Sulcalization, in phonetics, is the pronunciation of a sound, typically a sibilant consonant, such as English and , with a deep groove running along the back of the tongue that focuses the airstream on the teeth, producing a more intense sound. That is accomplished by raising the sides of the back of the tongue ("lateral contraction") and leaving a hollow along the mid-line. It is not clear if all sibilants are so grooved: Catford (1977) observed that the degree of sulcalization differs between places of articulation as well as between languages, but no language is known to contrast a grooved and non-grooved sibilant.
English , which allows various tongue positions without apparent distinction, may also receive its characteristic quality from being sulcal.
In phonology and historical linguistics, sulcalization is the development of such a groove in a non-sulcal consonant. For example, close vowels trigger the effect in Japanese, in which historic *tu and *ti have become and , respectively. A similar sound change as operated in the Senufo languages. (The palatalization of *tsi to in Japanese is a different process and does not occur in Senufo.)
Vowels may also be sulcalized, which has been described as giving them a "throaty" sound (Jones 1967:82). The vowel of Received Pronunciation, which is normally described as a rounded, is pronounced by some speakers without rounded lips for whom the characteristic quality is rather one of sulcality (Lass 1984:124).
One scholar has also suggested that the vowel in the RP pronunciation of words like bird, typically transcribed , is actually a sulcal schwa, retaining the sulcality of the original rhotic consonant. Accordingly, the realization of in other contexts, such as beard and scarce, is interpreted as the product of a loss of sulcality (Erickson 2003:197).