In phonetics, sulcalization 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. 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 , which allows various tongue positions without apparent distinction, may also receive its characteristic quality from being sulcal.