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EyeLink II User Manual version 2.12

(07/02/2006)

©

2002-2006 SR Research Ltd.

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2.3.6 Drift Correct Screen

Figure

2-7: EyeLinkII Drift Correction Screen

2.3.6.1 Purpose

The drift correct screen displays a single target to the participant and then
measures the difference between the computed fixation position during
calibration / validation and the target. This error reflects headband slippage or
other factors, which are then corrected for by the measured error.

To perform a drift correction, have the subject look at the first fixation point and
press the “Accept Fixation” button, or the ENTER or Spacebar key, to start the
validation.

If the drift correction error is too large, the drift correction will be performed
again. If the total drift since the last calibration is too large, the drift correct will
fail and you will be prompted to perform another calibration.

Calibration sequence
point

Sequence Options

Camera view with
threshold status

Status Panel

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Summary of Contents for II

Page 1: ...EyeLink II Head Fixed Eye Tracker User Manual Version 2 12 Copyright 1997 2006 SR Research Ltd EyeLink is a registered trademark of SR Research Ltd Mississauga Canada ...

Page 2: ...racker Application Operation 8 2 1 Starting the Host Tracker 8 2 2 Modes of Operation 8 2 3 EyeLink II Tracker Application Navigation 9 2 3 1 Offline Screen 10 2 3 2 Camera Setup Screen 12 2 3 3 Set Options Screen 16 2 3 4 Calibration Screen 21 2 3 5 Validation Screen 23 2 3 6 Drift Correct Screen 25 2 3 7 Output Screen 27 2 3 8 Record Screen 29 2 4 Status Panel 31 2 5 Mouse Simulation Mode 32 2 6...

Page 3: ...II Host PC 57 4 2 2 Recording from the EyeLink API 57 4 3 The EyeLink On Line Parser 57 4 3 1 Parser Operation 57 4 3 2 Parser Limitations 58 4 3 3 EyeLink Parser Configuration 58 4 3 4 Parser Data Type 59 4 3 5 Saccadic Thresholds 59 4 3 6 Pursuit Thresholds 60 4 3 7 Fixation Updates 60 4 3 8 Other Parameters 61 4 3 9 Sample Configurations 61 4 4 File Data Types 62 4 4 1 Samples 62 4 4 2 Position...

Page 4: ...m Eye Camera Images are blank or blue 88 Problem LED Warning on Host PC startup 88 Problem Host PC Warning Message or Image Loss 88 6 System Care 90 6 1 Maintenance 90 6 2 Storage and Transportation 91 7 Important Information 93 7 1 Safety 93 7 1 1 Electrical Isolation Safety 93 7 1 2 Eye Illumination Safety 93 7 2 Limited Hardware Warranty 94 7 3 Limited Software Warranty 95 7 4 Copyrights Tradem...

Page 5: ...tal Inputs and Outputs 97 8 3 1 Analog Data Output Assignments 98 8 3 2 Analog Data Types and Ranges 99 8 3 3 Scaling of Analog Position Data 99 8 4 Pupil Size Data 100 8 5 Time base and Data Strobe 100 8 5 1 Strobe Data Input 101 8 5 2 Over sampling and Toggle Strobe 101 ...

Page 6: ...igure 2 7 EyeLinkII Drift Correction Screen 25 Figure 2 8 EyeLinkII Output Screen 27 Figure 2 9 EyeLinkII Record Screen 29 Figure 2 10 EyeLink II Status Panel 31 Figure 3 1 Example Camera Setup Screen before Camera Setup 36 Figure 3 2 Size and Vertical Eye Camera Adjustments 38 Figure 3 3 Horizontal Adjustments of Eye Camera 39 Figure 3 4 Focusing the Eye Camera 40 Figure 3 5 Symptoms of Poor Pupi...

Page 7: ... medical equipment standards requires use of a medical grade power supply Entela Safety Mark Compliance of this product with UL 2601 1 CSA C22 2 N0 601 1 and IEC 60601 1 is certified by Entela an independent testing body CONTACT ADDRESS SR Research Ltd 5516 Main St Osgoode Ontario Canada K0A 2W0 Fax 416 352 5376 Phone 613 826 2958 Toll Free Phone 1 866 821 0731 North America Only http www eyelinki...

Page 8: ...ental considerations as well as the process followed to install the EyeLink II hardware and software on both the Host and Display computers B Windows Programmers Guide Provides suggestions on how to program experiments with EyeLink II in Windows including review of all sample experiments provided for Windows Document also details the EyeLink II Windows API C EyeLink Data Viewer User s Manual Intro...

