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Events
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One of the most significant aspects of the EyeLink II tracking system and the EDF file format is its on-line processing of eye-movement data to identify and record events such as fixations and saccades. This eliminates the need for recording of sample data for many types of research, and achieves a data compression of 20:1 or greater. Samples need only be recorded for data validation or if sample-by-sample eye position or velocity is required.
Events can record application data such as the time of a display change and experimental conditions, or real-time events such as button presses. Events also define the start and end of blocks of data in the EDF file, allowing applications to process data recorded with different data types.
Each event contains one or two timestamps (in milliseconds) and several data fields.