distinguish different sounds and to segment the speech stream they are

exposed to into units – eventually meaningful units – in order to acquire

words and sentences. Here is one reason that speech segmentation is challenging:

When you read, there are spaces between the words. No such spaces occur between

spoken words. So, if an infant hears the sound sequence “thisisacup,” it has to

learn to segment this stream into the distinct units “this”, “is”, “a”, and

“cup.” Once the child is able to extract the sequence “cup” from the speech

stream it has to assign a meaning to this word. Furthermore, the child has to

be able to distinguish the sequence “cup” from “cub” in order to learn that

these are two distinct words with different meanings. Finally, the child

has to learn to produce these words. The acquisition of native language phonology

begins in the womb and isn’t completely adult-like until the teenage years.

Perceptual abilities usually precede production and thus aid the development

of speech production. Prelinguistic development

= Perception = Children don’t utter their first words

until they are about 1 year old, but already at birth they can tell some

utterances in their native language from utterances in languages with different

prosodic features. 1 month

= Categorical perception = Infants as young as 1 month perceive

some speech sounds as speech categories. For example, the sounds and differ in

the amount of breathiness that follows the opening of the lips. Using a

computer generated continuum in breathiness between and , Eimas et al.

showed that English-learning infants paid more attention to differences near

the boundary between and than to equal-sized differences within the

-category or within the -category. Their measure, monitoring infant sucking-rate,

became a major experimental method for studying infant speech perception.

Infants up to 10–12 months can distinguish not only native sounds but

also nonnative contrasts. Older children and adults lose the ability to

discriminate some nonnative contrasts. Thus, it seems that exposure to one’s

native language causes the perceptual system to be restructured. The

restructuring reflects the system of contrasts in the native language.

4 months At four months infants still prefer

infant-directed speech to adult-directed speech. Whereas 1-month-olds only

exhibit this preference if the full speech signal is played to them,

4-month-old infants prefer infant-directed speech even when just

the pitch contours are played. This shows that between 1 and 4 months of

age, infants improve in tracking the suprasegmental information in the speech

directed at them. By 4 months, finally, infants have learned which features they

have to pay attention to at the suprasegmental level.

5 months Babies prefer to hear their own name to

similar sounding words. It is possible that they have associated the meaning

“me” with their name, although it is also possible that they simply recognize

the form because of its high frequency. 6 months

With increasing exposure to the ambient language, infants learn not to pay

attention to sound distinctions that are not meaningful in their native language,

e.g., two acoustically different versions of the vowel that simply

differ because of inter-speaker variability. By 6 months of age infants

have learned to treat acoustically different sounds that are

representations of the same sound category, such as an spoken by a male

versus a female speaker, as members of the same phonological category .

= Statistical learning = Infants are able to extract meaningful

distinctions in the language they are exposed to from statistical properties

of that language. For example, if English-learning infants are exposed to

a prevoiced to voiceless unaspirated continuum with the majority of the

tokens occurring near the endpoints of the continuum, i.e., showing extreme

prevoicing versus long voice onset times they are better at discriminating these

sounds than infants who are exposed primarily to tokens from the center of

the continuum. These results show that at the age of 6

months infants are sensitive to how often certain sounds occur in the

language they are exposed to and they can learn which cues are important to

pay attention to from these differences in frequency of occurrence. In natural

language exposure this means typical sounds in a language occur often and

infants can learn them from mere exposure to them in the speech they

hear. All of this occurs before infants are aware of the meaning of any of the

words they are exposed to, and therefore the phenomenon of statistical learning

has been used to argue for the fact that infants can learn sound contrasts

without meaning being attached to them. At 6 months, infants are also able to

make use of prosodic features of the ambient language to break the speech

stream they are exposed to into meaningful units, e.g., they are better

able to distinguish sounds that occur in stressed vs. unstressed syllables. This

means that at 6 months infants have some knowledge of the stress patterns in the

speech they are exposed and they have learned that these patterns are

meaningful. 7 months

At 7.5 months English-learning infants have been shown to be able to segment

words from speech that show a strong-weak stress pattern, which is the

most common stress pattern in the English language, but they were not able

to segment out words that follow a weak-strong pattern. In the sequence

‘guitar is’ these infants thus heard ‘taris’ as the word-unit because it

follows a strong-weak pattern. The process that allows infants to use

prosodic cues in speech input to learn about language structure has been termed

“prosodic bootstrapping”. 8 months

While children generally don’t understand the meaning of most single

words yet, they understand the meaning of certain phrases they hear a lot, such

as “Stop it,” or “Come here.” 9 months

Infants can distinguish native from nonnative language input using phonetic

and phonotactic patterns alone, i.e., without the help of prosodic cues. They

seem to have learned their native language’s phonotactics, i.e., which

combinations of sounds are possible in the language.

10-12 months Infants now can no longer discriminate

most nonnative sound contrasts that fall within the same sound category in their

native language. Their perceptual system has been tuned to the contrasts relevant

in their native language. As for word comprehension, Fenson et al. tested

10-11-month-old children’s comprehension vocabulary size and found a range from

11 words to 154 words. At this age, children normally have not yet begun to

speak and thus have no production vocabulary. So clearly, comprehension

vocabulary develops before production vocabulary.

= Production = Stages of pre-speech vocal development

Even though children do not produce their first words until they are

approximately 12 months old, the ability to produce speech sounds starts to

develop at a much younger age. Stark distinguishes five stages of early

speech development: = 0-6 weeks: Reflexive vocalizations =

These earliest vocalizations include crying and vegetative sounds such as

breathing, sucking or sneezing. For these vegetative sounds, infants’ vocal

cords vibrate and air passes through their vocal apparatus, thus

familiarizing infants with processes involved in later speech production.

