Anyone with a cat (or internet access) has likely observed their tendency to seek out and sit in boxes, bags, baskets, and even a simple square drawn on the ground, as demonstrated by Twitter’s #CatSquare trend.
A team of psychologists decided to use this feline behavior to investigate whether cats are susceptible to a well-known visual illusion: the Kanizsa square. A Kanizsa square is made of four small solid-colored circles, each with a right angle cut out so that only ¾ of the circle remains. These circles are arranged in a large square shape and rotated so that the missing parts face inwards, creating the illusion of an actual square sitting above them.
A 1988 study provided some evidence that cats perceive the Kanizsa square the same way that humans do, but that study only included two cats trained in a lab. Scientists behind a recent study, published in Applied Animal Behaviour Science, wanted to test a wider range of cats and capture their natural behavior at home. To do this, they turned to social media to recruit participants.
They asked cat owners to cut out three different stimuli: a real square, a Kanizsa square, and a rotated Kanizsa in which the circles were turned outwards, causing the illusion to fail. Each day, the cat owners placed two of these stimuli on the floor and then watched their cat for five minutes.
Thirty cats were tested over six days, and among them, they sat within the real square eight times, the Kanizsa square seven times, and in the rotated Kanizsa only once. In the trials where the cats had a choice between the real square and the Kanizsa square, they showed no preference between them. This indicates that cats may perceive illusory squares to be as valid, and as comforting, as real squares.
So, in addition to showing that cats really do like sitting in two-dimensional squares, the researchers also demonstrated that cats perceive some of the same visual illusions that humans do. Despite the many differences in the eyes and brains of humans and cats, we may see and interpret our environment in strikingly similar ways.