Matlab: Criteria for displaying screens to subjects

Question

I am delivering a psychology experiment in Matlab, where screens with questions will be presented to subject. The screen will also collect and display the subjects' responses. For example: Screen displays '2+3' and also displays what participant types (say, 99999), until they press enter.

GOAL: get it to stop displaying the question after 16 seconds if the participant has not yet pressed enter. (That is, stop displaying the screen if time=16sec OR if subject presses Enter.)

The problem revolves around the following code:

    While CurrentTime<TimeOut

    respond=GetChar() <-(Waits till user press enter)

    end

So whatever the statements we add before/after capturing respond statements is not executed.

Any help on how to work around this issue would be greatly appreciated! Thanks.

Answer 1

Here is an example, I presented an oval as an example, you can obviously replace that with whatever your stimuli are. Enter and Return are separate keys, I wasn't sure which you're looking for, so in the example the loop looks for either.

%% include at top of experiment / block
waitForResponseSeconds = 16; % number of second to wait for a response
enterKey = KbName('enter'); % numeric code for enter key
returnKeys = KbName('return'); % numeric code for return key(s)
responseKeys = [enterKey returnKeys];

wPtr = Screen('OpenWindow', 0, 0, [0 0 400 400]);


%% within the trial loop:
hasResponded = 0;

% present the stimulus (here the window pointer is called wPtr, you may
% need to adjust this depending on what you named the window pointer.
Screen('FillOval', wPtr, [100 0 100], [0 0 400 400]);

[~, Onset] = Screen('Flip', wPtr);


while ~hasResponded && ((GetSecs - Onset) <= waitForResponseSeconds) 

    [keyIsDown, secs, keyCode] = KbCheck;

    if any(keyCode(responseKeys))
        rt = 1000.*(secs-Onset); % get response time
        hasResponded = 1;
    end

    % Wait 1 ms before checking  again to prevent
    % overload of the machine at elevated priority
    WaitSecs(0.001);
end

%% end of exp
sca;