Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
The observer-averaged weighted alternative free-response receiver-operating characteristic curves for the three display modes. FF, fast-flicking (yellow); Inv, inverted display (green); Std, standard display (blue). For colour image see online.
