The Role of Natural Stimuli

The reasons why humans have the type of perception we do will never be completely discovered unless we also understand other types of perception observed in nonhuman animals. Among birds, particularly the pigeon has been shown to excel relative to humans in many of its visual capacities, which may have evolved in parallel with ours. But whereas pigeons displayed surprising categorization abilities in many visual discrimination experiments, they persistently failed on certain tasks, or only mastered them with great difficulty. These tasks included the use of configural information, completion of partially occluded objects and comprehension of abstract relations. However, if animals fail to master a specific task, it may not be a problem of lacking ability, but researchers may just have failed to discover the appropriate experimental conditions. A common attribute of most categorization tasks in which pigeons failed was the use of highly artificial stimulus materials, i.e., line drawings or abstract geometrical black-and-white figures. However, birds` visual worlds do not consist of stimuli of that kind, nor do birds in their natural environment respond to such stimuli. Probably, naturalistic images such as color photographs come closer to what pigeons encounter in their environment and what their visual system is prepared to process. The present study will examine whether the use of natural instead of artificial stimuli may be the key to success in visual categorization problems which have so far been considered extremely difficult or even unsolvable for pigeons.