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Psychtoolbox: An introduction

Sheraz Khan, PhD TRANSCEND Research, TAL Kenet Group Fellow, MGH. Psychtoolbox: An introduction. OUTLINE. Introduction to Psychtoolbox. Psychtoolbox by Simple Examples Psychtoolbox in practice at Martinos center. Introduction to Psychtoolbox.

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Psychtoolbox: An introduction

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  1. Sheraz Khan, PhD TRANSCEND Research, TAL Kenet Group Fellow, MGH Psychtoolbox: An introduction

  2. OUTLINE • Introduction to Psychtoolbox. • Psychtoolbox by Simple Examples • Psychtoolbox in practice at Martinos center.

  3. Introduction to Psychtoolbox • PsychToolbox is a collection of matlab functions written to make presenting visual stimuli easier. Remember to cite the Toolbox. "We wrote our experiments in MATLAB, using the Psychophysics Toolbox extensions (Brainard, 1997; Pelli, 1997)." • Psychtoolbox is widely used in visual psychophysics and there is a lot of documentation and knowledge around. http://psychtoolbox.org • MAC and Windows version available, MAC version has better control over hardware.

  4. Introduction to PsychToolbox • Installation • >> cd ~/Desktop • >> DownloadPsychtoolbox('current') • To get help • >>Screen OpenWindow? • >>Screen DrawText? • If screen freezes • ctrl-c % will stop execution • clear Screen % garbage collector of Screen • Cmd + option +escape % Ultimate

  5. Why use PsychToolbox ? • PsychToolbox is very strict about timing, so if accurate timing is important in your experiment PsychToolbox is good for that. • Because PsychToolbox using graphics acceleration you can use very fast drawing without any pixelation and other image processing artefacts • Lots of people in the world use it so it's easy to get help, and more importantly its FREE.

  6. Programming simple Stimuli • % Testing PsychToolbox • >> ScreenTest ***** ScreenTest: Testing Screen 0 ***** PTB-INFO: This is the OpenGL-Psychtoolbox version 3.0.8. Type 'PsychtoolboxVersion' for more detailed version information. PTB-INFO: Psychtoolbox is licensed to you under terms of the GNU General Public License (GPL). See file 'License.txt' in the PTB-INFO: Psychtoolbox root folder for a copy of the GPL license. PTB-INFO: OpenGL-Renderer is NVIDIA Corporation :: GeForce Go 7400/PCI/SSE2 :: 2.0.1 PTB-Info: VBL startline = 768 , VBL Endline = -1 TB-Info: Measured monitor refresh interval from VBLsync = 16.712593 ms [59.835118 Hz]. (50 valid samples taken, stddev=0.044112 ms.) PTB-Info: Reported monitor refresh interval from operating system = 16.666667 ms [60.000000 Hz]. PTB-Info: Small deviations between reported values are normal and no reason to worry. PTB-INFO: Using NVidia's GL_TEXTURE_RECTANGLE_NV extension for efficient high-performance texture mapping... ***** ScreenTest: Done With Screen 0 *****

  7. Programming simple Stimuli • % Initializing the program • >>screenNum=1; % Screen 0 is Laptop, Screen 1 will be projector • >>flipSpd=13; % a flip every 13 frames • % Opening Window on Screen, we want to used • >>[wPtr,rect]=Screen('OpenWindow',screenNum); • % wPtr pointer to the screen. • % Getting Screen refresh rate • >>monitorFlipInterval=Screen('GetFlipInterval', wPtr); • % 1/ monitorFlipInterval is the frame rate of the projector ***** ScreenTest: Testing Screen 0 ***** PTB-INFO: This is the OpenGL-Psychtoolbox version 3.0.8. Type 'PsychtoolboxVersion' for more detailed version information. PTB-INFO: Psychtoolbox is licensed to you under terms of the GNU General Public License (GPL). See file 'License.txt' in the PTB-INFO: Psychtoolbox root folder for a copy of the GPL license. PTB-INFO: OpenGL-Renderer is NVIDIA Corporation :: GeForce Go 7400/PCI/SSE2 :: 2.0.1 PTB-Info: VBL startline = 768 , VBL Endline = -1 TB-Info: Measured monitor refresh interval from VBLsync = 16.712593 ms [59.835118 Hz]. (50 valid samples taken, stddev=0.044112 ms.) PTB-Info: Reported monitor refresh interval from operating system = 16.666667 ms [60.000000 Hz]. PTB-Info: Small deviations between reported values are normal and no reason to worry. PTB-INFO: Using NVidia's GL_TEXTURE_RECTANGLE_NV extension for efficient high-performance texture mapping... ***** ScreenTest: Done With Screen 0 *****

