The role of skin-related information in pigeons’ categorization and recognition of humans in pictures

Pigeons have previously been shown to readily categorize pictures with and without humans and to also recognize the correspondence between live humans and pictures of them. Here, we investigated the role of skin-related features for their possible influence on pigeons' categorization and recognition of humans in pictures. Pigeons were tested with stimuli that contained parts of humans that were discolored (Test Grayscale) or whose surface was altered (Test Nonhuman Surface), as well as with stimuli showing objects whose outlines were filled with human skin (Test Nonhuman Shape). The results suggested that skin-related features were not critical for correct classification and recognition, but played an important accessory role.