Troy, N.Y. — The latest edition of the Oxford English Dictionary boasts 22,000 pages of definitions. While that may seem far from succinct, new research suggests the reference manual is meticulously organized to be as concise as possible — a format that mirrors the way our brains make sense of and categorize the countless words in our vast vocabulary.

“Dictionaries have often been thought of as a frustratingly tangled web of words where the definition of word A refers users to word B, which is defined using word C, which ends up referring users back to word A,” said Mark Changizi, assistant professor of cognitive science at Rensselaer Polytechnic Institute . “But this research suggests that all words are grounded in a small set of atomic words — and it’s likely that the dictionary ’s large-scale organization has been driven over time by the way humans mentally systematize words and their meanings.”

Dictionaries are built like an inverted pyramid. The most complex words (e.g., “albacore” and “antelope”) sit at the top and are defined by words that are more basic, and thus lower on the pyramid. Eventually all words are linked to a small number of words — called “atomic words,” such as “act” and “group”) — that are so fundamental they cannot be defined by simpler terms. The number of levels of definition it takes to get from a word to an atomic word is called the “hierarchical level” of the word. Changizi’s research, which was published online this week and will appear in the June print edition of the Journal of Cognitive Systems Research, indicates that the dictionaries we use every day utilize approximately the optimal number of hierarchical levels — and provide a visual roadmap of how the lexicon itself has culturally evolved over tens of thousands of years to help lower the overall “brain space” required to encode it, according to Changizi.

Many other human inventions — such as writing and other human visual signs — have been designed either explicitly or via cultural selection over time so as to minimize their demands on the brain, Changizi said. By conducting a series of calculations based on the estimation that the most complex words in the dictionary total around 100,000 different terms, and that the number of atomic words range from 10 to 60, Changizi was able to devise three signature features present in the most efficient dictionaries — as well as in their human counterpart, the brain. Most importantly, he discovered that the total number of words across all the definitions in the dictionary (and thus the size of the dictionary) changes in relation to the total number of hierarchical levels present. Optimal dictionaries should have approximately seven hierarchical levels, according to Changizi.

“The presence of around seven levels of definition will reduce the overall size of the dictionary, so that it is about 30 percent of the size it would be if there were only two hierarchical levels,” Changizi said. Additionally, users will find that there are progressively more words at each successive hierarchical level, and that each hierarchical level contributes mostly to the definitions of the words just one level above their own, according to Changizi, who put his three predictions to the test by studying actual dictionaries.

The Oxford English Dictionary and WordNet — a large, online lexical database of English, developed at Princeton University — were found to possess all three signatures of an economically organized dictionary, and thus were organized in such a way as to economize the amount of dictionary space required to define the lexicon, according to Changizi. “Somehow, over centuries, these revered reference books have achieved near-optimal organization,” Changizi said. “That optimality can likely be attributed to the fact that cultural selection pressures over time have shaped the organization of our lexicon so as to require as little mental space and energy as possible.”

Changizi believes his research has potential applications in the study of childhood learning, where scientists could analyze how students learn vocabulary words and possibly develop ways to optimize that learning process.

A newly discovered interplay of cells in one of the brain’s memory centers sheds light on how you recall your grocery list, where you laid your keys, and a host of important but fleeting daily tasks.

Scientists at Weill Cornell Medical College say their experiments with common goldfish are uncovering the secrets of a form of short-term recall known as “working memory.”

“We’ve now identified a mechanism that can organize the activity of groups of cells involved in this important form of recall,” says lead researcher Dr. Emre Aksay, assistant professor of computational neuroscience in the HRH Prince Alwaleed Bin Talal Bin Abdulaziz Al-Saud Institute for Computational Biomedicine at Weill Cornell Medical College in New York City.

“Furthermore, because deficits in working memory are often a precursor of schizophrenia, drugs that target this mechanism might someday help fight that debilitating disease,” he says.

The findings have been published in Nature Neuroscience.

Humans rely on their working memory every day to keep track of faces and names, tasks at school or in the workplace, and other important bits of information. “This process is distinct, neurologically speaking, from the storage and retrieval of longer-term memories,” explains Dr. Aksay, who is also assistant professor of physiology and biophysics at Weill Cornell.

