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with EyeLink Data Viewer or convert the EDF file to an ASC file to see the

correspondence between eye movements and the parser output.

4.3.3 EyeLink Parser Configuration

The saccadic detection parameters for the EyeLink 1000 on-line parser may

need to be optimized for the type of experimental investigation being performed.

For example, neuropsychophysical researchers may need to detect small

saccades amid pursuit or nystagmus, while reading researchers will need to

detect only large saccades and will want fixation durations maximized. This

section explains the function of, and suggests values for, the most useful parser

parameters.

Some experimentation may be required to select the best parameters. The user

can try different parser settings and perform recordings with full sample data

recorded. The eye-movement data can then be viewed with EyeLink Data Viewer

with saccades and blinks overlaid, to confirm the parsing accuracy. Once

correct parameters are determined, they can be set by the EyeLink 1000

commands over the link as part of the experimental setup, or the EyeLink 1000

configuration file PARSER.INI (REMPARSE.INI for the EyeLink Remote) or

FINAL.INI can be edited to change the default parameters.

4.3.4 Parser Data Type

Three eye-position data types are available from the EyeLink 1000 tracker for

each sample: raw pupil position, head-referenced angle, and gaze position (see

the section 4.4 “File Data Types” for more information). The parser can use any

one of these for detecting saccades and generating data for events.

The parser data type is set by the EyeLink command “recording_parse_type”. It

can be changed by editing the configuration file DEFAULTS.INI, or by sending a

command over the link. The text of the command is one of:

recording_parse_type = GAZE

recording_parse_type = HREF

recording_parse_type = PUPIL

4.3.5 Saccadic Thresholds

Three thresholds are used for saccade detection: motion, velocity, and

acceleration. The values of these are in degrees, degrees/sec, and degrees/sec²

respectively.

The velocity threshold is the eye-movement velocity that must be exceeded for a

saccade to be detected. A velocity threshold of 22 degrees per second allows