animal illusions
November 26, 2020 12:27 PM   Subscribe

Which optical illusions can animals see? "Visual illusions remind us that we are not passive decoders of reality but active interpreters. Our eyes capture information from the environment, but our brain can play tricks on us. Perception doesn’t always match reality. Scientists have used illusions for decades to explore the psychological and cognitive processes that underlie human visual perception. More recently, evidence is emerging that suggests many animals, like us, can perceive and create a range of visual illusions."
posted by dhruva (8 comments total) 12 users marked this as a favorite
 
NatGeo always interrupts my reading demanding my email address before I can finish the article. I'm sure it's an interesting read, but sadly I didn't get very far into it.
posted by hippybear at 1:54 PM on November 26, 2020 [5 favorites]


Other people dislike the paywall as much as I do. Possibly the same article but without photos?
posted by fiercekitten at 2:03 PM on November 26, 2020 [1 favorite]


I once printed out the rotating-snakes illusion mentioned in the article and showed it to one of my cats… her eyes got big and she started to smack the paper over and over. So I'm pretty sure cats can see that one, at least.
posted by Ampersand692 at 3:05 PM on November 26, 2020 [10 favorites]


NatGeo always interrupts my reading demanding my email address before I can finish the article.

What’s really galling is I first got a popup saying I had three free articles left for the month, then I got the “gimme your email to keep reading” message.
posted by Thorzdad at 3:20 PM on November 26, 2020 [2 favorites]


How Baader–Meinhof.

I saw this thing last night. It's an optical illusion that fools cats, and there are customer testimonials with videos that shows that it's a broad effect.
posted by porpoise at 6:12 PM on November 26, 2020


Here's a video of a cat attacking the rotating-snakes illusion.

I wish they had a video of lions attacking the illusion, though they did have a picture of what was left of the illusion after the experiment.
posted by eye of newt at 9:52 PM on November 26, 2020 [5 favorites]


That video is pretty much exactly how my cat reacted. Now I kind of wish I had a printer still — cheap cat toy, although so is a crumpled-up ball of paper.
posted by Ampersand692 at 7:57 AM on November 27, 2020 [1 favorite]


There is a whole wide and wonderful literature talking about how the same kind of exploits that capture our attention can evolve into the beautiful, elaborate, sexually selected displays that we marvel at in animals that one of my committee members has spent pretty much his entire career working on. Whether or not animals are fooled by illusions is such a fantastic way at understanding how senses can be fooled--or not fooled--and how on earth perceptual biases can shape communication and vice versa.

We often think about interspecific variation in sensory acuity being just a matter of range: bats can hear higher-frequency sounds than we can, and elephants can hear lower-frequency rumbles that humans can barely feel. But actually, different species of animals also have different sensitivities within their perceptual range at various points. This includes humans! For example, humans can hear from about 16 Hz up to about 16,000 kHz, but we aren't equally sensitive to all sounds that occur within that range. If you look at an audiogram [h/t here], which plots how loud a sound has to be before a human perceives it at a wide range of frequencies, you can see that a sound at about 2-4kHz requires way, way less amplitude (in dB) to be perceived than a sound closer to 25 Hz (or 0.025 kHz) does. That's because we're more sensitive to sounds in the 2-4 kHz range than we are to sounds in other frequency bands. (Incidentally, a baby's cry is centered at about 3.5 kHz, which is one reason that babies sound so gosh-darn loud--they aren't necessarily producing a stronger amplitude of sound than, say, a shouting man might; they're producing a loud sound right in the frequency range humans are most sensitive to.

If you look at other species, though, like this figure comparing human curves with marine mammals', you can see that different species often have very different curves with different "sweet spots" and "blind spots" in their frequency ranges even accounting for the variation in the overall range of frequencies. So if you're trying to create a noise that is very attention-grabbing for one species but not very attention-grabbing for, say, a local predator... maybe you pick your pitch wisely.

Or maybe you focus on the space between the notes--birds can't hear high frequencies like mammals can, but they are very very very good at assessing internote intervals and shoving syllables around. Or maybe you focus on a totally different sensory pathway. Animal senses are all good for different things and require a lot of processing power, so it makes sense to cut corners on things that aren't really very important and hone things that are important to specialize. (And to use signals on the important stuff for lots of uses, too, of course. For example, bats often sing to each other in ranges otherwise used for echolocation, and in several species we know bats can identify one another by the echolocatory calls they use to navigate--sort of like hearing your friend get around a room by yelling CHAD, CHAD, CHAD over and over.)

My point being: animal sensory landscapes are wildly different from our own, often in ways we are only beginning to capture. Some illusions fool some species but don't fool others at all, just as some forms of camouflage perplex humans (either because our color vision can see through them, as with hunters who hide from deer in day-glo orange, or since we can't perceive the thing a camouflaged organism might be mimicking, as with fluorescent pink flying squirrels) while working perfectly well for the animals that practice them. Figuring out what illusions work and what don't for which animals gets us a deeper understanding of what it might be like to inhabit such a wildly different perceptual landscape as well as the specific cognitive distortions expressed by our perception of the world around us that allow us to see an illusion at all.

This is wonderful, weird, wild stuff.
posted by sciatrix at 1:18 PM on November 28, 2020


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