Several studies have shown that physical attractiveness has a greater positive effect on the reward value of faces. Furthermore this effect of attractiveness on the reward value of faces has been shown to be stronger for smiling faces compared to faces with relatively negative expressions. These results then suggest that cues of positive social interest can modulate the reward value of other facial cues, potentially supporting efficient allocation of social effort. Recent research has also shown that in heterosexual men, an angry facial expression discounts the reward value of female faces, regardless of their attractiveness. Since previous neurobiological and behavioural studies have shown that heterosexual men find womenís faces more rewarding than menís faces, here we tested whether this effect of sex of face on reward is also modulated by emotional expression. Sixty-one young adult heterosexual men completed a motivated viewing paradigm to assess the reward value of menís and womenís faces displaying happy, sad, angry and fearful expressions. In this task, participants can actively control the length of time they view a face by pressing buttons to either increase or decrease viewing time, with longer viewing times indicating greater reward value. Analyses revealed a main effect of sex of face, whereby womenís faces were more rewarding than menís faces. As we had predicted, however, there was an interaction between sex of face and emotion. The effect of sex of face was greatest for smiling faces, and was also present for sad faces. However this effect was not present for fearful and angry faces. Our results present further evidence that cues of social interest and/or threat can modulate the effect of other cues on the reward value of faces.
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