Dual N-Back Brain Training Game
            
            Based on the task originally proposed by [1], and adapted by
            [2]. Dual N-Back has been shown to improve working memory over time.
            For more information see [3] and [4].
            
            Instructions
            
            The goal of each level is to remember the state of the game exactly N timesteps ago.
            
            
            The game board is a set of eight squares.
            They will flash in a random order, at three seconds intervals.
            When you recognize that the same square flashed exactly N steps ago, you press the
             button.
 button.
            
            
            Simultaneously, one letter is spoken at each time step.
            When you recognize that the same letter was spoken exactly N steps ago, you press the
             button.
 button.
            
            
                
                     
                
                
                    Example sequence for N=2 game.
                    The player must remember the state of the game board N steps ago.
                
 
             
            
            If you do well, N will increase on the next round.
            If you don't do so well, N will decrease on the next round (down to N=1).
            There are 20+N time steps in each round.
            
            
            Notes:
            
            
            This game is still in beta phase.
            Please be patient for your favorite feature.
            Planned features include
            a dark theme,
            a cloud-sync method for saving progress across devices,
            ability to start back at N=1 on demand,
            and more.
            
            
            For feature requests and bug reports please contact me at
            support@dual-n-back.io.
            I will do my best to respond quickly.
            
            
            Credits:
            
            
            Based on the work of [1], [2], and others.
            Audio clips adapted from [5], most of the icons are from [6].
            
            
            
                 This work is licensed under a
            
            Creative Commons Attribution-NonCommercial 4.0 International License.
            
            This work is licensed under a
            
            Creative Commons Attribution-NonCommercial 4.0 International License.
            
            [1]
            
            Jaeggi, S. M. et al. Does excessive memory load attenuate activation
            in the prefrontal cortex? Load-dependent processing in single and
            dual tasks: functional magnetic resonance imaging study. NeuroImage
            19, 210-225 (2003).
            
            
            [2]
            
            Blacker, K. J., Negoita, S., Ewen, J. B. & Courtney, S. M. N-back
            Versus Complex Span Working Memory Training. J Cogn Enhanc 1–21 (2017).
            doi:10.1007/s41465-017-0044-1
            [3]
            
            https://www.npr.org/sections/health-shots/2017/10/23/558767704/in-memory-training-smackdown-one-method-dominates
            
            [4]
            
            https://en.wikipedia.org/wiki/N-back#Dual_n-back
            
            [5]
            
            http://soundbible.com/2009-A-Z-Vocalized.html
            (Creative Commons Attribution 3.0 license)
            
[6]
            http://simpleicon.com/
            (Pretty much same as the CC Attribution license)