The Centers for Disease Control and Prevention have estimated that more than 2% of the U.S. population lives with disabilities caused by a severe closed-head injury (CHI), a trauma that batters but does not penetrate the skull. A common detriment suffered by some CHI victims is an impaired capacity for purposeful learning, such as takes place at school or on the job. Until recently, these victims were considered incapable of consciously making new memories or acquiring new skills. However, a new study gives evidence that severe CHI sufferers may be able to learn without the awareness that they are learning.
Heather M. Nissley and Maureen Schmitter-Edgecomb, psychologists at Washington State University in Pullman, studied implicit perceptual learning in 38 participants between the ages of 15 and 55 (Neuropsychol. 2002, 16 (1), 111122). Half the subjects had experienced a severe CHI at least one year before the study and had demonstrated an impaired ability to learn explicitly. Implicit learning is the ability to learn without an awareness of doing so, such as when children acquire and understand complex rules of grammar even though they may not be able to describe the rules or how they learned them. It is the opposite of explicit learning, such as learning the parts of speech in a classroom.
In the study, Nissley and Schmitter-Edgecomb 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 targets location was actually determined by an underlying pattern of relationships between the location and the arrangement of other numbers in the display. Despite slower search rates, the CHI groups improvement in locating the 6 was consistent with that of the control group, demonstrating that, like the uninjured participants, they learned perceptual information implicitlywithout conscious awareness.
These findings support the idea that two different neural mechanisms may support implicit and explicit learning. The authors think that their research holds promise for new approaches to remediation for severe CHI survivors.Perhaps over time, these people could learn to implicitly associate stimulus cues in their environment with a specific behavior or outcome. For example, they could implicitly learn to relate looking in or writing in a memory notebook with environmental cues repeatedly presented.