Imagine planning your schedule for the week and seeing the days on the calendar appear before you as a spiral staircase so real you feel like you could touch it. That's what it's like to have spatial-sequence synesthesia, a condition in which people perceive numbered sequences as visual patterns. Now researchers have shown that individuals with the condition have superior memories, recalling dates and historic events much better than can the average person.
Spatial-sequence synesthesia is one of several types of synesthesia, neural conditions in which senses combine in unusual ways. Grapheme-color synesthetes, for example, associate letters and numbers with colors; the number six might always look red to them. In other types of synesthesia, the word "cat" may create the taste of tomato soup, or the sound of a flute may appear as a blue cloud.
Recently, scientists have wondered if synesthesia--especially spatial-sequence synesthesia--might be linked to a superior ability to form memories. So psychologist Julia Simner of the University of Edinburgh in the United Kingdom tested for unusual mnemonic skills or other mental talents in 10 spatial-sequence synesthetes. Subjects had to quickly recall the dates of 120 public events occurring between 1950 and 2008, such as the year Nelson Mandela was freed from jail in South Africa (1990) or the year My Fair Lady won the Academy Award for best picture (1965). On average, non-synesthetic volunteers were off by about 8 years for each date, but the synesthetes were wrong by only about 4 years. They could also name almost twice as many events from specified years in their own lives than could the controls. "They have this subtle extra gift," says Simner.
The findings, reported in the November-December issue of Cortex, also suggest a link between spatial-sequence synesthesia and hyperthymestic syndrome--a condition in which individuals can recall events from any point in their life with perfect clarity. And that may mean, says Simner, that anyone who visualizes timelines may remember historical events better than others.
The study jibes with our knowledge of how memory works, says neuroscientist David Eagleman of the Baylor College of Medicine in Houston, Texas. "Putting things in spatial locations to memorize them harks back to the earliest mnemonic techniques that we know," he says. "These spatial-sequence synesthetes are getting that for free."