Two players, one test of attention — the sharper eye wins
Attention is the ability to pick out what matters and ignore the rest, and it is more trainable than most people expect. Psychologists have measured it for more than a century with very simple tasks: waiting for a signal and pressing as fast as possible, finding the one item that differs from its neighbours, or naming the colour of a word while ignoring what the word says. Each of them isolates a slightly different skill, from sheer speed to the ability to resist a distracting habit.
Turning those tests into a duel changes how they feel. Against a clock you are competing with yourself; against another person, every round has a winner and a loser, and a fraction of a second suddenly matters. Short series of rounds reward steadiness — one lucky answer is not enough to win — while a race against a timer rewards keeping your head as the pace picks up, and punishes guessing.
Like the site's private chat, a duel leaves nothing behind: there are no accounts, no rankings and no history, and the room vanishes when the two of you leave. The link you send carries the key that scrambles the moves, so the server only ever sees unreadable messages. It is a game for a break, a bet with a friend, or a quick check of who is sharper today — not a medical test of any kind.