Synchronization of a biofeedback system with an eye tracker through an audiovisual stimulus marker

In the last few years, many psychophysiology scientists have begun to use eye-tracking methodologies in conjunction with standard biofeedback systems. This approach has proven to be useful for analyzing visual stimuli and the physiological reactions they produce. To be fully effective, however, it is essential to have a marker on the biofeedback signals so that the exact time of a presented stimulus can be determined. While a specific scientist may not work on ‘‘evocated potential’’ or, in general, with short-time stimuli, it is essential to establish the time between the presented stimulus and when the physiological response occurs. In addition, synchronization between the eye tracker and biofeedback allows the addition of a series of signals from the eyes, such as dilation of the pupils and the distance between the pupils, to standard neurophysiology signals, allowing the assessment of the degree of relaxation or stress felt by the subjects. In this work, we show a technical solution for synchronizing eye tracker Tobii 1750 with a biofeedback ‘‘Procomp infiniti’’ using a TT-AV Sync. Also, we added some algorithms to this hardware tool in order to be able to conduct the desired data analysis. We used a Tobii 1750 monitor and a Biograph ‘‘Procomp infiniti’’. We conducted 500 synchronizations with the device in order to establish its precision, which we determined to be ±0.1 s. We also found that we could reduce the errors by using synchronization based on a visual marker (from black to white) simultaneously with synchronization based on an audio marker (from silence to beep). The hardware mentioned above for synchronizing biofeedback and the eye tracker is the TT-AV Sync, which was configured through a physical channel on biofeedback.