matlab for experimental research
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MATLAB for Experimental Research
Cont. PsychtoolboxDisplaying Images
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Screen (cont’d)
See examples on the site for Screen
ScreenIntro.mScreenBlackWhite.mFunScreen.m
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Displaying images in PTB: PutImage
% Read in image just like usual>> myimg = imread('sungod','jpg');
% Use PutImage function
Try >> Screen PutImage?
>> Screen('PutImage', w, myimg);>> Screen('Flip',w);
See: PutImageExample.m
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Displaying images in PTB: Texture
Preferred methodThe texture method is much faster and flexible compared to PutImage>> Screen MakeTexture?TextureIndex = Screen('MakeTexture', WindowIndex, imageMatrix, optional arguments…)
>> Screen DrawTexture?
See: TextureExample.m
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Textures% Read in image just like usualmyimg = imread(’sungod','jpg');
% make texture, nothing happens on screen.% this just prepares the image as texture on % offscreen window
mytex = Screen('MakeTexture', w, myimg);
Screen('DrawTexture', w, mytex); Screen('Flip',w);
Note where the image displays
See: TextureExample.m
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ImageAndTexture.m
Simple code that displays the same image with both methodsIf location is not specified, it will default to the center of the screen
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Textures, Screen, Window
What’s the difference between window, screen and texture?https://github.com/Psychtoolbox-3/Psychtoolbox-3/wiki/FAQ:-Textures,-Windows,-Screens
For more PTB notes, info, etc see file on the site called PTB_Notes.pdf (and also PTB_AdditionalNotes.pdf)
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Displaying in Specific Locations
� Let’s display an image on different locations on Screen.
� Download TextureTwoLocations.m and sungod.jpgfrom the class website and run the m file.
� Image is displayed first on the left and then on the right of the screen. And then both.
� Do you understand how we can specify where can display an image?
� Why do we see text and the images together only in the last part?
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Images at different locations on screen
� PutImage and DrawTexture both require a location for the image as an input argument.
� We need to calculate the coordinates of where we want to put your image (use your geometry knowledge).
� Start by calculating the coordinates of the center of the screen.
>> help RectCenter
� Then, calculate the coordinates of the image location relative to the center based on the image size
� Do you understand what is happening in lines 40-41 of TextureTwoLocations.m ?
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Moving stimuli� Movies can be made by changing the position of
the stimulus each frame
� Exercise: Draw a circle that moves randomly on screen without any of it crossing the top, bottom, left and right borders of the screen.
� How can you do that? Any ideas?
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RandomPath.m