How do I change this so that it will record responses?

Note: this is using Psychtoolbox

I'm trying to run an oddball task, where the participant has to press the spacebar when they see a square (10% of trials) and make no response when they see a circle (90% of trials). Currently this script is not collecting any keyboard responses. I suspect that this is due to the line:

while GetSecs() <=targettime(trialcount) + (stimdur = fixdur)

but I don't know how to change it to make it work.

The next part of the script is trying to make it so that if no response is made within a certain time, the fixation cross appears and then move onto the next trial.

                    if conditionsrand(trialcount) == 1
                        Screen('DrawTexture', window, Square, [], [], 0);
                    elseif conditionsrand(trialcount) == 2
                        Screen('DrawTexture', window, Circle, [], [], 0);
                    end

                    Screen('Flip', window);

                    targettime(trialcount) = GetSecs; % time of stimulus onset

    while GetSecs ()<= targettime(trialcount) + (stimdur + fixdur)
                          [keyIsDown, seconds, keyCode] = KbCheck();
                          if keyIsDown
                              responseKey = KbName(find(keyCode));
                              responsetime(trialcount) = seconds;
                              buttonpressed(trialcount) = 1;
                              if keyCode(KbName('ESCAPE')) == 1
                                  break
                              end
                          end

                          if GetSecs() + stimdur >= targettime(trialcount) % stimulus has been up for as long as it should be, so we erase it
                              DrawFormattedText(window, fix, 'center', 'center', textcolor);
                              Screen('Flip', window);
                              WaitSecs(fixdur);
                          end
                      end