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.

Most probably you have problems with while condition. How did you define current time and timeout? — zlon, Feb 01 '18 at 00:07

score 2 · Accepted Answer · answered Feb 03 '18 at 16:45

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;

Matlab: Criteria for displaying screens to subjects

1 Answers1