# OSX: Beginner Question: problem w/ Screen, Flip

**URL:** https://psychtoolbox.discourse.group/t/osx-beginner-question-problem-w-screen-flip/689
**Category:** Uncategorized
**Created:** [March 22, 2005, 10:50pm UTC](https://psychtoolbox.discourse.group/t/osx-beginner-question-problem-w-screen-flip/689 "2005-03-22T22:50:34Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![Allen\_Ingling](https://avatars.discourse-cdn.com/v4/letter/a/a183cd/32.png) [@Allen\_Ingling](https://psychtoolbox.discourse.group/u/Allen_Ingling)
#### Post date: [March 22, 2005, 10:50pm UTC](https://psychtoolbox.discourse.group/t/osx-beginner-question-problem-w-screen-flip/689/1 "2005-03-22T22:50:34Z")

</div>

Hi all,  
I am new to Matlab and Psychtoolbox, though I do have experience programming. I am   
trying to learn Matlab & PTB in order to run some pretty straightforward memory   
experiments using paired associates. For example, presenting "Arch = Sandal" and then   
later showing "Arch = ???" and requiring the participant to respond with an answer.   
  
I'm working under Mac OS X.  
  
Right now I'm just trying to figure out how displaying things works. The whole Screen   
system is foreign to me, and I've been unable to gain an understanding of it through the   
help functions or through anything I've found online. Here's a specific problem I'm having:  
  
I'm working with the basic "Hello World" demo provided with PTB, and have added a short   
matrix of word pairs which are displayed in a for loop. Everything looks fine, until I hit a   
key after the 'Hit any key to exit.' appears. Then, the last word pair that was shown ("arch   
= sandal") is shown again briefly, apparently while the window is being closed, or   
something. I'll paste my code below.   
  
I think this might have something to do with Screen('Flip'). I'm not clear on what   
exactly that function does or why, but I know that it's somehow necessary. Thanks very   
much for any assistance,  
Jason  
  
  
wordpairs = {...   
'comment' 'hint';...  
'cluster' 'necklace';...  
'kiln' 'hammer';...  
'custom' 'tomb';...  
'rim' 'granite';...   
'arch' 'sandal'}  
  
try  
 screens=Screen('Screens');  
 screenNumber=max(screens);   
 w=Screen('OpenWindow', screenNumber,0,[],32,2);  
 Screen('FillRect', w, [0, 0, 0, 255]);  
 Screen('TextFont',w, 'Courier');  
 Screen('TextSize',w, 50);  
 Screen('TextStyle', w, 0);  
  
 for loopCond = 1:size(wordpairs,1)  
 Screen('DrawText', w, [wordpairs{loopCond,1} ' = ' wordpairs{loopCond,2}], 100, 100,   
[0, 0, 255, 255]);  
 Screen('Flip',w);   
 WaitSecs(1);   
 end  
  
 Screen('DrawText', w, 'Hello World!', 100, 100, [0, 0, 255, 255]);  
 Screen('TextFont',w, 'Times');  
 Screen('TextSize',w, 30);  
 Screen('DrawText', w, 'Hit any key to exit.', 100, 300, [255, 0, 0, 255]);  
 Screen('Flip',w);  
 KbWait;  
 Screen('CloseAll');  
catch  
 Screen('CloseAll');  
 rethrow(lasterror);  
end