How can i Visualize feature of Convolutional neural network? in matlab2016

i have been using deepDreamImage to visualize Features of CNN but it is showing error like: Error using deepDreamImage Expected input number 3, channel, to be an array with all of the values <= 20. through this code layer=2; name = convnet.Layers(layer).Name channels = 1:56;

    I = deepDreamImage(convnet,layer,channels, ...
    'PyramidLevels',1);

    figure
    montage(I)
    title(['Layer ',name,' Features'])

in first Conv Layer there are20 filters of size 5*5. please if anyone can help me it would be a great pleasure for me... thanks in advance