Page 9: ...ine data parsing occurs making eye events such as saccade fixation and blink available within 25 ms to the display computer The EyeLink II system consists of two miniature cameras which are mounted onto a head restraint No mirrors are used in the EyeLink II system making it very robust and easy to set up Two eye cameras allow binocular eye tracking or easy selection of the subject s dominant eye w...

Page 10: ...if disk the partitioning utility included with self installation kit is used during installation Functions either as standalone tracker or connected to display computer through 10BASE T Ethernet cable In standalone configuration data output is to hard disk or through optional analog output card Response box or game pad connected by a USB port Keyboard display and pointing device are used to contro...

Page 11: ...on using EyeLink II API allowing development of extensive experimental paradigms Display Applications can configure and control the EyeLink tracker and have access to real time data including gaze position response box button presses and keyboard Applications need only support display generation and control of the experiment sequence and should rely on the tracker for creating the data file and re...

Page 12: ...ple Rate Average Delay Filter Off On Noise RMS Stability Pupil Only 250 or 500Hz 3 ms 5 ms 7 ms 0 01 Affected by headband slip and vibration 1 4 2 Operational Functional Specifications Image Processing Fully Digital Pupil Tracking Hyper acuity Resolution Gaze 0 005 Velocity Noise 3 average Pupil Size Resolution 0 1 of diameter Eye Tracking Range 30 horizontal 20 vertical in pupil only mode Gaze Tr...

Page 13: ...000 XP MS DOS Macintosh Classification Class II grounding optional type BF conductive path from computer chassis to metal parts on the headband Power Supply Requirements Powered from host computer power supply 160W or greater power supply recommended Medical grade power supply is required for 601 1 compliance Operating conditions 15 C to 35 C 20 80 humidity non condensing ambient pressure 101 kPa ...

Page 14: ...mmercial environment This equipment generates uses and can radiate radio frequency energy and if not installed and used in accordance with the instruction manual may cause harmful interference to radio communications Operation of this equipment in a residential area is likely to cause harmful interference in which case the user will be required to correct the interference at the users expense WARN...

Page 15: ...lly controlled by the Display PC via the Ethernet link The degree of Display PC control is dependent only on the display application itself It is possible to have full control of the tracker via the Display PC however this also requires the most display application programming A common scenario is to have the application on the display PC control the eye tracker to start subject setup and calibrat...

Page 16: ... II tracker interface consists of a set of setup and monitoring screens which may be navigated by means of the host PC mouse key shortcuts or from the Display PC application via link commands Figure 2 1 Screen Overview of EyeLink II Tracker Program Each of the modes shown in the diagram above has a special purpose Where possible each screen has a distinctive appearance as shown in the figure Scree...

Page 17: ...ny screen the key combination CTRL ALT Q will exit the EyeLink tracker program 2 3 1 Offline Screen Figure 2 2 EyeLinkII Offline Screen 2 3 1 1 Purpose The off line mode is the default start up screen for EyeLink II The main secondary screens can be accessed via the navigation buttons on the left hand side of the screen 2 3 1 2 Main Functions Press to go to the camera setup screen Keys ENTER Camer...

Page 18: ...periment setup Keys S go to Set options Select Exit EyeLink to end the EyeLink II program Keys Ctrl Alt Q Exit EyeLink Press Help F1 to access the online help page for Camera Setup All available key shortcuts are also listed on the Help screen Keys F1 open Help screen 2 3 1 3 Key Shortcuts ENTER Press to enter camera setup O Press to go to the Output screen S Press to go to the Set Options screen ...

Page 19: ...en for most EyeLink II setup functions From this screen the eye and head tracking cameras can be set up and their images can be thresholded Eye s to be tracked tracking mode and options can also be set Calibration Validation and Drift correction can also be performed from this screen Image Display Attributes Tracking Mode S l ti Camera Select and Status C t l Selected eye s to track ...

Page 20: ...Here 250 Hz is selected Note that in Pupil CR mode 500Hz is not available Keys F toggles sampling Frequency selection Toggles display of crosshair in eye camera images Keys X toggle crosshair display Toggles display of threshold coloring in eye camera images Keys T toggle threshold coloring display Select to present the camera display image on the Display Monitor To select the camera to display as...

Page 21: ...ecord to go to the output screen from which you can start a manual recording session This button is usually only access when using the EyeLink II in standalone mode Keys O go to Output screen Select Set Options to go to the EyeLink II options screen where a variety of system options and settings can be configured Note that any value on this screen can be programmatically overridden by the API duri...

Page 22: ...reased gaze calculation error Keys D go to Drift correction screen 2 3 2 3 Key Shortcuts Key Function and Select between left eye camera head camera and right eye camera R Select Right eye for recording L Select left eye for recording B Select both eyes for recording F Toggle sampling frequency selection A Auto threshold selected image X Toggle crosshair display T Toggle threshold coloring display...

