We are constantly inundated with new information, and to manage it effectively it's sometimes necessary to forget old, irrelevant memories.

Researchers at Vanderbilt University have now developed an algorithm that mimics this kind of forgetfulness in robots, as a way to filter out less useful information.

"Forgetting is a critical capability when operating in dynamic environments," says PhD student Sanford Freedman, who presented the group's data filtering-software, called ActSimple, in a paper published at the IASTED Robotics and Applications conference held this week in Cambridge, MA.

ActSimple draws on two facets of human memory: time-based decay, or the way that memories disappear over time, and interference, which is the failure to recall information due to other memories competing for attention. ActSimple assigns different pieces of data values depending on how often they are used, and how similar it is to other pieces of information.

To test the software, the researchers used it to control a simulated robot that measured the strength of WiFi signals in a virtual environment. The robot recorded WiFi readings on a scale of 1-100, as it moved through the virtual setting and these WiFi readings also had different levels of noise (errors) associated with them. At intervals, the robot relied on its memory to create an estimated WiFi signal map by recalling signal strength information it had gathered and stored. The researchers tested ActSimple against four other algorithms, including one that strictly disregarded the oldest information, and another that out filtered random information.

The Team found that on average, ActSimple created the most reliable estimated WiFi map. Interestingly, when the robot "remembered" everything--that is, used all of its gathered information (errors and all)--it generated the least accurate map overall.

Why do we remember some seemingly mundane details of our day while forgetting others? Researchers from Caltech are chipping away at this question by studying the brains of epilepsy patients undergoing a procedure to locate the source of their seizures.

Ueli Rutishauser, a researcher at the California Institute of Technology, in Pasadena, recorded electrical activity from single neurons in part of the brain responsible for memory in these patients as they looked at a series of pictures. He later showed the patients another set of pictures, some new and some previously shown, and asked them which they had seen before. He then searched for differences in the brain activity recorded when the patients were shown pictures that would later be forgotten or remembered.

Rutishauser found that a patient was highly likely to remember a picture if the activity of a single neuron was correlated to a broader electrical rhythm in the brain called the theta rhythm--this four-to-eight hertz rhythm results from large populations of neurons firing synchronously. The correlation "also predicts the confidence that they will remember it," he says. "If they remember it strongly, the correlation will be even stronger. If they are guessing, the correlation will be weak."

It's not yet clear what regulates the phenomena, it might be a function of attention, motivation or some unknown property of the internal circuit dynamics of the brain, says Rutishauser. "We want to figure out what regulates it so that we can change it, perhaps allowing for the creation of stronger memories." The research was presented at the Society for Neuroscience conference in Chicago this week.

In this illustration of the Casimir force, a tiny gold sphere and plate experience "stiction" (right). But with the right combination of materials, as at left, where a gold sphere is paired with a silica plate, the Casimir force reverses, becoming repulsive. Future nanoscale devices might take advantage of this effect. Credit: U. Christensen

When two objects are so close together that the distance between them is about the same size as quantum fluctuations called virtual particles, they're pulled together. This effect, caused by the Casimir force, is not something that humankind has had to worry about until recently. But as researchers develop nanomechanical devices for communications and computation, so-called "stiction" has emerged as a potential stumbling block that might, for example, limit the density of memory chips. But there's a flip side to the Casimir force that might enable, rather than hinder, nano devices. Hendrik Casimir, who described his eponymous force in 1948, and Evgeny Lifshitz, who expanded his work, predicted that at slightly larger distances, this force should turn repulsive. Now researchers at Harvard University and the National Institutes of Health have seen this repulsive force in the lab for the first time.

The researchers reversed the Casimir force through their choice of materials. Whether the force is attractive or repulsive, it turns out, depends on the relative dielectric permittivities of the two surfaces and of the medium that lies between them. (Dielectric permittivity is a material property that describes how a material interacts with electrical fields.) When the researchers brought together a gold-coated sphere about 40 micrometers in diameter and a silica plate, both submerged in the liquid bromobenzene, they measured a repulsive Casimir force. The gold sphere was attached to an atomic force microscope, which was used to detect this repulsion. These results are described in the journal Nature.

These results suggest that it should be possible to create stictionless, friction-free nanomechanical devices based on what the researchers call quantum levitation. It's not yet clear what applications will be found for quantum levitation, but according to a press release from Harvard, the researchers have filed a U.S. patent covering nano devices based on the phenomenon. Think friction-free ball bearings and ultrasensitive chemical detectors.

The Harvard researchers were led by Federico Capasso, a physicist who developed the first quantum-cascade laser at Bell Labs in the mid-1990s. He has also been featured in our 10 Emerging Technologies section in 2007 for his work on optical antennas.