From Table 1a, we find that both the combinations of Bi-LSTM with Bi-RNN and Bi-LSTM outperform the combination of Bi-LSTM and MLP without any features.
the combination of Bi-LSTM and Bi-LSTM achieves the best result 83.90% without any feature, and its F1-score is about 1.5% higher than the model of Bi-LSTM+MLP.