Eye tracking experiments

1. Eye tracking experiments August 29th, 2014 Daniel Schreij VU CognitivePsychology departement http://ems.psy.vu.nl/userpages/data-analysis-course

2. Today • Creating eye tracking experiments using OpenSesame and PyGaze • Get from EDF (Eyelink Data Format) to other more easily usable data formats • Analyze data with Pandas and Python

3. PyGaze • Download from http://www.pygaze.org • Standalone Python module to communicate with anyEyetracker, with a unified interface (so the code for each eye tracker is the same) • Has OpenSesame plug-in

4. Pygaze | Items InitializeEyetracker(connection & calibration) Drift correct Log message(s) Start recording Stop recording Pause recording

5. PyGaze | Typical experiment Basic steps • Calibrate • Per trial/block • Drift correct • Per trial • Start recording • Log variables • Stop recording

6. PyGaze | Another way • Start recording at beginning of experiment and stop at the end • Drift correct is done afterwards • Preferable for pupil dilation data, or similar experiments that require a constant dat stream (even in between trials)

7. PyGaze | Initialize

8. PyGaze | Logging messages

9. Data files • After you have run your experiment you often get data files in proprietary formats (.EDF) • Developers like you to use their tools... • You can then either • Use proprietary tools to look at data • export them to a textual format • Working with the data in textual format enables you to use your own tool chain such as Python and all its modules

10. Data Files | EDF • Eyelink data format • You can import them to Eyelink Data viewer and then create reports • Saccade, fixation, etc. • You can use the tool EDF2ASC to convert the EDF file to an ASCII format and then parse ityourself (or withavailable scriptshttps://github.com/tknapen/analysis_tools/ )

11. Data Files | EDF2ASC MSG 2436129 TRIALID T1Rg200 0 0 220 200 START 2436164 LEFT RIGHT EVENTS PRESCALER 1 VPRESCALER 1 EVENTS GAZE LEFT RIGHT SFIX L 2436164 SFIX R 2436164 MSG 2436678 SYNCTIME MSG 2436678 DRAWN NEW TARGET EFIX L 2436164 2436832 672 321.7 246.8 1422 EFIX R 2436164 2436832 672 321.7 242.1 1683 SSACC L 2436836 SSACC R 2436836 ESACC R 2436836 2436872 40 323.6 247.4 496.5 250.2 6.75 276.4 SFIX R 2436876 ESACC L 2436836 2436876 44 324.3 251.6 500.5 247.4 6.93 273.3 MSG 2436878 ERASED OLD TARGET SFIX L 2436880 EFIX R 2436876 2437000 128 492.7 249.2 1682 SSACC R 2437004 EFIX L 2436880 2437004 128 499.8 245.0 1323 SSACC L 2437008 ESACC L 2437008 2437028 24 506.6 242.2 565.4 251.1 2.35 151.4 ESACC R 2437004 2437028 28 493.9 248.5 551.7 258.4 2.29 147.2

12. Eyelink Data Viewer

13. Eyelink Data Viewer | Fixations

14. Eyelink Data Viewer | Saccades

15. Eyelink Data Viewer | Samples

16. Eyelink Data Viewer | Heatmap

17. EDF | Saving variables • During the experiment, youcansend trial variables to the Eyelinktobestored in the EDF file • Ifyouuse the appropriate syntax, the EDV willrecognizethem as variables (andnot as random messages) • These variables canbeincluded in reportswhichyou subject toyour analysis scripts later • ALWAYS SAVE AS MUCH OPENSESAME VARIABLE DATA AS POSSIBLE TO THE EDF FILE

18. EDF | Variable syntax !V TRIAL_VAR <variable_name> <variable_value>In OpenSesame, sendthiswithsend_command() in script exp.eyetracker.send_command("!V TRIAL_VAR RespTime 350") • Alternatively, youcanuse the pygaze_log item

19. Example experiment

20. Example Experiment | log variables Setting background image:!V IMGLOAD FILL <path/to/image>

21. Eyelink Data Viewer | Variables

22. Eyelink Data Viewer | Variables

23. Eyelink Data Viewer | Interest Periods • ExampleOpenSesame script forshowing stimuliself.fix_canvas.show()self.sleep(1000)exp.eyetracker.send_command("SHOWING target display")self.target_canvas.show() • Right before target display is shown, Eyelinkreceives the message"SHOWING target display"

24. Eyelink Data Viewer | Interest Periods

25. Eyelink Data Viewer | Interest Periods

26. Eyelink Data Viewer | Interest Periods Full trial period From Target presentation

27. Eyelink Data Viewer | Interest Areas • Just like variables, you can send commands during your experiment to define interest areas in your display area • It is also possible to draw these interest areas after all data has been collected (but this is much more work)

28. Eyelink Data Viewer | Interest Areas • Basic syntax !V IAREA <shape> <index> <left x> <top y> <right x> <bottom y> [label] • For a rectangle !V IAREA RECTANGLE 1 10 5 20 15 cue • For a circle !V IAREA ELLIPSE 2 300 200 400 300 target • For a custom shaped polygon !V IAREA FREEHAND <id> <x1, y1> <x2, y2 > ... <xn, yn> [label]

29. Eyelink Data Viewer | Interest Areas

31. Eyelink Data Viewer | Reports • EDV has options to export EDF data to other tabular formats as csv or Excel • You can create reports containing lists of • Saccades • Fixations • Interest areas • Samples • Trials

32. Eyelink Data Viewer | Reports

33. Eyelink Data Viewer | Reports

34. Reports | Analysis • You can use your favorite software to read in and start analyzing these report files • Excel, MatLab, R, SPSS, Pandas, etc. • For pandas raw_data = pd.read_csv("SaccadeReport.csv")

35. Analysis example try: raw_data except: raw_data= pd.read_csv("ExampleData.csv",sep=";") # Drop empty columns (don't know why these are there....) raw_data= raw_data.drop(raw_data.columns[-10:],axis=1) # Filter data to only contain real and correct trials work_data= raw_data.query("TRIAL_INDEX > 96 and correct==1") # Only get first saccades criteria = "CURRENT_SAC_INDEX == 1 and " criteria += "CURRENT_SAC_NEAREST_END_INTEREST_AREA_LABEL != '.'" first_saccades= work_data.query(criteria) # Create pivot table cols = ["onset","CURRENT_SAC_NEAREST_END_INTEREST_AREA_LABEL"] fs_pt= first_saccades.pivot_table("rt",index="cue", columns=cols, aggfunc="count") # Plot data (fs_pt/fs_pt.sum().sum()).plot(kind="bar")

36. Analysis example

37. # RT pivot table cols = ["onset","CURRENT_SAC_NEAREST_END_INTEREST_AREA_LABEL"] fs_pt= first_saccades.pivot_table("rt",index="cue", columns=cols,aggfunc="mean") fs_pt.plot(xlim=[-0.5,1.5],ylim=[650,1000],style="o-")