inst/docs/99_gazedata_codebook.md

In tjmahr/lookr: Tools to Analyze Looking While Listening or Visual World Eyetracking Experiments

Codebook for Gazedata

These are columns contained in one .gazedata file.

## 'data.frame':    12573 obs. of  26 variables:
##  $ Subject              : int  1 1 1 1 1 1 1 1 1 1 ...
##  $ Session              : int  1 1 1 1 1 1 1 1 1 1 ...
##  $ ID                   : int  1 2 3 4 5 6 7 8 9 10 ...
##  $ TETTime              : num  1.36e+12 1.36e+12 1.36e+12 1.36e+12 1.36e+12 ...
##  $ RTTime               : int  37312 37329 37345 37362 37378 37395 37412 37428 37445 37461 ...
##  $ CursorX              : int  692 695 695 690 688 686 687 690 692 685 ...
##  $ CursorY              : int  532 527 522 517 518 519 521 526 532 519 ...
##  $ TimestampSec         : int  1360680900 1360680900 1360680900 1360680900 1360680900 1360680900 1360680900 1360680900 1360680900 1360680900 ...
##  $ TimestampMicrosec    : int  777681 794301 811051 827673 844297 860924 877667 894289 910915 927535 ...
##  $ XGazePosLeftEye      : num  0.355 0.352 0.359 0.353 0.35 ...
##  $ YGazePosLeftEye      : num  0.439 0.441 0.436 0.435 0.442 ...
##  $ XCameraPosLeftEye    : num  0.613 0.613 0.614 0.614 0.614 ...
##  $ YCameraPosLeftEye    : num  0.837 0.838 0.838 0.838 0.838 ...
##  $ DiameterPupilLeftEye : num  3.59 3.53 3.58 3.51 3.49 ...
##  $ DistanceLeftEye      : num  547 547 547 547 547 ...
##  $ ValidityLeftEye      : int  0 0 0 0 0 0 0 0 0 0 ...
##  $ XGazePosRightEye     : num  0.367 0.372 0.366 0.366 0.367 ...
##  $ YGazePosRightEye     : num  0.449 0.438 0.434 0.427 0.421 ...
##  $ XCameraPosRightEye   : num  0.468 0.468 0.468 0.468 0.469 ...
##  $ YCameraPosRightEye   : num  0.807 0.807 0.808 0.808 0.808 ...
##  $ DiameterPupilRightEye: num  3.46 3.38 3.36 3.39 3.33 ...
##  $ DistanceRightEye     : num  545 545 545 545 545 ...
##  $ ValidityRightEye     : int  0 0 0 0 0 0 0 0 0 0 ...
##  $ TrialId              : int  1 1 1 1 1 1 1 1 1 1 ...
##  $ Target               : chr  "ImageL" "ImageL" "ImageL" "ImageL" ...
##  $ Stimulus             : chr  "CarrierStim" "CarrierStim" "CarrierStim" "CarrierStim" ...

The main eye-tracking variables are straightforward. (Descriptions adapted from the Tobii T60XL manual.)

• XGazePosLeftEye: Horizontal screen position of gaze for left eye.
• YGazePosLeftEye: Vertical screen position of gaze for left eye.
• XCameraPosLeftEye: Horizontal location of left pupil in camera image. 0 = left edge, 1 = right edge.
• YCameraPosLeftEye: Vertical location of left pupil in camera image. 0 = top edge, 1 = bottom edge.
• DiameterPupilLeftEye: Size (mm) of the left pupil.
• DistanceLeftEye: Distance (mm) from eyetracker to left eye.

Validity Codes

The validity codes are described in detail in the Timing Guide for Tobii Eye Trackers white paper:

The TET Server provides validity codes for each eye with every gaze data point. The validity code is a measure of the system’s certainty that it has recorded the correct data. The validity code ranges from 0 to 4, with the following interpretations for each value: 0 The system is certain that it has recorded all relevant data for the particular eye, and that the data recorded belongs to the particular eye (no risk of confusing left eye with right eye by the system). 1 The system has only recorded one eye, and has made some assumptions and estimations regarding if the recorded eye is left or right. However, it is still highly probable that the estimations done are correct. The validity code on the other eye is in this case always set to 3. 2 The system has only recorded one eye, and has no way of determining if this is the left or the right eye. 3 The system is confident that the actual gaze data is actually incorrect or corrupted. The other eye will always have validity code 1. * 4 The actual gaze data is missing or definitely incorrect. A couple of gaze data with validity code 4 on both eyes, followed by a number of gaze data with validity code 0 on both eyes, are usually a sure sign of a blink.

During search mode each sample that does not contain information on eye position is marked as a non valid data point. It is recommended that the validity codes are always used for data filtering, to remove data points which are obviously incorrect. For most studies, we recommend removing all data points with a validity code of 2 or higher.

Here are the possible combinations of validity codes. Table adapted from the Tobii Toolbox for Matlab guide.

Left eye code | Right eye code | Eyes detected | Eye identification :-----------: | :------------: | :-----------: | :--------------------: 0 | 0 | Both | Correctly identified 4 | 0 | Right | Correctly identified 0 | 4 | Left | Correctly identified 3 | 1 | Right | Estimated as probable 1 | 3 | Left | Estimated as probable 2 | 2 | One eye | Uncertain 4 | 4 | None | Uncertain

tjmahr/lookr documentation built on May 31, 2019, 3:41 p.m.