 Later it was combined with connectionist temporal classification (CTC) in stacks of LSTM RNNs.In 2015, Google's speech recognition reportedly experienced a dramatic performance jump of 49% through CTC-trained LSTM, which they made available through Google Voice Search.In 2006, publications by Geoff Hinton, Ruslan Salakhutdinov, Osindero and Teh
 showed how a many-layered feedforward neural network could be effectively pre-trained one layer at a time, treating each layer in turn as an unsupervised restricted Boltzmann machine, then fine-tuning it using supervised backpropagation.