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PyGaze (eye tracking)
Overview
About
Supported eye trackers
Installing PyGaze
PyGaze OpenSesame plug-ins
Example
Function overview
About
PyGaze is a Python library for eye tracking. A set of plug-ins allow you to use PyGaze from
within OpenSesame. As of OpenSesame 2.9.0, these plug-ins are included by default in the
OpenSesame Windows packages.
For more information on PyGaze, visit:
http://www.pygaze.org/
Please cite PyGaze as:
Dalmaijer, E., Mathôt, S., & Van der Stigchel, S. (2013). PyGaze: An open-source, cross-platform toolbox
for minimal-eﬀort programming of eyetracking experiments. Behavior Research Methods .
doi:10.3758/s13428-013-0422-2
Supported eye trackers
Currently, PyGaze supports the following eye trackers:
EyeLink – For information on how to run OpenSesame with PyLink support, see
/devices/eyelink.
EyeTribe – Works out of the box.
SMI – SMI support is experimental.
Tobii – Tobii support is experimental.
PyGaze also includes two dummy eye trackers for testing purposes:
Simple dummy – Does nothing.
Advanced dummy – Mouse simulation of eye movements.
Installing PyGaze
If you use the oﬃcial Windows package of OpenSesame, PyGaze is already installed. If not,
you can install PyGaze as follows:
1. Download the PyGaze source code (.zip) from
https://github.com/esdalmaijer/PyGaze. (Do not download the standalone Windows
packages provided on the PyGaze website.)
2. Extract the .zip archive somewhere.
3. Inside, you will ﬁnd these folders:
opensesame_plugins: As the name suggests, this folder contains the OpenSesame
plug-ins, and need to be copied to (one of) the plugin folders, as described here:
/plug-ins/installation/
pygaze: This is the PyGaze Python library. You need to copy this to a folder in the
Python path. On Windows, you can copy this folder to the OpenSesame program
folder.
4. Done!
PyGaze OpenSesame plug-ins
The following PyGaze plug-ins are available:
pygaze_init – Initializes PyGaze. This plug-in is generally inserted at the start of the
experiment.
pygaze_drift_correct – Implements a drift correction procedure.
pygaze_start_recording – Puts PyGaze in recording mode.
pygaze_stop_recording – Puts PyGaze out of recording mode.
pygaze_wait – Pauses until an event occurs, such a saccade start.
pygaze_log – Logs experimental variables and arbitrary text.
Example
For an example of how to use the PyGaze plug-ins, see the PyGaze template that is
included with OpenSesame.
Below is an example of how to use PyGaze in a Python inline_script. For a list of available
functions, see Function overview .
from openexp.canvas import canvas
from openexp.keyboard import keyboard
# Create a keyboard and a canvas object
my_keyboard = keyboard(exp, timeout=0)
my_canvas = canvas(exp)
# Loop ...
while True:
# ... until space is pressed
key, timestamp = my_keyboard.get_key()
if key == 'space':
break
# Get gaze position from pygaze ...
x, y = exp.pygaze_eyetracker.sample()
# ... and draw a gaze-contingent fixation dot!
my_canvas.clear()
my_canvas.fixdot(x, y)
my_canvas.show()
Function overview
To initialize PyGaze in OpenSesame, insert the pygaze_init plug-in into your experiment.
Once you have done this, an exp.pygaze_eyetracker object will be available, which oﬀers
the following functions:
class pygaze_eyetracker
A generic Python library for eye tracking.
