Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Relative perception of the world

04.12.2015

Optical illusions show how the fly brain processes contrast and motion information

If the price of a product is reduced, willingness to buy increases – the product appears cheaper even though it is perhaps still too expensive. Our perception of the world is therefore often relative: we compare what we see with a reference point – in this case with the price before the discount. The same applies to the perception of luminance stimuli. An object appears brighter if the background is dark, and darker if the background is bright. Optical illusions help to analyze the perception of such relative contrast signals. What happens, however, at cellular level in the brain is largely unknown. Scientists at the Max Planck Institute of Neurobiology in Martinsried have now used behavioural experiments on the fruit fly Drosophila to show that spatial contrast information and motion stimuli are processed in different neural circuits.


The bar in this contrast illusion is uniformly grey, even if the right side of the bar appears darker than the left. If the luminance of the grey bar now changes, both humans and flies see a motion illusion.

© MPI of Neurobiology


Using sophisticated behavioural testing apparatus, neurobiologists are decoding the fruit fly's perception and the underlying neural circuits.

© MPI of Neurobiology

Optical illusions lead the observer to believe that they see something which actually isn't there. But this is not due to any problem with our eyesight. Instead, the specific conditions of the illusion show how the brain analyzes our environment. Several effects are based on relative perception: an object seems smaller if it is placed in the vicinity of large objects, or larger, if it is surrounded by smaller objects. Other illusions are based on spatial contrast. A uniformly grey bar in front of a background with a luminance gradient appears as if one side of the bar is darker than the other. Motion illusions, in contrast, simulate movement where there is none. If the previously mentioned grey bar brightens and darkens dynamically against the background gradient, for example, this gives the impression of movement. This illusion is known as a contrast motion illusion.

To understand how the brain processes the optical information, Alexander Borst and his Department at the Max Planck Institute of Neurobiology are studying a master of motion vision: the fly. Based on previous findings relating to the fly's motion vision, the animals are not supposed to respond to motion illusions like the contrast motion illusion. “Naturally, we wanted to know more about this”, says Armin Bahl, lead author of the study published in the scientific journal Neuron. The scientists used a sophisticated behavioural testing apparatus for their investigations: tethered to a small hook, the fly walks on an air-suspended polystyrene ball surrounded by a virtual environment. The movement of the ball indicates the direction in which the fly is walking. This in turn allows conclusions to be drawn about the animal's perception. When the scientists tested the contrast motion illusion in this experimental setup, they were surprised: flies responded very robustly to the illusions and perceived a supposed movement in the same direction, just as the human observers did.

Division of labour in the fly brain

To examine the new findings in greater detail, the researchers used genetic silencing to switch off the cells in the fly brain that are responsible for motion vision. Such flies are completely motion-blind, as a behavioural experiment proves: if a fly is surrounded by a rotating striped cylinder, wild-type flies will rotate concurrently with the movement – to the right if the cylinder turns to the right and to the left if the rotation is in a leftward direction. This innate behaviour exhibited by flies and many other animals is known as the optomotor response. It helps animals, and us humans as well, to stabilize our course and to fly or walk in a straight line. Motion-blind flies, in contrast, display no optomotor response.

When the scientists showed the contrast motion illusion to motion-blind flies, however, they did not find any difference compared to the behaviour of normal flies. “That was a really surprising result”, recalls Armin Bahl. The scientists concluded from this that spatial contrast and motion are computed and processed in different areas of the brain. “All the evidence suggests that the fly brain analyzes what it sees via a variety of neural channels: one channel for motion, another for spatial contrast and very probably additional channels for other features of the visual environment”, summarizes Armin Bahl. In response to the question of whether this is also the case for humans, Alexander Borst's answer is: "Very likely! The human visual system is also highly modular.” This work on contrast vision in flies thus helps us to understand how the brain perceives and processes the various stimuli in its environment.


Contact

Dr. Stefanie Merker
Max Planck Institute of Neurobiology, Martinsried
Phone: +49 89 8578-3514

Email: merker@neuro.mpg.de


Prof. Dr. Alexander Borst
Max Planck Institute of Neurobiology, Martinsried
Phone: +49 89 8578-3251

Fax: +49 89 8578-3252

Email: borst@neuro.mpg.de


Original publication
Armin Bahl, Etienne Serbe, Matthias Meier, Georg Ammer and Alexander Borst

Neural mechanisms for Drosophila contrast vision
Neuron, 3 December 2015

Dr. Stefanie Merker | Max Planck Institute of Neurobiology, Martinsried
Further information:
https://www.mpg.de/9766118/drosophila-contrast-vision

Further reports about: Drosophila Max Planck Institute Neurobiology Neuron Optical animals cylinder fly fly brain movement spatial

More articles from Life Sciences:

nachricht Bare bones: Making bones transparent
27.04.2017 | California Institute of Technology

nachricht Link Discovered between Immune System, Brain Structure and Memory
26.04.2017 | Universität Basel

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Bare bones: Making bones transparent

27.04.2017 | Life Sciences

Study offers new theoretical approach to describing non-equilibrium phase transitions

27.04.2017 | Physics and Astronomy

From volcano's slope, NASA instrument looks sky high and to the future

27.04.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>