Sulcalization

In articulatory phonetics, sulcalization (from Latin: sulcus 'groove') is the pronunciation of a sound with a deep, longitudinal concavity (groove) down the back of the tongue (the dorsum), roughly opposite of the uvula.¹²

Sulcalization is accomplished by raising the sides of the dorsum, leaving a hollow along the midline.³⁴

Some linguists extend the term sulcalization to refer more broadly to the general presence of a longitudinal concavity along the tongue midline, rather than being strictly posterior (see § Grooved fricatives). In this sense, sulcalization is the functional inverse of lateralization: sulcalization raises the sides of the tongue to direct airflow along the midline, whereas lateralization lowers the sides of the tongue to direct airflow over the sides (blocking airflow along the midline).

However, this contrast does not necessitate mutual exclusivity; for example, the "dark l" [ɫ] may involve both posterior dorsal sulcalization³ alongside its characteristic anterior coronal lateralization.

Sulcalization has typically been associated with rhotics such as a 'bunched' or 'molar' r [ɹ̈]⁵⁶ and r-colored vowels,⁷⁸⁹² as well as 'dark' or 'throaty' quality sounds,⁴ either more velar-like (such as [ɫ])³¹⁰ or more pharyngeal-like (such as [ɒ]).¹¹¹²

No spoken language is known to make a phonemic distinction between sulcalized and ordinary vowels.⁴ However, it has been reported that for some speakers of Received Pronunciation (RP), the vowel /ɒ/, which is normally described as rounded, is pronounced with neutral or spread lips, and is instead given its characteristic quality through a "hollowing or sulcalization of the tongue-body".¹¹

One scholar has also suggested that the vowel in the RP pronunciation of words like bird, typically transcribed /ɜː/, is actually a sulcal schwa, retaining the sulcality of the original rhotic consonant. Accordingly, the realization of the /ə/-element of the centring diphthongs /ɪə̯/, /ʊə̯/, /ɛə̯/ in words such as near, pure and scare, is interpreted as the product of a loss of sulcality.⁹ Similarly to the case of RP /ɜː/, it has been noted that the rhotacized equivalent /ɝ/ in American English is strongly sulcalized.⁸

Palatograms of [s], which is grooved, and [θ], which is slit

Some linguists have referred to grooved fricatives, a similar but distinct articulatory concept, as sulcalized,¹¹³ though this should not be confused with the more common definition described above.^a As with the more common definition of sulcalization, grooved fricatives also involve forming a groove down the center of the tongue (such as in some realizations of /s/ in the English words sit and case).¹³ They contrast with slit fricatives, which are pronounced with the tongue flat.¹⁴

The grooved–slit distinction primarily applies to anterior consonants.¹⁵ Unlike the more common definition of sulcalization, which typically refers to a posterior hollowing, grooved fricatives involve raising the sides of the tongue to focus the turbulent airstream on the teeth, producing an anterior hollowing. This results in a more intense sound, typically associated with sibilants.¹⁴¹⁶ Slit fricatives, with a flatter shape, have a wider and more dispersed airflow channel.¹⁴

J. C. Catford observed that the degree of tongue grooving differs between places of articulation as well as between languages; however, no language is known to phonemically contrast fricatives based purely on the presence or absence of tongue grooving.¹⁷ Nonetheless, linguists sometimes make a phonetic distinction for certain fricative allophones that occur at the same place of articulation as a grooved or slit counterpart.

For example, [t̞] (a lenited allophone of /t/ found in some English dialects) is commonly described as slit, to distinguish it from grooved [s];¹⁸¹⁹²⁰ though it has also been noted that additional articulatory factors may go into the distinction between grooved [s] and slit [t̞].²¹

Historically, the terms grooved fricative and sibilant have sometimes been used synonymously (and by extension, slit fricative and non-sibilant), though the reality of sibilant shapes is more complex; not all sibilants may share this feature, nor may it be unique to sibilants.¹ For instance, /ʃ/ is widely regarded to be characterized by a convex doming of the tongue rather than a concave grooving,²² and therefore has been defined as slit;²³ conversely, ultrasound imaging has shown /θ/ in English to exhibit grooving similar to /s/, despite being typically regarded as slit.²⁴

It was once proposed for the IPA to include a diacritic to distinguish grooved and slit fricatives,²³ but the proposal was rejected.²⁵ While lacking diacritics for the feature specifically, the extIPA chart includes [θ͇] and [ð͇] to denote slit alveolar fricatives,²⁶ which the authors have noted form a contrastive graphical pair with the more commonly seen [s̪] and [z̪], denoting grooved dental fricatives.^15b