This praying mantis is sporting some unusual eyewear:
3D glasses.
Jenny: Would you like to hold her on your hand?
Ali: Oh my god, she moves in a kind of strikey sort of way.
These simple bits of coloured plastic are helping
untangle the inner workings of the mantis brain.
Ali: Oh my god.
I’m Ali Jennings and I’ve come to Newcastle in the UK,
where researchers are testing mantis’s sophisticated visual abilities
and mapping the brain cells responsible for their 3D vision.
Jenny: So the cool thing about praying mantids are, as far as we know at the moment,
they're the only insects that actually have stereoscopic depth perception.
Stereoscopic vision in humans involves some pretty complex neural circuitry.
Understanding how such a small insect brain manages the task
could help engineers design machines that can see in 3D.
Ali: She is beautiful.
Mantis brains: How to see in 3D
Praying mantises are formidable hunters.
Like humans, their depth perception depends on having two eyes set slightly apart,
so that each eye sees the world from a slightly different angle.
Comparing the two images allows the brain to estimate how far away an object is.
For decades people have used 3D glasses to create the illusion of depth.
Two images can be laid on top of each other,
each a different colour and in a slightly different position.
Coloured lenses filter out one of the colours so that each eye only sees one of the images,
tricking the brain into thinking it’s seeing a 3D object.
Jenny: So what’s going on here is we’re displaying this disc twice, once for your
left eye and once for your right eye, in two slightly different positions.
Jenny Read is using 3D glasses to test stereoscopic or 3D vision in mantises,
but the images work just as well on humans.
Ali: Yeah it’s like a single black spot that’s just jumped out of the screen.
It’s about there.
I feel like a mantis.
Just like me, when a mantis thinks it sees something within striking distance,
it tries to grab it.
And Jenny uses this behaviour to test their 3D vision.
Jenny: So we can use our 3D to manipulate the apparent distance of objects and when
an animal reaches out and tries to grab it, then we know it’s seeing it in 3D.
Jenny: There she goes.
Ali: That’s amazing.
But mantis vision doesn’t work exactly like ours – they can see some things that we can’t.
Jenny showed me another kind of stimulus,
where the solid circles were replaced by this moving pattern.
The mantis grabs out as before, apparently seeing a 3D shape,
but when I looked I couldn’t make sense of it.
Ali: Ah!
I can see a circle but it’s not 3D.
Urgh. It’s weird.
Jenny: So in this image your left eye is looking at a pattern of random dots and your right
eye is looking at a completely different unrelated random pattern of dots.
The mismatched inputs in each eye meant my brain couldn’t interpret what I was seeing
as a single object. But mantis vision is different – it seems to be based more on change –
in other words which bits of the image are moving.
But how does it work?
To find out Ronny Rosner has begun to map the nerve cells involved.
Ali: What’s that noise?
Ronny: These are the electrical pulses neurons use to communicate with each other.
Ronny places electrodes inside individual neurons in a mantis’s brain and records
electrical signals while showing the mantis the 3D moving circle.
Ronny: And it looks like this neuron might actually be a visual neuron. I think it responded
to our swirling disc stimulus.
Ronny uses this set up to figure out what it is particular neurons are responding to.
Once he’s found an interesting neuron, it’s off to the microscope to have a closer look.
Ronny: So what you are seeing here is an actual nerve cell in the praying mantis brain that
has been stained. And now finally we know how the neuron actually looks like
which we recorded earlier on.
Ronny is then able to construct 3D images of each nerve cell he studies.
Ronny: This particular cell is one of the most exciting neurons we recorded from, because
it responds to prey-like objects in the striking range of the praying mantis.
Ali: So when we saw the mantis striking a neuron like that would have been firing.
Ronny: Exactly.
And you can get a better understanding in this way of where the neuron might receive input,
right here for example, or here, and where it might send its output, here or here.
Ronny hopes to build a map of all the neurons involved in 3D vision in the mantis.
Since they’re relatively small and simple creatures, you might expect that the wiring behind their
stereoscopic vision would also be very simple.
But Ronny and Jenny are discovering some surprisingly sophisticated circuitry.
Jenny: What Ronny’s finding is that there’s actually a multitude of neurons, different
classes of neurons that are tuned to different distances and different directions.
So it seems like the circuitry underlying mantis stereopsis is surprisingly complex and actually
quite similar to what we find in mammals.
But mantises do see differently to us. They base their depth perception on changes and
movement in the images they’re seeing.
Jenny: And it seems that using change in this way may be the key to making stereopsis simple
enough to be implemented in an insect brain.
Ali: So if you can work out the circuitry behind mantis 3D vision,
can you use that in some way?
Jenny: Yeah, I think so. People have already tried to give machines 3D stereoscopic vision
but many of those algorithms have been based very much on human style stereopsis.
Which of course might be entirely appropriate for some applications, but there are other situations
where for example if you had a very low power robot, maybe an autonomous drone, where it
has to be lightweight, can’t have a lot of battery life, then maybe mantis stereopsis
which is based on change over time might be a good avenue to explore.
A robot with mantis-like vision could be simple yet effective.
And having another model of stereopsis to work from
could help engineers come up with a whole new design for robot vision.
But actually figuring out every element of these complex circuits will take more time,
more experiments,
and of course more mantises wearing tiny 3D glasses.
Ali: I'm just wondering, like, so basically can it, can it stab through my skin...
Jenny: No, no, don't worry, it can't do that.
Ali: I mean, that, that's...
Jenny: Well, I mean, not significantly. Not a lot through your skin.
There's not gonna be like major blood.
Ali: Wow, that is so unreassuring.