During been provided by investigating infantile and adult

During the first two years of a human’s life the greatest amount
of rapid language development occurs that a human will ever experience in their
life (Fernald, Swingley & Pinto, 2001). This rapid language development is
facilitated by; speech perception and word learning. Firstly, speech perception
helps infantile language development to occur through categorical perception, which
utilises phoneme categories so acoustic information can be split up into more
manageable units of sound to learn. These phonetic categories are not just
restricted to native languages but rather infants are able to also perceive
phonetic categories that appear in non-native languages. Adults also help by
using infant directed speech, so infants are able to grasp information at a
slower pace. Secondly, infants are able to develop language through the
learning of word boundaries developed through segmentation cues, so they
understand that units of sounds create meaning. To learn the meaning of words
that they acquire through segmentation cues, infants also use referents in the
world that they can use to associate to words, so that semantic and conceptual
information can be learnt.


But firstly, before infants can learn to speak they need to be
able to perceive speech. Speech perception is an important component in
learning languages for infants and to do this they form categories
(Pierrehumbert, 2003). These categories are initiated using a
perception-production loop that creates the categories using environmental
stimuli that then inform the formation of further categories (Pierrehumbert,
2003). This assists infants to perceive more manageable units of acoustic
information as a full word is a very complex set of sound information for an
infant to learn and splitting up a word into sounds make it easier for the
infants to perceive language. The categories, themselves, are based on phonemes
which are distinct units of sound that are psychological constructs that cause
one word to differ in its meaning from another (Chomsky & Halle, 1968) with
further phonetic categorical information arising from the statistical
likelihood of one phoneme following another (Maje, Weber & Gerken, 2002; Kuhl,
2004). Evidence of this use of categories in infants’ speech perception
development has been provided by investigating infantile and adult voice onset
times (VOT). Voice onset time is the time difference between the change in the
glottal aperture (an opening between the vocal cords and the arytenoid
cartilages) and the vocalisation of a sound (Lisker & Abramson, 1967). Both
infants and adults have been demonstrated to use phonetic categories by VOT
(McMurray & Aslin, 2005) with infants performing on the same level as
adults. Being born with basic phonetic skills means that infants can rapidly
learn words to form speech perception at a high standard not that far below
that of adults (Dehaene-Lambertz & Gliga, 2004). As infantile
knowledge of these categories changes infantile perception of language improves
vastly (Kuhl & Iverson, 1995) with the changes occurring in the first six
months of life is when the perceptual space is reorganised, and the phonetic
categories are established (Hazan& Barrett, 2000). Therefore, the key to
the success of infants’ perception of language lies in the use of phonetic
categories.  After this initial increase
in learning, categorical phonetic perception becomes a less important component
in language development because they know phonetic differences to an extent
enough for them to begin the learning of whole words and what their meaning are
(Eimas et al, 1971). The learning of phonetic categories is therefore important
to speech perception development and without this development of being able to
perceive words infants would not be able to carry on to learn meaning produced
in language.

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This decrease in categorical perception is also demonstrated in
the perception of non-native languages. Even though infants are able to
discriminate non-native language voice onset time contrasts, something that
adults are unable to do (Aslin et al, 1981), infants use the phonetic
categories of different languages to perceive speech less and less (Werker et
al, 2007) as their knowledge of words increases. The infants demonstrate, at
the same time as a decline in non-native perception, an increase in performance
at native language contrasts (Kuhl et al, 2006). Without the learning of
non-native languages infants are able to neurally commit to their native
language. Overall this suggest that through not discriminating initially
infants are able to perceive phonetic categories to a greater extent but after
achieving this and beginning to discriminate, they are able to develop their
understanding of their native language phonetic categories more. Non-native
language phonetic categories are never reinitiated during a person’s life so
never again can language development occur so quickly and so accurately (De Bot & Schrauf, 2010) showing that infants
acquire language in different ways than adults, facilitating more rapid
language development.


On the other hand, infants do not support their language
development by themselves, with adults playing a large role through infant
directed speech. Infant directed speech is a change of vocalisation of words
when an adult talks to an infant as opposed with talking to an adult (adult
directed speech) (Cooper & Aslin, 1990). There is a far longer voice onset
time in infant directed speech with stops (a consonant in which the vocal tract
is blocked so air flow cease (Ladefoged & Maddieson, 1998)) being over
specified (Englund, 2005; Sundberg, 1998). This means that when adults speak to
infants their speech is over emphasised leading adults to lay out the
categorisation of phonemes by separating out the word. Infants are then able to
use these categories and apply them to more fluent adult directed speech where
the categories are not sounded out for them so they able to perceive language
at a normal pace. Again, this shows that phonetic categories are an integral
part of language development as when adults help facilitate them through infant
directed speech, infants are able to perceive language better in their


