matlab - How to terminate a task based on time, regardless of trial number (Psychtoolbox) -

i need make timer starts counting @ beginning of multi-phase delay task, , ends delay task after period of time has passed, moving on next part of experiment. now, i'd end task after 2 seconds have passed.

in code below, included example can paste editor. used part of stroop task delay task consists of 1 phase (in actual code there 3 phases, simplified task question)-- press 1 key red, 2 key green, , 3 key blue. each phase runs 6 trials. (just 1 set of 6 trials 1 phase now).

i'd task (all phases together) last period of time, , terminate @ time set regardless of trial number. if 2 seconds have passed, task should end if on phase 1, trial number 3 of 6.

the code below commented out (while loop numsecondsstart , numsecondsend) current attempt. i'm not sure such loop go (around phase loop, around trial loop?) thanks!

code:

clear  close  kbname('unifykeynames');  %%%%%%%%%%%%%%%%%%%%%%%%%%%%  [window, rect]=screen('openwindow',0);  red=kbname('1'); green=kbname('2'); blue=kbname('3');      keysofinterest=zeros(1,256);     keysofinterest([red, green, blue])=1;     kbqueuecreate(-1, keysofinterest);     kbqueuestart;   wordcolors = {'red', 'green', 'blue'};  rgbcolors = [1000 0 0; 0 1000 0; 0 0 1000];  starttime=screen('flip',window);  kbqueueflush;  % numsecondsstart = getsecs;  % while (numsecondsend-numsecondsstart) == 1  phase = 1      design=repmat([1 2 3], 2, 2)';      if phase == 1          designrand=design(randperm(length(design)),:);          word=wordcolors(designrand(1:6));          color=rgbcolors(designrand(:,2),:);      end      trial=1:6          if phase == 1          drawformattedtext(window, word{trial},  'center'  ,'center', color(trial,:));           waitsecs(rand+.5)           starttime=screen('flip',window);           [pressed, firstpress]=kbqueuecheck;           endtime=kbqueuewait();            rttext=sprintf('response time =%1.2f secs',endtime-starttime);           drawformattedtext(window,rttext,'center'  ,'center',[255 0 255]);           vbl=screen('flip',window);           screen('flip',window,vbl+1);           numsecondsend =getsecs;          end     end end  %                 break;  % end  listenchar(0);   showcursor();  screen('closeall');  

i think tic , toc friends here...

i not use while in favour of following: (assuming iteration has started allowed finish)

add tic; want timing start, not inside loop or else reset timer each iteration.

add following within for loop, either @ beginning or end

if toc >= 2     break end 

this break out of for loop first time reaches , 2 seconds or more have passed