Eight experiments were conducted to examine different aspects of hen’s visual behaviour, and to assess whether hens responded to photographs in the same way they do to the real objects that were depicted in the photographs. In Experiment 1, six hens were trained to perform either a conditional discrimination (successive) or forced-choice discrimination (simultaneous) between flickering (25 Hz) and steady lights. A descending method of limits procedure was then used to increase the flicker speed by 5 Hz over blocks of 20 trials until percentages correct decreased below 55%. The critical flicker fusion frequency of hens was found to range between 68.5 and 95.4 Hz (at a luminance of 300 cd/m2). In Experiment 2, hens were trained to discriminate between steady images presented on a TFT screen, and tested for transfer of that discrimination to a CRT monitor at different refresh rates, on which the images were assumed to appear flickering. It was found that hens showed transfer across all refresh rates with coloured stimuli, but that the degree of transfer decreased as refresh rate decreased with stimuli that were discriminable only on shape. In Experiment 3, a similar decrease in accuracy was shown as refresh rate decreased using a range of stimuli. However, hens did not learn to discriminate all stimuli, and thus transfer could not be assessed with some stimuli. Experiment 4, hens were trained with flickering images and showed relatively high transfer to less flickering, or steady, images. In Experiment 5, a procedure was developed to assess whether hens transferred a discrimination of 3D object to 2D photographs of those objects, and vice versa. In Experiment 6, hens were trained to discriminate stimuli of different colours, or of different shapes. The hens learned to discriminate, and transferred this discrimination, with the coloured shapes. The hens also learned to discriminate the same colour (but differently shaped) stimuli, however, further testing showed that an extraneous variables had come to control behaviour. As a result, the equipment was modified for Experiments 7 and 8. In both experiments, only three of the six hens showed discrimination to any degree, and none transferred this discrimination to photographs or objects. It was concluded that hens do not respond to objects depicted in pictures in the same way they do to the real objects. Thus, these experiments show that that animals’ visual systems need to taken into account when visual stimuli are used in research, and researchers first need to establish that animals can see the visual stimuli and that the method of stimulus presentation is species appropriate if images are to be used as representatives of real world stimuli
