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Superior visual performance in nocturnal insects

Neural principles and bio-inspired technologies

Eric Warrant University of Lund, Lund, Sweden

Starlight is 100 million times dimmer

than sunlight

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Under a rainforest canopy light levels can be a further 100

times dimmer

Problem

Vision becomes unreliable in

dim light

Tarsier

Lesley Goodman

Compound Eyes

Compound Eyes

Fred Delcomyn

Dan-Eric Nilsson

Apposition eyes

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Superposition eyes

Photo: Michael Pfaff

The first animal known to see colour at night Kelber, Balkenius & Warrant Nature 2002

Photo: Michael Pfaff

The first animal shown to use the Milky Way for navigation Experiments under the natural sky and in the Johannesburg Planetarium

Dacke et al., Current Biology 2013

Scarabaeus satyrus

The nocturnal sweat bee Megalopta genalis

Photo: Ajay Narendra

Panamanian rainforest Barro Colorado Island

Does Megalopta use vision at night?

Landmark experiments

Warrant et al. Current Biology 2004

0.002 cd/m2

18:48 0.002 cd/m2

18:40 0.01 cd/m2

18:58 0.0001 cd/m2

18:58 0.0001 cd/m2

At night, when Megalopta is flying, how many photons are absorbed by each

photoreceptor every second?

4.7 photons s-1

•

“bumps”

300 ms

2 m

V

Measured hole contrast: 72%

Simple calculations of signal and noise show this to be about 100 times too little light for Megalopta to see its nest entrance at night!

18:45, 0.006 cd/m2, real time (2.3 s)

Landing precision in dim light (high-speed camera with IR illumination)

Emily Baird

18:45, 0.006 cd/m2, slowed down 10x

How can we account for this major anomaly?

Hypothesis: nocturnal bees might improve visual reliability by neurally summing photons in time and space

(Integration time ∆ t ) (Pixel size Δρp )

It is better to see a brighter world that is coarser and slower than to

see nothing at all

Spatial summation

Section: Wulfila Gronenburglamina

medulla

lobula

central brain

retina

Is the finest spatial frequency (νmax) that an animal can see at a given light intensity

improved by spatial and temporal summation?

(Units of ν : stripe cycles per degree of visual space)

activity window

Warrant 1999 Vision Research; Theobald et al. 2006 Journal of Experimental Biology

Optimum summationAt any given image intensity and velocity, the finest visible spatial frequency occurs at specific extents

of spatial and temporal summation, that is at a specific integration time (Δt) & pixel size (Δρp)

ν max

Warrant 1999 Vision Research

Without spatiotemporal summation

With optimal spatiotemporal summation

Thank You