The many evils of social media notwithstanding, millions of users agree that some of its most delightful aspects include viral illusions and cute cat videos. The potential for synergy was vast in retrospect—but only realized in 2013, when Rasmus Bååth, a cognitive scientist from Lund University in Sweden, blended both elements in a YouTube video of his kitten attacking a printed version of Akiyoshi Kitaoka’s famous “Rotating Snakes” illusion.  

The clip, which has been viewed more than 6 million times as of this writing, led to subsequent empirical research and an internet survey of cat owners, where 29% of respondents answered that their pets reacted to the Rotating Snakes. The results, published in the journal Psychology in 2014, indicated—though not conclusively—that cats experience illusory motion when they look at the Rotating Snakes pattern, much as most humans do.

Now, a team of researchers from University of Padova, Italy, Queen Mary University of London in the UK, and the Parco Natura Viva—Garda Zoological Park in Bussolengo, Italy, has collected additional evidence that cats—in this case, big cats—find the Rotating Snakes Illusion fascinating.     

Intrigued by the earlier study on house cats, Christian Agrillo of the University of Padova and his collaborators set out to determine whether lions at Parco Natura Viva were similarly susceptible to motion illusions, as well as explore the possibility that such patterns might serve as a source of visual enrichment for zoo animals. Their findings were published last month in Frontiers in Psychology.

The team collected behavioral data from Parco Natura Viva’s three resident lionesses, Safia, Kianga, and Lubaya. To find out if the lionesses were specifically interested in the Rotating Snakes pattern, Agrillo and his colleagues devised three different sets of stimuli: the Rotating Snakes illusion, plus two control designs. One of the two control stimuli was identical in content to the Rotating Snakes, except with a scrambled sequence of color segments that nullified the illusory motion effect. The second control stimulus was a very simplified pattern made of the same basic elements as the Rotating Snakes illusion.  

Visual patterns presented to the lionesses: A) Rotating Snakes illusion, B) Control 1, and C) Control 2. A and B are similarly complex, but only the sequence in A elicits the perception of illusory motion in human observers. From Regaiolli et al, Frontiers in Psychology 2019. Credit: Christian Agrillo

To avoid competition between the animals, the scientists displayed three copies of each stimuli, so that each lioness had her own set of displays to interact with. Nine video recording sessions, lasting 5 hours each, took place over a one-month period. The team also collected data about the lionesses’ individual and social behavior, both before the visual stimuli were introduced to their habitat, and also during the same time period in which animals had access to the visual patterns.

Arrangement of visual displays in the outdoor area of the lionesses’ enclosure. From Regaiolli et al, Frontiers in Psychology 2019. Credit: Parco Natura Viva

Two lionesses (Lubaya and Safia) out of three preferred the Rotating Snakes illusion over the two control visual patterns.  Video footage showed the animals engaging with the illusion, by scratching, biting or dragging the displays. These actions suggested that they were attracted by the illusory motion.

Lioness engagement aftermath. The lionesses ripped the Rotating Snakes to shreds, while leaving the simple, non-illusory display (upper right) relatively intact. From Regaiolli et al, Frontiers in Psychology 2019. Credit: Parco Natura Viva

The third lioness (Kianga) did not react differently to the illusory and non-illusory stimuli, but exhibited positive behavioral changes that were associated to the introduction of the visual patterns. Specifically, she decreased her self-grooming (excessive grooming can indicate stress in felines) and increased her attentive behaviors, suggesting that the visual enrichment provided by the displays had a beneficial  effect on her wellbeing.

The results of this preliminary investigation add one more species to the growing list of non-human animals that are susceptible to motion illusions—which besides cats big and small, includes rhesus monkeys, guppies and zebrafish. The recent findings also call for future explorations of visual illusions as part of the enrichment programs of zoo animals, the study’s authors concluded.

In the meantime—and considering the state of the displays after the lionesses were done with them—just ditch your illusion wardrobe when in striking distance of a giant cat.