Fig. 1.

Experimental tasks. (A) Preference task 1. In each trial, subjects were presented with a food item for 3 s and asked to rate their preference for it on an eight-point scale. (B) Examples of a Self trial and a Computer trial during the Choice task. In a Self trial, subjects were asked to choose one of two foods which they preferred. In a Computer trial, they were asked to simply pick the item that a computer randomly chose (highlighted by a red square). A cue was presented for 1.5 s followed by a brief delay (500 ms), and two foods were presented for 5 s. (C) Preference task 2. Subjects were presented with the same food stimuli as in Preference task 1 and asked to rate their preference again. However, during Preference task 2, past decisions by themselves or a computer (e.g., “You rejected it”, etc.) were also displayed under each picture. For items not used in the Choice task, only pictures of foods were presented.