Inversion produces opposite size illusions for faces and food

Abstract

Faces are important communicative signals in humans and face perception is believed to involve specialised mechanisms in the visual system. Several other categories of stimuli are also thought to involve specialised processes, including bodies, letters, places, and food. A recently described face size illusion shows that upright faces appear physically smaller than identical inverted faces. This illusion appears to be highly face-specific, not occurring for other stimulus categories, such as bodies, letters, and hands. In this study, we investigated whether an analogous size inversion illusion occurs for items of food, a category which has recently been found to also involve specialised processes in the visual system. The results provided a clear replication of the face size illusion, with upright faces seen as smaller than inverted faces. In contrast, items of food and everyday objects showed an effect in the opposite direction, appearing larger when upright than when inverted. These results provide further evidence for the highly face-selective nature of the face size illusion. They also provide evidence for a different size illusion which affects visual perception of food.