Experimental design.

Notes: The experiment comprised ten sessions, in each of which up to 30 subjects participated (265 in total). Each session comprised three stages: a DG, a communication stage and a TG. In each session, five subjects were the recipients in the DG (50 in total) and did not participate in stages two and three. The other subjects (215 in total) were assigned to one of four experimental condition: control (veiled), disclose veiled, declare veiled and disclose unveiled. In the three veiled conditions, subjects were informed only after the DG what parts two and three of the experiment comprised. In the unveiled condition it was known to subjects from the beginning what parts two and three would comprise (also see the SI File S1).