Page 23: ...l when doing manual recording sessions that are not driven by a Display PC using the EyeLink II API When using the EyeLink II API to drive stimulus presentation these settings are normally set by the Display application via a set of API calls The Default Settings should be sufficient for many tracking applications EyeLink Data File component Analog Output selection Data and system sensitivity EyeL...

Page 24: ...r Redisplay the first calibration or validation fixation dot Keys I Repeat First Point Select Force Manual Accept to manually accept each calibration and validation fixation point Select Lock Eye After Cal to lock the recording eye on the Display PC keyboard if performing a monocular recording In Mouse Simulation mode the Host PC mouse simulates eye movement and can be used for experiment debuggin...

Page 25: ...s noise by a factor of 2 to 3 Keys F2 toggles File Sample Filter levels Note By changing the file sample filter from high to another value this will affect EyeLink Data Viewer and other analysis tool calculations SR Research Ltd recommends leaving this value set to High Select Link Analog Filter Each increase in filter level reduces noise by a factor of 2 to 3 but introduces a 1 sample delay to th...

Page 26: ...I Input Port Data Select to view previous screen Keys ESC Previous Screen Select to view camera setup screen Keys ENTER Camera Setup Press Help F1 to access the online help page for Set Option All available key shortcuts are also listed on the Help screen Keys F1 open Help screen Press Revert to Last to restore the EyeLink II settings to the values loaded the last time the tracker was started Pres...

Page 27: ...itivity F2 File sample data filter level F3 Link Analog data filter level F File data contents selection 3 Raw eye position in samples 4 HREF eye position in samples G Gaze position and resolution in samples B Button flags in samples I Input Port data in samples A Analog output data selection ENTER Camera Setup screen ESC Return to previous screen F1 HELP screen L Revert to configuration from last...

Page 28: ...he calibration is automatically checked when finished and diagnostics given Calibration should be performed after camera setup and before Validation The two camera images along with threshold values are at the bottom left of the screen The eyes to be calibrated as well as the calibration type as defined in the Set Options screen or via the EyeLink API are indicated beside the camera images at the ...

Page 29: ... sequence Sequence pacing selected in the setup options menu Keys A Auto Trigger Press to accept calibration fixation Only works after calibration dot sequence has finished Keys ENTER Accept Fixation 2 3 4 3 Key Shortcuts Key Function F1 Help screen ESC Camera setup A Auto calibration set to the pacing selected in Set Options menu Auto trigger ON EyeLink accepts current fixation if it is stable Du...

Page 30: ...gaze accuracy of the calibration In addition the average offset is used to perform an immediate drift correction The functionality available in the Validate screen is very similar to that of the Calibrate screen Validation should only be performed after Calibration To perform a validation have the subject look at the first fixation point and press the Accept Fixation button or the ENTER or Spaceba...

Page 31: ... accept fixation value only when the participants gaze is stable Keys ENTER 2 3 5 3 Key Shortcuts Key Function F1 Help screen ESC Camera setup A Auto calibration set to the pacing selected in Set Options menu Auto trigger ON EyeLink accepts current fixation if it is stable During Validation ESC Exit to Camera Setup F1 Help screen M Manual validation Auto trigger turned off A Auto validation set to...

Page 32: ...dband slippage or other factors which are then corrected for by the measured error To perform a drift correction have the subject look at the first fixation point and press the Accept Fixation button or the ENTER or Spacebar key to start the validation If the drift correction error is too large the drift correction will be performed again If the total drift since the last calibration is too large ...

Page 33: ...ll the key functions for the Validation screen and gives an brief overview of the role of drift correction Keys ENTER Stop the Drift Correction Not Used Press to accept fixation value only when the participants gaze is stable Keys ENTER 2 3 6 3 Key Shortcuts Key Function ENTER Begins or accepts ESC Rejects drift correction value if one has been created or exits drift sequence F1 Help screen ...

Page 34: ...ts are controlled from the Set Options screen Recording may be manually started from the Output screen or by an application via the Ethernet link Manual recording may be terminated by switching back to the to the OUTPUT screen If the recording was initiated and a menu of options will appear allowing faster drawing and file transfer 2 3 7 2 Main Functions Press to go to the Previous screen Keys ESC...

Page 35: ...on this screen can be programmatically overridden by the API during experiment setup Keys S go to Set options Press Help F1 to access the online help page for Camera Setup All available key shortcuts are also listed on the Help screen Keys F1 opens Help screen Press to begin recording EyeLink data Keys Enter or O Press to Open Data File Keys O Open File 2 3 7 3 Key Shortcuts ESC Camera Setup Scree...

