Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Rethinking How the Brain Sees Visual Features

16.07.2003


Brain scientists will have to rethink the current theory of how the visual processing region of the brain is organized to analyze basic information about the geometry of the environment, according to Duke neurobiologists. In a new study reported in the June 26, 2003, Nature, they studied the visual-processing region -- called the visual cortex -- of ferrets, as the animals’ brains responded to complex patterns.



The results, they said, indicated that clusters of neurons in that region do not specialize in recognizing a particular combination of stimulus features, as previously believed. Rather, individual clusters react to a broad range of stimulus combinations -- combinations that can be predicted by understanding the fundamental spatial and temporal properties of the visual stimulus. The scientists’ research was supported by the National Eye Institute.

The visual cortex -- a layer of brain tissue at the back of the head -- is the first area within the cerebral cortex that processes neural signals from the eye. It performs the basic tasks of recognizing the geometric features of a scene before relaying that information to higher brain regions, where such basic visual data are transformed into the conscious perception of the visual world.


Current theory of visual cortex organization holds that in mammals, including humans, the visual cortex consists of overlapping "feature maps." Each map is an orderly arrangement of neuronal clusters that represents a particular stimulus feature, such as the orientation of edges, their direction of motion, or their spacing. Before these new experiments were performed, it was thought that the response properties of neurons could be predicted by their location relative to the places in the visual cortex where different feature maps overlap. In this view, clusters of neurons are "specialists" for the detection of certain combinations of visual features, such as a set of parallel lines of a certain orientation, spaced a certain distance apart and moving at a specific speed.

In their experiments, Duke neurobiologists -- graduate student Amit Basole, Assistant Professor Leonard White and Professor David Fitzpatrick -- decided to go beyond previous studies in which animals were exposed only to simple visual stimuli consisting of parallel bars, or gratings, with different spacings and moving at different speeds at a right angle to the bars.

"Studies with gratings can tell you a lot," said Fitzpatrick. "For example, you can get a sense of maps of orientation if you change the orientation of the grating. And you can also get information about how properties like spatial frequency are mapped by changing the distance between the bars in the grating, and mapping how that changes patterns of neural activity.

"The underlying assumption was that, in a sense there was a ‘place code’ for stimulus combinations," said Fitzpatrick. "So, a particular orientation, spatial frequency or direction would activate a certain cluster of neurons in the cortex; and changing the orientation, direction or spatial frequency would shift the locus of activity in a predictable way -- one that signified which attribute had been changed."

However, said Fitzpatrick, "these stimuli are really limiting because you can only look at certain stimulus combinations." To explore how the visual cortex reacted to more complex combinations of stimuli, the researchers exposed ferrets to patterns consisting of short line segments whose orientation, length, direction and speed of motion could be varied independently.

Said White, "With these texture patterns, we have the ability to let different properties interact with one another in ways that are closer to the kinds of stimulus interactions that are often present in the visual environment." A striking example of such interactions is the so-called barber pole illusion, he said.

"While the barber pole is moving horizontally as the pole spins about its axis, it creates a perception that the lines are moving up," said White. "The perception induced by the interaction between the orientation of the lines and the direction of motion is the sort of phenomenon that Amit was seeking to understand in terms of neural responses."

The researchers used a technique called optical imaging to detect brain activity in the animals’ visual cortex by shining light of wavelengths that specifically revealed increased blood flow to more active areas. Also, to confirm that the images portrayed actual increases in brain activity, the researchers also recorded electrical activity of individual neurons in different cortical regions during exposure to the patterns.

The effects of changing the visual stimuli on the activity patterns in the animals’ brains were surprising, said Fitzpatrick.

"From the prevailing view, if you kept the orientation of the bars constant and varied the other parameters, you might not expect to see much of a change in the maps of activity," said Fitzpatrick. But, in fact, we saw shifts in activity that were much greater than we expected, and the patterns looked identical to those that were produced by textures that had different combinations of line orientation, direction, length and speed.

"So, this makes clear that thinking about maps in the cortex as consisting of clusters devoted to particular combinations of features is too simplistic when you’re dealing with stimuli that are much more like those you encounter in the visual world," he said.

"What we’re seeing is that a given spot in the cortex seems to be integrating a number of different stimulus components. All of these components figure into what determines the activation of a given spot in the map."

In this new way of thinking about the visual cortex, it is still possible to consider the clusters of neurons as specialists; neurons in these new studies responded to complex visual patterns with remarkable selectivity, said Fitzpatrick. However, these findings show that what these clusters specialize in is not the recognition of a unique combination of stimulus features, but the detection of a narrow band of spatial and temporal information that may be produced by a surprising large combination of stimulus features.

The researchers plan further studies to attempt to understand how the visual cortex is organized -- for example, seeking to obtain faster snapshots of brain activity, to obtain more detail in changes in brain activity. They are also working with other colleagues to create mathematical models that might reveal the strategy by which the brain has organized its visual perceptual circuitry.

For additional information, contact:

Dennis Meredith
phone: (919) 681-8054
email: dennis.meredith@duke.edu

Dennis Meredith | Duke University
Further information:
http://www.duke.edu

More articles from Studies and Analyses:

nachricht Drone vs. truck deliveries: Which create less carbon pollution?
31.05.2017 | University of Washington

nachricht New study: How does Europe become a leading player for software and IT services?
03.04.2017 | Fraunhofer-Institut für System- und Innovationsforschung (ISI)

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: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>