Feats of Strength Begin a Lizard's Day Thu, 28 Aug 2008 00:00:00 -0700 Male Jamaican anole lizards begin and end the day with displays of reptilian strength -- push-ups, head bobs and extensions of a colorful neck flap, or dewlap -- to defend their territory, according to a new study.
"Anoles are highly visual species, so in that sense it is not surprising that they would use visual displays to mark territory," said Terry J. Ord, a postdoctoral researcher at UC Davis and at Harvard University's Museum of Comparative Zoology. The lizards are the first animals known to mark dawn and dusk through visual displays, rather than the much better known chirping, tweeting, and other sounding off by birds, frogs, geckos and primates.
Ord studied four species of Jamaican forest lizard: Anolis lineatopus, Anolis sagrei, Anolis grahami, and Anolis opalinus. Females establish small territories allowing access to food and other resources, while males stake out larger territories allowing them access to several females. The males spend much of the day sitting on tree trunks and displaying head motions, push-ups, and dewlap extensions, all to warn other males away from their territory.
These displays of strength help avert actual physical confrontations between male lizards, which can be very fierce and destructive, Ord said.
Ord videotaped individual males at different times of day, from before dawn to dusk. In all four species, he found distinct peaks of activity at daybreak and for about two hours afterward, and again just before dark. Anoles leave their daytime perches at night to find safe shelter from nocturnal predators.
Scientists disagree on why birds chorus at dawn and dusk: competing ideas range from territorial defense to manifestations of circadian rhythms (the animal's internal clock). Ord said his work suggests male anoles use their morning displays primarily to mark territory.
"The dawn chorus may be a way of communicating having survived the night," Ord said. "If in the morning a bird doesn't hear its neighbor, or an anole doesn't see its neighbor, it may be an opportunity for the animal to expand its territory."
The research was funded by the National Geographic Society and National Science Foundation, and is published online by the journal American Naturalist. Memory Trick Shows Brain Organization Thu, 28 Aug 2008 00:00:00 -0700 A simple memory trick has helped show UC Davis researchers how an area of the brain called the perirhinal cortex can contribute to forming memories. The finding expands our understanding of how those brain areas that form memories are organized.
The brain puts together different items -- the what, who, where and when -- to form a complete memory. It was previously thought that this association process occurred entirely in a brain structure called the hippocampus, but this appears not to be the case, said Charan Ranganath, a professor at the UC Davis Center for Neuroscience and the Department of Psychology who led the research.
"We want to know how the brain areas that encode memory are organized," Ranganath said. "If your memory is affected by aging or Alzheimer's disease, is there a way to learn that can capitalize on the brain structures that may still be working well?"
Ranganath, along with graduate student Andrew Logan Haskins, Andrew Yonelinas, a UC Davis psychology professor and associate director of the Center for Mind and Brain, and Joel Quamme, a former UC Davis graduate student now at Princeton University, used functional magnetic resonance imaging (fMRI) to see which parts of the brain were active when volunteers memorized pairs of words such as "motor/bear" or "liver/tree." In this experiment, the volunteers either learned the pairs as separate words that could be fitted into a sentence, or as a new compound word, for example "motorbear," defined as a motorized stuffed toy.
"It's a sort of memory trick," Ranganath said.
When volunteers memorized word pairs as a compound word, the perirhinal cortex lit up, and this activity predicted whether the volunteers would be able to successfully remember the pairs in the future. The results suggest that the perirhinal cortex probably can form simple associations, such as between the parts of a complex object. This information is probably passed up to the hippocampus, which may create more complex memories, such as the place and time a specific object was seen.
The research, which was funded by grants from the National Institutes of Health, is published Aug. 28 in the journal Neuron. Robots Learn to Follow Thu, 28 Aug 2008 00:00:00 -0700 Whether driving on the highway or walking down the street, we pick up on both deliberate signals and unconscious cues to predict what other people are going to do and act accordingly. But robots have trouble following each other around, for example, when a leader turns a corner and disappears from sight. Researchers at UC Davis have come up with a control system that allows a robot to pick up on cues that the leader is about to turn, predict where it is going and follow it.
"The following problem is a quite fundamental problem in robotics," said Sanjay Joshi, associate professor of mechanical and aeronautical engineering at UC Davis. Robots that are better at following could be easier for people to work with, he said. A hospital robot could follow a doctor around the wards.
Humans use signals and unconscious cues to build a model that predicts where other people are going. Behavioral studies show that people unconsciously turn their heads a fraction of a second before making a left or right turn. Joshi and his team of researchers developed a control system that could take such behavioral cues into account in making decisions about which way to move.
Joshi, graduate student Michael Chueh, and undergraduate students William Au Yeung and Calvin Lei tested the system using a small commercially available robot, the Evolution Robotics Scorpion. The robot's camera could identify a target on the lead robot, and the robot's onboard computer could combine the target information with behavioral cue information.
Rather than have the lead robot signal the follower directly, the research team sent "behavioral cues" to the follower via wireless link. Effectively, the cues told the robot, "the leader might be about to turn right" or "might be about to turn left."
To develop a decision on how to move, the follower robot was programmed to take into account the lead robot's behavioral cues and the follower's prediction of the lead robot's movement, based on the leader's current speed and direction. Robots that incorporated behavioral information into their decisions performed much better at following the leader around corners than others, the researchers found.
"We think that if we can embed these cues in control systems, we can make following more reliable," Joshi said.
A paper describing the work is published in the August 2008 issue of IEEE Transactions on Industrial Electronics.
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