Page 36: ... precedes manual entry into Output mode to allow parameter preview This is the only mode in which analog data is produced and is usually the source mode for link and file data Any graphics drawn on the idle mode screen are re displayed on the screen to be used as a reference for the real time gaze position cursor 2 3 8 2 Main Functions Stops the recording of data to the EyeLink Data File Keys ESC ...

Page 37: ...6 2002 2006 SR Research Ltd 30 2 3 8 3 Key Shortcuts ESC Exit to output screen CTRL ALT A Abort trail menu After Trail Aborted S Setup Calibrate camera setup R Repeat Trail N Next Trail CTRL ALT T Terminate Experiment CTRL ALT Q Terminate program ...

Page 38: ...summarized as follows Pupil OK green Pupil present and can be tracked at selected sample rate SIZE yellow Occurs in pupil only 500 Hz and pupil CR tracking modes when the pupil size is larger than the maximum allowed pupil size MISSING red Pupil not present Corneal only operational in Pupil CR mode OK green Corneal reflection is present and can be tracked MISSING red Corneal reflection is not pres...

Page 39: ...oked from If your experiment will be using option settings that are non standard for your lab it makes sense to create a directory on the EyeLink Host PC for the experiment copy any configuration files into this directory that need to be modified for this experiment and to invoke the tracker from this directory The EDF files for an experiment are written to a disk partition and directory based on ...

Page 40: ...al ini configuration files are required if scene camera and video overlay options are installed in your system If you plan to change the default settings in the ini files please cut and paste the target commands to the final ini and make the modification in that file for the ease of future maintenance 2 7 Analog Data Types Position data and pupil size data are available in several types which are ...

Page 41: ...r the 5V to 5V output range it is 5V tan angle measured separately for vertical and horizontal rotations A calibration must be performed to properly obtain this measure Gaze This is actual gaze position on the display screen fully compensated for head position A calibration must be performed to obtain this measure The EyeLink II system offers integrated data recording and digital data transfer met...

Page 42: ...ting the EyeLink II Tracker application on the Host PC If the EyeLink software is not yet running on the host PC start it by typing CD C EYELINK2 EXE EYELINK2 IMPORTANT Remember to exit the EyeLink software by pressing the key combination CTRL ALT Q Do not switch off the computer while running the EyeLink II software as data may be lost Now start a simple sample example application on the Display ...

Page 43: ...tracking mode and other functions are on the left of the screen Figure 3 1 Example Camera Setup Screen before Camera Setup Throughout the EyeLink II software you can use the Host PC mouse to select options and navigate throughout the tracker screen Almost very button has an equivalent key shortcut The key shortcut mappings available for the currently displayed screen can be accessed via the Help b...

Page 44: ...camera setup From the Camera Setup screen select one of the eye cameras Until the cameras have been properly aimed you will probably not see the eye initially Start by rotating the selected camera up and down until part of the eye comes into view This is adjusted by lowering and raising the eye camera handle as in the bottom row of Figure 11 If the image becomes too dark or too light wait one seco...

Page 45: ...ye until the corners of the eye are just outside the image as in the top row of Figure 12 If the eye image is too small the eye tracking resolution will be poor if too large the pupil will leave the image at large eye rotations and be lost Hold the eye camera with one hand and loosen the rod clamp for that camera with the other hand by 1 2 turn Slide the camera up or down through the rod clamp gen...

Page 46: ... illuminator corneal reflections the 2 white circles should be at the bottom of the pupil lower the camera if they are too high Note The corneal reflections mentioned here are not the corneal reflections used by the system for headband movement compensation and are white with a position that should be at the bottom of the pupil The corneal reflection used in the Pupil CR mode is a single circle an...

Page 47: ...Threshold button or the A key when the eye camera image is selected The pupil of the eye should be solidly blue with no other colour in the image when the thresholding is properly set If large areas are colored the subject may have blinked press Auto Threshold again If the subject wears eyeglasses reflections may block the pupil in the image Reflections from the eye camera illuminators can be redu...

Page 48: ...hold too much as the pupil thresholding may be poor at other eye positions as in the first image in Figure 15 The pupil on the operator display should have a box drawn around it indicating that it has been detected If a shadow captures the pupil or it is clipped by the side of the camera window as in Figure 15 the box will disappear and the pupil will be lost On the Host PC a red warning message w...

Page 49: ... the experiment 3 4 Calibration The preceding steps set up the EyeLink II camera system to track the positions of the pupils of both eyes Almost all eye movement research requires information on the subject s point of gaze on a display of visual information such as a screen of text To compute this we need to determine the correspondence between pupil position in the eye camera image and gaze posit...

