We have all heard of calculating prodigies, those rare souls able to perform astounding feats with numbers. For many of these individuals, numbers have colors, flavors, sounds, or other qualities alien to the rest of us. Mental calculator Salo Finkelstein detested the number zero and adored 226. The Russian mnemonist S.V. Shereshevskii associated the number 87 with a visual image of a fat woman and a man twirling his mustache. This is known as synesthesia, the association of sensory qualities with inappropriate objects. A recent study suggests that most people may have a bit of number synesthesia. It might help explain the mysterious appeal of "charm" prices ending in the digit 9 (as in $19.99).
Research by Keith Coulter and Robin Coulter, to be published in The Journal of Consumer Research, implies that certain numbers just sound bigger than others. This in turn can affect the perception of discounts.
Coulter and Coulter begin by citing decades of research claiming that sounds pronounced with the front of the mouth (long a, e, and i; fricatives like f, s, and z) trigger associations with smallness. (Think of words like tiny and wee.) The vowels pronounced at the back of the mouth, like the oo in foot or goose, are linked to largeness. (Think huge or crowds oohing and ahhing something really big.) Crazy? Well consider how it applied to discounts in the study. Subjects were given "regular" and "sale" prices and asked to estimate the percentage discount. The guesstimated discounts were skewed by the sound effect. For instance, people estimated that a $3 product marked down to $2.33 was about a 28 percent discount. But when the product was marked down to $2.22, the estimated saving was only 24 percent. It was a bigger discount, really, but it didn't seem that way.
One explanation: Three, with a long e, sounds small, and two, with a back-of-the-mouth vowel, sounds large.
That doesn't prove the sounds were responsible. In one of the crucial experiments, Coulter and Coulter tested perceptions of the prices $7.01 and $7.88 with English and Chinese speakers. In English one is pronounced with the back of the mouth, and eight with the front. In Chinese, this is reversed. So were the perceptions of how big or small discounts were. The researchers use this to argue that it is indeed "phonetic symbolism" at work.
"Nine" has a long i, so it's one of the small-sounding digits. Assuming the hypothesis is right, prices ending in 9 would seem a little smaller than they would otherwise, enhancing the quick, largely unconscious perception of a good deal. But 9 isn't unique: it would seem that all the digits from 3 on up have a vowel or consonant sound supposedly associated with smallness. (Ironically, the truly bigger digits sound small. Zero is a problematic case: The fricative z might put it in the small category, but most people say "o" when reciting a phone number, and zeros at the end of a price aren't pronounced at all. $70 is "seventy dollars," not "seven-zero dollars.")
Obviously, retailers want to charge the largest "small-sounding" price (the sound they care about is ka-ching.) From that perspective, the use of 9 makes sense.
This study adds another to the growing list of guesses about how 9-ending prices "work." Coulter and Coulter believe that shoppers must "rehearse" prices — say them to themselves, at least silently — for the sounds to affect them. In the experiments, participants were told to repeat the sale prices to themselves. It's not clear whether this would apply to silent reading of a fast-food menu. Still, the experiment hints at what unexpected layers of meaning we may attach to simple numbers — including the ones with dollar signs.
Coulter, Keith S., and Robin A. Coulter (2010). "Small Sounds, Big Deals: Phonetic Symbolism Effects in Pricing." The Journal of Consumer Research.