Recognition of static and dynamic images of depth-rotated human faces by pigeons.

In three experiments, we examined pigeons' recognition of video images of human faces. In Experiment 1, pigeons were trained to discriminate between frontal views of human faces in a go/no-go discrimination procedure. They then showed substantial generalization to novel views, even though human faces change radically as viewpoint changes. In Experiment 2, the pigeons tested in Experiment 1 failed to transfer to the faces dynamically rotating in depth. In Experiment 3, the pigeons trained to discriminate the dynamic stimuli showed excellent transfer to the corresponding static views, but responses to the positive faces decreased at novel viewpoints outside the range spanned by the dynamic stimuli. These results suggest that pigeons are insensitive to the three-dimensional properties of video images. Consideration is given to the nature of the task, relating to the identification of three-dimensional objects and to perceptual classifications based on similarity judgments.