Matlab PTB not recognising labchart stimulated key presses

Hi all,

A labchart macro presses the i and e keys in the backrgound when certain thresholds are met. When no program is running, the command window picks up the i and e keys. However, when I run my PTB experiement, it can't find these key presses. If i manually press i and e, however, it works. Can someone advise on what's going on or how to solve this?

Section of script:

% please wait screen + countdown

function displayBlankScreenForDuration(params)

KbQueueCreate();

KbQueueStart();

Screen('FillRect', params.window, params.black);

totalTime = 60;

startTime = GetSecs();

endTime = startTime + totalTime;

inhaleTimes = [];

exhaleTimes = [];

breathingCycles = [];

while GetSecs < endTime

[pressed, firstPress] = KbQueueCheck();

if pressed

if firstPress(KbName('i'))

inhaleTime = firstPress(KbName('i'));

inhaleTimes(end+1) = inhaleTime;

disp('Inhale detected');

end

if firstPress(KbName('e'))

exhaleTime = firstPress(KbName('e'));

exhaleTimes(end+1) = exhaleTime;

disp('Exhale detected');

if ~isempty(inhaleTimes)

% Calc

breathingCycles(end+1) = exhaleTimes(end) - inhaleTimes(end);

end

end

end

remainingTime = round(endTime - GetSecs());

message = sprintf('Please wait - %d seconds remaining.', remainingTime);

Screen('FillRect', params.window, params.black);

Screen('TextSize', params.window, 40);

DrawFormattedText(params.window, message, 'center', 'center', params.white);

Screen('Flip', params.window);

WaitSecs(0.01);

end

Answer 1

[Manikanta Aditya]

Hey Danielle,

It seems that the issue you are facing is related to the interaction between your labchart macro and your PTB experiment. When the labchart macro is running, it sends key presses in the background, which are picked up by the command window. However, when your PTB experiment is running, it is unable to detect these key presses.

One possible solution is to modify your PTB script to directly listen for key presses using the 'KbCheck' function instead of using the 'KbQueue' function. Here's an example of how you can modify your script:

% please wait screen + countdown
function displayBlankScreenForDuration(params)

    KbQueueRelease(); % Release the KbQueue if it was created previously

    Screen('FillRect', params.window, params.black);
    totalTime = 60; 
    startTime = GetSecs();
    endTime = startTime + totalTime;

    inhaleTimes = []; 
    exhaleTimes = [];
    breathingCycles = [];

    while GetSecs < endTime
        [keyIsDown, secs, keyCode] = KbCheck();
        if keyIsDown
            if keyCode(KbName('i'))  
                inhaleTime = secs;
                inhaleTimes(end+1) = inhaleTime;
                disp('Inhale detected');
            end
            if keyCode(KbName('e')) 
                exhaleTime = secs;
                exhaleTimes(end+1) = exhaleTime;
                disp('Exhale detected');
                if ~isempty(inhaleTimes)
                    % Calc
                    breathingCycles(end+1) = exhaleTimes(end) - inhaleTimes(end);
                end
            end
        end

        remainingTime = round(endTime - GetSecs());
        message = sprintf('Please wait - %d seconds remaining.', remainingTime);

        Screen('FillRect', params.window, params.black);
        Screen('TextSize', params.window, 40);
        DrawFormattedText(params.window, message, 'center', 'center', params.white);
        Screen('Flip', params.window);

        WaitSecs(0.01); 
    end
end

I hope this helps!