Time-Frequency-Phase Analysis for Automatic Detection of Ocular Artifact in EEG Signal using S-Transform

Artifacts are unwanted components in the EEG signals which may affect the EEG signal reading, thereby not allowing the signal to be interpreted properly. One of the most common artifacts is the ocular artifact. This artifact arises due to the movement of the eye including eye blink. In most cases, detection of ocular artifacts in EEG signals is done by skilled professionals who are small in number. This paper proposes a new approach of automatic detection of ocular artifacts using the phase information present in the S-transform (ST) of EEG signal. S-transform of a signal provides absolutely referenced phase information of the signal in addition to time-frequency information. A time delay exists between the signals recorded by electrodes placed at different distances from the point of origin of the artifact. This time delay translates to phase delay in the frequency domain. The phase information of the EEG signal recorded from different electrodes placed in the frontal region is used to detect the artifacts which are generated near the region where the eye is located.