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I'm implementing a C3D-inspired neural network for human emotion recognition, the problem I'm facing is that altough the cost function is decreasing, for both training and validation sets, I do not appreciate any improvement in terms of accuracy, for neither of boths sets.

My cost function is the cross-entropy between the logits (output of the last layer) and the correct prediction

def tower_loss(name_scope, logit, labels):
    xent = tf.nn.sparse_softmax_cross_entropy_with_logits(logits=logit,labels=labels)
    cross_entropy_mean = tf.reduce_mean(xent)
    return cross_entropy_mean

Then, the optimizer uses the ADAM algorithm for minimizing the cost function as follows

loss = tower_loss(scope, logit, labels_placeholder)
train = tf.train.AdamOptimizer(1e-4).minimize(loss)

Although I'm seing the cost function decreasing, I haven't seen any improvement in the classification.

Additional info:

  • The xentropy of the validation set and the training set is not diverging.
  • The xentropy looks like is on the way of converging to 0.
  • The accuracy is not wrongly implemented (I see in the screen the outputs and the value is correct)
  • The network has been training now for 57.6K iterations (not much, but enough to see some increment in the performance, or not?)

Any extra question you need to aske, please feel free, or missing information, please ask it. Thanks a lot for all your time, and helping me with this problem.

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  • $\begingroup$ It can happen that there is a plateau in accuracy, for example at the prediction of the most common output, and it takes a while until the networks actually learns something useful and leaves the plateau. As long as the error is decreasing I would just wait. $\endgroup$ – BlindKungFuMaster Apr 4 '17 at 14:37
  • $\begingroup$ It is actually what I'm doing, just waiting, the error is still decreasing, and now the accuracy starts to show some movement. It is my first time with DL and I was not sure how much do I have to wait until the networks starts to figure things out. My main concern was if there was a conceptualization error from my side $\endgroup$ – Pablo Arnau González Apr 4 '17 at 15:24

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