Extra: Why animals see the world at different speeds

Future proof extra with Jonathan McRae, proudly supported by Research Ireland on Newstalk.

Now, what if I told you that a dragonfly is essentially living permanently in slow motion,

and that a deep sea crustacean is experiencing the world in a completely different way?

A new study in nature suggests that animals don't just see the world differently,

they experience it at different speeds, co-author Dr. Kevin Healy, head of the macroecology lab

at the University of Galway joins me now. Welcome to the program, Kevin.

Congratulations on the paper. Nature is always a great journal to be published in.

Talk to me a little bit about your work and why you're interested in how animals perceive time

under their own environments.

Yeah, so we were interested in, like you say, how different animals perceive the world.

And one of the ways you perceive the world that we often forget about is what we call temporal

perception. That is how you perceive time, move, and past itself.

And as you mentioned, there are some animals perceive it a lot differently to us.

So one of the ways you can think about it is different animals have different

frame rates of the world. So they can see events at kind of a faster scale or a slower scale.

So on one end, the extreme end, you have things like dragonflies,

which you can see in what we call a flicker fusion rate of a 300 hertz.

What that means is they have a frame rate, a maximum frame rate in their visual system

of 300 frames per second. So if you can imagine every second,

it's sliced up to 300 still images almost stacked up together for that dragonfly.

On the other opposite end of the scale, you have things like starfish and your garden snails.

They can't even see one frame per second. So their flicker fusion rate,

the measure that we use, is something around 0.5, 0.65 hertz.

So again, that's about a frame every two seconds.

So for them, the world is basically a blurb.

So if you can imagine you're driving in the car and you look at the side window,

everything's kind of blurred past you. It's called motion blurb.

That's your visual system, not coping with the speed events happening around you.

And basically just kind of blurring all those images together and giving you this kind of messy

view of the world. So yeah, we're interested to understand why there's this difference between animals.

I know you didn't do experiments yourself with this paper,

it was an analysis of all the information inside there.

But how do we know the refresh rate of an animal?

Yeah, so that's a great question. So some of our team actually did do some experiments with humans,

which is kind of easy in compared to some other animals.

And what we do is we measure a thing called the flicker fusion rate,

sort of critical flicker fusion rate. And it's a very simple concept really.

So if you had a bulb in front of you and you had a flashing at say,

on and off 10 times per second, and you'd ask the observer, can you see that flashing?

They say, yes, then you go, okay, you can see 10 frames per second.

Then you keep increasing that flashing up and up until the observer says,

I can't see that anymore. So for humans, you can do this flashing on and off.

And we pretty much reach our limit at 65 flashes per second.

At 65 flashes per second, it looks like constant light to us.

Exactly. So after that, you're just saying the light is on.

You can't tell whether it's alternating on or off or whether it's just a solid light.

And in fact, that's probably happening to many of the listeners right now,

many lights are on AC current, which means that they're flickering on and off at an incredibly

high rate, something around a tree, tree 30 or something like that. So we can't see many things

of the world around us like that because our eyes aren't fast enough.

So for other animals, obviously, you can't always ask an animal.

You can do behavioral experiments, but it's tricky.

So what you do is you use what's called a retro-electrogram,

which is you hook an electrode up to the cornea of the eye,

depending on the type of eye you're talking about.

And you can actually directly measure the neurons firing rate

as they pick up that information.

And you can actually see the neurons firing in concert

with that flashing light. So you can actually see the frequency of flashing

matching the light.

And then as soon as you can't see it anymore, it goes steady.

So it's a really nice way that you can measure pretty much any animal out there,

very simple that way.

And what's nice about that is it's a real clear limit that you can say,

this animal cannot see past this frame rate full stock.

Yeah, I love that because in this program, we often come across approximations,

but this sends a really nice, clean signal that you can actually say,

certainly with animals with specific standardized sort of eyes,

you know, as we see the world.

There are lots of animals, of course, that do not have standardized.

For example, compound eyes or eyes that sort of stretch the definition of eye

completely, either other animals that aren't included in the study

or are included in the study that have completely different eyes to us.

No, we were able to include across the range of eye types.

So for example, I mentioned we have starfish in the study.

So you can measure, again, you can, for starfish day of many eyes,

and yes, they do have eyes, you can measure for each of,

in that case, they have many small simple eyes.

And you can find a neuron associated with those small eyes,

and basically see how that neuron is firing itself.

So you can do it for compound eyes, such as an insects,

relatively easily as well.

It's the same idea you just find where the neuron is

and pick up that firing race.

Right. So if you have numerous eyes,

and they are one a second, say you had 60 eyes,

would that not be 60 frames a second if they were firing at different times?

Yeah, no, that's a great question.

So one, the way we looked at is what is for any photoreceptor.

So that could be, you know, for us, our whole eye, I guess,

you know, because we have the one set of neurons going through

or for a compound eye, you could look at every specific one.

We just want to see what as the maximum any eye could do,

any photoreceptive structure could do.

So we, we, of course, it's very simplistic when I'm saying

is that that firing, that that frame per second,

because you could have one part of the eye,

not all are retinal cells aren't firing in sync, right?

So you can get around that.

And that's what insects are probably doing as well.

But there is still that limit.

You can look at any photoreceptor and say,

that's as fast as it gets, that's it.

Doesn't, there's no change to it effectively.

All right, but if we then look at the eyes of a starfish

and we consider that evolution forces us to often choose,

I mean, I use that word very loosely,

between certain adaptations for our environment,

there's effort that goes into being able to sense light

and process it.

