Mid vowel
A mid vowel is a vowel sound produced with the body of the tongue positioned at an intermediate height in the oral cavity, neither raised close to the hard palate as in high vowels nor lowered toward the floor of the mouth as in low vowels.[1] This tongue height classification is a core feature in articulatory phonetics, distinguishing mid vowels by their moderate jaw opening and balanced vocal tract configuration.[2] Examples in English include the /ɛ/ in "bet" (mid front unrounded lax), the /eɪ/ diphthong in "bait" (mid front unrounded tense), and the /oʊ/ in "boat" (mid back rounded tense), alongside central variants like the schwa /ə/ in "sofa" and /ʌ/ in "but."[3][2] Mid vowels further vary along dimensions of tongue advancement (front, central, or back) and lip rounding (rounded or unrounded), contributing to a wide array of sounds across languages.[1] In the International Phonetic Alphabet (IPA), they are symbolized accordingly, such as /e/ for close-mid front unrounded or /ɔ/ for open-mid back rounded, reflecting subtle gradations within the mid category.[2] Tense mid vowels typically involve greater muscular effort and a higher tongue position compared to lax ones, influencing duration and quality; for instance, tense /e/ contrasts with lax /ɛ/ in many dialects.[3] These vowels play a pivotal role in phonological systems, often serving as markers of stress, grammatical distinctions, or lexical contrasts in diverse languages worldwide.[1]Definition and Characteristics
Articulatory Features
Mid vowels are characterized by an intermediate tongue height, positioned approximately midway between the raised configuration for close vowels and the lowered configuration for open vowels. This placement occurs in the midsagittal plane of the vocal tract, where the tongue body is neither maximally elevated toward the hard palate nor depressed toward the floor of the mouth. Concurrently, the jaw adopts a semi-open posture, allowing for a moderate pharyngeal cavity size that distinguishes mid vowels from both higher and lower counterparts.[4] The articulatory production of mid vowels relies heavily on the precise vertical and horizontal positioning of the tongue body. Vertically, the tongue arch reaches a height that balances constriction and openness in the oral cavity, while horizontally, it can be advanced for front mid vowels, centralized for neutral variants, or retracted for back mid vowels. These adjustments shape the vocal tract resonance without extreme bunching or spreading, enabling variations within the mid height category across languages. For instance, front mid vowels involve forward tongue advancement, whereas back mid vowels feature posterior retraction, all while maintaining the core mid-level elevation.[5][4] Lip rounding plays a secondary role in mid vowel articulation, primarily affecting the labial configuration without influencing the vowel's height classification. Rounded mid vowels, typically associated with back positions, involve protrusion and narrowing of the lips to modify the front cavity resonance, whereas unrounded variants maintain neutral or spread lip postures. This rounding enhances the perceptual distinctiveness of certain mid vowels but does not alter the fundamental tongue-jaw positioning that defines their mid status.[4] Standard phonetic models, such as the cardinal vowel system developed by the International Phonetic Association, provide reference points for mid vowel positions by establishing idealized articulatory targets. In this system, mid vowels occupy the central band of the vowel quadrilateral, with specific loci for front, central, and back realizations at both close-mid and open-mid levels, serving as benchmarks for cross-linguistic comparison and phonetic training.[4]Acoustic Features
Mid vowels exhibit distinct acoustic properties primarily characterized by their formant frequencies, which reflect the resonance patterns in the vocal tract during production. The first formant (F1) serves as the key indicator of vowel height, with mid vowels typically displaying F1 values between 400 and 600 Hz. This intermediate range distinguishes them from close (high) vowels, which have lower F1 frequencies (often below 300 Hz), and open (low) vowels, which have higher F1 values (typically above 700 Hz). These F1 measurements are derived from spectrographic analyses of sustained vowels produced by adult speakers.[6] The second formant (F2) provides cues to vowel frontness or backness, showing considerable variation among mid vowels. Front mid vowels, such as those with an unrounded tongue configuration, exhibit higher F2 frequencies in the range of 1800–2200 Hz, creating a brighter auditory quality. In contrast, back mid vowels have lower F2 values, generally 800–1200 Hz, resulting in a more muffled resonance. Lip rounding further influences these patterns by lowering F2 frequencies in back mid vowels due to the protrusion and narrowing effect on the vocal tract, which shifts formant energies downward and enhances perceptual backness.[6] Auditorily, mid vowels are perceived through the balanced openness conveyed by their moderate F1, allowing listeners to categorize them as intermediate in height relative to extremes. Perception studies demonstrate that F1 frequency maps directly onto phonological height features, with categorical boundaries around 9.8 Erb separating mid from high vowels, enabling reliable discrimination in continuum tests. However, in noisy or ambiguous conditions, mid vowels may occasionally be confused with near-high or near-low counterparts if F1 values fall near these boundaries, as shown in feature-based listening experiments where discrimination peaks align with height contrasts but valleys occur at transitional zones. These perceptual cues stem from the mid-level tongue positioning that shapes the vocal tract resonances.[7]Classification and Subtypes
True Mid Vowels
