Category: Memory

This novel finding suggests that our memory system can adaptively bias its processing towards forming new memories or retrieving old ones based on recent experiences. For example, when you walk into a restaurant or for the first time, your memory system can both encode the details of this new environment as well as allow you to remember a similar one where you recently dined with a friend. The results of this study suggest that what you did right before walking into the restaurant can determine which process is more likely to occur.

Previous scholarship has demonstrated that both encoding new memories and retrieving old ones depend on the same specific brain region — the hippocampus. However, computational models suggest that encoding and retrieval occur under incompatible network processes. In other words, how can the same part of the brain perform two tasks that are at odds with each other?

At the heart of this paradox is distinction between encoding, or forming a new memory, and memory retrieval, or recalling old information. Specifically, encoding is thought to rely on pattern separation, a process that makes overlapping, or similar, representations more distinct, whereas retrieval is thought to depend on pattern completion, a process that increases overlap by reactivating related memory traces.

With this in mind, the researchers saw a potential resolution to this neurological paradox — that the hippocampus can be biased towards either pattern completion or pattern separation, depending on the current context?

To address this question, the researchers conducted an experiment in which participants rapidly switched between encoding novel objects and retrieving recently presented ones. The researchers hypothesized that processing the novel objects would bias participants' memory systems towards pattern separation while processing the old ones would evoke pattern completion biases.

Specifically, they were shown a series of objects that fell into three categories: novel objects (i.e., an initial presentation of an image, such as an apple or a face), repeated objects, or objects that were similar but not identical to previously presented ones (e.g., an apple with slightly different shape from the initial image). Participants were then asked to identify each as new (first presentation), old (exact repetition), or similar (not exact repetition). The similar items were the critical study items since they contained a little old and little new information. Thus, participants could either notice the novel details or incorrectly identify these stimuli as old.

The researchers found that participants' ability to notice the new details and correctly label those stimuli as 'similar' depended on what they did on the previous trial. Specifically, if they encountered a new stimulus on the preceding trial, participants were more likely to notice the similar trials were similar, but not old, items.

By contrast, in another experiment, the researchers demonstrated that the same manipulation can also influence how we form new memories. In this study, the researchers tested how well participants were able to form links between overlapping memories. They found that participants were more likely to construct these links when the overlapping memories were formed immediately after retrieving an unrelated old object as compared to identifying a new one. This suggests that after processing old objects, participants were more likely to retrieve the associated memories and link them to an ongoing experience.

"We've all had the experience of seeing an unexpected familiar face as we walk down the street and much work has been done to understand how it is that we can come to recognize these unexpected events," said Lila Davachi, an associate professor in NYU's Department of Psychology and the study's senior author. "However, what has never been appreciated is that simply seeing that face can have a substantial impact on your future state of mind and can allow you, for example, to notice the new café that just opened on the corner or the new flowers in the garden down the street."

"We spend most of our time surrounded by familiar people, places, and objects, each of which has the potential to cue memories," added Katherine Duncan, the study's first author who was an NYU doctoral student at the time of the study and is now a postdoctoral researcher at Columbia University. "So why does the same building sometimes trigger nostalgic reflection but other times can be passed without notice? Our findings suggest that one factor maybe whether your memory system has recently retrieved other, even unrelated, memories or if it was engaged in laying down new ones."

Co-author Arhanti Sadanand assisted with the research as an NYU undergraduate. She begins medical school at Virginia Commonwealth University this fall.

"The observed difference in arithmetic accuracy between the sexes may arise from a the willingness to risk being wrong by answering from memory before one is sure of the correct answer," said Drew Bailey, a recent recipient of a Ph.D. in psychological science from MU. "In our study, we found that boys were more likely to call out answers than girls, even though they were less accurate early in school. Over time, though, this practice at remembering answers may have allowed boys to surpass girls in accuracy."

The MU study followed approximately 300 children as they progressed from first to sixth grade. In the first and second grades, the boys' tendency to give an answer quickly led to more answers in total, but also more wrong answers. Girls, on the other hand, were right more often, but responded more slowly and to fewer questions. By sixth grade, the boys were answering more problems and getting more correct.

"Developing mathematical skill may be part 'practice makes perfect' and part 'perfect makes practice,'" Bailey said. "Attempting more answers from memory gives risk-takers more practice, which may eventually lead to improvements in accuracy. It also is possible that children who are skilled at certain strategies are more likely to use them and therefore acquire more practice."

"Parents can give their children an advantage by making them comfortable with numbers and basic math before they start grade school, so that the children will have fewer trepidations about calling out answers," said David Geary, MU professor of psychological science and co-author of the study. "As an adult, it seems easy to remember basic math facts, but in children's brains the networks are still forming. It could be that trying to answer a problem from memory engages those networks and improves them, even if the answers aren't correct at first. In time, the brain develops improved memories and more correct answers result."