And so I'm wondering with a starfish's eyes seemingly so poor,

why does it advise at all?

Well, they're quite simple eyes in the example of starfish,

but it's still quite useful to know whether it's basically

very bright or very dark.

That can tell a starfish whether it's out in the open

or under some rocks under some nice cover.

Right.

It can tell you if there's a looming shadow over you,

which could be a potential predator.

So in evolution, it's the case of good enough is often good enough.

So you don't have to have a perfect image of the world,

but a good enough image that's useful for you.

Let's talk about the dragonfly then,

because the dragonfly, of course, is the opposite.

You kind of refer to how it sees it,

so almost like bullet time,

like, you know, that everything seems just low

that would be for us very slow down.

What sort of frame rate does it have?

Do you set something about 300?

What does that mean in terms of how it perceives this environment?

And why does it need to be so high-deaf

when it comes to this ability to see things very clearly

and very quickly?

Yeah, sure.

So a dragonfly is a really lovely case of this,

because so it can see about 300 frames per second

as the way we're kind of saying it.

So that basically means that they can see all that really small movement.

So if you imagine a kind of an evening in your watching birds fly around

or insects flying around,

it's a bit blurry.

You can't quite get the detail of the movement.

But for a dragonfly,

it can really see the very clear movement of those small flies.

And that's really important,

because that's what it does.

It's a predator of flies,

and it does it on the wing.

So it's almost like a jet fighter flying very fast,

maneuvering very quickly.

And so it needs that really fine-scale information

in order to track and then capture its prey.

And that's what our study was really about.

So why do we see starfish have very, very slow eyes?

Well, something like a dragonfly has very fast eyes.

The reason as we found in our study was

things that can fly,

and things that are what we would call pursuit predators.

They can see a lot more quickly,

because they need to.

Evolutionists selected them to have those fast eyes

so they can act on that fine-scale information.

Do we have any idea what it feels like then

to be a dragonfly?

I mean, is there any analogy that you think works

knowing what you know about how they see?

We get this question all the time,

and it's kind of a tricky one

because so we feel time at our 65 frames per second

and that's kind of how we feel it.

So it's almost impossible to push yourself

into a dragonfly's perspective.

Because for them, 300 frames per second is just normal.

So that's just how they feel.

But from our perspective,

if we just kept in our human brains,

it would probably look like that bullet time.

So you could see that those fine-scale movements,

they would just seem like seamless movement.

They wouldn't be at all this blur.

But the thing is, you can never know what it's like

to sense that time

because then you'd have to be a dragonfly

and you couldn't really process that information.

So that's one of those things

that you can never understand

what something feels like in another organism

because you're trying to use your human brain

and its experiences to understand there.

So the answer is we can't really say that.

I'm very much to understand the human experience.

Talk to me about the interesting patterns you see

because there were some correlations in the study

between those who saw fast, those who saw slow

and their environments

or the sort of behaviors that they have.

Yeah, sure. So the first big thing we saw

was things that could fly

and things that were what we call

pursuit predators could see faster.

And that makes sense.

They move fast so they need to see faster.

But we found some other interesting things as well.

So we found, for example,

things in light environments,

so diurnal animals like ourselves,

they can see faster than things in darker environments

like nocturnal animals or deep sea animals.

And the reason for that is in a darker environment,

you actually don't really want your eyes to be that fast.

You want your eyes to be better at just picking up

any light at all.

You're kind of trading it off.

So any photographers out there might know

if you want to take photos of stars and stuff.

One of the tricks you can do is just

basically allow a longer time for light

to hit the film itself.

So you basically extend that time frame.

And our eyes and dark environments do that as well.

They don't fire as quickly,

so they can catch a few more photons

to make sure what they're seeing is there.

So to really capture that.

And so we see that that change between

darker and light environments.

The other thing we found was in marine environments,

we saw what we call ballistic predators.

So the term we came up with ourselves,

which are those predators that kind of sit there.

And when they see a prey,

they lunge at it and that's kind of the interaction.

So pursue predators have this big lung chase

like a cheetah, for example.

Our ballistic predators are more like a sit and weight lunge

and it's all in.

And we saw that the marine ballistic predators

could see quite fast,

but the terrestrial ones couldn't.

We didn't understand the first why,

but what we think is happening here

is in the terrestrial environment,

something like a jumping spider,

so like a zebra spider that we get here in Ireland.

What they do is they sit and they wait for their prey.

When they see it, they track it,

make their little calculations and then jump.

Once they've jumped, that's it.

They can't do anything else anymore.

They're in their airborne.

They can't maneuver.

So having fast eyes in that scenario

doesn't really help you that much.

Because once you've committed,

you can't act on any changes the predators do.

And so it's not really worth the investment.

In a marine environment, however,

so a pike going a lunging at a prey,

they can move every little millisecond

right up until the end of the interaction.

This would require further experiments, for example.

But this is what we think may be happening

in those two different environments.

It was not expected at all in our results.

Yeah, it's really exciting to kind of see things

that are new and try and figure out why might that be.

Thank you so much for talking to us about this research.

I'd love to have you back on

because this is just,

it's always great to have new insights,

particularly from Irish researchers.

It's Dr. Kevin Healy from University of Goldways,

School of Natural Sciences.

Thanks very much for your time.

Future proof extra with Jonathan McRae,

proudly supported by Research Ireland.

On News Talk.