In phonetics, sulcalization is the pronunciation of a sound, typically a sibilant consonant such as English /s/ and /z/, with a deep groove running along the back of the tongue that focuses the airstream on the teeth, producing a more intense sound. This 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 grooved in this manner; 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 [ɹ], 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 this effect in Japanese, where historical *tu and *ti have become [tsu] and [tɕi], respectively, as well as in languages such as Senoufo. (The palatalization of *tsi to [tɕi] in Japanese is a different process, and does not occur in Senoufo.)
Vowels may also be sulcalized, which has been described as giving them a "throaty" sound (Jones 1967:82). The /ɒ/ vowel of Received Pronunciation, which is normally described as a rounded, is pronounced by some speakers without rounded lips; for these speakers, 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 [ɜ], is actually a sulcal schwa, retaining the sulcality of the original rhotic consonant; accordingly, he interprets the realization of /ə/ in other contexts such as beard and scarce as the product of a loss of sulcality (Erickson 2003:197).