"Next trial" button

Hello,

I have an experiment, the code of which is as follows:

function exWindowButtonMotionFcn

clc; % clear command window

figure; % open figure

files = dir(fullfile('pictures','*.png'));
index = randperm(length(files));
picture1 = files(index(1)).name;
picture2 = files(index(2)).name;
image1 = fullfile('pictures',picture1);
image2 = fullfile('pictures',picture2);
subplot(1,2,1); imshow(image1); title(picture1);
subplot(1,2,2); imshow(image2); title(picture2);

uicontrol('Style', 'text',...
        'Position', [200 45 200 20],...
        'String','How related are these pictures?');
uicontrol('Style', 'text',...
        'Position', [50 45 100 20],...
        'String','Unrelated');
uicontrol('Style', 'text',...
        'Position', [450 45 100 20],...
        'String','Closely related');
uicontrol('Style','pushbutton','String','Next Trial',...
        'Position', [250 350 100 20],...
        'Callback','next');

h = uicontrol(gcf,...
   'Style','slider',...
   'Min' ,0,'Max',50, ...
   'Position',[100 20 400 20], ...
   'Value', 25,...
   'SliderStep',[0.02 0.1], ...
   'BackgroundColor',[0.8,0.8,0.8]);

set(gcf, 'WindowButtonMotionFcn', @cb);

lastVal = get(h, 'Value'); 

function cb(s,e)
    if get(h, 'Value') ~= lastVal 
    lastVal = get(h, 'Value'); 
    fprintf('Slider value: %f\n', lastVal); 
    end
end

end

This function randomly displays two pictures from a directory on the screen, along with a scroll bar, and prompts for the user to indicate on the scroll bar the degree of relatedness/similarity between the two pictures. It works fine.

However, what I want to do is create a function 'next', which will be triggered by pressing the 'Next Trial' button. When you press the button, I want the experiment to be "reset" ... that is, two NEW random pictures will be shown, and the scrollbar reset to the middle. So each trial is a standalone, and you cycle through them by pressing the 'next trial' button.

How do I do this? I have searched for about half an hour and cannot find ANY indication of how to do this on Mathworks.