Page 50: ...ponse to commands from the EyeLink II system The Host PC display will also display the raw pupil position as a moving colored circle and a thresholded eye camera image A status bar at the bottom right of the display reports the progress of the calibration The pupil position cursor s will jump about when the subject looks about on the display and becomes still when properly fixating the calibration...

Page 51: ... before it disappears If automatic sequencing has been enabled targets will be presented and fixations collected without further intervention Each time a new target is displayed the subject quickly makes a saccade to it The EyeLink II system detects these saccades and the fixation following producing an automated sequencing system NOTE Sequencing may halt if the setup of one or both eyes causes pu...

Page 52: ... for one or few selected points without having to restart the calibration procedure This is especially helpful for those subjects whose calibration data is hard to get When the last calibration target has been presented the calibration will be evaluated At the bottom of the Calibration screen each eye s calibration is graded and displayed as follows GOOD green background No obvious problems found ...

Page 53: ...ration the indicators are green Should any of the indicators display a colour other than green there is a problem with the setup that must be addressed to prevent data loss Indicates Status of Pupil OK Pupil is visible SIZE Pupil is too large MISSING Pupil is missing The pupil status error message SIZE highlighted in yellow indicates that the size of the pupil is too large To reduce the pupil size...

Page 54: ...e calibration is used to estimate the gaze position of the subject and the error difference between target position and computed gaze position is estimated Note since EyeLink II tracker version 2 0 a scaling factor is built in for automatically generated validation point positions to pull in the corner positions see the validation_corner_scaling command setting in the calibr ini file This is used ...

Page 55: ...rror the subject may simply have mis fixated that point and the validation may be repeated to check this press ESC to return to the Camera Setup screen and V to repeat the validation If a regular pattern is seen i e all fixations on the left side are too low there was probably a calibration or camera setup problem In this case press ESC to return to the Camera Setup screen and re calibrate If a bi...

Page 56: ...I during recording allowing the operator to see where the subject is looking and detect problems with eye tracking errors or of subject inattention Applications can create similar feedback displays by sending drawing commands to EyeLink II before recording begins TRACK displays the gaze position as a red cursor on the subject display The cursor can be toggled on and off by the G key on the Display...

Page 57: ... There are two ways of performing an online drift correction during recording If it is very likely that the subject will look at a particular point across trials a reference position for drift correction could be defined at that position This can be done by editing the value of online_dcorr_refposn in the calibr ini or final ini file under c eyelink2 exe directory of the host PC or more preferably...

Page 58: ... point in the Host PC tracker program to exit to the command prompt 3 9 EyeLink II Setup Summary It is suggested that you try the procedures in this section until you feel comfortable with EyeLink II setup and can get reliable calibrations This is a summary of the steps detailed in the practice session It assumes no setup problems are encountered Start EyeLink II on the operator PC Start TRACK on ...

Page 59: ...ted The EyeLink II tracker has a trial abort menu built in which may be used in experiments to terminate trials where setup problems are seen The Setup menu may then be used to fix eye setup or calibration and the interrupted trial may be restarted or skipped This sequence requires co operation from the experiment application and example code is given the developer s kit 3 11 Next Steps Other Samp...

Page 60: ...leted the EDF file is closed and transferred via the link from the EyeLink hard disk to the Windows PC vi At the end of the experiment the window is closed and the EyeLink II library is closed Each trial begins by performing a drift correction where the subject fixates a target to allow the eye tracker to correct for any drift errors Press the space bar to perform the drift correction Recording is...

Page 61: ...me experiment is a gaze contingent display where the part of the display the subject is looking at is changed or where the entire display is modified depending on the location of gaze These require high sampling rates and low delay which the EyeLink II tracker can deliver through the link This template demonstrates how to use the link s real time gaze position data to display a gaze contingent win...

Page 62: ...m left to right then back again repeatedly The second block presents a red which moves right to left then changes to when moving left to right repeatedly The third block presents white dots at three locations along the horizontal axis The final fourth block presents a white dot a few seconds later another white dot is shown The original white dot then fades away This presentation pattern is repeat...

Page 63: ...ovement events such as saccades and fixations subject responses and synchronizing events from the experimental application Both streams are time synchronized for easy analysis The file is organized into blocks of data one for each recording session Each block may have samples events or both Also the data items recorded in each sample or event may be configured at recording and are available at the...

Page 64: ... be started and stopped Refer to Chapter 2 of this manual EyeLink II Tracker Application Operation for information 4 2 2 Recording from the EyeLink API Most eye movement research involves running many subjects through a sequence of experimental trials with tens or hundreds of recording blocks per file This is best done by remote control over the link from an experimental application The connection...

