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Multiple generative models (beta-VAE, InfoGAN, Glow, etc.) claim the capabilities to disentangle and control high-level factors in their generated samples. For instance, for a VAE decoder network F(z) mapping z to a sample of image/audio/whatever, in which z is a, say, n-dimensional latent code, then the models often demonstrate that manipulating some dimension of z would control the high-level features of generated sample, like emotion of face, speed of speech, etc. (See the picture in the paper as a sample)

Now the question comes that: why the disentangled factors fall to match those human-interpretable features?

Indeed, VAE-like models encouraged disentanglement by enforcing Gaussians with diagonal covariance in latents, however it seems that those disentanged dimensions are not necessarily ensured to impact human-interpretable characteristic separately in the generated samples. It is somehow more "natural" if the dimensions could only control some characteristics in generated samples that are difficult to be concisely interpreted (e.g. whether the photo is taken under sunlight), or could control a set of multiple characteristcs (for each dimension separately).

More, though some disentangled and interpretable factors (as demonstrated in the papers, like lighting of images and F0 of audios) are quite "basic", many other factors appear to be more high-level and require human interpretation, unlike other automatically emerged structures in NNs (e.g. edge detectors in trained CNNs). For example, human emotion (whether smile or not), azimuth, require human knowledge to extract from an image. It is even more weird when the models learn such factor unsupervised.

Some of the issues could be interpreted as cognitive bias: we could always pick up a handful of meaningful&interpretable dimensions in the latents, leaving hundreds of meaningless dimensions away. But based on my coleagues and my own experience of training and using such models, I don't think that this bias could cover the entire case.

So why the models learn to view the world (i.e. their training data) in the ways same with ours?

beta-VAE sample

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Well, I don't think the dimensions are as disentangled as they first appear. I think I once remember a paper (unfortunately I couldn't find it just now) in which the authors applied a random linear transformation on the latent space of some generative model, only to find that the resulting disentangled factors were subjectively just as disentangled as before.

It is somehow more "natural" if the dimensions could only control some characteristics in generated samples that are difficult to be concisely interpreted (e.g. whether the photo is taken under sunlight), or could control a set of multiple characteristcs (for each dimension separately).

Just taking a quick examination of the above images: The first figure shows variation in azimuth, but that dimension also seems to control hair color and lighting. In the second figure, in addition to smiling, there seems to be variation in the amount of hair, and in the size of the eyes as well. In the third figure, figures on the right seem significantly more feminine than on the left. I think it's fair to say that each dimension does NOT cleanly map onto a human concept.

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  • $\begingroup$ Wow that paper seems to be convincing. So such sucessful "disentanglement" are simply cognitive bias? Could you recollect anything about the paper (title, conference, authors, anything)? Thanks! $\endgroup$
    – dy.octa
    Commented Jun 24, 2019 at 9:23

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