Researchers make new discovery about brain’s 3-D shape processing

While previous studies of the brain suggest that processing of objects and places occurs in very different locations, a Johns Hopkins University research team has found that they are closely related.

In research funded by the National Institutes of Health and published today in the journal Neuron, a team led by Johns Hopkins researcher Charles E. Connor reports that a major pathway long associated with object shape also carries information about landscapes and other environments.

Siavash Vaziri, then a biomedical engineering graduate student and now a post-doctoral fellow in the Connor lab, studied how neurons in the ventral visual pathway of the monkey brain respond to 3-D images. In one channel of the ventral pathway, neurons responded to small, discrete objects as expected. But in a neighboring, parallel channel, the researchers were surprised by the overwhelming responsiveness of many neurons to large-scale environments that surround the viewer, extending beyond the field of view.

"We were entirely surprised ourselves," said Connor, senior author of the paper. "Based on decades of research, we expected that all neurons in the ventral pathway would be primarily concerned with objects."

The ventral pathway is one of the two major branches of high-level visual processing in humans and other primates. It is sometimes called the “what” pathway, based on its role in identifying objects based on their shapes and colors.

"Dr. Vaziri’s finding is exciting because it puts environmental shape information together with object shape information in two densely connected neighboring channels. This could be a site for integrating object information into environmental contexts in order to understand scenes," Connor said.

Vaziri used microelectrodes to study how individual neurons responded to a large variety of 3-D shapes projected onto a large screen. Depth structure was conveyed by shading, texture gradients, and stereopsis, the effect used in 3-D movies. The shape stimuli evolved during the experiment based on the neuron’s responses, sometimes in the direction of small objects near the viewer, sometimes in the direction of environments filling the screen and surrounding the viewer.

Connor, a professor of neuroscience and the director of the Zanvyl Krieger Mind/Brain Institute at Johns Hopkins, is a noted expert on the neural mechanisms of object vision. His research focuses on deciphering the algorithms that make object vision possible and explain the nature of visual experience.

"Many people would say that vision is our richest and most vivid experience," said Connor. "We want to understand the brain events that create that experience."

Connor said that the next step will be to understand how object and environment information are integrated between the two channels.

"We don’t typically experience objects in isolation," Connor said. "We experience scenes, that is, environments containing multiple objects. We now think that the ventral pathway may be where all that information gets put together to create scene understanding."

Neurons express ‘gloss’ using three perceptual parameters

Japanese researchers showed monkeys a number of images representing various glosses and then they measured the responses of 39 neurons by using microelectrodes. They found that a specific population of neurons changed the intensities of the responses linearly according to either the contrast-of-highlight, sharpness-of-highlight, or brightness of the object. This shows that these 3 perceptual parameters are used as parameters when the brain recognizes a variety of glosses. They also found that different parameters are represented by different populations of neurons. This was published in the Journal of Neuroscience.

The gloss of an object surface provides information about the condition of that object. For instance, whether it is wet or dry, whether food is fresh or old. Several gloss-related physical parameters such as specular reflectance and diffuse reflectance have been described and used in computer graphics so far. However, the parameters used when neurons respond to gloss have not yet been found.

A Japanese research group led by Hidehiko Komatsu, professor of the National Institute for Physiological Sciences (NIPS), National Institutes of Natural Sciences (NINS), in collaboration with the Advanced Telecommunications Research Institute International (ATR) prepared 16 images representing various glosses and showed them to monkeys. In a circumscribed area in the inferior temporal cortex of the brain, neurons strengthened their responses proportionately as the contrast-of-highlight and/or sharpness-of-highlight got higher. Neural responses also vary greatly depending on the brightness, for instance, whether the object is black, gray, or white. Furthermore, the perceptual gloss parameters of the presented image could be fairly precisely predicted from the strengths of the population neural responses.

By the application of these findings in an artificial image recognition system, the researchers are expecting that it would be able to develop robots that recognize gloss like humans.

'Haven't my neurons seen this before?'

The world grows increasingly more chaotic year after year, and our brains are constantly bombarded with images. A new study from Center for the Neural Basis of Cognition (CNBC), a joint project between Carnegie Mellon University and the University of Pittsburgh, reveals how neurons in the part of the brain responsible for recognizing objects respond to being shown a barrage of images. The study is published online by Nature Neuroscience.

The CNBC researchers showed animal subjects a rapid succession of images, some that were new, and some that the subjects had seen more than 100 times. The researchers measured the electrical response of individual neurons in the inferotemporal cortex, an essential part of the visual system and the part of the brain responsible for object recognition.

In previous studies, researchers found that when subjects were shown a single, familiar image, their neurons responded less strongly than when they were shown an unfamiliar image. However, in the current study, the CNBC researchers found that when subjects were exposed to familiar and unfamiliar images in a rapid succession, their neurons — especially the inhibitory neurons — fired much more strongly and selectively to images the subject had seen many times before.

"It was such a dramatic effect, it leapt out at us," said Carl Olson, a professor at Carnegie Mellon. "You wouldn’t expect there to be such deep changes in the brain from simply making things familiar. We think this may be a mechanism the brain uses to track a rapidly changing visual environment."

The researchers then ran a similar experiment in which they used themselves as subjects, recording their brain activity using EEG. They found that the humans’ brains responded similarly to the animal subjects’ brains when presented with familiar or unfamiliar images in rapid succession. In future studies, they hope to link these changes in the brain to improvements in perception and cognition.