Function list:
function pygaze_eyetracker.calibrate()
function pygaze_eyetracker.close()
function pygaze_eyetracker.connected()
function pygaze_eyetracker.draw_calibration_target(x, y)
function pygaze_eyetracker.draw_drift_correction_target(x, y)
function pygaze_eyetracker.drift_correction(pos=None, ﬁx_triggered=False)
function pygaze_eyetracker.ﬁx_triggered_drift_correction(max_dev=60,
min_samples=30, pos=None, reset_threshold=10)
function pygaze_eyetracker.get_eyetracker_clock_async()
function pygaze_eyetracker.log(msg)
function pygaze_eyetracker.log_var(var, val)
function pygaze_eyetracker.pupil_size()
function pygaze_eyetracker.sample()
function pygaze_eyetracker.send_command(cmd)
function pygaze_eyetracker.set_detection_type(eventdetection)
function pygaze_eyetracker.set_draw_calibration_target_func(func)
function pygaze_eyetracker.set_draw_drift_correction_target_func(func)
function pygaze_eyetracker.set_eye_used()
function pygaze_eyetracker.start_recording()
function pygaze_eyetracker.status_msg(msg)
function pygaze_eyetracker.stop_recording()
function pygaze_eyetracker.wait_for_blink_end()
function pygaze_eyetracker.wait_for_blink_start()
function pygaze_eyetracker.wait_for_event(event)
function pygaze_eyetracker.wait_for_ﬁxation_end()
function pygaze_eyetracker.wait_for_ﬁxation_start()
function pygaze_eyetracker.wait_for_saccade_end()
function pygaze_eyetracker.wait_for_saccade_start()
function pygaze_eyetracker.calibrate()
Calibrates the eye tracking system. The actual behavior of this function depends on the
type of eye tracker and is described below.
EyeLink:
This function will activate the camera-setup screen, which allows you to adjust the
camera, and peform a calibration/ validation procedure. Pressing ‘q’ will exit the setup
routine. Pressing ‘escape’ will ﬁrst trigger a conﬁrmation dialog and then, upon
conﬁrmation, raises an Exception.
EyeTribe:
Activates a simple calibration routine.
Returns:
Returns True if calibration succeeded, or False if not; in addition a calibration log is added
to the log ﬁle and some properties are updated (i.e. the thresholds for detection
algorithms).
Type: bool
function pygaze_eyetracker.close()
Neatly closes connection to tracker. Saves data and sets self.connected to False.
function pygaze_eyetracker.connected()
Checks if the tracker is connected.
Returns:
True if connection is established, False if not; sets self.connected to the same value.
Type: bool
function pygaze_eyetracker.draw_calibration_target(x, y)
Draws a calibration target.
Arguments:
x – The X coordinate
Type: int
y – The Y coordinate
Type: int
function pygaze_eyetracker.draw_drift_correction_target(x, y)
Draws a drift-correction target.
Arguments:
x – The X coordinate
Type: int
y – The Y coordinate
Type: int
function pygaze_eyetracker.drift_correction(pos=None,
ﬁx_triggered=False)
Performs a drift-correction procedure. The exact behavior of this function on the type of
eye tracker and is described below. Because drift correction may fail, you will generally
call this function in a loop.
EyeLink:
Pressing ‘q’ during drift-correction will activate the camera-setup screen. From there,
pressing ‘q’ again will cause drift correction to fail immediately. Pressing ‘escape’ will give
the option to abort the experiment, in which case an Exception is raised.
Keywords:
pos – (x, y) position of the ﬁxation dot or None for a central ﬁxation.
Type: tuple, NoneType
Default: None
fix_triggered – Boolean indicating if drift check should be performed based on
gaze position (True) or on spacepress (False).
Type: bool
Default: False
Returns:
A boolean indicating if drift check is ok (True) or not (False).
Type: bool
function pygaze_eyetracker.ﬁx_triggered_drift_correction(max_dev=60,
min_samples=30, pos=None, reset_threshold=10)
Performs a ﬁxation triggered drift correction by collecting a number of samples and
calculating the average distance from the ﬁxation position
Keywords:
pos – (x, y) position of the ﬁxation dot or None for a central ﬁxation.
Type: tuple, NoneType
Default: None
min_samples – The minimal amount of samples after which an average deviation is
calculated.
Type: int
Default: 30
max_dev – The maximal deviation from ﬁxation in pixels.
Type: int
Default: 60
reset_threshold – If the horizontal or vertical distance in pixels between two
consecutive samples is larger than this threshold, the sample collection is reset.
