Differential asymmetries for positive and negative emotion: hemisphere or stimulus effects?

Two experiments were carried out to determine whether expressive asymmetries in facial stimuli might underlie evidence of differential hemispheric responses to positive and negative emotion. Experiment 1 systematically varied stimulus orientation; Experiment 2 included both normally oriented and reversed (mirror-image) faces. We replicated previous reports of a left field advantage for happy faces and a right field superiority for sad faces only when normally oriented faces were used. Mirror-image stimuli tended to produce the opposite pattern of results, and a combination of the two (Exp. 2) eliminated the visual field differences for each emotion. The findings underscore the importance of controlling for stimulus asymmetries in visual laterality studies, and are discussed in terms of current notions about the lateralization of both the perception and expression of emotion.