However, language has the fundamental use of conveying information
with words being the carriers of that information and infants cannot understand
what a word is based on phonetic categories alone. Learning words is achieved
by infants through various steps. First, they learn word boundaries using
segmentation cues based on syllables. Infants learn what letters make sense as
a word by learning the probability that one syllable is likely to follow
another (Aslin, 2016). For example, infants learn that the syllable of flow is
most likely to come before the syllable of er and that it is very
unlikely for these two syllables to be the other way around. There are various
other cues, like stress cues, other than learning statistical likelihood of
sequential syllables. This is particularly relevant to the English language as
around 90% of English words have their first syllable stressed (Cultler &
Carter, 1987). This means that English-speaking infants are able learn word
boundaries around these stress cues as it helps identify when a new word is
beginning. However, it must be noted that this is not applicable to all
languages. Syllabic stress changes position in many words in the many other languages
(Roach, 1982) so stress cues cannot be used to explain how, globally, all
infants learn words. This causes, the more utilised method used to be word
segmentation (Johnson & Jusczyk, 2001) as it means that infants can
understand the boundaries when the acoustical cues, like stress, are changed.
Acoustical cues can change with each speaker but statistical cues like
segmentation remain the same throughout a language, so they are a greater aid
to language development. Therefore, segmentation cues are important in word
learning and furthermore language development as without words language cannot
be understood.


Infants also rely far more heavily on immediate statistical
information and do not learn further patterns in non-adjacent syllables
(Newport & Aslin, 2004). Patterns of no-adjacent syllables is essentially
the arrangement rules of a language as a whole, but infants rather use the
statistical likelihood of one syllable following another (a form of
segmentation). This method ensures that the language development capacity
within the first year of life is not limited. It has been shown that infants
that perform well on speech segmentation tasks before they reach 12 months of
age have larger vocabularies when they reach 24 months of age (Newman, Ratner,
Jusczyk, Jusczyk & Dow, 2000). This shows that segmentation cues are
important to language development as it allows infants to learn words faster
and form a better vocabulary affecting their long-term language development.


Segmentation cues, however, only suggest how infants are able to
identify word boundaries in speech. How infants are able to understand the
meaning of these is an issue that infants need to overcome. They do this by
learning the meaning of words mostly through identifying referents in the
world. These referents have been identified when infants are being tested on
their word knowledge with the provision of pictures helping infants in their
word retrieval (Dapretto & Bjork, 2000). This shows that the infants learn
the meaning of words using visual perceptual information and associate a word
with a visual object. This, like infant directed speech, in its self is
facilitated by adults when infants begin to develop language. When infants
attend to a real object parents have a tendency to vocally label whatever the
child is attending to (Samuelson & McMurray, 2016). Due to repetition,
infants begin to associate a word with an object and therefore they learn the
meaning of the word and know to use it when referring to the object, leading
the infants to develop language.


But this concept of learning through association is shallow and
there is the suggestion of the use of further information. Infants utilise far
more the conceptual information that they are receiving to understand what a
word means (Waxman & Gelman, 2009). Infants are not just taking in the
superficial information that they are being provided with. If that were the
case, when being presented with various different balls, like rugby balls and
footballs, the infants would not be able to apply the word ball to the rugby
ball because when they learnt the word ball they applied it to a round object
not to the concept of a ball has the purpose of being thrown. Preissler and
Carey (2004) demonstrated this use of conceptual information through how
infants were better at matching a two-dimensional image of a whisk with a three-dimensional
whisk than with another two-dimensional image. That means that they do not
abstract the meaning of the word whisk as a two-dimensional silver wiry object
but rather that it is an object that is used to mix. This shows that infants
learn words and their meaning through real world referents as this provides
in-depth conceptual information that they are able to apply to new objects and
they can then use this language for themselves.


In conclusion, infantile language development is a complex system
that requires perception and word learning. The speed at which this occurs is
aided by perceptual categories, infant directed speech segmentation cues and real-world
referents. These methods stop being utilised to such a large extent after the
initial rapid phase of language development in infancy as they are no longer
necessary to aid language development meaning that when adults want to learn
new languages they cannot do so anywhere near as effectively as infants learn
languages. Overall, there is a particular emphasis on the importance of
statistical likelihood when infants perceive speech and when they learn the
meaning of words. This means that despite the universality of language
acquisition (Saffran, 2002) that infants do not have an innate knowledge of
words and their meaning. Infants instead are born with functions such as
learning statistical information that help them to learn and develop language.