The amount of information we can remember from a visual scene is extremely limited and the source of that limit may lie in the posterior parietal cortex, a region of the brain involved in visual short-term memory, Vanderbilt psychologist René Marois and graduate student J. Jay Todd have found. Their results were published in the April 15 edition of Nature.
"Visual short-term memory is a key component of many perceptual and cognitive functions and is supported by a broad neural network, but it has a very limited storage capacity," Marois said. "Though we have the impression we are taking in a great deal of information from a visual scene, we are actually very poor at describing its contents in detail once it is gone from our sight."
Previous findings have determined that an extensive network of brain regions supports visual short-term memory. In their study, Todd and Marois showed that the severely limited storage capacity of visual short-term memory is primarily associated with just one of these regions, the posterior parietal cortex.
Todd and Marois used functional magnetic resonance imaging (fMRI), a technique that reveals the brain regions active in a given mental task by registering changes in blood flow and oxygenation in these regions, to identify where the capacity limit of visual short-term memory occurs.
The brains of research participants were scanned with fMRI while they were shown scenes containing one to eight colored objects. After a delay of just over a second, the subjects were queried about the scene they had just viewed.
While the subjects were good at remembering all of the objects in scenes containing four or fewer objects, they frequently made mistakes describing displays containing a larger number of objects, indicating that the storage capacity of visual short-term memory is about four.
The fMRI results revealed that activity in the posterior parietal cortex strongly correlated with the number of objects the subjects were able to remember. The magnitude of the neural response in this brain area increased with the number of objects viewed up to about four and leveled off after that, even when additional objects were presented.
A different team led by Edward Vogel of the University of Oregon at Eugene were able to use signals measured by electrodes attached to the scalp to precisely measure the size of each person's visual working memory.
A large increase in the subject's brain activity on the four-dot test indicated that his or her memory capacity had not been pushed to its limit. No increase in electrical activity indicated that his or her working memory had topped out on the two-dot test. By graphing these responses, the team worked out the exact size of each subject's working memory.
It is likely that the measured differences in visual memory have some genetic basis. With that in mind it would be interesting to use Vogel's technique to compare measured visual working memory with BDNF gene variations that affect visual and episodic memory capabilities.
Another team at Northwestern University and Drexel University has used fMRI to demonstrate that the problem solving mechanism that produces the "Eureka!" moment of discovering an answer works by a different mental mechanism than what is used to solve problems by more conventional methods.
Mark Jung-Beeman and colleagues mapped both the location and electrical signature of neural activity using functional magnetic resonance imaging (fMRI) and the electroencephalogram (EEG). Neural activity was mapped with fMRI while the participants were given word problems--which can be solved quickly with or without insight, and evoke a distinct Aha! moment about half the time they're solved. Subjects pressed a button to indicate whether they had solved the problem using insight, which they had been told leads to an Aha! experience characterized by suddenness and obviousness.
While several regions in the cerebral cortex showed about the same heightened activity for both insight and noninsight-derived solutions, only an area known as the anterior Superior Temporal Gyrus (aSTG) in the right hemisphere (RH) showed a robust insight effect. The researchers also found that 0.3 seconds before the subjects indicated solutions achieved through insight, there was a burst of neural activity of one particular type: high-frequency (gamma band) activity that is often thought to reflect complex cognitive processing. This activity was also mapped to the aSTG of the RH, providing compelling convergence across experiments and methods.
Problem-solving involves a complex network of brain regions to encode, retrieve, and evaluate information, but these results show that solving verbal problems with insight requires at least one additional component. Further, the fact that the effect occurred in RH aSTG suggests what that process may be: integration of distantly related information. Distinct neural processes, the authors conclude, underlie the sudden flash of insight that allows people to "see connections that previously eluded them."
Some problems are easier to solve because they require the use of straightforward procedures which has been trained to use. For example, if one solves a math problem with a known method of solution then there is no "Eureka!" moment when one calculates the answer. Whereas when a solution found by noticing previously unobserved connections there is more a sense of revelation. It is this latter case that involves a burst of activity in a part of the brain called the anterior Superior Temporal Gyrus (aSTG).
“For thousands of years, people have said that insight feels different from more straightforward problem-solving,” he said.
“We believe this is the first research showing that distinct computational and neural mechanisms lead to these breakthrough moments.”
The paper by Mark Jung-Beeman et. al. is available online here: Neural Activity When People Solve Verbal Problems with Insight.
It would be interesting to know whether people who are considered more creative in their fields have a bigger anterior Superior Temporal Gyrus (aSTG). Every time a part of the brain is discovered as key for some function the obvious question that arises is just how valuable would it be to enhance that part of the brain. The aSTG for reaching insights and the posterior parietal cortex for working short-term visual memory both strike me as useful areas to enhance to make one better at scientific and engineering work.
On the subject of other brain functions that it would be great to enhance see my post Low Latent Inhibition Plus High Intelligence Leads To High Creativity?
|Share |||Randall Parker, 2004 April 14 01:44 PM Brain Creativity|