The face-in-the-crowd effect: when angry faces are just cross(es).

A common theme running through much of the visual recognition literature is that faces are special. Many studies now describe evidence for the idea that faces are processed in a dedicated center in cortex. Studies have also argued for the presence of evolutionarily expedient pathways dedicated to the processing of certain facial expressions. Evidence for this proposal comes largely from visual search tasks which have established that threatening expressions are more rapidly detected than other expressions: the 'face-in-the-crowd effect'. One open criticism of this effect is that it may be due to low-level visual artifacts, rather than biological preparedness. One attempt at controlling low-level differences has been to use schematic line-drawing versions of faces. This study aimed to discover if there might be alternative issues with schematic stimuli. The first study replicated the face-in-the-crowd threat advantage for schematic faces, but also measured a comparable effect using stimuli comprised of obliquely oriented lines. Similar results were achieved with these stimuli rotated, which had the effect of removing any residual resemblance to a face. The results suggest that low-level features probably underlie the face-in-the-crowd effect described for schematic face images, thereby undermining evidence for a search advantage for specific facial expressions.