// instruments · the criterion
the criterion
Signal detection, on yourself. A patch of noise flashes; sometimes a faint target hides inside it. You say yes or no, sixty times. Afterward, two numbers: how sharply you told signal from noise, and which way you leaned when unsure.
aim for a level where you get roughly 70–85% right. too easy and d′ pins high; too hard and it collapses to guessing. screen brightness matters — turn it up, sit still.
// the point
Two numbers, not one.
d′ is how sharply you tell signal from noise. c is which way you lean when unsure — it is not error, it is a stance. c > 0 is cautious, biased toward “no”; c < 0 is liberal, biased toward “yes.” A cautious person and a sharp-eyed person are different measurements. You can raise one without touching the other.
// what this is
This is signal detection theory — Green & Swets (1966), computed per Stanislaw & Todorov (1999): d′ = z(H) − z(FA) and c = −0.5·(z(H) + z(FA)), where z is the inverse standard-normal CDF (probit, via Acklam's approximation). Rates of 0 or 1 make z infinite, so the log-linear correction (Hautus 1995) adds 0.5 to hits and false alarms and 1 to the trial totals before forming the rates. It measures your sensitivity and bias on this task, this session — not a personality, not a diagnosis. Screen brightness and effort move the numbers.
If something heavier is going on, /dangers.
// kin
ceiling — self-knowledge, marked honestly · introspection-ceiling — the limit, written up