User manual

82 Data Files

4. Data Files

The EDF file format is used by the EyeLink tracker and supporting applications

to record eye-movements and other data. It is designed to be space-efficient and

flexible, allowing for complete records of experimental sessions and data. It

adapts to monocular and binocular recording, with backwards-compatibility for

future enhancements. The EyeLink 1000 EDF file format is backwards

compatible with the original EyeLink and EyeLink II EDF file format.

The EDF file format is a platform-portable binary record of eye-position and

synchronization events. This format is used directly for EyeLink Data Viewer

application, and may be translated by the EDF2ASC utility into a text-format

ASC file. This file lists most of the important data in the EDF file in a more

easily accessible format, but at the expense of much larger file size.

Note: By changing the File Sample Filter from Extra to Standard or Off, this will

affect EyeLink Data Viewer, EDF2ASC, and other analysis tool data

calculations. SR Research Ltd. recommends leaving the “File Sample Filter”

setting on the Set Options screen to “Extra”.

4.1 File Contents

The EDF files contain two streams of data: eye-position samples (up to 2000 per

second produced from the EyeLink tracker, depending on the system model)

and events (eye-movement events such as saccades and fixations, subject

responses, and synchronizing events from the experimental application). Both

streams are time-synchronized for easy analysis. The file is organized into

blocks of data, one for each recording session. Each block may have samples,

events, or both. Also, the data items recorded in each sample or event may be

configured at recording, and are available at the block start to aid in analysis.

Samples are time-stamped in milliseconds and contain monocular or binocular

eye-position data in eye-rotation angle (HREF) or display-gaze coordinated

(GAZE). Pupil sizes as area or diameter are also recordable. Samples may also

contain eye-movement resolution (used to compute true velocity or saccadic

amplitudes), button presses, or the status of digital inputs.

Eye-movement events record eye position changes identified by the EyeLink

tracker's on-line parser, such as fixations, blinks, and saccades. Both the onset

and end of these events are marked, allowing samples to be assigned to eye-

movement periods without complex algorithms. Important data for analysis

such as average position for fixations and peak velocity for saccades is also

recorded in the events. Other events record subject responses (such as button

presses) and synchronization and data messages from applications. These can