MATLAB Programming/Psychtoolbox/Example Code

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Examples

• Imageviewer - show an image on the screen (OSX)
• OpenManyScreens - open a window on all connected displays (OSX)
• xsearch - generic visual search code (OS9/WIN)
• ImgShow - loads a series of images from disk and displays them for the period of time specified, in random order (OS9/WIN)
• eyelink toolbox - use an sr-research eyelink video eyetracker together with the cross-platform opengl psychtoolbox (OSX/win)

Helpful scripts

• MATLAB Programming/Psychtoolbox/Version independent scripts - Scripts to allow you to write programs that run on all versions of psychtoolbox.

Code Snippets

• Function that takes a list of desired keys and returns the number of the one that was pressed and is nearer to the front of the list that was passed. It ignores other keypresses.

 function keyPressed = getKeys(keysWanted) % keysWanted is a matrix list of keys you are 
                                           % waiting for e.g, [124 125 kbName('space')]
  FlushEvents('keydown');
  success = 0;
  while success == 0
   pressed = 0;
   while pressed == 0
    [pressed, secs, kbData] = KbCheck;
   end;
    for i = 1:length(keysWanted)
      if kbData(keysWanted(i)) == 1
       success = 1;
       keyPressed = keysWanted(i);
       FlushEvents('keydown');
       break;
      end;
    end;
    FlushEvents('keydown');
   end;

• Wait for a key press, continue after two seconds

  tEnd=GetSecs+2;
  while ~KbCheck & GetSecs<tEnd
    % Sleep one millisecond after each check, so we don't
    % overload the system in Rush or Priority > 0
    WaitSecs(0.001);
  end

• Bring command window to front. Even though it won't come in front of a window opened by Screen, it is useful to include this, as it allows you to type e.g. Screen('Closeall') to close the window of a crashed program

commandwindow;

• Issue: KbCheck doesn't appear to wait for key presses, exits loop earlier then expected, continues to return key presses. Solution: make sure you first wait for any keys to be released. For example:

commandwindow;
touch=1;
while touch==1
    [touch, secs, keycode] = KbCheck;
    % Sleep one millisecond after each check, so we don't
    % overload the system in Rush or Priority > 0
    WaitSecs(0.001);
end
touch = 0;
i=0;
while ~touch
 % Sleep one millisecond after each check, so we don't
 % overload the system in Rush or Priority > 0
 WaitSecs(0.001);
 [touch, secs, keycode] = KbCheck;
 fprintf('.');
 if i==50
  fprintf('\n');
  i=0;
 end
 i=i+1;
end
clc; % clear command window, removing any typed characters
fprintf('\ntouch down\n\n');