Before revision:  Users pointed to the letters that they wanted to type just by moving their head. The head movements of the users are recorded by the camera. The recorded gestures are then translated into a cluster sequence. The translation module is implemented using CNN-RNN, Conv3D, and a modified GRU based model that uses pre-trained embedding rich in head pose features .
After revision:  Users pointed to the letters that they wanted to type . A front-facing smartphone camera recorded the head movements. A bidirectional GRU based model that uses pre-trained embedding rich in head pose features .