Type: int
Default: 10
Returns:
A boolean indicating if drift check is ok (True) or not (False).
Type: bool
function pygaze_eyetracker.get_eyetracker_clock_async()
Returns the diﬀerence between tracker time and PyGaze time, which can be used to
synchronize timing
Returns:
The diﬀerence between eyetracker time and PyGaze time.
Type: int, ﬂoat
function pygaze_eyetracker.log(msg)
Writes a message to the log ﬁle.
Arguments:
msg – A message.
Type: str, unicode
function pygaze_eyetracker.log_var(var, val)
Writes a variable’s name and value to the log ﬁle
Arguments:
var – A variable name.
Type: str, unicode
val – A variable value
function pygaze_eyetracker.pupil_size()
Returns the newest pupil size sample; size may be measured as the diameter or the area
of the pupil, depending on your setup (note that pupil size mostly is given in an arbitrary
units).
Returns:
Returns pupil size for the eye that is currently being tracked (as speciﬁed by
self.eye_used) or -1 when no data is obtainable.
Type: int, ﬂoat
function pygaze_eyetracker.sample()
Returns newest available gaze position.
Returns:
An (x,y) tuple or a (-1,-1) on an error.
Type: tuple
function pygaze_eyetracker.send_command(cmd)
Directly sends a command to the eye tracker (not supported for all brands; might
produce a warning message if your setup does not support direct commands).
Arguments:
cmd – The command to be sent to the eye tracker.
Type: str, unicode
function pygaze_eyetracker.set_detection_type(eventdetection)
Set the event detection type to either PyGaze algorithms, or native algorithms as
provided by the manufacturer (only if available: detection type will default to PyGaze if
no native functions are available)
Arguments:
eventdetection – A string indicating which detection type should be employed:
either ‘pygaze’ for PyGaze event detection algorithms or ‘native’ for manufacturers
algorithms (only if available; will default to ‘pygaze’ if no native event detection is
available)
Type: str, unicode
Returns:
Detection type for saccades, ﬁxations and blinks in a tuple, e.g. (‘pygaze’,’native’,’native’)
when ‘native’ was passed, but native detection was not available for saccade detection.
Type: tuple
function pygaze_eyetracker.set_draw_calibration_target_func(func)
Speciﬁes a custom function to draw the calibration target. This will function will override
Speciﬁes a custom function to draw the calibration target. This will function will override
the default draw_calibration_target.
Arguments:
func – The function to draw a calibration target. This function should accept two
parameters, for the x and y coordinate of the target.
Type: function
function pygaze_eyetracker.set_draw_drift_correction_target_func(func)
Speciﬁes a custom function to draw the drift-correction target. This function will
override the default draw_drift_correction_target.
Arguments:
func – The function to draw a drift-correction target. This function should accept
two parameters, for the x and y coordinate of the target.
Type: function
function pygaze_eyetracker.set_eye_used()
Logs the eye_used variable, based on which eye was speciﬁed (if both eyes are being
tracked, the left eye is used). Does not return anything.
function pygaze_eyetracker.start_recording()
Starts recording. Sets self.recording to True when recording is successfully started.
function pygaze_eyetracker.status_msg(msg)
Sends a status message to the eye tracker, which is displayed in the tracker’s GUI (only
available for EyeLink setups).
Arguments:
msg – A string that is to be displayed on the experimenter PC, e.g.: “current trial:
%d” % trialnr.
Type: str, unicode
function pygaze_eyetracker.stop_recording()
Stops recording. Sets self.recording to False when recording is successfully stopped.
function pygaze_eyetracker.wait_for_blink_end()
Waits for a blink end and returns the blink ending time. Detection based on Dalmaijer et
al. (2013) if EVENTDETECTION is set to ‘pygaze’, or using native detection functions if
EVENTDETECTION is set to ‘native’ (NOTE: not every system has native functionality; will
fall back to ;pygaze’ if ‘native’ is not available!)
Returns:
Blink ending time in milliseconds, as measured from experiment begin time.
