function ptb_path

ptb_root = 'C:\_Toolboxes\Psychtoolbox3.0.12\';

if ~any(which('Screen'))
    if exist(ptb_root,'dir')
        
        
        pp = genpath(ptb_root); addpath(pp);
        
        rmpath([ptb_root 'PsychBasic\MatlabWindowsFilesR2007a\']);
        rdir = [ptb_root 'PsychBasic\MatlabWindowsFilesR2007a\'];
        addpath(rdir);
    else
        try
            Screen('Windows')
        catch
            error('Psychtoolbox not found')
        end
    end
end