how to get psychtoolbox to wait for keypress but move on if it hasn't recieved one in a set time

Question

kwn500 2016-11-2

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/310311-how-to-get-psychtoolbox-to-wait-for-keypress-but-move-on-if-it-hasn-t-recieved-one-in-a-set-time

编辑： Edan Daniel 2023-5-18

i'm trying to code an experiment, where a participant must make an orientation judgement (more clockwise or more anticlockwise with the keyboard). i want to code it so that if they don't make a response within, say 2 seconds the code continues.

i have tried things like while WaitSecs(2) < 2; [secs, keyCode, deltaSecs] = KbWait(); end

But this doesn't save the variables for use outside of the while loop. Thanks in advance!

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Mihaela Duta 2016-11-5

3
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/310311-how-to-get-psychtoolbox-to-wait-for-keypress-but-move-on-if-it-hasn-t-recieved-one-in-a-set-time#answer_242085

编辑：Mihaela Duta 2016-11-5

在 MATLAB Online 中打开

There are some missing details in the specification given in the question, so I am going to make the following assumptions:

Item one only one key-press is expected - let's say a press on the left or right arrow key
Item two immediately after the response is given the waiting for response stops - the time taken to make the response is the reaction time

The follwing code should implement your requirements according to the above assumptions

% improve portability of your code acorss operating systems 
KbName('UnifyKeyNames');
% specify key names of interest in the study
activeKeys = [KbName('LeftArrow') KbName('RightArrow')];
% set value for maximum time to wait for response (in seconds)
t2wait = 2; 
% if the wait for presses is in a loop, 
% then the following two commands should come before the loop starts
% restrict the keys for keyboard input to the keys we want
RestrictKeysForKbCheck(activeKeys);
% suppress echo to the command line for keypresses
ListenChar(2);
% get the time stamp at the start of waiting for key input 
% so we can evaluate timeout and reaction time
% tStart can also be the timestamp for the onset of the stimuli, 
% for example the VBLTimestamp returned by the 'Flip'
tStart = GetSecs;
% repeat until a valid key is pressed or we time out
timedout = false;
% initialise fields for rsp variable 
% that would contain details about the response if given
rsp.RT = NaN; rsp.keyCode = []; rsp.keyName = [];
while ~timedout,
    % check if a key is pressed
    % only keys specified in activeKeys are considered valid
    [ keyIsDown, keyTime, keyCode ] = KbCheck; 
      if(keyIsDown), break; end
      if( (keyTime - tStart) > t2wait), timedout = true; end
  end
  % store code for key pressed and reaction time
  if(~timedout)
      rsp.RT      = keyTime - tStart;
      rsp.keyCode = keyCode;
      rsp.keyName = KbName(rsp.keyCode);
  end
% if the wait for presses is in a loop, 
% then the following two commands should come after the loop finishes
% reset the keyboard input checking for all keys
RestrictKeysForKbCheck;
% re-enable echo to the command line for key presses
% if code crashes before reaching this point 
% CTRL-C will reenable keyboard input
ListenChar(1)

6 个评论
显示 4更早的评论隐藏 4更早的评论

Barbara Fiorani 2020-10-29

What rsp.RT = NaN; stand for?

Edan Daniel 2023-5-18

编辑：Edan Daniel 2023-5-18

It's the initialization of the reaction time field (RT) in the response (rsp) structure. That is, setting that until a reaction time is recorded, rsp.RT equals nothing (NaN). If a key press is detected, this field should be updated as follows (as seen a few lines below the line in question in Mihaela's example)

rsp.RT = keyTime - tStart;

That is, replacing the NaN with the recorded reaction time: the difference between the start time, and the time of key press. If no key press is detected, this field will not be updated, and will keep holding a 'NaN' indicating no reaction time was recorded.

请先登录，再进行评论。