Type: int, ﬂoat
function pygaze_eyetracker.wait_for_blink_start()
Waits for a blink start and returns the blink starting time. Detection based on Dalmaijer
et al. (2013) if EVENTDETECTION is set to ‘pygaze’, or using native detection functions if
EVENTDETECTION is set to ‘native’ (NOTE: not every system has native functionality; will
fall back to ;pygaze’ if ‘native’ is not available!)
Returns:
Blink starting time in milliseconds, as measured from experiment begin time
Type: int, ﬂoat
function pygaze_eyetracker.wait_for_event(event)
Waits for an event.
Arguments:
event – An integer event code, one of the following:
3 = STARTBLINK
4 = ENDBLINK
5 = STARTSACC
6 = ENDSACC
7 = STARTFIX
8 = ENDFIX
Type: int
Returns:
A self.wait_for_* method is called, depending on the speciﬁed event; the return value
of corresponding method is returned.
function pygaze_eyetracker.wait_for_ﬁxation_end()
Returns time and gaze position when a ﬁxation has ended; function assumes that a
‘ﬁxation’ has ended when a deviation of more than self.pxﬁxtresh from the initial ﬁxation
position has been detected (self.pxﬁxtresh is created in self.calibration, based on
self.ﬁxtresh, a property deﬁned in self.init). Detection based on Dalmaijer et al. (2013) if
EVENTDETECTION is set to ‘pygaze’, or using native detection functions if
EVENTDETECTION is set to ‘native’ (NOTE: not every system has native functionality; will
fall back to ;pygaze’ if ‘native’ is not available!)
Returns:
A time, gazepos tuple. Time is the end time in milliseconds (from expstart), gazepos is a
(x,y) gaze position tuple of the position from which the ﬁxation was initiated.
Type: tuple
function pygaze_eyetracker.wait_for_ﬁxation_start()
Returns starting time and position when a ﬁxation is started; function assumes a ‘ﬁxation’
has started when gaze position remains reasonably stable (i.e. when most deviant
samples are within self.pxﬁxtresh) for ﬁve samples in a row (self.pxﬁxtresh is created in
self.calibration, based on self.ﬁxtresh, a property deﬁned in self.init). Detection based on
Dalmaijer et al. (2013) if EVENTDETECTION is set to ‘pygaze’, or using native detection
functions if EVENTDETECTION is set to ‘native’ (NOTE: not every system has native
functionality; will fall back to ;pygaze’ if ‘native’ is not available!)
Returns:
A time, gazepos tuple. Time is the starting time in milliseconds (from expstart), gazepos
is a (x,y) gaze position tuple of the position from which the ﬁxation was initiated.
Type: tuple
function pygaze_eyetracker.wait_for_saccade_end()
Returns ending time, starting and end position when a saccade is ended; based on
Dalmaijer et al. (2013) online saccade detection algorithm if EVENTDETECTION is set to
‘pygaze’, or using native detection functions if EVENTDETECTION is set to ‘native’ (NOTE:
not every system has native functionality; will fall back to ;pygaze’ if ‘native’ is not
available!)
Returns:
An endtime, startpos, endpos tuple. Endtime in milliseconds (from expbegintime);
startpos and endpos are (x,y) gaze position tuples.
Type: tuple
function pygaze_eyetracker.wait_for_saccade_start()
Returns starting time and starting position when a saccade is started; based on Dalmaijer
et al. (2013) online saccade detection algorithm if EVENTDETECTION is set to ‘pygaze’, or
using native detection functions if EVENTDETECTION is set to ‘native’ (NOTE: not every
system has native functionality; will fall back to ;pygaze’ if ‘native’ is not available!)
Returns:
An endtime, startpos tuple. Endtime in milliseconds (from expbegintime); startpos is an
(x,y) gaze position tuple.
Type: tuple
Copyright 2010-2015 Sebastiaan Mathôt // Download as .tar.gz // Revision #219810 on Thu Jul 2 20:29:15 2015