hback: N-back memory game

Based on a recent [research paper](http://www.pnas.org/cgi/content/abstract/0801268105v1) that claims fluid intelligence could be improved by training working memory, I wrote up a dual n-back test memory game in Haskell and gtk2hs. This is an alpha release: all comments are most welcome.

Gameplay
--------

The n-back memory game tests whether the player can remember if the nth previous turn matches the current one. The dual n-back test will measure how well the player can remember both visual and graphic stimuli simultaneously.

Given a difficulty level n, the player is expected to remember on each turn whether the nth previous sound or graphic (or both) matches the current one, and toggle the appropriate button(s). The graphic flashes for 500ms and the player has another 2.5 seconds to answer.

The training game consists of b block iterations, where each block will present (20+n) visual and audio stimuli. After each iteration, the difficulty of the n-back test may increase or decrease, depending on the performance of the player: the goal is to constantly keep the player at peak concentration.

Installation
------------

     % tar -xzf hback-0.0.tar.gz
     % cd hback-0.0

Game can be played without system-wide installation:

     % make trial
     % ./hback

If you like what you see, feel free to install it:

     % make build
     % make install    # you may need root privileges for this
     % rehash
     % hback

hback takes two optional arguments:

     % ./hback b n
         - b determines the number of block iterations (eg. try 20 for an effective daily workout)
         - n determines the initial level (defaults to 1)