Interestingly this paper by Phillips et al showed that while adults see the orange circles as different sizes, children under the age of 7 are not so easily fooled. They hypothesize that this sensitivity to context develops slowly overtime due to increasing exposure and correct interpretation of 2D representations of 3D scenes.
Are animals fooled by this illusion too?
Some animals perceive this illusion in the same way as humans do, for instance the bottlenose dolphin. In contrast, dogs have been reported to see the exact opposite of this illusion, where the circle on the left appears larger and baboons don’t see the illusion at all.
What about insects?
A 2017 study by Dyer et al. showed that honeybees are also fooled by contextual size illusions, but only when viewed by free flying bees where they could view the illusion at any distance. However, when the bees were restricted to only viewing the illusion at one set distance they did not respond to the illusion.
For those of us that design visual stimuli it’s important to not only take into account context but also to understand that what we see, as humans, could be vastly different from how the stimulus is perceived by insects and other animals.