Fig 1. Experimental Design.

The experimental paradigm comprised four distinct sessions. In Rating Session 1 subjects rated all images. These images were then paired on the basis of matched ratings. In Choice Session 1 subjects could freely choose (by either pressing or not pressing a button) or a computer chose at random. In Rating Session 2 subject rated all images again while text informed subjects as to what occurred in Choice Session 1. Finally, in Choice Session 2 the pairs the computer chose beforehand in Choice Session 1 were displayed. Subjects freely chose again by performing or omitting a button press like in Choice Session 1. This experiment was conducted in two independent samples with two different stimulus sets (positive and negative valence). Comparing the value change from Rating Session 1 to 2 for chosen and unchosen items before revaluation and after revaluation provided a measure of choice-induced value change. We tested whether this choice-induced value change was modulated by action or inaction (Go/No Go) and by valence. The frequency of choice expressed in a response Go or No Go allows us to test for a bias induced by action on choice itself.