Page 65: ...on of very small saccades may require off line processing as the special filtering and computation of global velocity cannot be performed on line In smooth pursuit research the parser is less sensitive to small back up saccades opposite to the direction of pursuit than forward saccades due to the low peak velocity of back up saccades The parser only looks ahead in the data a short time 8 msec to c...

Page 66: ...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 sec respectively The velocity threshold is the eye movement velocity that must be exceeded for a ...

Page 67: ...ound of smooth eye motion as fast as 70 sec While acceleration can be used to detect these saccades velocity data must also be used for reliable detection of all saccades The EyeLink II parser raises the saccadic velocity threshold during pursuit by the average velocity over the last 40 milliseconds This is reliable and does not degrade parser performance during non pursuit eye movements During lo...

Page 68: ...pdate_accumulate 100 4 3 8 Other Parameters The EyeLink II PARSER INI configuration file contains other commands that configure the parser These are of several types Verification delays These set the time in milliseconds that the parser requires a detector output saccadic velocity or acceleration thresholds or missing pupil for blink to be stable before the parser changes its state and sends event...

Page 69: ...ither from the experimental application of from changes in the eye data Both samples and events can report eye data in several forms These are discussed in the description of sample data Eye movement data is parsed by the EyeLink II tracker on line and used to generate eye movement events which are discussed with application messages and button events 4 4 1 Samples Samples are records of eye posit...

Page 70: ...nsate for subject head motions The processed data in one or all of these forms may be recorded in the samples Data is written as x y coordinate pairs or two pairs for binocular data The types of position data available are explained below 4 4 2 1 PUPIL Pupil position data is raw x y coordinate pairs from the eye cameras It has not been converted to eye angles or to gaze position There may be a non...

Page 71: ...cities as described below The eye rotation angles may be directly computed from the HREF x y pairs There are several methods of specifying eye rotation angles The angular distance eye rotation magnitude between any two HREF points is directly computable The C code to compute this angle is given below Remember to multiply the result by 57 296 to get the angle in degrees angle acos f f x1 x2 y1 y2 s...

Page 72: ...n or a resolution of 0 0045 degree Actual EyeLink II resolution is limited only by measurement noise which is less than 2 units RMS 0 01 degree or 40 seconds of arc in pupil only mode and approximately 4 units RMS 0 022 degree or 88 seconds of arc in pupil corneal reflection mode 4 4 2 4 Gaze Resolution Data For gaze position unlike the HREF data the relationship between visual angle and gaze posi...

Page 73: ...ch sample Button ports bits and polarity may be set in the EyeLink II tracker configuration file BUTTONS INI The button data consists of two 8 bit fields recorded as a 16 bit number The lower 8 bits contain the current status of the 8 buttons bit 0 if off 1 if pressed Each of the upper 8 bits will be set to 1 if its button has changed since the last sample The least significant bit in each byte co...

Page 74: ...field provides Pascal string compatibility and allows binary data to be recorded in the message Current EyeLink applications only support text messages with zero terminated strings It is also recommended that messages be shorter than 250 characters 4 5 2 Buttons Each button event records a change in state pressed or released 1 or 0 of up to 8 buttons or input port bits monitored by the EyeLink II ...

Page 75: ...e end time is actually the time of the last sample in the condition so length of a condition must be computed as the difference between the end and start times plus the time between samples 2 or 4 milliseconds End events also contain summary data on the condition as well average gaze position of a fixation for example The main classes of data events are summarized below 4 5 3 1 Record Blocks Each ...

Page 76: ...le data in the files to be processed by saccade or fixation in a single pass The data contained in STARTFIX and ENDFIX events may be configured by modifying the DATA INI file for the EyeLink II tracker For most research only simple fixation statistics are required such as average position and pupil size STARTFIX events may also be configured to contain only the start time of the fixation Other dat...

Page 77: ... end gaze data angular resolution All of these data may appear in the ENDSACC event that terminates the fixation Only the starting data can appear in the STARTSACC event that initiates the fixation In a sorted EDF file or a text ASC file produced by EDF2ASC that contains both samples and events the STARTSACC event will precede the first sample in the file that is part of the fixation and the ENDSA...

Page 78: ... pupil position These are sensed by the EyeLink II parser and marked as saccades The sequence of events produced is always STARTSACC STARTBLINK ENDBLINK ENDSACC Note that the position and velocity data recorded in the ENDSACC event is not valid All data between the STARTSACC and ENDSACC events should be discarded The duration of the blink may be computed by either the duration of the missing pupil...

Page 79: ... II tracker are used to set which eye s are used Recording of gaze and pupil area is essential for mast work and resolution is important if velocity is to be computed later Recording of HREF data is optional 4 6 2 Event Data Eye movement events are generated by processing one of the types of eye movement data PUPIL HREF or GAZE as specified by the recording_parse_type command This command may be e...

