如何在有限的时间内呈现刺激，并仍然使用Psychtoolbox记录反应

Question

对于我的实验，我想向参与者展示一个刺激和一些说明。然后 2 秒后，我希望刺激消失，但指令保留，直到参与者做出反应。参与者应该能够在提出刺激后立即做出反应，并在提出刺激后最多 10 秒做出反应。将记录响应时间。

使用我当前的代码，参与者直到 2 秒后(刺激消失后(才能做出响应。当指令保留在屏幕上时，刺激是否只出现 2 秒钟，但参与者能够在展示刺激后立即做出反应？

%Show the instructions and the stimulus   
Screen('DrawTexture', window, randFaceTexture2);
DrawFormattedText(window, [instructions1], 'center', 600)
stimTime = Screen('Flip', window);
WaitSecs(2);
%Stimulus disappears but instructions remain 
DrawFormattedText(window, [instructions1], 'center', 600)
Screen('Flip', window);
if GetSecs() <= stimTime + 10
keyIsDown = 0;
startTime = GetSecs();
while 1
[keyIsDown, secs, keyCode] = KbCheck;
FlushEvents('keyDown');
if keyIsDown
nKeys = sum(keyCode);
if nKeys == 1
if keyCode(yes) || keyCode(no)
reactionTime = 1000*(GetSecs - startTime);
response = KbName(keyCode);
Screen('Flip', window);
break;
elseif keyCode(escKey)
ShowCursor;
fclose(outfile);
Screen('CloseAll');
return 
end 
keyIsDown = 0;
keyCode = 0;
end 
end 
end 
else 
line3 = 'Sorry you''re out of time';
DrawFormattedText(window, line3, 'center', 'center');
Screen('Flip', window);
keyIsDown = 0;
rt = 0;
end

Answer 1

不要使用WaitSecs()来控制刺激在屏幕上的时间量，而是在经过适当的时间量后在响应检查循环中关闭刺激。下面是一个片段，显示了对上述代码的相关更改。我省略了您如何轮询响应的详细信息。顺便说一句，我认为您使用"if GetSecs(( <= stimTime + 10"可能无法实现您想要的，在您的代码中，此语句只会被计算一次并且永远是正确的。

% time in seconds for the stimulus to remain onscreen
timeForStimulus = 2;
% time for the participant to respond, in seconds
timeToRespond = 10;
%Show the instructions and the stimulus
Screen('DrawTexture', window, randFaceTexture2);
DrawFormattedText(window, [instructions1], 'center', 600)
stimTime = Screen('Flip', window);
stimOnScreen = 1;
while GetSecs() <= (stimTime + timeToRespond)
% turn the stimulus off, if the stim is on and the stim time has elapsed
if (stimOnScreen == 1) && (GetSecs() > (stimTime + timeForStimulus))
%Stimulus disappears but instructions remain
DrawFormattedText(window, [instructions1], 'center', 600)
Screen('Flip', window);
stimOnScreen = 0;
end
% poll for keyboard response, etc.
end