  8. Programming Simple Stimuli • % Finding Black and white • >>black=BlackIndex(wPtr); • >>white=WhiteIndex(wPtr); • % Filling the screen with Black and wait • >>Screen('FillRect',wPtr,black); • >>Screen(wPtr, 'Flip'); • >>WaitSecs(2);

  9. Programming Simple Stimuli • % make a rectangle in the middle of the screen flip colors and size • % Fill the screen with Black • >>Screen('FillRect',wPtr,black); • >>vbl=Screen(wPtr, 'Flip'); % collect the time for the first flip with vbl • % Make a rectangle in the middle of the screen flip colors and size • for i=1:10 • Screen('FillRect',wPtr,[0 0 255], [100 150 200 250]); • vbl=Screen(wPtr, 'Flip', vbl+(flipSpd*monitorFlipInterval)); • % flip 13 frames after vbl • Screen('FillRect',wPtr,[255 0 0], [100 150 400 450]); • vbl=Screen(wPtr, 'Flip', vbl+(flipSpd*monitorFlipInterval)); • End • % Color; Left, Right, Top, Bottom

  10. Programming Simple Stimuli • % Fill the screen with Black • >>Screen('FillRect',wPtr,black); • >>vbl=Screen(wPtr, 'Flip'); • % Make circles flip colors & size • for i=1:10 • Screen('FillOval',wPtr,[0 180 255], [ 500 500 600 600]); • vbl=Screen(wPtr, 'Flip', vbl+(flipSpd*monitorFlipInterval)); • Screen('FillOval',wPtr,[0 255 0], [ 400 400 900 700]); • vbl=Screen(wPtr, 'Flip', vbl+(flipSpd*monitorFlipInterval)); • end • % Color; Starting Horizontal, Starting Vertical; Ending Horizontal, Ending Vertical

  11. Programming Simple Stimuli • % Fill the screen with Black • >>Screen('FillRect',wPtr,black); • >>vbl=Screen(wPtr, 'Flip'); • % make lines that flip colors size & position • >>for i=1:10 • Screen('DrawLine',wPtr,[0 255 255], 500, 200, 700 ,600, 5); • vbl=Screen(wPtr, 'Flip', vbl+(flipSpd*monitorFlipInterval)); • Screen('DrawLine',wPtr,[255 255 0], 100, 600, 600 ,100, 5); • vbl=Screen(wPtr, 'Flip', vbl+(flipSpd*monitorFlipInterval)); • >>end • % Color; Starting Horizontal, Starting Vertical; Ending Horizontal, Ending Vertical

  12. Programming Simple Stimuli • % Fill the screen with Black • >>Screen('FillRect',wPtr,black); • >>vbl=Screen(wPtr, 'Flip'); • % Texture is the great way of storing Images • >>image2D=255*rand(100, 100); • >>textureIndex=Screen('MakeTexture', wPtr, image2D); • >>Screen('DrawTexture', wPtr, textureIndex); • >>Screen(wPtr, 'Flip'); • >>WaitSecs(2);

  13. Programming Simple Stimuli • % Fill the screen with Black • >>Screen('FillRect',wPtr,black); • >>vbl=Screen(wPtr, 'Flip'); • % Initialize the Keyboard input • >>KbName('UnifyKeyNames'); % Unify Max OS X, OS 9 • >>[sec keyCode]=KbPressWait; % wait for the key press • >>keyCode=find(keyCode~=0); • % Drawing Test • >>Screen('TextSize', wPtr , 150);% font size • >>Screen('DrawText', wPtr, num2str(keyCode), 200, 20, [255 50 255]); • >>vbl=Screen(wPtr, 'Flip'); % Starting Horizontal vertical position • >>WaitSecs(2);

  14. Programming Simple Stimuli • % Fill the screen with Black • >>Screen('FillRect',wPtr,black); • >>vbl=Screen(wPtr, 'Flip'); • % Combining the stimuli • >>for i=1:10 • Screen('FillRect',wPtr,[0 0 255], [100 150 200 250]); • Screen('DrawLine',wPtr,[0 255 255], 500, 200, 700 ,600, 5); • Screen('FillOval',wPtr,[0 180 255], [ 500 500 600 600]); • Screen('TextSize', wPtr , 150); • Screen('DrawText', wPtr, 'FUNKY!!', 200, 20, [255 50 255]); • vbl=Screen(wPtr, 'Flip', vbl+(flipSpd*monitorFlipInterval)); • >>end

  15. Programming Real Stimuli Local Connectivity in the visual cortex: From Polat and Norcia (Polat and Norcia, 1996), who discovered the paradigm (Polat and Sagi, 1993), and were the first to investigate it using VEPs. They showed that responses to b and d deviated from the linear sum of responses to (a+c) and (e+c) respectively, the difference being attributable to local connectivity.

