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Phonological development

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Phonological development is the process by which children learn to organize sounds into meaningful language. This journey begins with phonology, which is the study of how sounds function within a language. To master speech, a child must first learn to distinguish different sounds. They must also learn to segment the continuous speech stream they hear into individual units. In spoken language, there are no spaces between words like there are in printed text. An infant might hear the sequence "thisisacup" and must learn to divide it into "this," "is," "a," and "cup." Once a sound unit like "cup" is extracted, the child assigns it a meaning. They must also learn to distinguish "cup" from "cub" to understand they are different words.

infantvocaltract1
infantvocaltract1

Perceptual abilities, or the ability to hear and categorize sounds, usually develop before production, which is the ability to speak. This development begins in the womb and continues until the teenage years. At just one month old, infants show categorical perception. This means they perceive certain speech sounds as belonging to specific categories. For example, the sounds /b/ and /p/ differ by the amount of breathiness following the opening of the lips. In a 1971 study, Eimas et al. used a computer-generated continuum of breathiness to test English-learning infants. They monitored the infant's sucking rate to measure their attention. They found infants paid more attention to differences near the boundary between /b/ and /p/ than to differences within a single category.

Eimas
Eimas

As infants grow, they refine how they track suprasegmental information. This refers to the pitch, rhythm, and stress patterns of speech. At four months, infants prefer infant-directed speech over adult-directed speech. They can even recognize these preferences when only the pitch contours are played. By five months, babies often prefer hearing their own names. By six months, infants use statistical learning to process their ambient language. They notice how often certain sounds occur. If a language has a bimodal distribution, where sounds occur mostly at the extreme ends of a continuum, infants learn to discriminate them better. They also learn to ignore sound variations that are not meaningful, such as different voices speaking the same vowel.

At six months, infants use prosodic features to help them segment speech. This process is called "prosodic bootstrapping." They use the stress patterns of their language to find word boundaries. In English, which often uses a strong-weak or "trochaic" stress pattern, seven-month-old infants can segment words using this rhythm. However, they struggle to segment words that follow a weak-strong pattern. By nine months, infants understand phonotactics. This is the rule for which combinations of sounds are possible in their native language. By twelve months, the perceptual system has been tuned to the specific contrasts of the native language.

Speech production follows a specific sequence of developmental stages. The first stage, from birth to six weeks, involves reflexive vocalizations. These include crying and vegetative sounds like breathing or sneezing. These sounds help infants familiarize themselves with their vocal apparatus. From six to sixteen weeks, infants enter the cooing and laughter stage. Cooing is often triggered by social interaction and sounds similar to vowels. Between sixteen and thirty weeks, infants engage in vocal play. They combine vowel and consonant-like sounds into longer sequences. During this time, they produce vowels first, followed by back consonants like [g] and [k] around two to three months. Front consonants like [m], [n], and [p] appear around six months.

Baby, Crying baby, Moscow, Russia
Baby, Crying baby, Moscow, Russia

Between six and ten months, children enter the stage of reduplicated or canonical babbling. This involves repeating consonant-vowel syllables, such as "bababa." At this stage, babbling begins to show "babbling drift," where the sounds are influenced by the language the infant hears. For example, nine-month-old French-learning infants produce more prevoiced stops than English-learning infants. From ten to fourteen months, infants move to nonreduplicated or variegated babbling. They combine different vowels and consonants into complex syllable strings. They may also use "protowords," which are invented words used consistently for specific meanings. Around twelve to fourteen months, children typically produce their first real words.

infantvocaltract1
infantvocaltract1

Understanding language and speaking it develop at different rates. Comprehension vocabulary, the words a child understands, usually grows faster than production vocabulary. At ten to eleven months, a child's comprehension may range from 11 to 154 words, even if they cannot speak yet. By sixteen months, comprehension can range from 92 to 321 words, while production is typically around 50 words. At fourteen months, children can distinguish between different "words" if they sound very different, like "lif" and "neem." However, they struggle with similar-sounding words like "bih" and "dih" because the cognitive load of learning meaning makes phonological distinction harder.

adultvocaltract
adultvocaltract
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File:Eimas.jpg
Eimas.jpg
3 month old infant cooing in response to...
File:Baby, Crying baby, Moscow, Russia.jpg
Baby, Crying baby, Moscow, Russia.jpg
File:infantvocaltract1.jpeg
infantvocaltract1.jpeg
File:adultvocaltract.jpeg
adultvocaltract.jpeg
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