= 6-16 weeks: Cooing and laughter = Infants produce cooing sounds when they

are content. Cooing is often triggered by social interaction with caregivers

and resembles the production of vowels. = 16-30 weeks: Vocal play =

Infants produce a variety of vowel- and consonant-like sounds that they combine

into increasingly longer sequences. The production of vowel sounds precedes the

production of consonants, with the first back consonants being produced around

2–3 months, and front consonants starting to appear around 6 months of

age. As for pitch contours in early infant utterances, infants between 3 and

9 months of age produce primarily flat, falling and rising-falling contours.

Rising pitch contours would require the infants to raise subglottal pressure

during the vocalization or to increase vocal fold length or tension at the end

of the vocalization, or both. At 3 to 9 months infants don’t seem to be able to

control these movements yet. = 6-10 months: Reduplicated babbling =

Reduplicated babbling contains consonant-vowel syllables that are

repeated in reduplicated series of the same consonant and vowel. At this stage,

infants’ productions resemble speech much more closely in timing and vocal

behaviors than at earlier stages. Starting around 6 months babies also

show an influence of the ambient language in their babbling, i.e.,

babies’ babbling sounds different depending on which languages they hear.

For example, French learning 9-10 month-olds have been found to produce a

bigger proportion of prevoiced stops in their babbling than English learning

infants of the same age. This phenomenon of babbling being influenced by the

language being acquired has been called babbling drift.

= 10-14 months: Nonreduplicated babbling Infants now combine different vowels and

consonants into syllable strings. At this stage, infants also produce various

stress and intonation patterns. During this transitional period from babbling

to the first word children also produce “protowords”, i.e., invented words that

are used consistently to express specific meanings, but that are not real

words in the children’s target language. Around 12–14 months of age children

produce their first word. Infants close to one year of age are able to produce

rising pitch contours in addition to flat, falling, and rising-falling pitch

contours. Development once speech sets in

At the age of 1, children only just begin to speak, and their utterances are

not adult-like yet at all. Children’s perceptual abilities are still

developing, too. In fact, both production and perception abilities

continue to develop well into the school years, with the perception of some

prosodic features not being fully developed until about 12 years of age.

= Perception = 14 months

Children are able to distinguish newly learned ‘words’ associated with objects

if they are not similar sounding, such as ‘lif’ and ‘neem’. They cannot

distinguish similar sounding newly learned words such as ‘bih’ and ‘dih’,

however. So, while children at this age are able to distinguish monosyllabic

minimal pairs at a purely phonological level, if the discrimination task is

paired with word meaning, the additional cognitive load required by learning the

word meanings leaves them unable to spend the extra effort on distinguishing

the similar phonology. 16 months

Children’s comprehension vocabulary size ranges from about 92 to 321 words. The

production vocabulary size at this age is typically around 50 words. This shows

that comprehension vocabulary grows faster than production vocabulary.

18-20 months At 18–20 months infants can distinguish

newly learned ‘words’, even if they are phonologically similar, e.g. ‘bih’ and

‘dih’. While infants are able to distinguish syllables like these already

soon after birth, only now are they able to distinguish them if they are

presented to them as meaningful words rather than just a sequence of sounds.

Children are also able to detect mispronunciations such as ‘vaby’ for

‘baby’. Recognition has been found to be poorer for mispronounced than for

correctly pronounced words. This suggests that infants’ representations

of familiar words are phonetically very precise. This result has also been taken

to suggest that infants move from a word-based to a segment-based

phonological system around 18 months of age.

= Fast-mapping = Of course, the reason why children need

to learn the sound distinctions of their language is because then they also have

to learn the meaning associated with those different sounds. Young children

have a remarkable ability to learn meanings for the words they extract from

the speech they are exposed to, i.e., to map meaning onto the sounds. Often

children already associate a meaning with a new word after only one exposure.

This is referred to as “fast mapping”. At 20 months of age, when presented with

three familiar objects and one unfamiliar object, children are able to

conclude that in the request “Can I have the zib,” zib must refer to the

unfamiliar object, i.e., the egg piercer, even if they have never heard

that pseudoword before. Children as young as 15 months can complete this

task successfully if the experiment is conducted with fewer objects. This task

shows that children aged 15 to 20 months can assign meaning to a new word after

only a single exposure. Fast mapping is a necessary ability for children to

acquire the number of words they have to learn during the first few years of

life: Children acquire an average of nine words per day between 18 months and

6 years of age. 2–6 years

At 2 years, infants show first signs of phonological awareness, i.e., they are

interested in word play, rhyming, and alliterations. Phonological awareness

does continue to develop until the first years of school. For example, only about

half of the 4- and 5-year olds tested by Liberman et al. were able to tap out the

number of syllables in multisyllabic words, but 90% of the 6-year-olds were

able to do so. Most 3-4-year olds are able to break simple

consonant-vowel-consonant syllables up into their constituents. The onset of a

syllable consists of all the consonants preceding the syllable’s vowel, and the

rime is made up of the vowel and all following consonants. For example, the

onset in the word ‘dog’ is and the rime is . Children at 3–4 years of age were

able to tell that the nonwords and would be liked by a puppet whose

favorite sound is . 4-year olds are less successful at this task if the onset of

the syllable contains a consonant cluster, such as or . Liberman et al.

found that no 4-year-olds and only 17% of 5-year-olds were able to tap out the

number of phonemes in a word. 70% of 6-year-olds were able to do so. This

might mean that children are aware of syllables as units of speech early on,

while they don’t show awareness of individual phonemes until school age.

Another explanation is that individual sounds do not easily translate into

beats, which makes clapping individual phonemes a much more difficult task than