The study, "The codevelopment of skill at and preference for use of retrieval-based processes for solving addition problems: Individual and sex differences from first to sixth grades," was published in the Journal of Experimental Child Psychology. David Geary is Curators' Professor and a Thomas Jefferson Fellow in the Department of Psychological Sciences in the College of Arts and Science. Drew Bailey will be starting as a post-doctoral fellow at Carnegie Mellon University this fall.

These kinds of oversights occur in professions as diverse as aviation and computer programming, but research from psychological science reveals that these lapses may not reflect carelessness or lack of skill but failures of prospective memory.

In an article in the August issue of Current Directions in Psychological Science, a journal of the Association for Psychological Science, R. Key Dismukes, a scientist at the NASA Ames Research Center, reviews the rapidly growing field of research on prospective memory, highlighting the various ways in which characteristics of everyday tasks interact with normal cognitive processes to produce memory failures that sometimes have disastrous consequences.

Failures of prospective memory typically occur when we form an intention to do something later, become engaged with various other tasks, and lose focus on the thing we originally intended to do. Despite the name, prospective memory actually depends on several cognitive processes, including planning, attention, and task management. Common in everyday life, these memory lapses are mostly annoying, but can have tragic consequences. "Every summer several infants die in hot cars when parents leave the car, forgetting the child is sleeping quietly in the back seat," Dismukes points out.

Many examples of prospective memory involve intending to do something at a particular time, such as going to a doctor's appointment, or on a particular occasion, such as congratulating a friend the next time you see her. However, much of what we intend to do in our everyday lives, whether at home or at work, involves habitual tasks repeated over time. And when it comes to these kinds of habitual tasks, our intentions may not be explicit. We usually don't, for example, form an explicit intention to insert the key in the ignition every time we drive a car — the intention is implicit in our habitual routine of driving.

In previous research, Dismukes and colleagues identified several types of situations that can lead to prospective memory failures. They found that interruptions and disruptions to habitual processes, which are irritating enough in everyday life, can be fatal in some occupational settings. In fact, several airline catastrophes have occurred because pilots were interrupted while performing critical preflight tasks — after the interruption was over, the pilots skipped to the next task, not realizing that the interrupted tasks hadn't been finished.

For all the negative attention that multitasking has received in recent years, it is perhaps no surprise that multitasking is also a major cause of prospective memory failures. We seem to have adapted fairly well to juggling several tasks simultaneously. But research shows that when a problem arises with whatever task we're currently focused on, we become vulnerable to cognitive tunneling, forgetting to switch our attention back to the other tasks at hand.

To defend against prospective memory failures and their potentially disastrous consequences, professionals in aviation and medicine now rely on specific memory tools, including checklists. Research also reveals that implementation intentions, identifying when and where a specific intention will be carried out, can help guard against such failures in everyday life. Dismukes points out that having this kind of concrete plan has been shown to improve prospective memory performance by as much as two to four times in tasks such as exercising, medication adherence, breast self-examination, and homework completion.

Along with checklists and implementation intentions, Dismukes and others have highlighted several other measures that can help to remember and carry out intended actions:

• Use external memory aids such as the alerting calendar on cell phones
• Avoid multitasking when one of your tasks is critical
• Carry out crucial tasks now instead of putting them off until later
• Create reminder cues that stand out and put them in a difficult-to-miss spot
• Link the target task to a habit that you have already established

"Rather than blaming individuals for inadvertent lapses in prospective memory, organizations can improve safety by supporting the use of these measures," argues Dismukes. He suggests that scientists should combine laboratory research with observations of human performance in real-world settings to better understand how prospective memory works and to develop practical strategies to avoid lapses.

In 2011, research led by Virginia Rauh, ScD, Co-Deputy Director of CCCEH, established a connection between prenatal exposure to chlorpyrifos and deficits in working memory and IQ at age 7. Earlier this year, a follow-up study showed evidence in MRI scans that even low to moderate levels of exposure during pregnancy may lead to long-term, potentially irreversible changes in the brain. The latest study, led by Megan Horton, PhD, explored the impact of sex differences and the home environment on these health outcomes.

Dr. Horton and colleagues looked at a subset of 335 mother-child pairs enrolled in the ongoing inner-city study of environmental exposures, including measures of prenatal chlorpyrifos in umbilical cord blood.

When the children reached age 3, the researchers measured the home environment using the Home Observation for Measurement of the Environment (HOME) criteria, including two main categories:

1) environmental stimulation, defined as the availability of intellectually stimulating materials in the home and the mother's encouragement of learning; and

2) parental nurturance, defined as attentiveness, displays of physical affection, encouragement of delayed gratification, limit setting, and the ability of the mother to control her negative reactions.

The researchers tested IQ at age 7.

While home environment and sex had no moderating effect on IQ deficits related to chlorpyrifos exposure, the researchers uncovered two intriguing findings related to sex differences, albeit of borderline statistical strength: first, that chlorpyrifos exposure had a greater adverse cognitive impact in boys as compared to girls, lowering working memory scores by an average of three points more in boys than girls (96.5 vs. 99.8); and second, that parental nurturing was associated with better working memory, particularly in boys.

