Severe closed-head injury (CHI), like those caused by car accidents or falls - leading causes of workplace injuries and fatalities - can impair the ability for purposeful learning like that found in a classroom or in job training sessions. The Centers for Disease Control have estimated that 5.3 million Americans, a little more than two percent of the U.S. population, currently live with disabilities resulting from CHI.
However, there might be hope.
Psychologists have evidence that severe-CHI survivors may still be able to learn without even realizing that they''re learning. This kind of learning, called "implicit," may be supported by a separate, earlier-evolving brain mechanism than the "explicit" type. In implicit learning, for example, children normally acquire and understand the complex rules of grammar - although (even as adults) they may not be able to describe the rules or how they learned them. In explicit learning, they formally learn the parts of speech in the classroom. CHI has long been known to hurt explicit learning.
Two Washington State University researchers studied implicit perceptual learning in 19 participants between the ages of 15 and 55 at least one year after they sustained severe closed-head injuries, most of them in motor vehicle accidents but some in falls of greater than 10 feet. All had been in a coma for at least 24 hours.
Heather M. Nissley, M.S., and Maureen Schmitter-Edgecombe, Ph.D., compared the CHI survivors'' implicit perceptual learning with that of 19 non-injured controls, to learn whether the injured participants retained the capacity to learn without explicitly intending to learn, in the absence of awareness.
These findings, which are reported in the article "Perceptually Based Implicit Learning in Severe Closed-Head Injury Patients" in the January issue of Neuropsychology, may aid the effort to help restore the cognitive abilities of CHI survivors, who often are impaired during young adulthood. Neuropsychology is published by the American Psychological Association (APA).
The first to study implicit learning in CHI using a perceptual task, Nissley and Schmitter-Edgecombe asked participants to identify the location of a target number - 6 - on a computer screen, as it moved in a seemingly random fashion around a matrix of numbers. Participants did not know that the target''s location was actually determined by an underlying pattern of relationships between that location and the arrangement of other numbers in the display. Despite slower search rates, the CHI group''s improvement in locating the "6" was consistent with that of the control group. They demonstrated this implicit learning even though they were clearly impaired on tests of explicit learning and memory.
The findings support the idea that there may be two different neural mechanisms: one for implicit and another for explicit learning. What''s more, it also is likely that implicit learning is not a single, unified learning process.
Some have argued that the brain areas underlying implicit learning developed earlier in evolution and thus are more unchanging and resilient across individuals than later-evolving areas. This means that implicit learning is more immune to neurological injury (as well as to age and other individual differences such as intelligence and education). Additionally, with the ability to learn implicitly, people can acquire new information about their environment even though their ability to learn things explicitly has been compromised.
The findings hold promise for new approaches for rehabilitation of survivors of severe closed-head injury, say researchers. "Persons with CHI generally perform better on tasks that require automatic as opposed to controlled, or explicit, processes," says Schmitter-Edgecombe, "suggesting that automatic processes could be exploited in [rehabilitation]."
For example, therapists could "teach" complex skills by breaking them down into sub-components that can be learned implicitly and/or made automatic.
by Sandy Smith ([email protected])