Page 80: ... be sent over the link The command is followed by a list of data types and options selected from the list below Keyword Effect LEFT RIGHT limits data to one or both eyes usually include both LEFT and RIGHT FIXATION includes fixation start and end events FIXUPDATE includes fixation pursuit state update events SACCADE includes saccade start and end events BLINK includes blink start and end events ME...

Page 81: ...red by file with percentage of time recorded as blocks Fixations Total fixations with number of exceptionally short 100 msec and long 1500 msec Events Count of messages saccades blinks button presses Samples Total recorded samples count of missing data gaps Resolution Average angular resolution of gaze data pixels per visual degree Ordering UNSORTED message if file needs sorting During file scanni...

Page 82: ...ype and general data These are discussed below and then summarized in a table at the end of the section 4 8 2 1 File Selection File names for EDF file inputs are specified with the first filename on the command line This may have wildcards and to specify a set of files If more than one file matches the specification EDF2ASC will prompt for each file name Press Y to process the file N to skip it A ...

Page 83: ...e output in the ASC file The desired data type is specified by sg for gaze position data the default sh for HREF data and sp for raw pupil position data If the desired data type is not present in the file a warning message will be logged and another data type will be used The type of position data reported for eye movement events saccades and fixations is determined by the type of eye position dat...

Page 84: ... option resulting in a listing of file messages and data blocks This is useful as a summary of file structure when designing analysis software for experiments Finally message events can also be removed with the nmsg no messages option Examples of the most useful sets of sample and event selection options are edf2asc ns no samples just events edf2asc neye just samples messages button events and dat...

Page 85: ...nt default res outputs resolution data if present vel outputs velocity data in samples if possible s or ne outputs sample data only e or ns outputs event data only nse blocks output of start events nmsg blocks message event output neye outputs only non eye events for sample only files miss string replaces missing data in ASC file with string setres xr yr uses a fixed xr yr resolution always defres...

Page 86: ... 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 samp...

Page 87: ...ATS Monocular time xp yp ps Monocular with velocity time xp yp ps xv yv Monocular with resolution time xp yp ps xr yr Monocular with velocity and resolution time xp yp ps xv yv xr yr Binocular time xpl ypl psl xpr ypr psr Binocular with velocity time xpl ypl psl xpr ypr psr xvl yvl xvr yvr Binocular with and resolution time xpl ypl psl xpr ypr psr xr yr Binocular with velocity and resolution time ...

Page 88: ...2006 SR Research Ltd 81 psr right pupil size area or diameter xv yv instantaneous velocity degrees sec xvl yvl left eye instantaneous velocity degrees sec xvr yvr right eye instantaneous velocity degrees sec xr yr X and Y resolution position units degree ...

Page 89: ...pl saccadic amplitude degrees xvr yvr right eye instantaneous velocity degrees sec xr yr X and Y resolution position units degree 4 9 3 1 Messages MSG time message A message line contains the text of a time stamped message This will have been sent to the EyeLink II tracker by an application and contains data for analysis or timestamps important events such as display changes or subject responses T...

Page 90: ...solution for the block if samples are present it is computed from samples else it summarizes any resolution data in the events Note that resolution data may be missing this is represented by a dot instead of a number for the resolution 4 9 3 4 Fixations SFIX eye stime EFIX eye stime etime dur axp ayp aps EFIX eye stime etime dur axp ayp aps xr yr The start of fixations are reported with a SFIX lin...

Page 91: ...s for each eye simplifying data analysis 4 9 3 6 Blinks SBLINK eye stime EBLINK eye stime etime dur Blinks periods of data where the pupil is missing are reported by the SBLINK and EBLINK lines The time of the start of the blink is indicated by the SBLINK line which can be eliminated with the EDF2ASC nse option The eye is L or R indicating the eye s data that produced the event The end and duratio...

Page 92: ... larger prescaler usually 10 to add precision to the data EVENTS data type eyes data options This specifies what types of data is present in event lines as a sequence of keywords The data type is one of GAZE HREF or PUPIL The eyes recorded will be one or two words LEFT RIGHT or both The data option keywords currently supported are o RES for resolution data both may be present o RATE for the sample...

Page 93: ... with unwanted information can simply be skipped Processing of events and samples will depend on what type of analysis is to be performed For many cognitive eye movement analyses MSG line text specifying experimental conditions EFIX event data and BUTTON event times from each block are used to create data files for statistical analysis For neurological research samples between SFIX and EFIX events...

Page 94: ...EyeLink II User Manual version 2 12 07 02 2006 2002 2006 SR Research Ltd 87 ...

