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Comment by nl | Hacker News Reader

People are missing the point here.

Yes, 15% accuracy doesn't seem great.

BUT the detector built its own categories(!). It managed to find 20,000 different categories of objects in Youtube videos, and one of these categories corresponded to human faces, and another to cats.

Once the experimenters found the "face detection neuron" and used it to test faces THAT neuron managed 81.7% detection rate(!).

Forget the singularity, and just think about how amazing that is. The system trained itself - without human labelling - to distinguish human faces correctly over 80% of the time.

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You're in danger of missing the point too far in the other direction. The system just returns yes/no as to whether an image has a face in it, and if it was hard-coded to respond "no" it would score 64.8%.

Obviously this is extremely impressive work, and given that Google gives away 1e9 core hours a year, I'd like to see how much further they can push this network (which only used 16e3x3x24 ~ 1e6 hours). But this isn't like scoring 80% in a written exam.

I'm also impressed by how readable the paper was. Apart from a few paragraphs of detailed maths this should be accessible to anyone who's read the wikipedia article on neural networks.

http://googleblog.blogspot.com/2011/04/1-billion-computing-c...

* The system just returns yes/no as to whether an image has a face in it, and if it was hard-coded to respond "no" it would score 64.8%.*

Yes, that is true. But ~80% correct is still a significant result.

I was hoping people would read beyond the 15% headline figure to understand exactly what than number meant.

> BUT the detector built its own categories(!).

It's not revolutionary. Clustering algorithms and neural nets are plenty.

Really, what differentiates this network is its scale.

And, thanks to scale, that some of the clusters corresponds to high level concepts. According to the article, earlier attempts have mostly resulted in low level concepts like "edge" or "blob" to be detected.

Also, it was (again, from the article) plausible but not a given that high level concepts could be found from unlabeled data.

That "cat" is one of the high level concept you get from using random Youtube videos as raw data is both impressive, and slightly amusing.

Exactly. Regarding your remark about edge detectors: such self-organizing neural nets are organized into hierarchical layers, and early layers' units are going to learn to become detectors of statistically common components of the input image, in the same way as the initial layers of the visual system perform blob and edge detection (retina, lateral geniculate nucleus, V1). In mathematical terms, these early units learn the conditional principal components of the inputs. The layers that are built upon these detectors, if correctly organized, are going to build upon this initial abstraction and learn more complex features: for instance to find these these edges in relative positions (to each other). Eventually, up the abstraction chain, units detect such statistically frequent features as the shape of cat's ears (common in youtube videos, I imagine), etc...

(Sorry I wrote that fast, I hope it's understandable)

The performance is due more to the architecture than to the scale. The scale is to handle all that data. But the feature learning performance has to do with their layered sparse learning technique which is brilliant. Although, their autoencoder neural network is actually learning a decomposition on the data so the neural part is kind of a red herring.

That you get high level features instead of edges is not the impressive part - you can just as well write a sparse non negative matrix factorization algorithm that will efficiently learn/represent eyes, lips and noses as features of faces unsupervised.

Clustering algorithms operate on features, which typically have to be designed by hand. The appeal of deep learning is that it discovers good features automatically.

Feature sensitivity is typically hand-crafted only because it's the practical thing to do. Neural nets can easily learn visual features. See the LISSOM neural nets for a good example of self-organized learning of features.

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