A friend sensitive to the care needed for newborns and their moms was touched by a sign promising "Infant Hearing Testing." The sight of the sequential hearing and testing got her thinking about the five senses: sight, of course, plus touch; then there's smell, taste, and hearing. (来源：EnglishCN.com)

Why, she wondered, are four of the five senses brief, one-syllable nouns, while one of them—hearing—is a more cumbersome gerund (or verbal noun)? We're pleased to be able to say her query did not fall on deaf ears.

As to why four out of five external senses have noun senses that physically resemble their verb senses, we can't offer any more explanation than this: English is quirky. But we can point out that those five senses do have other labels, too: sight is also known as vision; taste as gustation; smell as olfaction; touch as taction; and hearing as audition.

Neither taction nor audition seem especially common, and we are happy to speculate about why that might be. Touch is well-established, and may be more easily understood than taction. And of course audition has multiple meanings, so that Infant Audition Testing might prove confusing.