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.
Cumulated number of studies 1976-2015, assigned by the external validity of the viewing conditions (field vs. lab) and the required response mode (natural vs. artificial), respectively to the categories “field/natural,” “lab/natural,” and “lab/artificial.”
