User manual

Data Files

Pupil size measurements are affected by up to 10% by pupil position, due to the

optical distortion of the cornea of the eye, and camera-related factors. If

research using pupil size is to be performed, the subject should not move their

eyes during the trials. They can be presented with a fixation point with aural

stimulus presentation, or a single stimulus position at display center may be

used. It is also possible to counterbalance stimulus position during the

experiment.

4.4.4 Button Data

The state of up to 8 buttons or input port bits may be recorded in each sample.

Button ports, bits, and polarity may be set in the EyeLink 1000 tracker

configuration file BUTTONS.INI.

The button data consists of two 8-bit fields, recorded as a 16-bit number. The

lower 8 bits contain the current status of the 8 buttons (bit = 0 if off, 1 if

pressed). Each of the upper 8 bits will be set to 1 if its button has changed

since the last sample. The least-significant bit in each byte corresponds to

button 1, and the most-significant to button 8.

4.5 Events

One of the most significant aspects of the EyeLink 1000 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. Data for each event is compressed, and an extendable data format allows

compatibility with future expanded file formats.

Note that not all the event data listed here is available through the EDF2ASC

translator program.

4.5.1 Messages

The most flexible event type is the message event. A message is most often text,

but can contain any type of binary data as well, up to a maximum of 300 bytes.

Messages are created by application software, and forwarded over the link to the