True mid vowels refer to vowel sounds with the tongue positioned at the precise midpoint of the vertical dimension in the vowel space, midway between close (high) and open (low) extremes. This height is distinct from close-mid and open-mid vowels, which occupy higher and lower positions within the mid range. In standard phonetic classifications, such as those used in the International Phonetic Alphabet (IPA), true mid vowels are typically represented without diacritics for height adjustment when central, emphasizing their neutral positioning.[8] True mid vowels are less common outside central positions, primarily manifesting in central unrounded or rounded forms like the schwa [ə] or [ɵ], due to articulatory challenges of maintaining an exact midpoint in non-central positions. Front or back true mid vowels are exceptionally uncommon, as most vowel systems favor asymmetries that pull them toward close-mid or open-mid realizations. While rare, some languages like Kensiu maintain phonemic contrasts between true mid, close-mid, and open-mid vowels within the same frontness series, highlighting their specialized role in natural phonologies.[9] In historical phonetic theory, Daniel Jones' cardinal vowel system, introduced in the early 20th century, maps the vowel space as a standardized quadrilateral using peripheral reference vowels, including close-mid (e.g., , ) and open-mid (e.g., [ɛ], [ɔ]), providing a theoretical benchmark for measuring deviations in real speech, though actual recordings emphasized the peripheral positions.[10] A prototypical example of a true mid central vowel is the unstressed schwa [ə] in English, as realized in words like "sofa" or the first syllable of "button," where it exhibits the neutral midpoint height in casual speech.[8] This realization underscores the vowel's frequent appearance in reduced, unstressed contexts across many languages, reinforcing its status as the most common true mid variant.[9]Close-Mid and Open-Mid Distinctions
Close-mid vowels are characterized by a tongue position that is raised higher in the mouth compared to open-mid vowels, placing it approximately halfway between the positions for close (high) vowels and a true mid vowel. This articulatory configuration results in an acoustic profile where the first formant (F1) typically falls in the range of 300-500 Hz for adult male speakers, reflecting the relatively constricted vocal tract. Representative examples include the unrounded front close-mid vowel /e/, as in the French word fête, and the rounded back close-mid vowel /o/, as in Spanish poco. Open-mid vowels, in contrast, involve a lower tongue position, closer to that of open (low) vowels, leading to a more open vocal tract configuration. Acoustically, their F1 frequency is generally higher, ranging from 500-700 Hz for adult male speakers, which corresponds to greater oral cavity resonance. Examples include the unrounded front open-mid vowel /ɛ/, as in English bet, and the rounded back open-mid vowel /ɔ/, as in French porte. The International Phonetic Alphabet (IPA) vowel chart delineates the mid vowel space by dividing it into close-mid (upper mid) and open-mid (lower mid) categories, effectively splitting the overall mid height into approximate halves to facilitate systematic notation and description. However, perceptual studies reveal challenges in distinguishing these subtypes near the true mid boundary, where acoustic cues like F1 values around 500 Hz lead to listener ambiguity, with identification accuracy dropping significantly in psychophysical tests.[11] Interactions between rounding and frontness further modulate the perception of close-mid versus open-mid distinctions, as lip rounding lowers higher formants (F2 and F3), potentially enhancing the perceived height of the vowel by altering spectral prominence. For example, the rounded close-mid front vowel /ø/, as in French peu, may be perceived as relatively higher than its unrounded counterpart /e/ due to this acoustic reinforcement, while frontness amplifies F2 separation, aiding overall subtype differentiation in auditory processing.[12]Phonetic Notation
IPA Symbols for Mid Vowels
In the International Phonetic Alphabet (IPA), mid vowels are primarily represented through symbols that denote their height and backness, with the mid central unrounded vowel symbolized as [ə], commonly known as the schwa, which serves as the core notation for a true mid position without dedicated symbols for other exact true mid variants like front or back equivalents.[13] Subtypes are distinguished using close-mid and open-mid categories, where close-mid vowels include for front unrounded, [ø] for front rounded, [ɤ] for back unrounded, and for back rounded, while open-mid vowels encompass [ɛ] for front unrounded, [œ] for front rounded, [ʌ] for back unrounded (often central-leaning), and [ɔ] for back rounded.[14] These symbols span the front-to-back spectrum to capture articulatory variations: front unrounded mid vowels use and [ɛ]; front rounded use [ø] and [œ]; central unrounded relies on [ə] for mid, with [ɘ] for close-mid and [ɜ] for open-mid; back unrounded employs [ɤ] for close-mid and [ʌ] for open-mid; and back rounded utilizes and [ɔ].[13] In the IPA vowel chart, known as the trapezium, mid vowels occupy the central row, positioned between the close (high) and open (low) rows to reflect tongue height, with horizontal placement indicating frontness to backness from left to right, facilitating a visual representation of the oral cavity's vowel space.[14] The symbols for mid vowels trace their origins to the founding of the IPA in 1888 by the Phonetic Teachers' Association, which introduced provisional notations like e and o for mid positions based on earlier systems such as Henry Sweet's Romic alphabet, though these were marked as temporary and later refined.[15] Subsequent 20th-century revisions, including those in 1900 (adding [ə] explicitly for the mid central vowel), 1921 (introducing central notations like [ɘ] and [ɵ]), and 1932 (standardizing height distinctions), progressively stabilized the current set through iterative updates to enhance phonetic precision and cross-linguistic applicability.[15] Further refinements occurred in the late 20th and early 21st centuries, such as the 1989 and 2015 chart updates, which improved symbol rendering for better Unicode compatibility without altering the core mid vowel inventory.[13]| Height Category | Front Unrounded | Front Rounded | Central Unrounded | Back Unrounded | Back Rounded |
|---|---|---|---|---|---|
| Close-Mid | [ø] | [ɘ] | [ɤ] | ||
| Mid | - | - | [ə] | - | - |
| Open-Mid | [ɛ] | [œ] | [ɜ] | [ʌ] | [ɔ] |