multiple KbChecks in one loop

Hi,

I'm trying to collect multiple button presses per trial with KbCheck. The experimental task will be for a subject to press sequences of 6-10 numbers as fast as possible.

Here's how I think it should work, but it doesn't. For some reason, only the first button that's being pressed is collected 6x in the answer vector. It seems like the button somehow gets 'stuck', so that in the next iteration it appears to be down still.

answer = [0,0,0,0,0,0];
accepted_keys = [KbName('1!'), KbName('2@'), KbName('3#'), KbName('4$')];

responded = 0;
 
while responded == 0 
    [keyIsDown,secs, keyCode, deltaSecs] = KbCheck;
    for cc = 1:length(answer)
        if any(keyCode(accepted_keys))
              answer(cc) = find(keyCode)
              responded = 1; 
        end
        WaitSecs(0.001)
    end 
    
end 

In another attempt, I tried to collect button presses as character strings, which does the trick of collecting several button presses after another, but now it's too slow to register very fast button presses (which I suppose is due to the rather low efficiency of my loop structure).

key_answer = ['']
key = 0;

while length(key_answer) < 6
    [KeyIsDown, secs, KeyCode] = KbCheck;
    
    if KeyIsDown==1 & key==0 
        key=find(KeyCode)
    end   

    if KeyIsDown==0 & key~=0 
        temp = KbName(key) 
        key_answer(end+1)=temp(1)
        key=0
    end

end

Does anyone have an idea how to fix it either one of them? Any help is appreciated!

[prabhat kumar sharma]

Hi Annemarie,

I understand that initial approach with KbCheck has the right idea but needs some adjustments to accurately capture multiple button presses without getting "stuck" on the first detected key.

1.Refinement for Collecting Button Presses

answer = zeros(1,6); % Initialize answer vector
accepted_keys = [KbName('1!'), KbName('2@'), KbName('3#'), KbName('4$')];
count = 1; % To keep track of the number of accepted key presses

while count <= length(answer)
    [keyIsDown, ~, keyCode] = KbCheck;
    if keyIsDown
        pressedKeys = find(keyCode);
        % Check if any of the pressed keys are in the accepted keys
        for i = 1:length(pressedKeys)
            if any(pressedKeys(i) == accepted_keys)
                answer(count) = pressedKeys(i);
                count = count + 1;
                break; % Break after registering an accepted key
            end
        end
        % Wait until all keys are released
        while KbCheck; end
    end
end

2.Refinement for Collecting Button Presses as Strings

key_answer = ''; % Initialize as an empty string
while length(key_answer) < 6
    [keyIsDown, ~, keyCode] = KbCheck;
    if keyIsDown
        key = find(keyCode);
        % Assuming 'key' will only contain one element for simplicity
        if ~isempty(key)
            temp = KbName(key);
            key_answer(end+1) = temp(1); % Append the character to the string
            % Wait until all keys are released
            while KbCheck; end
        end
    end
end

I hope it helps!