Compared to people with normal vision, those who were blind at birth tend to have excellent memories. Now, a new study shows that blind individuals are particular whizzes when it comes to remembering things in the right order.
The findings are a good example of the familiar adage that "practice makes perfect" and reveal that mental capabilities may be refined or adjusted in order to compensate for the lack of a sensory input, according to researchers Noa Raz and Ehud Zohary of Hebrew University.
"Our opinion is that the superior serial memory of the blind is most likely a result of practice," Zohary said. "In the absence of vision, the world is experienced as a sequence of events. Since the blind constantly use serial-memory strategies in everyday circumstances, they tend to develop superior skills."
For example, the blind tend to navigate the world by forming "route-like" sequential representations. Blind people also rely on serial-memory strategies to identify otherwise indistinguishable objects, such as different brands of yogurt that vary only in their labeling, the researchers noted. According to their own reports, in order to correctly choose a desired item, the blind typically place objects in a fashioned order and give them ordinal tags, such as "the 3rd item on the left." Thus, a memory for the order in which items are encountered may be especially important for blind people's ability to create mental pictures of a scene.
In the new study, the researchers tested the performance of 19 congenitally blind individuals and individually matched sighted controls in two types of memory tasks: item memory and serial memory. In the item-memory tasks, subjects were asked to identify 20 words from a list they heard. In the serial-memory tasks, subjects had to remember not only the words, but also their ordinal position in the list.
Those who were blind recalled more words than the sighted, indicating a better memory overall, they found. Their greatest advantage, however, was the ability to remember longer word sequences according to their original order.
The blind individuals' remarkable edge in item recall resulted not from a specific advantage in remembering the first words in the list, or the most recent words. Rather, the blind showed a better memory for all of the words, regardless of where they fell. That result suggested that the key to their success may lie in representing item lists as word chains, perhaps by generating associations between adjacent items.
The researchers said they plan to further explore the underlying mental processes responsible for the differences in memory skill by using imaging techniques that measure brain activity.
The researchers include Noa Raz, Ella Striem, Golan Pundak, Tanya Orlov, and Ehud Zohary of Hebrew University in Jerusalem, Israel. This study was funded by the McDonnell Foundation grant #220020046.
Reference: Raz et al.: "Superior Serial Memory in the Blind: A Case of Cognitive Compensatory Adjustment." Publishing in Current Biology 17, 1--5, July 3, 2007. DOI 10.1016/j.cub.2007.05.060.
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