how to code not responding as a correct answer?

For my experiment for certain stimuli I want participants to push the spacebar but for other stimuli I want participants to inhibit their responses. For this I want to be able to code that no keyboard response is correct or rather that a spacebar response to specific stimuli would be incorrect.

How would I go about this?

Answer 1

[David Fink]

If your application is in a figure, you can set a function that is called when a key is pressed. Then, since one of your responses is not to do anything, you will need to have a timer to determine when the next question should be displayed. You could use a global variable to store the user's response

Global variable in script/main function:

userResponse = 'nothing';

Whenever a key is pressed, call myFunction(key) (this code is written in script/main function):

fig = figure();
set(fig,'KeyPressFcn',@(fig,evt) myFunction(evt.Key));

In myFunction(key), you can check what key was pressed:

function myFunction(key)
  if strcmp(key,'space')
    userResponse = 'space';
  else
    userResponse = 'other key';
  end
end

Declare a timer in the script/main function

questions = ('Press Space', 'Do nothing', ...);
responses = ('space', 'nothing', ...);
q = 0;
tim = timer('BusyMode','drop', ...
            'ExecutionMode','fixedrate', ...
            'Period',timer_period, ...
            'TimerFcn',@myTimerFcn);
start(tim);

The timer function can check what the input was and advance the figure to the next question

function myTimerFcn(~,~)
  if q > 0
    if strcmp(responses(q),userResponse)
      disp('Correct!');
    else
      disp('Incorrect :(');
    end
  end

    % reset response
    userResponse = 'nothing';

    % go to next question
    q = q + 1;

    % Only keep going if there are more questions
    if q <= numel(questions)
      % display questions(q)
    else
      stop(tim);
      % terminate program
    end
  end