Update matrix inside KeyPressFcn

I'm trying to update a matrix with response times inside a function within KeyPressFcn in a figure. how can i do that?

my code (not working, 'responses' doesn't get updated):

hf=figure('Toolbar','none','Menubar','none','NumberTitle','off',...
    'Units','normalized','position',[0 0 1 1],'Color',[1 1 1]);

for trial = 2:trial_num
    tic
    set(hf, 'KeyPressFcn', ...
    @(fig_obj , eventDat) myFunction(fig_obj, eventDat, trial, same_or_not, yes_no,toc, responses));
    pause(0.05)
    axis off
    set(letter_text,'String',trial_letters(trial))
    pause(0.75)
    axis off
    set(letter_text,'String','')
    set(yes_no,'String','') 
end

function myFunction(~, eventDat, trial, same_or_not, yes_no, toc, responses) 
    key = eventDat.Key;
    if (key == 'space')
       responses(trial,1) = 1;
       responses(trial,4) = toc;
       if (same_or_not(trial) == 1) 
            set(yes_no,'String','yes') 
            set(yes_no,'Color',[0 1 0]) 
       else
            set(yes_no,'String','no') 
            set(yes_no,'Color',[1 0 0]) 
       end
    end
end

Thanks

[Stephen23]

As an aside, for callback functions it is often simpler to use the cell array syntax rather than defining an anonymous function:

set(hf, 'KeyPressFcn', {@myFunction, trial, same_or_not, yes_no,toc, responses});

The called function remains the same.

Answer 1

[Stephen23]

MATLAB is pass-by-value, so when you change responses inside the callback function it does get changed... but only inside that function workspace. But because you never save or allocate this value to anything then it is simply discarded when that callback finishes. I think this may be what you are referring to when you write "not working, 'responses' doesn't get updated".

If you want the changed responses array to be returned to the calling function's workspace then you need to specify this: you will need to use one of the methods specified in the MATLAB documentation for passing data between callback functions:

https://www.mathworks.com/help/matlab/creating_guis/share-data-among-callbacks.html

I would recommend that you use nested functions, which are simple, intuitive, and easy to debug. For your code it would also mean that you do not need to pass those arrays as input arguments:

function [...] = mainfun(...)
...
responses = [...];
...
for trial = ...
    ...
    set(hf, 'KeyPressFcn', {@myFunction, trial});
    ... 
end
...
    function myFunction(~, eventDat, trial)
        responses(trial,...) = ...
    end
...
end

When the callback is called it can access all of the variables in the main function's workspace. The only argument that you will need to pass explicitly is the loop iteration variable, as my code shows.

[jonathan fried]

Thank you! you r a great hero of our time