In a recent post, we discussed how the cognitive processing of numbers may be rooted in the human body. It should come as no surprise then, that the way we think about numbers is deeply spatial. This phenomenon has a snappy title: The Spatial-Numerical Association of Response Codes, or SNARC, effect.
In the seminal 1993 study that uncovered the SNARC effect, cognitive neuroscientist Stanislas Dehaene and colleagues conducted a series of experiments on number processing. They were interested in the way we discern and distinguish even and odd numbers. In one experiment, subjects were shown numbers between 0 and 9 on a computer screen. They were asked to determine whether each number was odd or even by pressing one of two response keys, one with the left hand and one with the right.
Subjects reacted faster to small numbers like 1 and 2 when they pushed the button with their left hand. Larger numbers like 8 and 9 elicited faster responses when the right hand was doing the clicking. The researchers hypothesized that this difference has to do with spatial associations we have with numbers. We—in America, at least—orient numbers in space, with smaller integers associated with the left side of space, and larger numbers to the right. As a result, processing speed is faster when numbers are located where they “should” be. That’s the SNARC effect in a nutshell.
So where does the SNARC effect come from? Is it hardwired in all humans? Are numbers inherently spatial? Most experts agree that this is not the case.
A recent study suggests that our cognitive architecture for processing numbers is influenced by language. In 2009, Israeli researcher Samuel Shaki studied the SNARC effect across language groups. Using methodology similar to Dehaene’s 1993 study, Shaki tested the SNARC effect in subjects from three different countries. One group of subjects was Canadian, who read English words and Arabic numbers from left to right. Another group was Palestinian, who read Arabic words right to left, as well as the numbers of the Hindu-Arabic numeral system. The third group was composed of Israelis, who read Hebrew from right to left, but Arabic numbers from left to right.
Canadians showed a typical SNARC effect, with fast left side responses for smaller integers. Palestinians had a reversed SNARC effect, associating smaller numbers with the right side of space and larger numbers with the left side. Israelis, with their conflicting reading directions for letters and numbers, showed the weakest SNARC effect. These results strongly suggest that spatial-numerical associations are influenced by culturally specific reading and writing systems for both letters and numbers.
The SNARC effect may be culturally acquired, but it is also highly flexible. Just one year before Shaki’s cross-cultural study was published, Scottish research Martin Fischer examined the malleability of the SNARC effect. Experimenters asked participants to read cookbook recipes on a computer screen. In one group, the recipes were SNARC-congruent, with smaller numbers on the left side of the line of text and larger numbers on the right. For example: “Take 2 potatoes and fry them for 9 minutes.” In the SNARC-incongruent group, the recipe would instead read, “Take 9 potatoes and fry them for 2 minutes,” with the larger number oriented on the left side of the screen and the smaller number on the right.
After about 40 minutes of exposure to the SNARC-incongruent recipes, subjects showed a significantly diluted SNARC effect. This suggests that our spatial-numerical associations are not fixed, but are sensitive to experiences in the here and now.
To sum up: We tend to conceptualize numbers spatially. Experiments across language groups have shown that the spatial associations we make with numbers are not innate, but appear to be shaped by language. On top of that, these associations can also be influenced by stimuli in the present.
We still have a lot to learn about the SNARC effect. A particularly interesting question is how the effect manifests itself (or doesn’t) in speakers and writers of vertically written languages like Japanese and Chinese. Another question for further research is how fluency in multiple languages may moderate the potency and direction of the SNARC effect. With researchers exploring these and other questions, we may one day have a fuller understanding of our curiously spatial approach to numbers.
Shaki S., Fischer M. H., & Petrusic W. M. (2009). Reading habits for both words and numbers contribute to the SNARC effect. Psychonomic Bulletin & Review, 16, 328–331.
Dehaene, S., Bossini, S., & Giraux, P. (1993). The mental representation of parity and numerical magnitude. Journal of Experimental Psychology: General, 122, 371–396.
Photo courtesy of Natashi Jay: http://www.flickr.com/photos/tizzlin/4900963734/sizes/m/in/photostream/