Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

The bigger and brighter an object, the harder it is to perceive its motion

17.07.2003


Bigger and brighter isn’t better, at least not when trying to view moving objects.



That is the counter-intuitive result of a study performed by a team of Vanderbilt psychologists which sheds new light on one of the most sophisticated processes performed by the brain: identifying and tracking moving objects.

“The bigger an object, the easier it is to see. But it is actually harder for people to determine the motion of objects larger than a tennis ball held at arms length than it is to gauge the motion of smaller objects,” says Duje Tadin, first author of the paper on the study appearing in the July 17 issue of the journal Nature. Tadin is a graduate student in psychology at Vanderbilt and his co-authors are postdoctoral fellow Lee A. Gilroy and professors Joseph S. Lappin and Randolph Blake.


In the article, the researchers show that this unexpected result is due to the way in which visual signals are processed in the part of the brain known as the medial temporal visual area or MT, one of the 30-plus cortical centers involved in processing visual signals. Their findings support the hypothesis that the neurons in MT employ a mechanism called “center-surround receptive field organization.” This same mechanism, which acts to highlight differences, is found in a number of other senses, including touch, hearing and smell.

In the visual system, the center-surround organization is a clever way that nature has developed for filtering out spurious signals caused by shifting patterns of light that fall on the retina that don’t have anything to do with the movement of objects in the external world.

One of the most difficult things that the brain does is pick out objects from the visual background. Objects can differ from the background in a number of different ways, including texture, color, brightness, binocular displacement (the difference in image placement in each eye due to the distance between them) and motion. So the brain uses these and a number of other visual clues to pick out individual objects.

Information from the eyes goes first to the primary visual cortex at the very back of the brain. Here the information is separated into different characteristics, such as texture, color, brightnes and motion.

But how does the brain “see” motion? Just detecting shifting light patterns is not enough. Each time you shift your eyes or move your body, for example, the patterns on the retina change in ways that must be ignored. That is where the researchers think that center-surround receptive field organization comes in. Neurons in the primary visual cortex relay motion information to the neurons in MT, an area that Vanderbilt neuroscientist Jon Kaas helped discover. Experiments indicate that in the center of the visual field MT each neuron “monitors” an area that is the size of a tennis ball held at arms length. However, each neuron is not just affected by what happens in this central area. It is also influenced by the responses of the neurons that monitor a surrounding area about the size of a soccer ball (held at arms length).

The central-surround mechanism works as follows. Each neuron has a preferred direction: right, left, up, down, sideways, et cetera. If a neuron that prefers right motion detects a motion to the right while the neurons in its surround area are not registering any motion, then it fires vigorously. If the neurons in its surround area are stimulated by leftward motion, however, then it sometimes fires even more vigorously. But, if the surrounding neurons are also registering motions to the right, the neuron does not fire. This inhibitory effect is the hallmark of the center-surround mechanism.

“This is what causes moving objects to stand out distinctly even against moving backgrounds,” Lappin comments, “But when objects are the size of the surround area or larger, then they tend to be treated as background motion and so are less visible.”

The researchers discovered this effect when they analyzed the results of a series of psychophysical experiments in which human observers were asked to determine the direction of motion of patterns of varying speed, size and contrast that were flashed briefly on a screen. Not only did these experiments confirm that people have more trouble determining the motion of larger objects, they also showed that this effect was greatest in conditions of high contrast. The influence of surrounding neurons weakens as contrast levels decline.

“This shows that the visual system adapts to the amount of information available. When visual information is plentiful, it uses a differentiation strategy to identify moving objects. As light levels drop, however, it switches to an integration strategy that uses the available information more efficiently,” says Lappin.

Once the researchers had successfully documented the odd side-effect of this motion-enhancing mechanism – that it is harder to determine the motion of larger objects – they designed a series of follow-on experiments that pinpointed the effect to MT. They did so by applying what is known about how MT works to predict how observers should respond to another set of experiments, running the experiments and comparing the results with the predictions. For example, they knew that MT neurons are not very responsive to color. So they revised their experiments so that the patterns were produced by color motion. As predicted, they found that the center-surround effects did not appear.

David F. Salisbury | EurekAlert!
Further information:
http://www.exploration.vanderbilt.edu

More articles from Studies and Analyses:

nachricht WAKE-UP provides new treatment option for stroke patients | International study led by UKE
17.05.2018 | Universitätsklinikum Hamburg-Eppendorf

nachricht First form of therapy for childhood dementia CLN2 developed
25.04.2018 | Universitätsklinikum Hamburg-Eppendorf

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

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

Im Focus: Explanation for puzzling quantum oscillations has been found

So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics

Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...

Im Focus: Dozens of binaries from Milky Way's globular clusters could be detectable by LISA

Next-generation gravitational wave detector in space will complement LIGO on Earth

The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...

Im Focus: Entangled atoms shine in unison

A team led by Austrian experimental physicist Rainer Blatt has succeeded in characterizing the quantum entanglement of two spatially separated atoms by observing their light emission. This fundamental demonstration could lead to the development of highly sensitive optical gradiometers for the precise measurement of the gravitational field or the earth's magnetic field.

The age of quantum technology has long been heralded. Decades of research into the quantum world have led to the development of methods that make it possible...

Im Focus: Computer-Designed Customized Regenerative Heart Valves

Cardiovascular tissue engineering aims to treat heart disease with prostheses that grow and regenerate. Now, researchers from the University of Zurich, the Technical University Eindhoven and the Charité Berlin have successfully implanted regenerative heart valves, designed with the aid of computer simulations, into sheep for the first time.

Producing living tissue or organs based on human cells is one of the main research fields in regenerative medicine. Tissue engineering, which involves growing...

Im Focus: Light-induced superconductivity under high pressure

A team of scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg investigated optically-induced superconductivity in the alkali-doped fulleride K3C60under high external pressures. This study allowed, on one hand, to uniquely assess the nature of the transient state as a superconducting phase. In addition, it unveiled the possibility to induce superconductivity in K3C60 at temperatures far above the -170 degrees Celsius hypothesized previously, and rather all the way to room temperature. The paper by Cantaluppi et al has been published in Nature Physics.

Unlike ordinary metals, superconductors have the unique capability of transporting electrical currents without any loss. Nowadays, their technological...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Save the date: Forum European Neuroscience – 07-11 July 2018 in Berlin, Germany

02.05.2018 | Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

 
Latest News

Supersonic waves may help electronics beat the heat

18.05.2018 | Power and Electrical Engineering

Keeping a Close Eye on Ice Loss

18.05.2018 | Information Technology

CrowdWater: An App for Flood Research

18.05.2018 | Information Technology

VideoLinks
Science & Research
Overview of more VideoLinks >>>