Imagery-perception interaction depends on the shape of the image: a reply to Farah (1989).

Farah (1989) reported that point threshold stimuli are detected better if they appear at spatial locations in the visual field that are covered by an image. By replicating her experiment with 3 instead of the original 2 images, we found that the effect depends on the shape of the mentally projected image. A second experiment with 9 different shapes revealed that the effect is modulated by the compactness and the size of the image--it is enhanced with increasing compactness and attenuated with increasing size. These findings do not unequivocally support the idea that imagery and perception interact because both processes share the same representational medium. Rather, they suggest that imagery can cause a figure-ground segregation in the visual field and that the shape of the figure may determine the amount of attention that is allocated to different sections in the visual field.