Indexing the archive…
Your Universe of Digital Possibilities
A handful of coloured squares appears for a blink. Then they come back, one ringed: did it change? Do it forty times at four set sizes and the instrument reads off your capacity — how many items one glance holds — and fits two rival models of memory to your answers. Two more rooms: twelve letters that fade within a second, and a night scene that changes too slowly to see.
For a change-detection test that probes one item of N: if K of them are held, a change to a held item is always caught and the rest are guessed, so the hit rate H exceeds the false-alarm rate FA by K/N. Below capacity K follows N; above it, K levels off — at about four.
The distance between the “changed” and “same” evidence distributions in units of their spread, from the hit and false-alarm rates through the inverse normal z. Unlike percent correct it does not move when the observer simply says “changed” more often. A log-linear correction keeps it finite at 0 and 1.
The letters available d ms after the flash — the cued row’s score times the number of rows — falling from A0 towards what whole report gives. Sperling plotted the curve; the exponential is the standard summary of it, fitted here by least squares.
The seventh percept is a limit, not an illusion. What reaches the eye is rich; what one glance carries forward is a few items, and the rest is rebuilt from the world on the next look — which is why a slow change in plain view can go unseen. How the same limit shapes counting is The Tally; how a memory is stored at all is The Engram; how noise sets what can be told apart is The Noise.