Data Format and Data Structure

XML data (download sample data here) has the following data elements:

<root>:

<root> block contains all the information for the experimental data. It contains <trial> elements. Each data file only has one <root> block.

<trial>:

<trial> block contains all the information for a single trail. Each block has <fix> and <sacc> elements, id is a unique number for the trial and it starts from 0. Each trial has an <invalid> tag, which represents whether the current trial is valid or not.

example of a <trial> block:

<trial id="0">
......
<invalid>false</invalid> //is trial valid or not?
</trial>.

<fix>:

<fix> block contains all the information for a fixation, each fixation block may have the following tags:

<eye>: the eye with which the current fixation event is associated.

<st>: start time stamp in milliseconds.

<et>: end time stamp in milliseconds

<dur>: duration (in milliseconds) of the current fixation.

<x>/<y>: average X, Y coordinates of the current fixation.

<pupil>: average pupil size (diameter) in arbitrary units for the current fixation.

<blink>*: duration (in milliseconds) of a blink which occurred prior to the current fixation.

<raw>*: the shifted pixels of the start (sx/sy) and end (ex/ey) X, Y coordinates  to the average X, Y  coordinates of the current fixation.

<inf>/<inb>* : the raw data information of a forward/backward interval in this fixation.

<id>: a unique number starting from 0 (based on temporal order, where even numbers are used for the right eye and odd for the left eye).

* means optional tag

example of a <fix> block:

<fix>
    <eye>R</eye>
    <st>1004661</st>
    <et>1004792</et>
    <dur>132</dur>
    <x>289.2</x>
    <y>215.0</y>
    <pupil>1370</pupil>
    <blink>104</blink>
    <raw sx="-2.4" sy="5.2" ex="-1.5" ey="0.5"/>
    <inf name="forward_1" sx="-0.2" sy="3.3" ex="-0.2" ey="-1.6" dur="90" />
    <inb name="backward_1" sx="-0.6" sy="0.2" ex="-0.2" ey="-1.6" dur="80" />
    <id>118</id>
</fix>

<sacc>:

<sacc> block contains all the information for a saccade, each saccade block will have the following tags:

<eye>: the eye with which the current fixation event is associated.

<st>: start time stamp in milliseconds.

<et>: end time stamp in milliseconds

<dur>: duration (in milliseconds) of the fixation.

<x>/<y>: X, Y coordinates of the start position.

<tx>/<ty>: X, Y coordinates of the end position.

<ampl>: the total visual angle traversed by the saccade is reported by <ampl>, which can be divided by (<dur>/1000) to obtain the average velocity.

<pv>: the peak values of gaze velocity in visual degrees per second.

<id>: a unique number starting from 0 (based on temporal order, even numbers for right eye, odd for left eye).

example of a <saccade> block:

<sacc>
    <eye>R</eye>
    <st>940236</st>
    <et>940246</et>
    <dur>11</dur>
    <x>370.2</x>
    <y>308.1</y>
    <tx>347.2</tx>
    <ty>310.6</ty>
    <ampl>0.68</ampl>
    <pv>74</pv>
    <id>116</id>
</sacc>