New research challenges a common idea of how ML algorithms "think" about certain tasks

The conception goes something like this: because of their ability to discard useless information, a class of machine learning algorithms called deep neural networks can learn general concepts from raw data, like identifying cats generally after encountering tens of thousands of images of different cats in different situations.

This seemingly human ability is said to arise as a byproduct of the networks' layered architecture. Early layers encode the "cat" label along with all of the raw information needed for prediction.

Subsequent layers then compress the information, as if through a bottleneck. Irrelevant data, like the color of the cat's coat, or the saucer of milk beside it, is forgotten, leaving only general features behind. Information theory provides bounds on just how optimal each layer is, in terms of how well it can balance the competing demands of compression and prediction.

There’s a long-standing idea that as raw inputs get transformed to these intermediate representations, the system is trading prediction for compression, and building higher-level concepts through this information bottleneck.

Researchers however, uncovered a surprising weakness when they applied this explanation to common classification problems, where each input has one correct output (e.g., in which each picture can either be of a cat or of a dog). In such cases, they found that classifiers with many layers generally do not give up some prediction for improved compression. They also found that there are many "trivial" representations of the inputs which are, from the point of view of information theory, optimal in terms of their balance between prediction and compression.

While the idea of compressing inputs may still play a useful role in machine learning, this research suggests it is not sufficient for evaluating the internal representations used by different machine learning algorithms.


#MachineLearning #Algorithms #Prediction

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