Domestic cats see visual illusions like humans

Domestic cats are fooled into seeing things which are not there because of visual illusions just like people. This is my interpretation of a study which is published on the Science Direct website. The study is called: If It Fits I Sits: A citizen science investigation into illusory contour susceptibility in domestic cats. I am going to provide my interpretation of this study and hope that it is correct. I am doing this because the words of the study are almost unintelligible and the outcome of the study is not entirely clear. Also, without wishing to be too negative, I am not sure how useful this knowledge is.

Will Pavia of The Times newspaper confirms that my interpretation of this study is correct when he writes that: “The study showed that cats discerned ‘illusory contours’, something infants begin to see when a few months old. In domestic cats this may be in part a product of their environment, with its walls, edges, ledges and piano tops.”


As I understand the study, the scientist wanted to know why domestic cats sit inside drawings on the floor, which are square or circular. We know that domestic cats love to sit or curl up inside boxes because of the sense of security that they provide. In my opinion, they also like the pressure of the box against their sides, for the same reason. But it is a bit bemusing to see domestic cats walking into squares taped onto the ground and apparently obtaining the same feeling of security even though there is nothing there.

Cat fooled into believing they are sitting inside a box
Cat fooled into believing they are sitting inside a box
Two useful tags. Click either to see the articles: Toxic to cats | Dangers to cats

The question posed was whether the cats were seeing a visual illusion of a box.


Visual illusions or illusionary contours

There is an image called a Kanizsa Triangle. You can see it below. The way the image is drawn gives people the illusion that there is an inverted triangle, slightly raised off the paper, in the middle of the illustration. This is a visual illusion because our brains are tricked into believing that the triangle is there. It is the “spatially separate fragments” (the Pacman objects and the other drawings) which provide the illusion.

Kanizsa Triangle
Kanizsa Triangle. Image: Wikipedia, user: Fibonacci under creative commons license.

Here is a photo by GABRIELLA SMITH of a grey cat settling into an illusory box:

Cat stays inside illusory box
Cat stays inside illusory box. Photo: GABRIELLA SMITH

Citizen science investigation

What the scientist mean by this is that they used ordinary people to participate in this investigation as to whether domestic cats can also see visual illusions. This is a weakness as it raises the question as to how accurate the the finding are and the same was small (see below).

Study conclusion

It appears that the study concluded that cats are susceptible to the Kanizsa Triangle illusion that you see above which suggest that like humans they perceive illusionary or ‘subjective contours’ as they are called. To be clear, subjective contours means seeing the visual illusion which is that they see an edge without it being drawn and without a change along the edge in terms of colour or darkness and lightness.

Study difficulties

I perceive some difficulties in the study because although some 500 pet cats and their owners expressed an interest in the study only 30 completed all six of the study’s trials over the course of two months last summer. Of those cats which participated 9 of the cats sat inside the illusory contours for at least three seconds. They selected the Kanizsa Triangle just as much as they did the square. The cats treated the illusory square the same as the real square.


The study appears to provide us with the insight that domestic cats have brains that are similarly wired to ours at least in this regard. We know, by the way, that their eyesight is also very similar to ours although they see reds less well and they see better at night than humans. I’ve written about this some time ago and you can see some pictorial examples as to what cats see compared to people by clicking this link.


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