In Brief

After a severe head injury from a car accident or a serious fall people can still implicitly learn from visual cues even though their memory and explicit learning are neurologically impaired, according to a new study by Washington State University researchers Heather M. Nissley and Maureen Schmitter-Edgecombe, PhD.

The study is the first to explore implicit learning using a perceptually based task in people who sustained a closed-head injury. The researchers say their findings support the idea that there may be different neural mechanisms for implicit and explicit learning.

In the study, the researchers compared the reaction times of 19 participants who had a severe closed-head injury with a noninjured control group to a series of matrices displayed on a computer screen. Participants were asked to pick out the number "6" in the briefly flashed field of 36 numbers by indicating in what quadrant the number appeared. Unknown to the participants, there were only four matrices, each with the number "6" in a different quadrant.

Both groups reduced their reaction times as the matrices continued to appear--indicating that they were learning the pattern--and retained their learning after a 20-minute delay. When the relationships between the four matrices and the quadrant location of the "6" was scrambled, reaction times increased. Tests showed that few of the participants had any explicit knowledge that there was a pattern to the matrices, which meant that they learned the pattern unconsciously.

Moreover, while the closed-head injury group's reaction times were slower, they improved and retained implicit learning at about the same rate as the control group--a finding that shows the injured participants implicitly learned perceptual information as well as noninjured individuals despite having clear impairments in explicit learning and memory.

The researchers say the findings could hold promise for new approaches to helping survivors of closed-head injuries. It's possible, they speculate, that the injured could learn to implicitly associate stimulus cues in their environment with a specific behavior outcome. For example, learning to associate looking or writing in a memory notebook with environmental cues. However, they say that more research is needed to tease out these possibilities.

The study, "Perceptually based implicit learning in severe closed-head injury patients," appears in the February issue of the APA journal Neuropsychology (Vol. 16, No. 1).

--D. SMITH