APPENDIX AVI212 Manual do Utilizador descarregar pdf (Página 200)

BeGaze 2.3

193

Unit

data with head tracking

degrees

Further Reading:

Dario D. Salvucci & Joseph H. Goldberg:

Identifying Fixations and Saccades in Eye-Tracking Protocols

In: Proceedings of the Eye Tracking Research and Applications

Symposium (pp. 71-78). New York, 2000

7.4 High Speed Event Detection

In the High Speed Event Detection method, Saccade is selected as

primary event. The Built-In Detector will first search for saccade

events, using a velocity based algorithm. Blinks and fixations are

computed and derived from the primary saccade events.

Saccade Detection

From the gaze stream all velocities are calculated. From all velocities the

peaks are detected. A peak is defined as the peak value of velocities

above the Peak Threshold [º/s]. The peak could indicate a saccade, but

as we are not sure, yet, we call it saccade-like event. To detect the start

of the saccade-like event, we search for the first velocity to the left which

is lower than the fixation velocity threshold. To detect the end of the

saccade-like event, we search for the first velocity to the right which is

lower than the fixation velocity threshold. The fixation velocity threshold is

an internal value calculated from the first peak less velocities of the

velocity stream. We assume the saccade-like event a real saccade, if

the distance between start and end exceeds the Minimum Saccade

Duration [ms] and

the single peak value lies in the range of 20% to 80% of the distance

between start and end

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APPENDIX AVI212 Manual do Utilizador Página 200