Page 95: ... from the Display PC to the EyeLink II PCI card in Host PC Restart the EyeLink II Tracker application on the Host PC Problem LED Warning on Host PC startup If a warning message concerning LED currents or safety circuits appears at startup or if the EyeLink software terminates with such a message there may be a problem with the headband headband cable or EyeLink card If such an error occurs 1 Make ...

Page 96: ... EyeLink card and possibly the marker set to SR Research for testing and repair This is because there are no user serviceable parts on the EyeLink II card or on the headband Be sure to follow the packing instructions you received with the system when repackaging the EyeLink II into it s shipping case Under normal circumstances SR Research will send a replacement system to you ...

Page 97: ...e clamp and then use a soft dry clean cloth or facial tissue to gently rub the vertical part of the arms Use light pressure and up and down strokes only After cleaning restore the arms to their fully raised position If the headband cable feels stiff or begins to form loops it has become twisted This twist must be removed to restore the flexibility of the cable and to avoid shortening its life The ...

Page 98: ...he packaged unit to operation To pack the headband 1 Tighten the height adjustment and rear clamps as far as possible 2 Loosen the upper clamps and slide the camera arms up as far as possible 3 Tilt the arms up so the cameras are nearly parallel to the headband frame and point the cameras down 4 To prevent scratching of the arms and head camera place the cardboard spacers between the arms and the ...

Page 99: ...rom the computer and place it into its anti static bag then into its slot in the foam Close the shipping case checking for excessive pressure that may indicate an obstruction Ensure the latches are closed the place the case inside its cardboard shipping box This box may then be sealed and shipped without additional padding by courier ...

Page 100: ...the Ethernet cable is 601 1 compliant Even with the use of a medical grade power supply direct connection of other AC powered devices to the EyeLink II host PC may provide sources of leakage currents above those permitted by the 601 1 standards For this reason digital inputs or analog outputs from the host PC and connected to another PC or to recording devices may affect the 601 1 certification Th...

Page 101: ...he EyeLink II product components are integrated with are excluded from this warranty unless expressly agreed to be otherwise in writing by SR Research Ltd contact the original computer manufacturer for service and support for the computer system itself This warranty is extended to the original end purchaser only Proof of original date of installation is required for warranty service will be perfor...

Page 102: ...d for the use and results obtained from the software SR Research will fix reported software error in a best effort fashion and can not provide a guarantee of solution availability time THIS EXPRESS LIMITED WARRENTY IS IN LIEU OF ALL OTHER WARRENTIES EXPRESS OR IMPLIED INCLUDING ANY IMPLIED WARRENTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE IN NO EVENT WILL SR RESEARCH LTD BE LIABLE ...

Page 103: ...tal input and output ports may be used including the game ports and the printer port of the EyeLink II host computer 8 1 Analog Data Quality The EyeLink II analog output system is intended for use with commercial data collection systems such as LabView or for backwards compatibility with existing eye tracking software and systems However analog data transfer may significantly degrade data quality ...

Page 104: ...to the analog outputs will depend on what these outputs are connected to typically this is another computer with an analog input card 8 2 3 Noise and Filtering It is very important to make sure these connections are made in way that does not introduce noise into the data so connections between the analog output terminals and the analog input terminals must be as short as possible If the analog inp...

Page 105: ...d 3 for port B Here is an example of defining a button on port A and assigning port B as the input port create_button 8 2 0x01 1 button 8 input A0 0 is active input_data_ports 3 digital inputs B0 B7 as input port input_data_mask 0xFF use all bits 8 3 1 Analog Data Output Assignments The EyeLink II system outputs analog voltages on 3 to 6 channels depending on the mode of operation monocular or bin...

Page 106: ...l CR data is also available for applications that implement their own calibrations 8 3 3 Scaling of Analog Position Data Each of the types of position data is scaled to match the selected analog output voltage range Several variables in analog ini set what proportion of the expected data range for each type will be represented at the output and what the total voltage range will be Total analog vol...

Page 107: ...tion of fixations outside the display Scaling to recover gaze position data is more complex as the numerical value is partially dependent on the display coordinates The following formulas do the conversion in several stages with R being the voltage range proportion and S being the proportion of screen width or height R voltage minvoltage maxvoltage minvoltage S R maxrange minrange minrange Xgaze S...

Page 108: ...quisition on analog input devices equipped for this or to trigger interrupt driven acquisition The characteristics of this strobe pulse may be set in the analog ini file with the strobe being active high or active low and with duration between 5 and 2000 microseconds The onset of the strobe is also delayed from the time that analog outputs change in order to allow outputs to settle to the new volt...

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