User manual

98 Data Files

4.5.3.5 Blinks

In general, the saccadic amplitude will be slightly less than the distance

between average position of the preceding and following fixations, as saccades

do not include sub-threshold velocity parts of the eye movement that precede

and follow the rapid phase.

The STARTBLINK and ENDBLINK events bracket parts of the eye-position data

where the pupil size is very small, or the pupil in the camera image is missing

or severely distorted by eyelid occlusion. Only the time of the start and end of

the blink are recorded.

Blinks are always preceded and followed by partial occlusion of the pupil,

causing artificial changes in pupil position. These are sensed by the EyeLink

1000 parser, and marked as saccades. The sequence of events produced is

always:

• STARTSACC

• STARTBLINK

• ENDBLINK

• ENDSACC

Note that the position and velocity data recorded in the ENDSACC event is not

valid. All data between the STARTSACC and ENDSACC events should be

discarded. The duration of the blink may be computed by either the duration of

the missing pupil between the STARTBLINK and ENDBLINK events, or the

difference between the ENDSACC and STARTSACC events in the sequence.

Fixation immediately preceding and following blinks should be examined

carefully, as they may have been truncated or produced by the blink process.

Discarding fixations shorter than 100 ms proceeding or following blinks will

eliminate most artifacts.

4.6 Setting File Contents

The data recorded in samples and events may be set in the EyeLink 1000

configuration file DATA.INI, or by sending commands to the tracker across the

link, via the API eyecmd_printf(). Similar commands exist for samples and

events sent over the link for real-time applications.