How AI Works: From Sorcery to Science by Ronald T. Kneusel

Author:Ronald T. Kneusel
Language: eng
Format: epub, pdf
Publisher: No Starch Press, Inc.
Published: 2024-10-15T00:00:00+00:00

Figure 5-1: Example MNIST digits (top) and scrambled versions of the same digits (bottom)

The scrambled digits are incomprehensible to me. The pixel information between the original and scrambled digits is the same—that is, the same collection of pixel values is present in both—but the structure is largely gone, and I can no longer discern the digits. I claim that a traditional neural network treats its inputs holistically and isn’t looking for structure. If that’s the case, a traditional neural network shouldn’t care that the digits have been scrambled; it should learn just as well when trained using the original or the scrambled dataset. As it turns out, that’s precisely what happens. The model learns equally well; scrambling changes nothing in terms of performance. Note, though, that the scrambled test digits must be used with the scrambled model; we shouldn’t expect the model to work when trained on one dataset and tested on the other.

We at present know only one fact about CNNs: they pay attention to structure in their inputs. Knowing this, should we expect a CNN trained on the scrambled dataset to perform as well as one trained on the original dataset? The scrambled digits are uninterpretable by us because local structure in the images has been destroyed. Therefore, we might expect a model that similarly wants to exploit local structure to be unable to interpret the scrambled digits. And that is the case: a CNN trained on the scrambled dataset performs poorly compared to one trained on the original dataset.

Why can’t we easily interpret the scrambled digits? We must explore what happens in the brain during vision to answer that question. Then we’ll circle back to relate that process to what CNNs do. As we’ll learn, CNNs follow the old adage: when in Rome, do as the Romans (humans) do.

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Vincent van Gogh is my favorite artist. Something about his style speaks to me, something strangely peaceful from a man tormented by mental illness. I believe the peace emanating from his work reflects his attempt to calm the turmoil within.

Consider Figure 5-2. It shows Van Gogh’s famous 1889 painting of his bedroom in Arles. The image is in black and white, an unforgivable violence to Vincent’s use of color, but print restrictions require it.

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