The perception of visual illusions is not limited to humans but is also experienced by many non-human animals. These illusions occur due to errors in perception and can involve various characteristics such as size, brightness, color, shape, orientation, motion, or quantity. By studying these illusions and the differences between animals, we can gain insights into the evolution of visual systems.
A recent study published in iScience focused on European honeybees and European wasps and their perception of illusions of quantity. The Solitaire illusion, which causes a misperception of quantity based on the arrangement of dots in an image, was used in the study. Humans, capuchin monkeys, guppies, and bees have been found to perceive this illusion, while chimpanzees, rhesus monkeys, and domestic dogs do not seem to perceive it. Interestingly, younger children are less susceptible to the illusion than older children.
The misperception of quantities through visual illusions may have an evolutionary advantage in processing and comparing large numbers of items quickly and efficiently. For quantities greater than five, fast decisions may be more important than absolute accuracy, which would require manual counting.
European honeybees and wasps were chosen for the study because they are highly motivated to participate in behavioral experiments. The researchers trained and tested individually color-marked insects by providing them with a reward of sugar water. Previous studies have shown that honeybees can perform various numerical tasks and perceive spatial, movement, and color illusions.
Both honeybees and wasps were tested using the Solitaire illusion. They were presented with images containing blue and yellow dots and trained to choose the image with a higher quantity of yellow dots. The Solitaire illusion was then presented, where one image had yellow dots clustered in the middle and blue dots unclustered, while the other image had the opposite arrangement. Both insects chose the option with yellow dots clustered in the center, indicating an overestimation of the quantity of yellow dots. This perception of the illusion was similar to that of humans, capuchin monkeys, and guppies.
The study suggests that the perception of the Solitaire illusion occurs across a range of species, including humans, non-human primates, fish, and insects. This could be due to convergent evolution, where different species independently developed the ability to perceive the illusion based on their environmental requirements. Alternatively, it could be a result of conserved evolution, where a common ancestor perceived the illusion, and some species either retained or lost this perception.
Further research is needed to determine whether the Solitaire illusion induces a misperception of quantity or other cues that correlate with quantity.