Before revision:  To understand how such superior performance is achieved, we can probe a trained deep neural network by studying neuron activations, that is , combinations of neuron firings, at any layer of the network in response to a particular input.
After revision:  To understand how such superior performance is achieved, we can probe a trained deep neural network by studying neuron activations, i. e. , combinations of neuron firings, at any layer of the network in response to a particular input.