How to Visualize Hidden Layer Weights in a MATLAB Neural Network?

In Deep Learning Toolbox, you can extract weight matrices using net.IW (Input Weights) and net.LW (Layer Weights) or net.Layers for SeriesNetwork/DAGNetwork objects:

% For standard Feedforward Neural Network (net):
W1 = net.IW{1,1}; % Weights from input to 1st hidden layer
figure;
imagesc(W1);
colorbar;
title('Hidden Layer 1 Weight Matrix');
xlabel('Inputs'); ylabel('Neurons');

% For Deep Convolutional Networks (net):
convLayer = net.Layers(2);
W_conv = convLayer.Weights; % Size: [H W C Filters]
montage(rescale(W_conv));
title('Visualized Conv Filter Weights');