Import Gaze Data for EyeLink Eye Tracker • eyelinkReader

R package to import eye tracking recording generated by SR Research EyeLink eye tracker from EDF-files. It includes options to import events and/or recorded samples and extract individual events such as saccades, fixations, blinks, and recorded variables.

Installation

These instructions are also available as a vignette.

The library installation involves three easy (famous last words) steps.

Install SR Research EyeLink Developers Kit

This package relies on edfapi library that is as part of the EyeLink Developers Kit. Therefore, read_edf() function will not work without it but you will still be able to use utility functions. The EyeLink Developers Kit can be downloaded from www.sr-research.com/support website. Note that you need to register and wait for your account to be activated. Next, follow instructions to install EyeLink Developers Kit for your platform. The forum thread should be under SR Support Forum › Downloads › EyeLink Developers Kit / API › Download: EyeLink Developers Kit / API Downloads (Windows, macOS, Linux).

Configure R environment variables

The package needs to configure compiler flags for its dependency on EDF API library. Specifically, it needs to specify paths to include header files (edf.h, edf_data.h, and edftypes.h) and to the library itself. The package will try to compile using sensible defaults for each platform, i.e., default installation paths for EyeLink Developers Kit v2.1.1. However, these defaults may change in the future or you may wish to install the library to a non-standard location (relevant primarily for Windows).

If compilation with default paths fails, you need to define R environment variables as described below. These variables must be defined either in user or project .Renviron file. The simplest way to edit it is via usethis library and edit_r_environ() function. Type usethis::edit_r_environ() for user and usethis::edit_r_environ('project') for projects environments (note that the latter shadows the former, read documentation for details). Note that in the case of Windows, you do not need to worry about forward vs. backward slashes as R will normalize strings for you. Once you define the variables, restart session and check them by typing Sys.getenv() (to see all variables) or Sys.getenv("EDFAPI_INC") to check a specific one.

Windows

For the package to work on Windows, you must install Rtools. Please note that as of 31.05.2024, you need Rtool43 even if your R version is 4.4.x, the compilation fails with Rtools44.

Default values assume that the EyeLink Developers Kit is installed in c:/Program Files (x86)/SR Research/EyeLink (default installation path).

EDFAPI_LIB : path to edfapi.dll for 32-bit systems. Defaults to c:/Program Files (x86)/SR Research/EyeLink/libs.
EDFAPI_LIB64 (optional): path to edfapi64.dll for 64-bit systems. By default, the 64-bit library is in x64 subfolder, i.e., c:/Program Files (x86)/SR Research/EyeLink/libs/x64. This variable is optional, as the package will try to guess this by itself by appending /x64 to EDFAPI_LIB path. However, you should specify this variable explicitly if 64-libraries are in a non-standard folder (or SR Research changed it, or you just want to be sure).
EDFAPI_INC : path to C header files necessary for compilation. Specifically, the package requires edf.h, edf_data.h, and edftypes.h. Defaults to c:/Program Files (x86)/SR Research/EyeLink/Includes/eyelink.

Your .Renviron file should include lines similar to the ones below

EDFAPI_LIB="c:/Program Files (x86)/SR Research/EyeLink/libs"
EDFAPI_LIB64="c:/Program Files (x86)/SR Research/EyeLink/libs/x64"
EDFAPI_INC="c:/Program Files (x86)/SR Research/EyeLink/Includes/eyelink"

Linux

EDFAPI_INC : path to C header files necessary for compilation. Specifically, the package requires edf.h, edf_data.h, and edftypes.h. Defaults to /usr/include/EyeLink.

Your .Renviron file should include a line like this

EDFAPI_INC="/usr/include/EyeLink"

Mac OS

EDFAPI_LIB: path to EDF API framework. Defaults to /Library/Frameworks
EDFAPI_INC : path to C header files necessary for compilation. Specifically, the package requires edf.h, edf_data.h, and edftypes.h. Defaults to /Library/Frameworks/edfapi.framework/Headers

Your .Renviron file should include lines similar to the ones below

EDFAPI_LIB="/Library/Frameworks"
EDFAPI_INC="/Library/Frameworks/edfapi.framework/Headers"

Install the library

To install from CRAN

install.packages("eyelinkReader")

To install from github

library("devtools")
install_github("alexander-pastukhov/eyelinkReader", dependencies=TRUE)

Usage

The main function is read_edf() that imports an EDF file (or throws an error, if EDF API is not installed). By default it will import all events and attempt to extract standard events: saccades, blinks, fixations, logged variables, etc.

library(eyelinkReader)
gaze <- read_edf('eyelink-recording.edf')

Events and individual event types are stored as tables inside the eyelinkRecording object with trial column identifying individual trials. Trial 0 correspond to events (e.g, DISPLAY_COORDS message, etc.) sent to the eye tracker before the first trial.

View(gaze$saccades)

There is a basic utility for plotting saccades and fixations for an individual trial

plot(gaze, trial = 1, show_fixations = TRUE, show_saccades = TRUE)

or across trials

plot(gaze, trial = NULL, show_fixations = TRUE, show_saccades = FALSE)

The package also includes functions to parse non-standard events: recorded areas of interest (extract_AOIs) and trigger events that help to time events (extract_triggers). These need to be called separately.

gaze <- extract_AOIs(gaze)
gaze <- extract_triggers(gaze)

To import samples, add import_samples = TRUE and, optionally, specify which sample attributes need to be imported, e.g., sample_attributes = c('time', 'gx', 'gy'). All attributes are imported if sample_attributes is not specified. See package and EDF API documentation for the full list of attribute names.

# import samples with all attributes
gaze <- read_edf('eyelink-recording.edf', import_samples = TRUE)

# import samples with selected attributes
gaze <- read_edf('eyelink-recording.edf',
                 import_samples = TRUE,
                 sample_attributes = c('time', 'gx', 'gy'))

See also a vignette on package usage. Please refer to documentation on eyelinkRecording class for details on events and samples.

Further information on EDF file content

I have attempted to document the package as thoroughly as I could. However, for any question about specific attributes please refer to the EDF API manual and EyeLink documentation, which is supplied by SR Research alongside the library.