How do I set a certain duration for a stimuli presentation?

I have a small white spot presented on a grey background. I would like to have the spot stimuli on for 2 secs and then switch to only the grey background for 5 secs. I need help in setting the duration for each stimuli presentation. Also, I need the timing to be as accurate as possible.

[Chris McComb]

Are you after something like this?

   % Number of stimuli
   n = 5;  

   for i=1:1:n
     % Plot the spot
     h = plot(x_spot, y_spot);

     % Pause for 2 seconds
     pause(2);

     % Delete the spot
     delete(h);

     % Wait for 5 seconds
     pause(5);
   end

Answer 1

[Jos (10584)]

I suggest you do not use delete and pause. Here is an alternative

    x = [1 2 6 8 3] ;
    y = [7 1 3 9 6] ;

    stimtime = 1 ; % time to show a spot
    waittime = 2 ; % time to wait between spots

    % create a plot

    clf ; % clear current figure
    h = plot(NaN,NaN,'bo','markerfacecolor','r') ;
    set(gca,'xlim',[0 10],'ylim',[0 10]) ;

    for k=1:numel(x),
       set(h,'xdata',x(k),'ydata',y(k),'visible','on') ;
       drawnow ;
       tic ;

       while toc < stimtime, end

       set(h,'visible','off') ;
       drawnow ;
       while toc < stimtime+waittime, end

    end

[Kathryn Fransen]

Thank you for your answer. I see how tic and toc work for the example you presented, however, I am having a hard time getting it to work with my stimuli code. I have attached the stimuli code (I use the psychophysics toolbox, so I am not sure if this function will work without the toolbox?). I need to add a timing element to this code allowing for the spot image to be presented for 2 seconds, and then I will add in code for a blank grey background for 5 seconds. I then would like to make this loop 5 times. Do you have any suggestions on how I can use tic and toc with the stimuli I am working with? I have tried many things, but can't get anything to work.

[Jos (10584)]

I suggest you take a look at the help of the toolbox, and perhaps ask your question over there. This seems to be a very basic problem more related to psychophysics than to matlab itself.

http://psychtoolbox.org/forum/