How to display a number loop from one screen to another? (psychtoolbox, matlab)

Question

Hi I want to display on the screen using psychtoolbox matlab a number sequence (as a loop) changing from one screen to another screen as a DrawFormattedText. Is it possible?

This is part of the code I try

n_trials = 60; n=n_trials:-1:1;

function displayCue(w, cue, cueTime)
    Screen('FillRect', w, [0 0 0]);
    DrawFormattedText(w, cue, 'center', 'center',[255, 255, 255, 255]);
    Screen('Flip', w);
    WaitSecs(cueTime);
end

        % Display cue for 1 seconds
        displayCue(w, n, cueTime);

but I couldn't display the n on the screen, it's just black screen. Thank you!