Sound is at the beginning of language learning. Children have to learn to
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
clapping syllables. One reason why phoneme awareness gets much better once
children start school is because learning to read provides a visual aid
as how to break up words into their smaller constituents.
12 years Although children perceive rhythmic
patterns in their native language at 7–8 months, they are not able to reliably
distinguish compound words and phrases that differ only in stress placement,
such as ‘HOT dog’ vs. ‘hot DOG’ until around 12 years of age. Children in a
study by Vogel and Raimy were asked to show which of two pictures was being
named. Children younger than 12 years generally preferred the compound reading
to the phrasal reading. The authors concluded from this that children start
out with a lexical bias, i.e., they prefer to interpret phrases like these
as single words, and the ability to override this bias develops until late
in childhood. = Production =
12-14 months Infants usually produce their first word
around 12 –14 months of age. First words are simple in structure and contain the
same sounds that were used in late babbling. The lexical items they produce
are probably stored as whole words rather than as individual segments that
get put together online when uttering them. This is suggested by the fact that
infants at this age may produce the same sounds differently in different words.
16 months Children’s production vocabulary size at
this age is typically around 50 words, although there is great variation in
vocabulary size among children in the same age group, with a range between 0
and 160 words for the majority of children.
18 months Children’s productions become more
consistent around the age of 18 months. When their words differ from adult
forms, these differences are more systematic than before. These systematic
transformations are referred to as “phonological processes”, and often
resemble processes that are typically common in the adult phonologies of the
world’s languages. Some common phonological processes are listed below.
= Whole word processes = - Weak syllable deletion: omission of an
unstressed syllable in the target word, e.g., [nænæ] for ‘banana’
- Final consonant deletion: omission of the final consonant in the target word,
e.g., [pikʌ] for ‘because’ - Reduplication: production of two
identical syllables based on one of the target word syllables, e.g., [baba] for
‘bottle’ - Consonant harmony: a target word
consonant takes on features of another target word consonant, e.g., [ɡʌk] for
‘duck’ - Consonant cluster reduction: omission
of a consonant in a target word cluster, e.g., [kæk] for ‘cracker’
= Segment substitution processes = - Velar fronting: a velar is replaced by
a coronal sound, e.g., [ti] for ‘key’ - Stopping: a fricative is replaced by a
stop, e.g., [ti] for ‘sea’ - Gliding: a liquid is replaced by a
glide, e.g., [wæbɪt] for ‘rabbit’ 2 years
The size of the production vocabulary ranges from about 50 to 550 words at the
age of 2 years. Influences on the rate of word learning, and thus on the wide
range of vocabulary sizes of children of the same age, include the amount of
speech children are exposed to by their caregivers as well as differences in how
rich the vocabulary in the speech a child hears is. Children also seem to
build up their vocabulary faster if the speech they hear is related to their
focus of attention more often. This would be the case if a caregiver talks
about a ball the child is currently looking at.
4 years A study by Gathercole and Baddeley
showed the importance of sound for early word meaning. They tested the
phonological memory of 4- and 5-year-old children, i.e., how well these children
were able to remember a sequence of unfamiliar sounds. They found that
children with better phonological memory also had larger vocabularies at both
ages. Moreover, phonological memory at age 4 predicted the children’s
vocabulary at age 5, even with earlier vocabulary and nonverbal intelligence
factored out. 7 years
Children produce mostly adult-like segments. Their ability to produce
complex sound sequences and multisyllabic words continues to improve
throughout middle childhood. Biological foundations of infants’
speech development The developmental changes in infants’
vocalizations over the first year of life are influenced by physical
developments during that time. Physical growth of the vocal tract, brain
development, and development of neurological structures responsible for
vocalization are factors for the development of infants’ vocal
productions. = Infants’ vocal tract =
Infants vocal tracts are smaller, and initially also shaped differently from
adults’ vocal tracts. The infant’s tongue fills the entire mouth, thus
reducing the range of movement. As the facial skeleton grows, the range for
movement increases, which probably contributes to the increased variety of
sounds infants start to produce. Development of muscles and sensory
receptors also gives infants more control over sound production. The
limited movement possible by the infant jaw and mouth might be responsible for
the typical consonant-vowel alternation in babbling and it has even been
suggested that the predominance of CV syllables in the languages of the world
might evolutionarily have been caused by this limited range of movements of the
human vocal organs. The differences between the vocal tract
of infants and adults can be seen in figure 3 and figure 4 below.
= The nervous system = Crying and vegetative sounds are
controlled by the brain stem, which matures earlier than the cortex.
Neurological development of higher brain structures coincides with certain
developments in infants’ vocalizations. For example, the onset of cooing at 6 to
8 weeks happens as some areas of the limbic system begin to function. The
limbic system is known to be involved in the expression of emotion, and cooing in
infants is associated with a feeling of contentedness. Further development of
the limbic system might be responsible for the onset of laughter around 16
weeks of age. The motor cortex, finally, which develops later than the
abovementioned structures may be necessary for canonical babbling, which
start around 6 to 9 months of age. References