Monday, May 11, 2015

Yes, Neural Networks Have Grandmother Cells


The neural network portions of the above image come from Wikipedia.

The age-old debate about neural networks (both artificial and biological) is whether they have a grandmother cell, a neuron cell/node somewhere in the net that is activated when one's grandmother is viewed (assuming a biological vision scenario or computer vision application).

For biological neural networks, the jury is out, and the answer is leaning toward the "no" side. For artificial neural networks, if you Google for the answer, you'll almost always come across the admonishment to avoid grandmother cells in your neural networks. But to beginners to neural networks, this advice can be easily misunderstood.

More precisely, grandmother cells are to be avoided in the internal nodes. The reason is that internal nodes are supposed to be for latent variables, i.e., intermediate properties like "big eyes" or "big teeth". If an internal node is already recognizing grandma, then that is an indication of overfitting and that perhaps the neural network was created too large for the amount of training data or search space.

But all artificial neural networks whose job it is to classify images where one of the classes is grandma will have a grandmother cell, namely in the output layer. That's simply how you get your output from a classifier artificial neural network.

1 comment:

Henning said...

About time somebody stood up for grandma.