architectures, where do we actually begin?

Surprisingly, not with deep learning.

Before neural networks became practical, researchers were already exploring many of the ideas behind modern AI through much simpler machine learning models. One of the most influential examples is logistic regression, a model that researchers and practitioners still use widely today despite its age.

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