2. METHODOLOGY
2.1. Paradigm The presentation environment used in the study was developed using the Unity 3D [20] game development engine. Five on screen virtual buttons, placed in a horizontal arrangement at the top of the computer screen form the mY EP game controller used in the study. In order to avoid visual distractions in the immediate area surrounding each mY EP button, the buttons were placed centrally within a plain white background acquiring approximately 13% of the total screen space. Each mVEP button subtends a visual field of 1.24° length x 0.76° height with the red coloured vertical moving line being 0.66° in height. Each mVEP button has a number (1 to 5) placed directly on top which differentiates them from each other. The subject identifies which button to concentrate on when the number of the current target button changes from black to red. The users' instructions were to focus their attention on the moving line of the currently active button (Fig. 1 shows the basic (no graphics) level with the '2' button as currently active while '2' is also the users current target (number highlighted red). A button activation constitutes one horizontal movement of the vertical red line from the left hand side to the right hand side of the vacant rectangle (lasting 140 milliseconds). The timing protocol for this study followed closely to that of [17]. Each game level consisted of 300 trials. Each level lasted 540 seconds, during which each mY EP button will have been activated 60 times. ' During each trial, each of the five mY EP buttons are active a total of five times. Each button is highlighted in tum starting from 1 through to 5 in a linear fashion. In order to avoid user habituation, each of the buttons are activated in random order. The Stimulus Onset Asynchrony (SOA) between each button activation is 200ms. The motion of the vertical line moving from right to left in each button
lasts 140ms and the time between each button activation is 60ms. A diagram of the timing protocol used is shown in (Fig. 2).
Unity 3D scene. Each of the games presented to the subject depicted typical commercially available games from varied generations of gaming consoles namely the 3rd generation Nintendo Entertainment System (NES) [21], 4th generation Sega Mega Drive [22], 5th generation Sony Playstation [23], 6th generation Sony Playstation 2 [24] and the 7th generation Microsoft Xbox 360 [25]. The games chosen represent the graphical achievements from the respective generation of games console. The games used in the study (in order of release date) and their respective game console were Pac-Man (Level 2) [26] - a fast paced 2D based arcade game featuring brightly coloured, flashing graphics. The goal of the player is to keep the main character constantly moving around a maze shaped world in order to collect food and avoid the enemy characters. The actual game world remains fairly static within the scene (Nintendo NES, 1984) (Fig. 3). Sonic the Hedgehog (Level 3) [27] - a very fast paced 2D platform game featuring brightly coloured game background and very fast paced character. The goal of the player is to navigate the main character through the game world by jumping over obstacles, collecting rings and avoiding or killing enemy characters. The world