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This paper presents an articulatory-to-acoustic conversion method using electromagnetic midsagittal articulography (EMA) measurements as input features. Neural networks, including feed-forward deep neural networks (DNNs) and recurrent neural networks (RNNs) with long short-term term memory (LSTM) cells, are adopted to map EMA features towards not only spectral features (i.e. mel-cepstra) but also excitation features (i.e. power, U/V flag and F0). Then speech waveforms are reconstructed using the predicted spectral and excitation features. A cascaded prediction strategy is proposed to utilize the predicted spectral features as auxiliary input to boost the prediction of excitation features. Experimental results show that LSTM-RNN models can achieve better objective and subjective performance in articulatory-to-spectral conversion than DNNs and Gaussian mixture models (GMMs). The strategy of cascaded prediction can increase the accuracy of excitation feature prediction and the neural network-based methods also outperform the GMM-based approach when predicting power features.