SR Research EyeLink Portable Duo User Manual page 93

Start events contain the time of the start of the eye-movement condition. They
may also contain the state of the eye at the onset of the condition: for example,
the position and pupil size at the start of a fixation.
End events contain both the start and end time of the condition. The end time
is actually the time of the last sample in the condition, so length of a condition
must be computed as the difference between the end and start times plus the
time between samples (1, 2 or 4 milliseconds). End events also contain
summary data on the condition as well: average gaze position of a fixation, for
example.
Please note that when reading real-time data through the link, the event data
will be delayed from the corresponding sample. This is caused by the velocity
detector and event validation processing in the Host software. The time stamps
in the event reflect the true (sample) times.
4.5.3.1 Record Blocks
Each block of recorded data in an EDF file begins with one or both of a
STARTSAMPLES or STARTEVENTS event. These contain the time of the
recording start, and specify what data can be expected to follow. This allows for
flexible adaptation to almost any file-data configuration. Information included
in the start events include:
Which eye recorded from
•
Sample data rate
•
Sample data contents
•
Event data contents
•
Event types included
•
Gaze-position and velocity prescalers
•
Each block of recorded data ends with one or both of an ENDSAMPLES or
ENDEVENTS event. This simply terminates the data block, and specifies the
time that recording ended.
The text files generated from EDF files by the EDF2ASC translator utility create
a simplified form of START and END events. A single START or END line is
produced for both sample and event blocks, which specifies which eye was
recorded from, and whether samples, events, or both, are present in the
following data block. Other data is given on following SAMPLES, EVENTS,
PRESCALER, etc. lines.
4.5.3.2 Fixations
The on-line EyeLink tracker parser processes eye-position data, identifying
saccades and fixations and compiling data on these conditions. For fixations,
these data include:
The time of the first and last sample in the fixation
•
The eye that generated the event
•
Data Files
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