User manual

96 Data Files

4.5.3.3

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The time of the first and last sample in the fixation

• The eye that generated the event

• Average HREF or gaze position data

• Average pupil size

• Gaze-data angular resolution

All of this data may appear in the ENDFIX event that terminates the fixation.

Only the starting data can appear in the STARTFIX event that initiates the

fixation.

In a sorted EDF file or a text ASC file (produced by EDF2ASC) that contains

both samples and events, the STARTFIX event will precede the first sample in

the file that is part of the fixation, and the ENDFIX event will follow the last

sample in the fixation. This allows the sample data in the files to be processed

by saccade or fixation in a single pass.

The data contained in STARTFIX and ENDFIX events may be configured by

modifying the DATA.INI file for the EyeLink 1000 tracker. For most research,

only simple fixation statistics are required, such as average position and pupil

size. STARTFIX events may also be configured to contain only the start time of

the fixation.

Other data in the ENDFIX event may be useful for some types of analysis. The

resolution may be used to estimate angular distance between fixations.

Subtract the x and y position data for the fixations, divide by the average

corresponding resolution data, and compute the Euclidean distance:

dx = (x1 - x2) / ( (rx1 + rx2)/2.0);

dy = (y1 - y2) / ( (ry1 + ry2)/2.0);

dist = sqrt(dx*dx + dy*dy);

Fixation Updates

Data within a fixation can be broken into smaller time segments, useful for real-

time analysis and control via eye movements. FIXUPDATE events may be

produced at regular intervals within a fixation, and contain data for a specified

length of time within the fixation. The data recorded in the FIXUPDATE event is

similar to that in the ENDFIX event.

FIXUPDATE events are most useful in real-time applications using the link.

Recording samples in the EDF file is more useful for most psychophysical

research.