Do you remember how your breakfast plate was arranged this morning? Even if you don’t, your hippocampus might—and growing evidence suggests that there is a way to retrieve this unconscious memory: through your eye movements.
The latest study comes from the University of California, Davis, where neuroscientist Deborah Hannula and her team showed participants photographs of faces superimposed on scenes. Later the volunteers saw the individual scenes again and had to pick the matching faces. By tracking their eye movements, Hannula and her co-workers saw that even when volunteers picked the wrong face, their eyes were drawn for a longer time to the correct one.
Previous studies yielded similar results, but the findings have been controversial because of difficulties replicating them, Hannula says. Her study also showed that the participants’ hippocampus was active during the process, indicating that, contrary to conventional thinking, the brain region is involved not only in conscious memory processing but in other memory tasks as well.
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The findings suggest that eye movements can be a sensitive measure for both unconscious and conscious memories, Hannula says. This fact could open up new avenues for working with cognitively impaired patients, who may not be able to verbally or otherwise report what they remember.
The results also have implications for crime scene investigations, Hannula says. For example, eyewitnesses may unconsciously remember the face of a perpetrator. Even the eye movements of the person who committed the crime could betray important information. “Imagine the perpetrator used a knife that was in the butcher block on the counter next to the refrigerator,” she says. Viewing pictures of that scene would likely draw their eye movements to that butcher block.
Note: This story was originally printed with the title "Eye Giveaway"