  16. Programming Real Stimuli Specifications: Size of the objects: Size of the Gabors, visual separation between them Distance from the Screen Size of the Screen L, 55 cm D, 120 cm H, 41 cm

  17. Programming Real Stimuli • Normally in visual stimuli things are described in visual angle, so what it is ? Size is 1 degree, separation is 3 degrees Width=tand(1)*D, Width in screen percent=(Size/L)*100 Separation=tand(3)*D, Separation in screen percent=(Separation)/H*100

  18. Programming Real Stimuli • % Setting Parameters • >> nTrials = 40; • >>soa = 1.5; % Stimulus-Onset Asynchrony (SOA) • >>displayTime = 0.3; jitter = 0.1; • >>WidthOfGrid=4.88; Separation=20.25; • >>gratingMatrix=Gabors; • % Location of three gabors • >>L1=[50 50]; L2=[50 50-Separation]; L3=[50 50+Separation]; • % Configuring triggers • >>di = DaqDeviceIndex; • >>DaqDConfigPort(di,0,0); • >>DaqDOut(di,0,0);

  19. Programming Real Stimuli • % Setting Screen • >>whichScreen = max(Screen('Screens')); • >>rect=Screen(whichScreen,'Rect'); % Gets Screen dimensions • >>HideCursor; • >>window = Screen('OpenWindow', whichScreen); • % Color Setup • % Retrieves color codes for black and white and gray. • >>black = BlackIndex(window); • >>white = WhiteIndex(window); • >>gray = (black + white) / 2; % Computes the color code for gray.

  20. Programming Real Stimuli • % Giving Instruction to Subject • Screen('FillRect',window,gray); • Screen(window,'TextSize',txtSz); • Screen(window,'DrawText','Remember to keep your eyes',rect(3)/4,rect(4)/2-50); • Screen(window,'DrawText','on the + at the center',rect(3)/3.3,rect(4)/2); • Screen('Flip',window); • % Click to proceed • GetClick; • % Putting Cross in the center • Screen('FillRect',window,gray); • Screen(window,'TextFont',centerFont); • Screen(window,'TextSize',centerTxtSz); • Screen(window,'DrawText',centerChar,rect(3)/2,rect(4)/2,centerColour); • Screen('Flip',window);

  21. Programming Real Stimuli • [sourceRect targetRect]=rectGeneration(location,WidthOfGrid,rect) • % Decoding percent to actual screen • WidthOfGrid=round(max(rect)*WidthOfGrid/100); • halfWidthOfTgt=WidthOfGrid/2; • % sourceRect:: image area • sourceRect = [1 1 widthOfGrid widthOfGrid]; • % targetRect :: Actual Screen place and size • locationl = round(rect(3)*location(1)/100 - halfWidthOfTgt); • locationt = round(rect(4)*location(2)/100 - halfWidthOfTgt); • locationr = round(rect(3)*location(1)/100 + halfWidthOfTgt); • locationb = round(rect(4)*location(2)/100 + halfWidthOfTgt); • targetRect = [locationl locationt locationr locationb];

  22. Programming Real Stimuli • % Putting Three gabors on the Screen • [sourceRect targetRect]=rectGeneration(L1,WidthOfGrid,rect); • tex = Screen('MakeTexture',window,ceil((gray+gratingMatrix))); • Screen('DrawTextures', window, tex,sourceRect,targetRect); • [sourceRect targetRect]=rectGeneration(L2,WidthOfGrid,rect); • texu = Screen('MakeTexture',window,ceil((gray+gratingMatrix))); • Screen('DrawTextures', window, texu,sourceRect,targetRect,90); • [sourceRect targetRect]=rectGeneration(L3,WidthOfGrid,rect); • texd = Screen('MakeTexture',window,ceil((gray+gratingMatrix))); • Screen('DrawTextures', window, texd,sourceRect,targetRect,90); • Screen('Flip', window);

  23. Programming Real Stimuli • % Sending triggers • DaqDOut(di,0,4); %send trigger • DaqDOut(di,0,0); %clear trig

  24. Conclusion • All the source code for this talk is available on why n how wiki. • Best way to learn Pschytoolbox is to use it on the projector. • Always test the timing of your protocol. • Photo diode and oscilloscope is available in MEG.

  25. Thank you.

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