Question 25
Compared with the sigmoid activation, which of the following are correct reasons for preferring the ReLU activation in deep CNNs?
For positive inputs, ReLU does not saturate, so it avoids the gradient-killing that occurs in the flat tails of the sigmoid.
ReLU is preferred because it bounds every activation to the interval [0, 1], preventing activations from growing large.
ReLU is cheaper to evaluate — a simple thresholding at zero — whereas sigmoid/tanh require expensive exponentials.
The sigmoid's derivative peaks at only 0.25, so multiplying many such small factors across layers pushes gradients toward zero (vanishing gradient).