Experts in labs around the world have developed theories as to how this process works. “Its basis lies in the ability of specific neurons to maintain a level of activity in the absence of input — a persistent firing rate — that’s finely coordinated across related groups of cells,” Dr. Aksay says.

But how do these brain cells communicate which each other to coordinate this activity”

To find out, Dr. Aksay, along with colleagues Dr. David Tank of Princeton University, and Dr. Mark Goldman of Wellesley College, turned to the common goldfish.

“It’s really quite difficult to test the function of individual brain cells in primates and higher animals during behavior, but the goldfish’s memory centers are much more accessible to research,” Dr. Aksay explains. “We looked specifically at the fishes’ oculomotor system — the neural circuitry that directs the fish to shift its eyes left or right based on stimuli in the local environment.” Because stimuli can be ever-changing and fleeting, the fish relies on its short-term memory to help guide these eye movements.

Two groups of cells are involved in this oculomotor memory, one in each half of the brain. Each group contains two types of neurons — inhibitory cells and excitatory cells, and it is the inhibitory neurons that allow the two groups to interact. “In our experiments, we used pharmacologic means to interrupt either excitatory or inhibitory pathways, and then we watched what happened to persistent firing,” Dr. Aksay says.

When the excitatory pathways were dampened, the persistence was impaired — suggesting that excitation is essential to the sustained firing that working memory requires.

“The real surprise came when we turned off many of the inhibitory pathways,” Dr. Aksay says. In that case, persistent firing remained, but was often present at inappropriate times.

“It appears that the inhibitory cells are not key or even required to generate persistent firing,” the researcher says. “Instead, they send a message from one group to the other that helps coordinate two sides: the role of inhibition in this system is to make sure that only one group is generating persistent activity at a given time. In this way, the goldfish doesn’t get a mixed signal telling it to move its eyes in both directions at once.”

This new finding has big implications for our understanding of the neural processes underlying working memory and the instantaneous decision-making that goes on based on that knowledge.

It might also have broader applications for psychiatric illness, Dr. Aksay notes.

“Many schizophrenic individuals, for example, show severe deficits in working memory, and children with working memory problems are at heightened risk of developing schizophrenia as adults,” he says. Dysfunction in key inhibitory pathways that link brain cells has long been associated with these problems.

“These findings suggest that it is necessary to address not only deficits in excitatory pathways that lead to a lack of persistent firing but also dysfunction in inhibitory pathways that lead to a lack of coordination among groups of cells,” Dr. Aksay explains. “This strategy could provide improved treatment options for people with schizophrenia.”

Source: New York- Presbyterian Hospital/Weill Cornell Medical Center/Weill Cornell Medical College

A new study in this month’s Journal of Personality and Social Psychology explains why NPR listeners always think they are right. When it comes to financial decisions or even concerns about terrorism, people are likely to be influenced by what others think but repeated exposure to one viewpoint can have almost as much influence as exposure to shared opinions from multiple people.

Hearing an opinion multiple times increases the recipient’s sense of familiarity and in some cases gives a listener a false sense that an opinion is more widespread then it actually is.

In a series of six experiments that included 1044 students, from the University of Michigan, Princeton University, Rutgers University, University of Michigan – Dearborn, University of Toledo and Harvard University, researchers sought to understand individuals’ accuracy in identifying group norms and opinions. The experiments included dividing students into three groups, (three person control group, single opinion group and repeated opinions group).

Participants in the three person control group read three opinion statements each made by a different group member. The participants in the repeated opinion group read the same three statements but they were all attributed to one group member. Those in the single opinion control group read one opinion statement from one group member.

The studies found that an opinion is more likely to be assumed to be the majority opinion when multiple group members express their opinion. However, the study also showed that hearing one person express the same opinion multiple times had nearly the same effect on listener’s perception of the opinion being popular as hearing multiple people state his/her opinion.

“This study conveys an important message about how people construct estimates of group opinion based on subjective experiences of familiarity,” states lead author Kimberlee Weaver, (Ph.D), of Virginia Polytechnic Institute and State University. “The repetition effect observed in this research can help us to understand how our own impressions are influenced by what we perceive to be the reality of others. For example, a congressman may get multiple phone calls from a small number of constituents requesting a certain policy be implemented or changed, and from those requests must decide how voters in their state feel about the issue. This study sheds light on the cognitive processes that take place that may influence such a decision.”