Object/picture recognition in hens

• 2D stimuli have been used as substitutes for real animals or objects in animal research.
• Hens showed transfer between 2D photographs and 3D objects only when colour cues were present.
• No transfer occurred when discrimination was based only on shape.
• Hens do not respond to pictures as if they were the real stimuli.

Two experiments examined whether hens, Gallus gallus domesticus, would respond to photographs in the same way they do to the real objects depicted in the photographs. Experiment 1 assessed whether hens transferred a discrimination of differently coloured three-dimensional objects to two-dimensional photographs of those objects, and vice versa. All hens learned to discriminate between the stimuli and showed transfer to the alternative stimuli when the colour cues were present. In Experiment 2 transfer with stimuli that differed in shape only was examined. It was found that only three of the six hens learned to discriminate the stimuli to any degree, and that these three hens did not transfer this discrimination to the alternative stimuli. It was also found that previously learning an object discrimination did not aid the hens in learning to discriminate between photographs of the objects. These data suggest that the hens did not respond to the objects depicted in pictures in the same way they did to the real objects. The authors argue it cannot be assumed that all animals respond to two-dimensional pictures of stimuli in the same way as they do to the real three-dimensional stimuli and this should be established before researchers use two-dimensional stimuli as representatives of real world stimuli.