"There's something about boys that makes them a little more susceptible to both bad exposures and good exposures," says Dr. Horton. "One possible explanation for the greater sensitivity to chlorpyrifos is that the insecticide acts as an endocrine disruptor to suppress sex-specific hormones. In a study of rats, exposure to the chemical reduced testosterone, which plays a critical role in the development of the male brain."

Going forward, Dr. Horton will look at how sex and the home environment may influence the effects of prenatal exposure to other environmental toxicants, such as those found in air pollution. "I expect this information will be useful in efforts to develop new interventions to protect children from the potentially negative consequences of early exposure to harmful chemicals," says Dr. Horton.

The insecticide chlorpyrifos was widely used in homes until 2001 when the U.S. Environmental Protection Agency restricted indoor residential use, permitting continued commercial and agricultural applications. Since that time, a drop in residential levels of chlorpyrifos has been documented by Robin Whyatt, DrPH, Co-Deputy Director of CCCEH. The chemical continues to be present in the environment through its widespread use in agriculture (food and feed crops), wood treatments, and public spaces such as golf courses, some parks, and highway medians. People near these sources can be exposed by inhaling the chemical, which drifts on the wind. Low-level exposure can also occur by eating fruits and vegetables that have been sprayed with chlorpyrifos. Although the chemical is degraded rapidly by water and sunlight outdoors, it has been detected by the Columbia researchers in many urban residences several years after the ban went into effect. Many developing countries continue to use chlorpyrifos in the home setting.

In a new article in the August issue of Current Directions in Psychological Science, a journal of the Association for Psychological Science, Jennifer Wiley and Andrew Jarosz of the University of Illinois at Chicago explore the role of working memory capacity in both mathematical and creative problem solving.

Converging evidence from many psychological science studies suggests that high working memory capacity is associated with better performance at mathematical problem-solving. In fact, decreased working memory capacity may be one reason why math anxiety leads to poor math performance. Overall, working memory capacity seems to help analytical problem-solvers focus their attention and resist distraction.

However, these very features of working memory capacity seem to impair creative problem-solving. With creative problems, reaching a solution may require an original approach or a novel combination of diverse pieces of information. As a result, too much focus may actually impair creative problem solving.

The authors note that, in the real world, problems are not always distinctly divided into analytic and creative types — successful problem solving depends on the needs of a given situation.

But it's been challenging to quantify the underlying trends that dictate how individuals make predictions, given they may only have seen a small number of fights or have limited memory.

In a new study, scientists at the Wisconsin Institute for Discovery (WID) at UW-Madison develop a computational approach to determine whether individuals behave predictably. With data from previous fights, the team looked at how much memory individuals in the group would need to make predictions themselves. The analysis proposes a novel estimate of "cognitive burden," or the minimal amount of information an organism needs to remember to make a prediction.

The research draws from a concept called "sparse coding," or the brain's tendency to use fewer visual details and a small number of neurons to stow an image or scene. Previous studies support the idea that neurons in the brain react to a few large details such as the lines, edges and orientations within images rather than many smaller details.

"So what you get is a model where you have to remember fewer things but you still get very high predictive power — that's what we're interested in," says Bryan Daniels, a WID researcher who led the study. "What is the trade-off? What's the minimum amount of 'stuff' an individual has to remember to make good inferences about future events?"

To find out, Daniels — along with WID co-authors Jessica Flack and David Krakauer — drew comparisons from how brains and computers encode information. The results contribute to ongoing discussions about conflict in biological systems and how cognitive organisms understand their environments.

The study, published in the Aug. 13 edition of the Proceedings of the National Academy of Sciences, examined observed bouts of natural fighting in a group of 84 captive pigtailed macaques at the Yerkes National Primate Research Center. By recording individuals' involvement — or lack thereof — in fights, the group created models that mapped the likelihood any number of individuals would engage in conflict in hypothetical situations.

To confirm the predictive power of the models, the group plugged in other data from the monkey group that was not used to create the models. Then, researchers compared these simulations with what actually happened in the group. One model looked at conflict as combinations of pairs, while another represented fights as sparse combinations of clusters, which proved to be a better tool for predicting fights. From there, by removing information until predictions became worse, Daniels and colleagues calculated the amount of information each individual needed to remember to make the most informed decision whether to fight or flee.

"We know the monkeys are making predictions, but we don't know how good they are," says Daniels. "But given this data, we found that the most memory it would take to figure out the regularities is about 1,000 bits of information."

Sparse coding appears to be a strong candidate for explaining the mechanism at play in the monkey group, but the team points out that it is only one possible way to encode conflict.

Because the statistical modeling and computation frameworks can be applied to different natural datasets, the research has the potential to influence other fields of study, including behavioral science, cognition, computation, game theory and machine learning. Such models might also be useful in studying collective behaviors in other complex systems, ranging from neurons to bird flocks.

Future research will seek to find out how individuals' knowledge of alliances and feuds fine tunes their own decisions and changes the groups' collective pattern of conflict.

The research was supported by the National Science Foundation, the John Templeton Foundation through the Santa Fe Institute, and UW-Madison.