User manual

Data Files

103

• START events mark the beginning of each recording block, and END events

mark the end of each block. The START events also specifies which eye’s data

is present, and if samples, events, or both are present.

• Data-specification lines follow each START event. These specify the type of

data in samples and events in the block, and allow flexible data processing

without prescanning the file.

• All eye-movement samples and events occur between the START event and

the matching END event.

• All events and samples appear in temporal order. That is, the timestamps of

samples, end-time timestamps of eye-movement end events, and start-time

timestamps of all other events will be the same or greater than any preceding

data.

• Eye-data samples are nested between eye-movement start and end event. For

example, the first sample in a fixation will follow the SFIX event for that

fixation, and the EFIX event for a fixation will follow the last sample in the

fixation. This allows on-the-fly classification of samples as the data file is

read.

Before writing an analysis program to process an ASC file, it is helpful to

convert a small EDF file containing the data of interest, and examine it with a

word processor or print it out.

4.9.2 Sample Line Format

Sample lines contain time, position, and pupil size data. Optionally, velocity and

resolution data may be included. Several possible sample line formats are

possible. These are listed below.

Essentially, each sample line begins with a timestamp. Recordings done with a

2000 hz sampling rate will have two consecutive rows of the same time stamps.

The second row refers to the sample collected at 0.5 ms after the reported time

stamp. The time stamp field is followed by X and Y position pairs and pupil size

data for the tracked eye, and optionally by X and Y velocity pairs for the eye,

and resolution X and Y values. Missing data values are represented by a dot

("."), or the text specified by the "-miss" option to EDF2ASC.

SAMPLE LINE FORMATS

•

Monocular:

• Monocular, with velocity